POSIX shared memory redux

*** a/configure
--- b/configure
***************
*** 850,855 **** with_gnu_ld
--- 850,856 ----
  enable_largefile
  enable_float4_byval
  enable_float8_byval
+ enable_float8_byval
  '
        ac_precious_vars='build_alias
  host_alias
***************
*** 860,865 **** LDFLAGS
--- 861,867 ----
  LIBS
  CPPFLAGS
  CPP
+ CPPFLAGS
  LDFLAGS_EX
  LDFLAGS_SL
  DOCBOOKSTYLE'
***************
*** 28245,28254 **** fi
  if test "$PORTNAME" != "win32"; then
  
  cat >>confdefs.h <<\_ACEOF
! #define USE_SYSV_SHARED_MEMORY 1
  _ACEOF
  
!   SHMEM_IMPLEMENTATION="src/backend/port/sysv_shmem.c"
  else
  
  cat >>confdefs.h <<\_ACEOF
--- 28247,28256 ----
  if test "$PORTNAME" != "win32"; then
  
  cat >>confdefs.h <<\_ACEOF
! #define USE_POSIX_SHARED_MEMORY 1
  _ACEOF
  
!   SHMEM_IMPLEMENTATION="src/backend/port/posix_shmem.c"
  else
  
  cat >>confdefs.h <<\_ACEOF
*** a/configure.in
--- b/configure.in
***************
*** 1730,1737 **** fi
  
  # Select shared-memory implementation type.
  if test "$PORTNAME" != "win32"; then
!   AC_DEFINE(USE_SYSV_SHARED_MEMORY, 1, [Define to select SysV-style shared memory.])
!   SHMEM_IMPLEMENTATION="src/backend/port/sysv_shmem.c"
  else
    AC_DEFINE(USE_WIN32_SHARED_MEMORY, 1, [Define to select Win32-style shared memory.])
    SHMEM_IMPLEMENTATION="src/backend/port/win32_shmem.c"
--- 1730,1737 ----
  
  # Select shared-memory implementation type.
  if test "$PORTNAME" != "win32"; then
!   AC_DEFINE(USE_POSIX_SHARED_MEMORY, 1, [Define to select SysV-style shared memory.])
!   SHMEM_IMPLEMENTATION="src/backend/port/posix_shmem.c" 
  else
    AC_DEFINE(USE_WIN32_SHARED_MEMORY, 1, [Define to select Win32-style shared memory.])
    SHMEM_IMPLEMENTATION="src/backend/port/win32_shmem.c"
*** a/src/backend/bootstrap/bootstrap.c
--- b/src/backend/bootstrap/bootstrap.c
***************
*** 352,358 **** AuxiliaryProcessMain(int argc, char *argv[])
  
  	/* If standalone, create lockfile for data directory */
  	if (!IsUnderPostmaster)
! 		CreateDataDirLockFile(false);
  
  	SetProcessingMode(BootstrapProcessing);
  	IgnoreSystemIndexes = true;
--- 352,361 ----
  
  	/* If standalone, create lockfile for data directory */
  	if (!IsUnderPostmaster)
!           CreateDataDirLockFile(false,false);
! 	
! 	/* Hold on to the lock file for the life of this process. */
! 	AcquireDataDirLock();
  
  	SetProcessingMode(BootstrapProcessing);
  	IgnoreSystemIndexes = true;
*** /dev/null
--- b/src/backend/port/posix_shmem.c
***************
*** 0 ****
--- 1,469 ----
+ /*-------------------------------------------------------------------------
+  *
+  * posix_shmem.c
+  *	  Implement shared memory using POSIX facilities
+  *
+  * These routines represent a fairly thin layer on top of POSIX shared
+  * memory functionality.
+  *
+  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
+  * Portions Copyright (c) 1994, Regents of the University of California
+  *
+  *-------------------------------------------------------------------------
+  */
+ #include "postgres.h"
+ 
+ #include <signal.h>
+ #include <unistd.h>
+ #include <sys/file.h>
+ #include <sys/mman.h>
+ #include <sys/param.h>
+ #include <sys/stat.h>
+ #include <sys/types.h>
+ #ifdef HAVE_KERNEL_OS_H
+ #include <kernel/OS.h>
+ #endif
+ 
+ #include "miscadmin.h"
+ #include "libpq/md5.h"
+ #include "storage/ipc.h"
+ #include "storage/pg_shmem.h"
+ 
+ 
+ #define IPCProtection	(0600)	/* access/modify by user only */
+ #define IPCNameLength		31  /* Darwin requires max 30 + '\0' */
+ 
+ uint8	UsedShmemInstanceId = 0;
+ void	*UsedShmemSegAddr = NULL;
+ 
+ static void GenerateIPCName(uint8 instanceId, char destIPCName[IPCNameLength]);
+ static void *InternalIpcMemoryCreate(const char ipcName[IPCNameLength],uint8 instanceId, Size size);
+ static void IpcMemoryDetach(int status, Datum shmaddr);
+ static int POSIXSharedMemoryFD=-1;
+ 
+ 
+ /*
+  *	GenerateIPCName(instanceId, destIPCName)
+  *
+  * Generate a shared memory object key name using the implicit argument
+  * DataDir's pathname and the current instance id. A hash of the
+  * canonicalized directory path is used to construct the key name.
+  * Store the result in destIPCName, which must be IPCNameLength bytes.
+  */
+ static void
+ GenerateIPCName(uint8 instanceId, char destIPCName[IPCNameLength])
+ {
+   
+   /* This must be 30 characters or less for portability (i.e. Darwin).
+    * POSIX requires shared memory names to begin with a single slash. It 
+    * should not have any others slashes or any non-alphanumerics as the
+    * that is the broadest assumption of what is permitted in a filename.
+    * Also, case sensitivity should not be presumed.
+    *
+    * Collisions are averted by the fact that the shared memory region is 
+    * immediately unlinked.
+    * 
+    * The string is formed starting with a slash, then the identifier 'PG.',
+    * then the pid of the current process.
+    */
+   snprintf(destIPCName, IPCNameLength, "/PG.%6ld", (long int)getpid());
+ }
+ 
+ /*
+  *	InternalIpcMemoryCreate(ipcName, size)
+  *
+  * Attempt to create a new shared memory segment with the specified IPC name.
+  * Will fail (return NULL) if such a segment already exists.  If successful,
+  * attach the segment to the current process and return its attached address.
+  * On success, callbacks are registered with on_shmem_exit to detach and
+  * delete the segment when on_shmem_exit is called.
+  *
+  * If we fail with a failure code other than collision-with-existing-segment,
+  * print out an error and abort.  Other types of errors are not recoverable.
+  */
+ static void *
+ InternalIpcMemoryCreate(const char ipcName[IPCNameLength], uint8 instanceId, Size size)
+ {
+ 	int			fd;
+ 	int unlink_status=0;
+ 	int fstat_status=0;
+ 	int ftruncate_status=0;
+ 	void	   *shmaddr;
+ 	struct		stat statbuf;
+ 	
+ 	fd = shm_open(ipcName, O_RDWR | O_CREAT | O_EXCL, IPCProtection);
+ 
+ 	if (fd < 0)
+ 	{
+ 		/*
+ 		 * Fail quietly if error indicates a collision with existing segment.
+ 		 * One would expect EEXIST, given that we said O_EXCL.
+ 		 */
+ 		if (errno == EEXIST || errno == EACCES || errno == EINTR)
+ 			return NULL;
+ 
+ 		/*
+ 		 * Else complain and abort
+ 		 */
+ 		ereport(FATAL,
+ 				(errmsg("could not create shared memory segment: %m"),
+ 				 errdetail("Failed system call was shm_open(name=%s, oflag=%lu, mode=%lu).",
+ 						   ipcName, (unsigned long) O_CREAT | O_EXCL,
+ 						   (unsigned long) IPCProtection),
+ 				 (errno == EMFILE) ?
+ 				 errhint("This error means that the process has reached its limit "
+ 						 "for open file descriptors.") : 0,
+ 				 (errno == ENOSPC) ?
+ 				 errhint("This error means the process has ran out of address "
+ 						 "space.") : 0));
+ 	}
+ 	/* the race between creation and unlinking is protected by the shared memory pid file */
+ 
+ 	
+ 	unlink_status = shm_unlink(ipcName);
+ 	if(unlink_status<0)
+ 	  {
+ 	    /* It would be virtually impossible for us to fail to unlink a shared memory region we just created, but we need to handle this anyway- refuse to use this shared memory segment. */
+ 	    ereport(FATAL,
+ 		    (errmsg("could not unlink shared memory segment : %m"),
+ 		     errdetail("Failed system call was shm_unlink(name=%s).",ipcName)));
+ 	    return NULL;
+ 	  }
+ 	
+ 	/* Increase the size of the file descriptor to the desired length.
+ 	 * If this fails so will mmap since it can't map size bytes. */
+ 	fstat_status = fstat(fd, &statbuf);
+ 	if(fstat_status<0)
+ 	  {
+ 	    ereport(FATAL,
+ 		    (errmsg("could not fstat the shared memory segment : %m"),
+ 		     errdetail("Failed system call was fstat(fd=%d,stat=%p).",fd,&statbuf)));
+ 	    return NULL;
+ 	  }
+ 	if (statbuf.st_size < size)
+ 	  {
+ 	    ftruncate_status = ftruncate(fd, size);
+ 	    if(ftruncate_status<0)
+ 	      {
+ 		ereport(FATAL,
+ 			(errmsg("could not set the proper shared memory segment size : %m"),
+ 			 errdetail("Failed system call was ftruncate(fd=%d,size=%lu).",fd,size)));
+ 		  return NULL;
+ 	      }
+ 	  }
+ 	
+ 	/* OK, should be able to attach to the segment */
+ 	shmaddr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+ 
+ 	if (shmaddr == MAP_FAILED)
+ 	  elog(FATAL, "mmap with size=%ul and fd=%d failed: %m", (unsigned int) size, fd);
+ 
+ 	/* Register on-exit routine to detach new segment before deleting */
+ 	on_shmem_exit(IpcMemoryDetach, PointerGetDatum(shmaddr));
+ 
+ 	POSIXSharedMemoryFD = fd;
+ 	return shmaddr;
+ }
+ 
+ /****************************************************************************/
+ /*	IpcMemoryDetach(status, shmaddr)	removes a shared memory segment		*/
+ /*										from process' address space		*/
+ /*	(called as an on_shmem_exit callback, hence funny argument list)		*/
+ /****************************************************************************/
+ static void
+ IpcMemoryDetach(int status, Datum shmaddr)
+ {
+ 	PGShmemHeader  *hdr;
+ 	hdr = (PGShmemHeader *) DatumGetPointer(shmaddr);
+ 	
+ 	if (munmap(DatumGetPointer(shmaddr), hdr->totalsize) < 0)
+ 		elog(LOG, "munmap(%p, ...) failed: %m", DatumGetPointer(shmaddr));
+ }
+ 
+ /*
+  * PGSharedMemoryIsInUse
+  *
+  * Is a previously-existing shmem segment still existing and in use?
+  *
+  * The point of this exercise is to detect the case where a prior postmaster
+  * crashed, but it left child backends that are still running.	Therefore
+  * we only care about shmem segments that are associated with the intended
+  * DataDir.  This is an important consideration since accidental matches of
+  * shmem segment IDs are reasonably common.
+  */
+ bool
+ PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
+ {
+ 	char		ipcName[IPCNameLength];
+ 	PGShmemHeader  *hdr;
+ 	int			fd, isValidHeader;
+ 	
+ #ifndef WIN32
+ 	struct stat statbuf;
+ #endif
+ 	
+ 	/*
+ 	 * We detect whether a shared memory segment is in use by seeing whether
+ 	 * we can open it. If so, 
+ 	 */
+ 	GenerateIPCName((uint8) id1, ipcName);
+ 	fd = shm_open(ipcName, O_RDWR, 0);
+ 	if (fd < 0)
+ 	{
+ 		/*
+ 		 * ENOENT means the segment no longer exists.
+ 		 */
+ 		if (errno == ENOENT)
+ 			return false;
+ 
+ 		/*
+ 		 * EACCES implies that the segment belongs to some other userid, which
+ 		 * means that there is an different account with the same database open.
+ 		 */
+ 		if (errno == EACCES)
+ 			return true;
+ 	}
+ 
+ 	/*
+ 	 * Try to attach to the segment and see if it matches our data directory,
+ 	 * just as a sanity check. Note that this is not absolutely necessary
+ 	 * since the data directory is encoded in the IPC shared memory key name.
+ 	 * 
+ 	 * On Windows, which doesn't have useful inode numbers, we can't do this
+ 	 * so we punt and assume that the shared memory is valid (which in all
+ 	 * likelihood it is).
+ 	 */
+ #ifdef WIN32
+ 	close(fd);
+ 	return true;
+ #else
+ 	if (stat(DataDir, &statbuf) < 0)
+ 	{
+ 		close(fd);
+ 		return true;			/* if can't stat, be conservative */
+ 	}
+ 
+ 	hdr = (PGShmemHeader *) mmap(NULL, sizeof(PGShmemHeader), PROT_READ, MAP_SHARED, fd, 0);
+ 	close(fd);
+ 
+ 	if (hdr == (PGShmemHeader *) -1)
+ 		return true;			/* if can't attach, be conservative */
+ 
+ 	isValidHeader = hdr->magic == PGShmemMagic &&
+ 		hdr->device == statbuf.st_dev &&
+ 		hdr->inode == statbuf.st_ino;
+ 	munmap((void *) hdr, sizeof(PGShmemHeader));
+ 	
+ 	/*
+ 	 * If true, it's either not a Postgres segment, or not one for my data
+ 	 * directory.  In either case it poses no threat.
+ 	 * If false, trouble -- looks a lot like there are still live backends
+ 	 */
+ 	
+ 	return isValidHeader;
+ #endif
+ }
+ 
+ 
+ /*
+  * PGSharedMemoryCreate
+  *
+  * Create a shared memory segment of the given size and initialize its
+  * standard header.  Also, register an on_shmem_exit callback to release
+  * the storage.
+  *
+  * Dead Postgres segments are released when found, but we do not fail upon
+  * collision with non-Postgres shmem segments, although this is astronomically
+  * unlikely.
+  *
+  * makePrivate means to always create a new segment, rather than attach to
+  * or recycle any existing segment. Currently, this value is ignored as
+  * all segments are newly created (the dead ones are simply released).
+  *
+  * Port is ignored. (It is leftover from the SysV shared memory routines.)
+  */
+ PGShmemHeader *
+ PGSharedMemoryCreate(Size size, bool makePrivate, int port)
+ {
+ 	uint8			instanceId;
+ 	void		   *shmaddr;
+ 	PGShmemHeader  *hdr;
+ 	char			ipcName[IPCNameLength];
+ 	
+ #ifndef WIN32
+ 	struct stat		statbuf;
+ #endif
+ 
+ 	/* Room for a header? */
+ 	Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
+ 
+ 	/* Make sure PGSharedMemoryAttach doesn't fail without need */
+ 	UsedShmemSegAddr = NULL;
+ 
+ 	/* Loop till we find a free IPC key */
+ 	for (instanceId = 0; true; instanceId++)
+ 	{
+ 		/*
+ 		 * Try to create new segment. InternalIpcMemoryCreate encodes the data
+ 		 * directory path name into the IPC key name, so if this fails
+ 		 * one of three things has happened:
+ 		 * 1) there is another postmaster still running with the same data directory
+ 		 * 2) the postmaster in this directory crashed or was kill -9'd
+ 		 *		and there are backends still running.
+ 		 * 3) the postmaster in this directory crashed or was kill -9'd and there 
+ 		 *		are no backends still running, just an orpaned shmem segment
+ 		 *
+ 		 * Case 1 is handled by the postmaster.pid file and doesn't concern us here.
+ 		 * For case 2 & 3 we now should unlink the shmem segment so that it is
+ 		 * cleaned up, either now (case 3) or when the backends terminate (case 2). 
+ 		 * Then we should try the next instanceId to create a new segment so this
+ 		 * process can be up and running quickly.  
+ 		 */
+ 		GenerateIPCName(instanceId, ipcName);
+ 		shmaddr = InternalIpcMemoryCreate(ipcName, instanceId, size);
+ 		if (shmaddr)
+ 			break;				/* successful create and attach */
+ 
+ 		/*
+ 		 * The segment appears to be from a dead Postgres process, or from a
+ 		 * previous cycle of life in this same process.  Zap it, if possible.
+ 		 * This shouldn't fail, but if it does, assume the segment
+ 		 * belongs to someone else after all, and continue quietly.
+ 		 */
+ 		shm_unlink(ipcName);
+ 	}
+ 
+ 	/* OK, we created a new segment.  Mark it as created by this process. */
+ 	hdr = (PGShmemHeader *) shmaddr;
+ 	hdr->creatorPID = getpid();
+ 	hdr->magic = PGShmemMagic;
+ 
+ #ifndef WIN32
+ 	/* Fill in the data directory ID info, too */
+ 	if (stat(DataDir, &statbuf) < 0)
+ 		ereport(FATAL,
+ 				(errcode_for_file_access(),
+ 				 errmsg("could not stat data directory \"%s\": %m",
+ 						DataDir)));
+ 	hdr->device = statbuf.st_dev;
+ 	hdr->inode = statbuf.st_ino;
+ #endif
+ 
+ 	/* Initialize space allocation status for segment. */
+ 	hdr->totalsize = size;
+ 	hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
+ 
+ 	/* Save info for possible future use */
+ 	UsedShmemInstanceId = instanceId;
+ 	UsedShmemSegAddr = shmaddr;
+ 
+ 	return hdr;
+ }
+ 
+ #ifdef EXEC_BACKEND
+ 
+ /*
+  * PGSharedMemoryReAttach
+  *
+  * Re-attach to an already existing shared memory segment.	In the non
+  * EXEC_BACKEND case this is not used, because postmaster children inherit
+  * the shared memory segment attachment via fork().
+  *
+  * UsedShmemInstanceId and UsedShmemSegAddr are implicit parameters to this
+  * routine.  The caller must have already restored them to the postmaster's
+  * values.
+  */
+ void
+ PGSharedMemoryReAttach(void)
+ {
+ 	int		fd;
+ 	void   *hdr;
+ 	void   *origUsedShmemSegAddr = UsedShmemSegAddr;
+ 
+ 	Assert(UsedShmemSegAddr != NULL);
+ 	Assert(IsUnderPostmaster);
+ 
+ #ifdef __CYGWIN__
+ 	/* cygipc (currently) appears to not detach on exec. */
+ 	PGSharedMemoryDetach();
+ 	UsedShmemSegAddr = origUsedShmemSegAddr;
+ #endif
+ 
+ 	elog(DEBUG3, "attaching to %p", UsedShmemSegAddr);
+ 	hdr = (void *) PGSharedMemoryAttach(UsedShmemInstanceId);
+ 	if (hdr == NULL)
+ 		elog(FATAL, "could not reattach to shared memory (instanceId=%d, addr=%p): %m",
+ 			 (int) UsedShmemInstanceId, UsedShmemSegAddr);
+ 	if (hdr != origUsedShmemSegAddr)
+ 		elog(FATAL, "reattaching to shared memory returned unexpected address (got %p, expected %p)",
+ 			 hdr, origUsedShmemSegAddr);
+ 
+ 	UsedShmemSegAddr = hdr;		/* probably redundant */
+ }
+ 
+ 
+ /*
+  * Attach to shared memory and make sure it has a Postgres header
+  *
+  * Returns attach address if OK, else NULL
+  */
+ static PGShmemHeader *
+ PGSharedMemoryAttach(uint8 instanceId)
+ {
+ 	PGShmemHeader *hdr;
+ 	char		ipcName[IPCNameLength];
+ 	Size		size;
+ 	int fd;
+ 
+ 	fd = POSIXSharedMemoryFD;
+ 
+ 	if (fd < 0)
+ 		return NULL;
+ 
+ 	hdr = (PGShmemHeader *) mmap(UsedShmemSegAddr, sizeof(PGShmemHeader),
+ 								 PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+ 
+ 	if (hdr == MMAP_FAILED)
+ 	{
+ 		return NULL;			/* failed to mmap- unlikely */
+ 	}
+ 
+ 	if (hdr->magic != PGShmemMagic)
+ 	{
+ 		munmap((void *) hdr, sizeof(PGShmemHeader));
+ 		return NULL;			/* segment belongs to a non-Postgres app */
+ 	}
+ 	
+ 	/* Since the segment has a valid Postgres header, unmap and re-map it with the proper size */
+ 	size = hdr->totalsize;
+ 	munmap((void *) hdr, sizeof(PGShmemHeader));
+ 	hdr = (PGShmemHeader *) mmap(UsedShmemSegAddr, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+ 	
+ 	if (hdr == MMAP_FAILED)   /* this shouldn't happen */
+ 		return NULL;
+ 	
+ 	return hdr;
+ }
+ #endif   /* EXEC_BACKEND */
+ 
+ /*
+  * PGSharedMemoryDetach
+  *
+  * Detach from the shared memory segment, if still attached.  This is not
+  * intended for use by the process that originally created the segment
+  * (it will have an on_shmem_exit callback registered to do that).	Rather,
+  * this is for subprocesses that have inherited an attachment and want to
+  * get rid of it.
+  */
+ void
+ PGSharedMemoryDetach(void)
+ {
+ 	PGShmemHeader  *hdr;
+ 	if (UsedShmemSegAddr != NULL)
+ 	{
+ 		hdr = (PGShmemHeader *) UsedShmemSegAddr;
+ 		if (munmap(UsedShmemSegAddr, hdr->totalsize) < 0)
+ 			elog(LOG, "munmap(%p) failed: %m", UsedShmemSegAddr);
+ 		UsedShmemSegAddr = NULL;
+ 	}
+ }
*** a/src/backend/port/sysv_shmem.c
--- /dev/null
***************
*** 1,550 ****
- /*-------------------------------------------------------------------------
-  *
-  * sysv_shmem.c
-  *	  Implement shared memory using SysV facilities
-  *
-  * These routines represent a fairly thin layer on top of SysV shared
-  * memory functionality.
-  *
-  * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
-  * Portions Copyright (c) 1994, Regents of the University of California
-  *
-  * IDENTIFICATION
-  *	  src/backend/port/sysv_shmem.c
-  *
-  *-------------------------------------------------------------------------
-  */
- #include "postgres.h"
- 
- #include <signal.h>
- #include <unistd.h>
- #include <sys/file.h>
- #include <sys/stat.h>
- #ifdef HAVE_SYS_IPC_H
- #include <sys/ipc.h>
- #endif
- #ifdef HAVE_SYS_SHM_H
- #include <sys/shm.h>
- #endif
- #ifdef HAVE_KERNEL_OS_H
- #include <kernel/OS.h>
- #endif
- 
- #include "miscadmin.h"
- #include "storage/ipc.h"
- #include "storage/pg_shmem.h"
- 
- 
- typedef key_t IpcMemoryKey;		/* shared memory key passed to shmget(2) */
- typedef int IpcMemoryId;		/* shared memory ID returned by shmget(2) */
- 
- #define IPCProtection	(0600)	/* access/modify by user only */
- 
- #ifdef SHM_SHARE_MMU			/* use intimate shared memory on Solaris */
- #define PG_SHMAT_FLAGS			SHM_SHARE_MMU
- #else
- #define PG_SHMAT_FLAGS			0
- #endif
- 
- 
- unsigned long UsedShmemSegID = 0;
- void	   *UsedShmemSegAddr = NULL;
- 
- static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
- static void IpcMemoryDetach(int status, Datum shmaddr);
- static void IpcMemoryDelete(int status, Datum shmId);
- static PGShmemHeader *PGSharedMemoryAttach(IpcMemoryKey key,
- 					 IpcMemoryId *shmid);
- 
- 
- /*
-  *	InternalIpcMemoryCreate(memKey, size)
-  *
-  * Attempt to create a new shared memory segment with the specified key.
-  * Will fail (return NULL) if such a segment already exists.  If successful,
-  * attach the segment to the current process and return its attached address.
-  * On success, callbacks are registered with on_shmem_exit to detach and
-  * delete the segment when on_shmem_exit is called.
-  *
-  * If we fail with a failure code other than collision-with-existing-segment,
-  * print out an error and abort.  Other types of errors are not recoverable.
-  */
- static void *
- InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
- {
- 	IpcMemoryId shmid;
- 	void	   *memAddress;
- 
- 	shmid = shmget(memKey, size, IPC_CREAT | IPC_EXCL | IPCProtection);
- 
- 	if (shmid < 0)
- 	{
- 		/*
- 		 * Fail quietly if error indicates a collision with existing segment.
- 		 * One would expect EEXIST, given that we said IPC_EXCL, but perhaps
- 		 * we could get a permission violation instead?  Also, EIDRM might
- 		 * occur if an old seg is slated for destruction but not gone yet.
- 		 */
- 		if (errno == EEXIST || errno == EACCES
- #ifdef EIDRM
- 			|| errno == EIDRM
- #endif
- 			)
- 			return NULL;
- 
- 		/*
- 		 * Some BSD-derived kernels are known to return EINVAL, not EEXIST, if
- 		 * there is an existing segment but it's smaller than "size" (this is
- 		 * a result of poorly-thought-out ordering of error tests). To
- 		 * distinguish between collision and invalid size in such cases, we
- 		 * make a second try with size = 0.  These kernels do not test size
- 		 * against SHMMIN in the preexisting-segment case, so we will not get
- 		 * EINVAL a second time if there is such a segment.
- 		 */
- 		if (errno == EINVAL)
- 		{
- 			int			save_errno = errno;
- 
- 			shmid = shmget(memKey, 0, IPC_CREAT | IPC_EXCL | IPCProtection);
- 
- 			if (shmid < 0)
- 			{
- 				/* As above, fail quietly if we verify a collision */
- 				if (errno == EEXIST || errno == EACCES
- #ifdef EIDRM
- 					|| errno == EIDRM
- #endif
- 					)
- 					return NULL;
- 				/* Otherwise, fall through to report the original error */
- 			}
- 			else
- 			{
- 				/*
- 				 * On most platforms we cannot get here because SHMMIN is
- 				 * greater than zero.  However, if we do succeed in creating a
- 				 * zero-size segment, free it and then fall through to report
- 				 * the original error.
- 				 */
- 				if (shmctl(shmid, IPC_RMID, NULL) < 0)
- 					elog(LOG, "shmctl(%d, %d, 0) failed: %m",
- 						 (int) shmid, IPC_RMID);
- 			}
- 
- 			errno = save_errno;
- 		}
- 
- 		/*
- 		 * Else complain and abort.
- 		 *
- 		 * Note: at this point EINVAL should mean that either SHMMIN or SHMMAX
- 		 * is violated.  SHMALL violation might be reported as either ENOMEM
- 		 * (BSDen) or ENOSPC (Linux); the Single Unix Spec fails to say which
- 		 * it should be.  SHMMNI violation is ENOSPC, per spec.  Just plain
- 		 * not-enough-RAM is ENOMEM.
- 		 */
- 		ereport(FATAL,
- 				(errmsg("could not create shared memory segment: %m"),
- 		  errdetail("Failed system call was shmget(key=%lu, size=%lu, 0%o).",
- 					(unsigned long) memKey, (unsigned long) size,
- 					IPC_CREAT | IPC_EXCL | IPCProtection),
- 				 (errno == EINVAL) ?
- 				 errhint("This error usually means that PostgreSQL's request for a shared memory "
- 		  "segment exceeded your kernel's SHMMAX parameter.  You can either "
- 						 "reduce the request size or reconfigure the kernel with larger SHMMAX.  "
- 				  "To reduce the request size (currently %lu bytes), reduce "
- 					   "PostgreSQL's shared memory usage, perhaps by reducing shared_buffers "
- 						 "or max_connections.\n"
- 						 "If the request size is already small, it's possible that it is less than "
- 						 "your kernel's SHMMIN parameter, in which case raising the request size or "
- 						 "reconfiguring SHMMIN is called for.\n"
- 		"The PostgreSQL documentation contains more information about shared "
- 						 "memory configuration.",
- 						 (unsigned long) size) : 0,
- 				 (errno == ENOMEM) ?
- 				 errhint("This error usually means that PostgreSQL's request for a shared "
- 				   "memory segment exceeded available memory or swap space, "
- 						 "or exceeded your kernel's SHMALL parameter.  You can either "
- 						 "reduce the request size or reconfigure the kernel with larger SHMALL.  "
- 				  "To reduce the request size (currently %lu bytes), reduce "
- 					   "PostgreSQL's shared memory usage, perhaps by reducing shared_buffers "
- 						 "or max_connections.\n"
- 		"The PostgreSQL documentation contains more information about shared "
- 						 "memory configuration.",
- 						 (unsigned long) size) : 0,
- 				 (errno == ENOSPC) ?
- 				 errhint("This error does *not* mean that you have run out of disk space. "
- 						 "It occurs either if all available shared memory IDs have been taken, "
- 						 "in which case you need to raise the SHMMNI parameter in your kernel, "
- 		  "or because the system's overall limit for shared memory has been "
- 				 "reached.  If you cannot increase the shared memory limit, "
- 		  "reduce PostgreSQL's shared memory request (currently %lu bytes), "
- 				   "perhaps by reducing shared_buffers or max_connections.\n"
- 		"The PostgreSQL documentation contains more information about shared "
- 						 "memory configuration.",
- 						 (unsigned long) size) : 0));
- 	}
- 
- 	/* Register on-exit routine to delete the new segment */
- 	on_shmem_exit(IpcMemoryDelete, Int32GetDatum(shmid));
- 
- 	/* OK, should be able to attach to the segment */
- 	memAddress = shmat(shmid, NULL, PG_SHMAT_FLAGS);
- 
- 	if (memAddress == (void *) -1)
- 		elog(FATAL, "shmat(id=%d) failed: %m", shmid);
- 
- 	/* Register on-exit routine to detach new segment before deleting */
- 	on_shmem_exit(IpcMemoryDetach, PointerGetDatum(memAddress));
- 
- 	/*
- 	 * Store shmem key and ID in data directory lockfile.  Format to try to
- 	 * keep it the same length always (trailing junk in the lockfile won't
- 	 * hurt, but might confuse humans).
- 	 */
- 	{
- 		char line[64];
- 
- 		sprintf(line, "%9lu %9lu",
- 				(unsigned long) memKey, (unsigned long) shmid);
- 		AddToDataDirLockFile(LOCK_FILE_LINE_SHMEM_KEY, line);
- 	}
- 
- 	return memAddress;
- }
- 
- /****************************************************************************/
- /*	IpcMemoryDetach(status, shmaddr)	removes a shared memory segment		*/
- /*										from process' address spaceq		*/
- /*	(called as an on_shmem_exit callback, hence funny argument list)		*/
- /****************************************************************************/
- static void
- IpcMemoryDetach(int status, Datum shmaddr)
- {
- 	if (shmdt(DatumGetPointer(shmaddr)) < 0)
- 		elog(LOG, "shmdt(%p) failed: %m", DatumGetPointer(shmaddr));
- }
- 
- /****************************************************************************/
- /*	IpcMemoryDelete(status, shmId)		deletes a shared memory segment		*/
- /*	(called as an on_shmem_exit callback, hence funny argument list)		*/
- /****************************************************************************/
- static void
- IpcMemoryDelete(int status, Datum shmId)
- {
- 	if (shmctl(DatumGetInt32(shmId), IPC_RMID, NULL) < 0)
- 		elog(LOG, "shmctl(%d, %d, 0) failed: %m",
- 			 DatumGetInt32(shmId), IPC_RMID);
- }
- 
- /*
-  * PGSharedMemoryIsInUse
-  *
-  * Is a previously-existing shmem segment still existing and in use?
-  *
-  * The point of this exercise is to detect the case where a prior postmaster
-  * crashed, but it left child backends that are still running.	Therefore
-  * we only care about shmem segments that are associated with the intended
-  * DataDir.  This is an important consideration since accidental matches of
-  * shmem segment IDs are reasonably common.
-  */
- bool
- PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
- {
- 	IpcMemoryId shmId = (IpcMemoryId) id2;
- 	struct shmid_ds shmStat;
- 	struct stat statbuf;
- 	PGShmemHeader *hdr;
- 
- 	/*
- 	 * We detect whether a shared memory segment is in use by seeing whether
- 	 * it (a) exists and (b) has any processes attached to it.
- 	 */
- 	if (shmctl(shmId, IPC_STAT, &shmStat) < 0)
- 	{
- 		/*
- 		 * EINVAL actually has multiple possible causes documented in the
- 		 * shmctl man page, but we assume it must mean the segment no longer
- 		 * exists.
- 		 */
- 		if (errno == EINVAL)
- 			return false;
- 
- 		/*
- 		 * EACCES implies that the segment belongs to some other userid, which
- 		 * means it is not a Postgres shmem segment (or at least, not one that
- 		 * is relevant to our data directory).
- 		 */
- 		if (errno == EACCES)
- 			return false;
- 
- 		/*
- 		 * Some Linux kernel versions (in fact, all of them as of July 2007)
- 		 * sometimes return EIDRM when EINVAL is correct.  The Linux kernel
- 		 * actually does not have any internal state that would justify
- 		 * returning EIDRM, so we can get away with assuming that EIDRM is
- 		 * equivalent to EINVAL on that platform.
- 		 */
- #ifdef HAVE_LINUX_EIDRM_BUG
- 		if (errno == EIDRM)
- 			return false;
- #endif
- 
- 		/*
- 		 * Otherwise, we had better assume that the segment is in use. The
- 		 * only likely case is EIDRM, which implies that the segment has been
- 		 * IPC_RMID'd but there are still processes attached to it.
- 		 */
- 		return true;
- 	}
- 
- 	/* If it has no attached processes, it's not in use */
- 	if (shmStat.shm_nattch == 0)
- 		return false;
- 
- 	/*
- 	 * Try to attach to the segment and see if it matches our data directory.
- 	 * This avoids shmid-conflict problems on machines that are running
- 	 * several postmasters under the same userid.
- 	 */
- 	if (stat(DataDir, &statbuf) < 0)
- 		return true;			/* if can't stat, be conservative */
- 
- 	hdr = (PGShmemHeader *) shmat(shmId, NULL, PG_SHMAT_FLAGS);
- 
- 	if (hdr == (PGShmemHeader *) -1)
- 		return true;			/* if can't attach, be conservative */
- 
- 	if (hdr->magic != PGShmemMagic ||
- 		hdr->device != statbuf.st_dev ||
- 		hdr->inode != statbuf.st_ino)
- 	{
- 		/*
- 		 * It's either not a Postgres segment, or not one for my data
- 		 * directory.  In either case it poses no threat.
- 		 */
- 		shmdt((void *) hdr);
- 		return false;
- 	}
- 
- 	/* Trouble --- looks a lot like there's still live backends */
- 	shmdt((void *) hdr);
- 
- 	return true;
- }
- 
- 
- /*
-  * PGSharedMemoryCreate
-  *
-  * Create a shared memory segment of the given size and initialize its
-  * standard header.  Also, register an on_shmem_exit callback to release
-  * the storage.
-  *
-  * Dead Postgres segments are recycled if found, but we do not fail upon
-  * collision with non-Postgres shmem segments.	The idea here is to detect and
-  * re-use keys that may have been assigned by a crashed postmaster or backend.
-  *
-  * makePrivate means to always create a new segment, rather than attach to
-  * or recycle any existing segment.
-  *
-  * The port number is passed for possible use as a key (for SysV, we use
-  * it to generate the starting shmem key).	In a standalone backend,
-  * zero will be passed.
-  */
- PGShmemHeader *
- PGSharedMemoryCreate(Size size, bool makePrivate, int port)
- {
- 	IpcMemoryKey NextShmemSegID;
- 	void	   *memAddress;
- 	PGShmemHeader *hdr;
- 	IpcMemoryId shmid;
- 	struct stat statbuf;
- 
- 	/* Room for a header? */
- 	Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
- 
- 	/* Make sure PGSharedMemoryAttach doesn't fail without need */
- 	UsedShmemSegAddr = NULL;
- 
- 	/* Loop till we find a free IPC key */
- 	NextShmemSegID = port * 1000;
- 
- 	for (NextShmemSegID++;; NextShmemSegID++)
- 	{
- 		/* Try to create new segment */
- 		memAddress = InternalIpcMemoryCreate(NextShmemSegID, size);
- 		if (memAddress)
- 			break;				/* successful create and attach */
- 
- 		/* Check shared memory and possibly remove and recreate */
- 
- 		if (makePrivate)		/* a standalone backend shouldn't do this */
- 			continue;
- 
- 		if ((memAddress = PGSharedMemoryAttach(NextShmemSegID, &shmid)) == NULL)
- 			continue;			/* can't attach, not one of mine */
- 
- 		/*
- 		 * If I am not the creator and it belongs to an extant process,
- 		 * continue.
- 		 */
- 		hdr = (PGShmemHeader *) memAddress;
- 		if (hdr->creatorPID != getpid())
- 		{
- 			if (kill(hdr->creatorPID, 0) == 0 || errno != ESRCH)
- 			{
- 				shmdt(memAddress);
- 				continue;		/* segment belongs to a live process */
- 			}
- 		}
- 
- 		/*
- 		 * The segment appears to be from a dead Postgres process, or from a
- 		 * previous cycle of life in this same process.  Zap it, if possible.
- 		 * This probably shouldn't fail, but if it does, assume the segment
- 		 * belongs to someone else after all, and continue quietly.
- 		 */
- 		shmdt(memAddress);
- 		if (shmctl(shmid, IPC_RMID, NULL) < 0)
- 			continue;
- 
- 		/*
- 		 * Now try again to create the segment.
- 		 */
- 		memAddress = InternalIpcMemoryCreate(NextShmemSegID, size);
- 		if (memAddress)
- 			break;				/* successful create and attach */
- 
- 		/*
- 		 * Can only get here if some other process managed to create the same
- 		 * shmem key before we did.  Let him have that one, loop around to try
- 		 * next key.
- 		 */
- 	}
- 
- 	/*
- 	 * OK, we created a new segment.  Mark it as created by this process. The
- 	 * order of assignments here is critical so that another Postgres process
- 	 * can't see the header as valid but belonging to an invalid PID!
- 	 */
- 	hdr = (PGShmemHeader *) memAddress;
- 	hdr->creatorPID = getpid();
- 	hdr->magic = PGShmemMagic;
- 
- 	/* Fill in the data directory ID info, too */
- 	if (stat(DataDir, &statbuf) < 0)
- 		ereport(FATAL,
- 				(errcode_for_file_access(),
- 				 errmsg("could not stat data directory \"%s\": %m",
- 						DataDir)));
- 	hdr->device = statbuf.st_dev;
- 	hdr->inode = statbuf.st_ino;
- 
- 	/*
- 	 * Initialize space allocation status for segment.
- 	 */
- 	hdr->totalsize = size;
- 	hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
- 
- 	/* Save info for possible future use */
- 	UsedShmemSegAddr = memAddress;
- 	UsedShmemSegID = (unsigned long) NextShmemSegID;
- 
- 	return hdr;
- }
- 
- #ifdef EXEC_BACKEND
- 
- /*
-  * PGSharedMemoryReAttach
-  *
-  * Re-attach to an already existing shared memory segment.	In the non
-  * EXEC_BACKEND case this is not used, because postmaster children inherit
-  * the shared memory segment attachment via fork().
-  *
-  * UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
-  * routine.  The caller must have already restored them to the postmaster's
-  * values.
-  */
- void
- PGSharedMemoryReAttach(void)
- {
- 	IpcMemoryId shmid;
- 	void	   *hdr;
- 	void	   *origUsedShmemSegAddr = UsedShmemSegAddr;
- 
- 	Assert(UsedShmemSegAddr != NULL);
- 	Assert(IsUnderPostmaster);
- 
- #ifdef __CYGWIN__
- 	/* cygipc (currently) appears to not detach on exec. */
- 	PGSharedMemoryDetach();
- 	UsedShmemSegAddr = origUsedShmemSegAddr;
- #endif
- 
- 	elog(DEBUG3, "attaching to %p", UsedShmemSegAddr);
- 	hdr = (void *) PGSharedMemoryAttach((IpcMemoryKey) UsedShmemSegID, &shmid);
- 	if (hdr == NULL)
- 		elog(FATAL, "could not reattach to shared memory (key=%d, addr=%p): %m",
- 			 (int) UsedShmemSegID, UsedShmemSegAddr);
- 	if (hdr != origUsedShmemSegAddr)
- 		elog(FATAL, "reattaching to shared memory returned unexpected address (got %p, expected %p)",
- 			 hdr, origUsedShmemSegAddr);
- 
- 	UsedShmemSegAddr = hdr;		/* probably redundant */
- }
- #endif   /* EXEC_BACKEND */
- 
- /*
-  * PGSharedMemoryDetach
-  *
-  * Detach from the shared memory segment, if still attached.  This is not
-  * intended for use by the process that originally created the segment
-  * (it will have an on_shmem_exit callback registered to do that).	Rather,
-  * this is for subprocesses that have inherited an attachment and want to
-  * get rid of it.
-  */
- void
- PGSharedMemoryDetach(void)
- {
- 	if (UsedShmemSegAddr != NULL)
- 	{
- 		if ((shmdt(UsedShmemSegAddr) < 0)
- #if defined(EXEC_BACKEND) && defined(__CYGWIN__)
- 		/* Work-around for cygipc exec bug */
- 			&& shmdt(NULL) < 0
- #endif
- 			)
- 			elog(LOG, "shmdt(%p) failed: %m", UsedShmemSegAddr);
- 		UsedShmemSegAddr = NULL;
- 	}
- }
- 
- 
- /*
-  * Attach to shared memory and make sure it has a Postgres header
-  *
-  * Returns attach address if OK, else NULL
-  */
- static PGShmemHeader *
- PGSharedMemoryAttach(IpcMemoryKey key, IpcMemoryId *shmid)
- {
- 	PGShmemHeader *hdr;
- 
- 	if ((*shmid = shmget(key, sizeof(PGShmemHeader), 0)) < 0)
- 		return NULL;
- 
- 	hdr = (PGShmemHeader *) shmat(*shmid, UsedShmemSegAddr, PG_SHMAT_FLAGS);
- 
- 	if (hdr == (PGShmemHeader *) -1)
- 		return NULL;			/* failed: must be some other app's */
- 
- 	if (hdr->magic != PGShmemMagic)
- 	{
- 		shmdt((void *) hdr);
- 		return NULL;			/* segment belongs to a non-Postgres app */
- 	}
- 
- 	return hdr;
- }
--- 0 ----
*** a/src/backend/postmaster/autovacuum.c
--- b/src/backend/postmaster/autovacuum.c
***************
*** 368,373 **** StartAutoVacLauncher(void)
--- 368,376 ----
  			/* Lose the postmaster's on-exit routines */
  			on_exit_reset();
  
+                         /* Hold on to the data directory lock until this process dies. */
+                         AcquireDataDirLock();
+ 
  			AutoVacLauncherMain(0, NULL);
  			break;
  #endif
*** a/src/backend/postmaster/pgstat.c
--- b/src/backend/postmaster/pgstat.c
***************
*** 632,637 **** pgstat_start(void)
--- 632,640 ----
  			/* Lose the postmaster's on-exit routines */
  			on_exit_reset();
  
+ 			/* Hold on to the data directory lock for all long as we live.*/
+ 			AcquireDataDirLock();
+ 			
  			/* Drop our connection to postmaster's shared memory, as well */
  			PGSharedMemoryDetach();
  
*** a/src/backend/postmaster/postmaster.c
--- b/src/backend/postmaster/postmaster.c
***************
*** 484,489 **** PostmasterMain(int argc, char *argv[])
--- 484,490 ----
  	char	   *userDoption = NULL;
  	bool		listen_addr_saved = false;
  	int			i;
+         bool blockOnStartupLockOption = false;
  
  	MyProcPid = PostmasterPid = getpid();
  
***************
*** 529,535 **** PostmasterMain(int argc, char *argv[])
  	 * tcop/postgres.c (the option sets should not conflict) and with the
  	 * common help() function in main/main.c.
  	 */
! 	while ((opt = getopt(argc, argv, "A:B:c:D:d:EeFf:h:ijk:lN:nOo:Pp:r:S:sTt:W:-:")) != -1)
  	{
  		switch (opt)
  		{
--- 530,536 ----
  	 * tcop/postgres.c (the option sets should not conflict) and with the
  	 * common help() function in main/main.c.
  	 */
! 	while ((opt = getopt(argc, argv, "A:bB:c:D:d:EeFf:h:ijk:lN:nOo:Pp:r:S:sTt:W:-:")) != -1)
  	{
  		switch (opt)
  		{
***************
*** 537,542 **** PostmasterMain(int argc, char *argv[])
--- 538,546 ----
  				SetConfigOption("debug_assertions", optarg, PGC_POSTMASTER, PGC_S_ARGV);
  				break;
  
+                         case 'b':
+                                blockOnStartupLockOption = true;
+                                 break;
  			case 'B':
  				SetConfigOption("shared_buffers", optarg, PGC_POSTMASTER, PGC_S_ARGV);
  				break;
***************
*** 790,796 **** PostmasterMain(int argc, char *argv[])
  	 * For the same reason, it's best to grab the TCP socket(s) before the
  	 * Unix socket.
  	 */
! 	CreateDataDirLockFile(true);
  
  	/*
  	 * If timezone is not set, determine what the OS uses.	(In theory this
--- 794,800 ----
  	 * For the same reason, it's best to grab the TCP socket(s) before the
  	 * Unix socket.
  	 */
! 	CreateDataDirLockFile(true,blockOnStartupLockOption);
  
  	/*
  	 * If timezone is not set, determine what the OS uses.	(In theory this
*** a/src/backend/tcop/postgres.c
--- b/src/backend/tcop/postgres.c
***************
*** 3600,3606 **** PostgresMain(int argc, char *argv[], const char *username)
  		/*
  		 * Create lockfile for data directory.
  		 */
! 		CreateDataDirLockFile(false);
  	}
  
  	/* Early initialization */
--- 3600,3606 ----
  		/*
  		 * Create lockfile for data directory.
  		 */
! 		CreateDataDirLockFile(false,false);
  	}
  
  	/* Early initialization */
***************
*** 3618,3623 **** PostgresMain(int argc, char *argv[], const char *username)
--- 3618,3633 ----
  #else
  	InitProcess();
  #endif
+         if(IsUnderPostmaster)
+           {
+             /* acquire the lock file advisory lock (to eliminate multiple-postmaster race conditions) 
+              * postgresql backends (postmaster children) must acquire the read lock to signify that there are backends operating in the specific data directory
+              * this needs to be done after InitProcess because the function needs access to the shared memory proc array
+              */
+             AcquireDataDirLock();        
+           }
+ 
+ 
  
  	/* We need to allow SIGINT, etc during the initial transaction */
  	PG_SETMASK(&UnBlockSig);
*** a/src/backend/utils/init/miscinit.c
--- b/src/backend/utils/init/miscinit.c
***************
*** 44,57 ****
  #include "utils/memutils.h"
  #include "utils/syscache.h"
  
  
  #define DIRECTORY_LOCK_FILE		"postmaster.pid"
  
  ProcessingMode Mode = InitProcessing;
  
- /* Note: we rely on this to initialize as zeroes */
- static char socketLockFile[MAXPGPATH];
- 
  
  /* ----------------------------------------------------------------
   *		ignoring system indexes support stuff
--- 44,75 ----
  #include "utils/memutils.h"
  #include "utils/syscache.h"
  
+ /* Note: we rely on this to initialize as zeroes */
+ static char socketLockFile[MAXPGPATH];
  
  #define DIRECTORY_LOCK_FILE		"postmaster.pid"
+ static pid_t GetPIDHoldingLock(int fileDescriptor,bool exclusiveLockFlag);
+ static int AcquireLock(int fileDescriptor,bool exclusiveLockFlag,bool waitForLock);
+ static int ReleaseLock(int fileDescriptor);
+ void AcquireDataDirLock();
+ pid_t GetPIDHoldingDataDirLock();
+ static void WriteLockFileContents(char *lockFilePath,int lockFileFD,bool isPostmasterFlag,pid_t processPid,char *dataDirectoryPath,long startTime,int portNumber,char * socketDirectory);
+ 
+ /* enum used by CreateLockFile to report its success or error condition */
+ typedef enum
+   {
+     /* positive numbers refer to the PID of a conflicting lock-holding process, but not necessarily a postmaster */
+     CreateLockFileNoError=0, 
+     CreateLockFileFileError=-1, /*advises the caller to check the errno for the error */
+     CreateLockFileSharedLockAcquisitionError=-2,
+     CreateLockFileExclusiveLockCheckError=-3,
+   } CreateLockFileValue;
+ 
+ 
+ static CreateLockFileValue CreateLockFile(char *lockFilePath,bool amPostmaster,int *lockFileRetDescriptor,bool blockOnLockFlag);
  
  ProcessingMode Mode = InitProcessing;
  
  
  /* ----------------------------------------------------------------
   *		ignoring system indexes support stuff
***************
*** 627,635 **** GetUserNameFromId(Oid roleid)
  /*-------------------------------------------------------------------------
   *				Interlock-file support
   *
!  * These routines are used to create both a data-directory lockfile
!  * ($DATADIR/postmaster.pid) and a Unix-socket-file lockfile ($SOCKFILE.lock).
!  * Both kinds of files contain the same info:
   *
   *		Owning process' PID
   *		Data directory path
--- 645,653 ----
  /*-------------------------------------------------------------------------
   *				Interlock-file support
   *
!  * These routines are used to create a data-directory lockfile
!  * ($DATADIR/postmaster.pid).
!  * The file contains the info:
   *
   *		Owning process' PID
   *		Data directory path
***************
*** 642,963 **** GetUserNameFromId(Oid roleid)
   * A data-directory lockfile can optionally contain a third line, containing
   * the key and ID for the shared memory block used by this postmaster.
   *
-  * On successful lockfile creation, a proc_exit callback to remove the
-  * lockfile is automatically created.
   *-------------------------------------------------------------------------
   */
  
! /*
!  * proc_exit callback to remove a lockfile.
!  */
! static void
! UnlinkLockFile(int status, Datum filename)
! {
! 	char	   *fname = (char *) DatumGetPointer(filename);
! 
! 	if (fname != NULL)
! 	{
! 		if (unlink(fname) != 0)
! 		{
! 			/* Should we complain if the unlink fails? */
! 		}
! 		free(fname);
! 	}
! }
  
  /*
!  * Create a lockfile.
   *
!  * filename is the name of the lockfile to create.
!  * amPostmaster is used to determine how to encode the output PID.
!  * isDDLock and refName are used to determine what error message to produce.
   */
! static void
! CreateLockFile(const char *filename, bool amPostmaster,
! 			   bool isDDLock, const char *refName)
  {
! 	int			fd;
! 	char		buffer[MAXPGPATH * 2 + 256];
! 	int			ntries;
! 	int			len;
! 	int			encoded_pid;
! 	pid_t		other_pid;
! 	pid_t		my_pid,
! 				my_p_pid,
! 				my_gp_pid;
! 	const char *envvar;
! 
! 	/*
! 	 * If the PID in the lockfile is our own PID or our parent's or
! 	 * grandparent's PID, then the file must be stale (probably left over from
! 	 * a previous system boot cycle).  We need to check this because of the
! 	 * likelihood that a reboot will assign exactly the same PID as we had in
! 	 * the previous reboot, or one that's only one or two counts larger and
! 	 * hence the lockfile's PID now refers to an ancestor shell process.  We
! 	 * allow pg_ctl to pass down its parent shell PID (our grandparent PID)
! 	 * via the environment variable PG_GRANDPARENT_PID; this is so that
! 	 * launching the postmaster via pg_ctl can be just as reliable as
! 	 * launching it directly.  There is no provision for detecting
! 	 * further-removed ancestor processes, but if the init script is written
! 	 * carefully then all but the immediate parent shell will be root-owned
! 	 * processes and so the kill test will fail with EPERM.  Note that we
! 	 * cannot get a false negative this way, because an existing postmaster
! 	 * would surely never launch a competing postmaster or pg_ctl process
! 	 * directly.
! 	 */
! 	my_pid = getpid();
! 
! #ifndef WIN32
! 	my_p_pid = getppid();
! #else
! 
! 	/*
! 	 * Windows hasn't got getppid(), but doesn't need it since it's not using
! 	 * real kill() either...
! 	 */
! 	my_p_pid = 0;
! #endif
! 
! 	envvar = getenv("PG_GRANDPARENT_PID");
! 	if (envvar)
! 		my_gp_pid = atoi(envvar);
! 	else
! 		my_gp_pid = 0;
! 
! 	/*
! 	 * We need a loop here because of race conditions.	But don't loop forever
! 	 * (for example, a non-writable $PGDATA directory might cause a failure
! 	 * that won't go away).  100 tries seems like plenty.
! 	 */
! 	for (ntries = 0;; ntries++)
! 	{
! 		/*
! 		 * Try to create the lock file --- O_EXCL makes this atomic.
! 		 *
! 		 * Think not to make the file protection weaker than 0600.	See
! 		 * comments below.
! 		 */
! 		fd = open(filename, O_RDWR | O_CREAT | O_EXCL, 0600);
! 		if (fd >= 0)
! 			break;				/* Success; exit the retry loop */
! 
! 		/*
! 		 * Couldn't create the pid file. Probably it already exists.
! 		 */
! 		if ((errno != EEXIST && errno != EACCES) || ntries > 100)
! 			ereport(FATAL,
! 					(errcode_for_file_access(),
! 					 errmsg("could not create lock file \"%s\": %m",
! 							filename)));
! 
! 		/*
! 		 * Read the file to get the old owner's PID.  Note race condition
! 		 * here: file might have been deleted since we tried to create it.
! 		 */
! 		fd = open(filename, O_RDONLY, 0600);
! 		if (fd < 0)
! 		{
! 			if (errno == ENOENT)
! 				continue;		/* race condition; try again */
! 			ereport(FATAL,
! 					(errcode_for_file_access(),
! 					 errmsg("could not open lock file \"%s\": %m",
! 							filename)));
! 		}
! 		if ((len = read(fd, buffer, sizeof(buffer) - 1)) < 0)
! 			ereport(FATAL,
! 					(errcode_for_file_access(),
! 					 errmsg("could not read lock file \"%s\": %m",
! 							filename)));
! 		close(fd);
! 
! 		buffer[len] = '\0';
! 		encoded_pid = atoi(buffer);
! 
! 		/* if pid < 0, the pid is for postgres, not postmaster */
! 		other_pid = (pid_t) (encoded_pid < 0 ? -encoded_pid : encoded_pid);
! 
! 		if (other_pid <= 0)
! 			elog(FATAL, "bogus data in lock file \"%s\": \"%s\"",
! 				 filename, buffer);
! 
! 		/*
! 		 * Check to see if the other process still exists
! 		 *
! 		 * Per discussion above, my_pid, my_p_pid, and my_gp_pid can be
! 		 * ignored as false matches.
! 		 *
! 		 * Normally kill() will fail with ESRCH if the given PID doesn't
! 		 * exist.
! 		 *
! 		 * We can treat the EPERM-error case as okay because that error
! 		 * implies that the existing process has a different userid than we
! 		 * do, which means it cannot be a competing postmaster.  A postmaster
! 		 * cannot successfully attach to a data directory owned by a userid
! 		 * other than its own.	(This is now checked directly in
! 		 * checkDataDir(), but has been true for a long time because of the
! 		 * restriction that the data directory isn't group- or
! 		 * world-accessible.)  Also, since we create the lockfiles mode 600,
! 		 * we'd have failed above if the lockfile belonged to another userid
! 		 * --- which means that whatever process kill() is reporting about
! 		 * isn't the one that made the lockfile.  (NOTE: this last
! 		 * consideration is the only one that keeps us from blowing away a
! 		 * Unix socket file belonging to an instance of Postgres being run by
! 		 * someone else, at least on machines where /tmp hasn't got a
! 		 * stickybit.)
! 		 */
! 		if (other_pid != my_pid && other_pid != my_p_pid &&
! 			other_pid != my_gp_pid)
! 		{
! 			if (kill(other_pid, 0) == 0 ||
! 				(errno != ESRCH && errno != EPERM))
! 			{
! 				/* lockfile belongs to a live process */
! 				ereport(FATAL,
! 						(errcode(ERRCODE_LOCK_FILE_EXISTS),
! 						 errmsg("lock file \"%s\" already exists",
! 								filename),
! 						 isDDLock ?
! 						 (encoded_pid < 0 ?
! 						  errhint("Is another postgres (PID %d) running in data directory \"%s\"?",
! 								  (int) other_pid, refName) :
! 						  errhint("Is another postmaster (PID %d) running in data directory \"%s\"?",
! 								  (int) other_pid, refName)) :
! 						 (encoded_pid < 0 ?
! 						  errhint("Is another postgres (PID %d) using socket file \"%s\"?",
! 								  (int) other_pid, refName) :
! 						  errhint("Is another postmaster (PID %d) using socket file \"%s\"?",
! 								  (int) other_pid, refName))));
! 			}
! 		}
! 
! 		/*
! 		 * No, the creating process did not exist.	However, it could be that
! 		 * the postmaster crashed (or more likely was kill -9'd by a clueless
! 		 * admin) but has left orphan backends behind.	Check for this by
! 		 * looking to see if there is an associated shmem segment that is
! 		 * still in use.
! 		 *
! 		 * Note: because postmaster.pid is written in multiple steps, we might
! 		 * not find the shmem ID values in it; we can't treat that as an
! 		 * error.
! 		 */
! 		if (isDDLock)
! 		{
! 			char	   *ptr = buffer;
! 			unsigned long id1,
! 						id2;
! 			int			lineno;
! 
! 			for (lineno = 1; lineno < LOCK_FILE_LINE_SHMEM_KEY; lineno++)
! 			{
! 				if ((ptr = strchr(ptr, '\n')) == NULL)
! 					break;
! 				ptr++;
! 			}
! 
! 			if (ptr != NULL &&
! 				sscanf(ptr, "%lu %lu", &id1, &id2) == 2)
! 			{
! 				if (PGSharedMemoryIsInUse(id1, id2))
! 					ereport(FATAL,
! 							(errcode(ERRCODE_LOCK_FILE_EXISTS),
! 							 errmsg("pre-existing shared memory block "
! 									"(key %lu, ID %lu) is still in use",
! 									id1, id2),
! 							 errhint("If you're sure there are no old "
! 								"server processes still running, remove "
! 									 "the shared memory block "
! 									 "or just delete the file \"%s\".",
! 									 filename)));
! 			}
! 		}
! 
! 		/*
! 		 * Looks like nobody's home.  Unlink the file and try again to create
! 		 * it.	Need a loop because of possible race condition against other
! 		 * would-be creators.
! 		 */
! 		if (unlink(filename) < 0)
! 			ereport(FATAL,
! 					(errcode_for_file_access(),
! 					 errmsg("could not remove old lock file \"%s\": %m",
! 							filename),
! 					 errhint("The file seems accidentally left over, but "
! 						   "it could not be removed. Please remove the file "
! 							 "by hand and try again.")));
! 	}
  
! 	/*
! 	 * Successfully created the file, now fill it.  See comment in miscadmin.h
! 	 * about the contents.  Note that we write the same info into both datadir
! 	 * and socket lockfiles; although more stuff may get added to the datadir
! 	 * lockfile later.
! 	 */
! 	snprintf(buffer, sizeof(buffer), "%d\n%s\n%ld\n%d\n%s\n",
! 			 amPostmaster ? (int) my_pid : -((int) my_pid),
! 			 DataDir,
! 			 (long) MyStartTime,
! 			 PostPortNumber,
  #ifdef HAVE_UNIX_SOCKETS
! 			 (*UnixSocketDir != '\0') ? UnixSocketDir : DEFAULT_PGSOCKET_DIR
  #else
! 			 ""
  #endif
! 			 );
  
! 	errno = 0;
! 	if (write(fd, buffer, strlen(buffer)) != strlen(buffer))
! 	{
! 		int			save_errno = errno;
! 
! 		close(fd);
! 		unlink(filename);
! 		/* if write didn't set errno, assume problem is no disk space */
! 		errno = save_errno ? save_errno : ENOSPC;
! 		ereport(FATAL,
! 				(errcode_for_file_access(),
! 				 errmsg("could not write lock file \"%s\": %m", filename)));
! 	}
! 	if (pg_fsync(fd) != 0)
! 	{
! 		int			save_errno = errno;
! 
! 		close(fd);
! 		unlink(filename);
! 		errno = save_errno;
! 		ereport(FATAL,
! 				(errcode_for_file_access(),
! 				 errmsg("could not write lock file \"%s\": %m", filename)));
! 	}
! 	if (close(fd) != 0)
! 	{
! 		int			save_errno = errno;
  
! 		unlink(filename);
! 		errno = save_errno;
! 		ereport(FATAL,
! 				(errcode_for_file_access(),
! 				 errmsg("could not write lock file \"%s\": %m", filename)));
! 	}
  
! 	/*
! 	 * Arrange for automatic removal of lockfile at proc_exit.
! 	 */
! 	on_proc_exit(UnlinkLockFile, PointerGetDatum(strdup(filename)));
  }
  
  /*
!  * Create the data directory lockfile.
!  *
!  * When this is called, we must have already switched the working
!  * directory to DataDir, so we can just use a relative path.  This
!  * helps ensure that we are locking the directory we should be.
   */
! void
! CreateDataDirLockFile(bool amPostmaster)
  {
! 	CreateLockFile(DIRECTORY_LOCK_FILE, amPostmaster, true, DataDir);
  }
  
  /*
--- 660,888 ----
   * A data-directory lockfile can optionally contain a third line, containing
   * the key and ID for the shared memory block used by this postmaster.
   *
   *-------------------------------------------------------------------------
   */
  
! /* We hold onto the lockFile for the life of the process to hold onto the advisory locks. */
! static int DataDirLockFileFD = 0;
  
  /*
!  * Create the data directory lockfile.
   *
!  * When this is called, we must have already switched the working
!  * directory to DataDir, so we can just use a relative path.  This
!  * helps ensure that we are locking the directory we should be.
   */
! void
! CreateDataDirLockFile(bool amPostmaster,bool blockOptionFlag)
  {
!   char *lockFilePath=DIRECTORY_LOCK_FILE;
!   CreateLockFileValue error = CreateLockFile(lockFilePath,amPostmaster,&DataDirLockFileFD,blockOptionFlag);
!   if(error==CreateLockFileNoError)
!     {
!       return;
!     }
!   else if(error==CreateLockFileFileError)
!     {
!       ereport(FATAL,
!               (errmsg("failed operation on lock file at \"%s\": %m",lockFilePath)));
!     }
!   else if(error==CreateLockFileSharedLockAcquisitionError)
!     {
!       ereport(FATAL,
!               (errmsg("failed to acquire shared lock on file \"%s\": %m",lockFilePath)));
!     }
!   else if(error==CreateLockFileExclusiveLockCheckError)
!     {
!       ereport(FATAL,
!               (errmsg("failed to check for exclusive lock on file \"%s\": %m", lockFilePath)));
! 
!     }
!   else if(error>0)
!     {
!       /* error holds the pid of the conflicting process */
!       ereport(FATAL,
!               (errmsg("another postgresql process is running in the data directory \"%s\" with pid %d",DataDir,error),
!                errhint("kill the other server processes to start a new postgresql server")));
!     }
!   else
!     {
!       ereport(FATAL,
!               (errmsg("an unhandled locking error occurred")));
!     }
! }
  
! static CreateLockFileValue
! CreateLockFile(char *lockFilePath,bool amPostmaster,int *lockFileRetDescriptor,bool blockOnLockFlag)
! {
!   int success = 0;
!   pid_t pidHoldingLock;
!   int lockFileFD = 0;
! 
!   /* open the directory lock file- whether or not it already exists is irrelevant because we will check for file locks */
!   lockFileFD = open(lockFilePath, O_RDWR | O_CREAT, 0600);
!   if(lockFileFD<0)
!     {
!       return CreateLockFileFileError;
!     }
! 
!   if(!blockOnLockFlag)
!     {
!       /* Acquire the shared advisory lock without blocking*/
!       
!       success = AcquireLock(lockFileFD,false,false); 
!       if(success < 0)
!         {
!           /* We failed to acquire the read lock, which is unlikely because we no one should be holding an exclusive lock on it. */
!           return CreateLockFileSharedLockAcquisitionError;
!         }
!     }
!   else 
!     {
!       /* loop until we get the exclusive lock and the subsequent shared lock- waiting until the data directory is not being serviced is data directory postgresql hot standy mode*/
!       while(1)
!         {
!           success = AcquireLock(lockFileFD,true,true);
!           if(success < 0)
!             return CreateLockFileExclusiveLockCheckError;
!           
!           /* now we hold the exclusive lock, so demote to read lock, but be wary of the race condition whereby a different postmaster could also be waiting to grab the read lock too */
!           success = ReleaseLock(lockFileFD);
!           if(success < 0)
!             return CreateLockFileExclusiveLockCheckError;
!           
!           success = AcquireLock(lockFileFD,false,false);
!           if(success < 0)
!             {
!               /* d'oh- some other postmaster grabbed the exclusive lock in the meantime, so try again later */
!               pg_usleep(500L);
!               continue;
!             }
!           else
!             break;
!         }
!     }
! 
!   
!   /* Determine if acquiring an exclusive (write) lock would be denied. If so, there is another postmaster or postgres child process running, so abort. */
!   pidHoldingLock = GetPIDHoldingLock(lockFileFD,true);
!   if(pidHoldingLock < 0)
!     {
!       /* checking for a lock failed */
!       return CreateLockFileExclusiveLockCheckError;
!     }
!   else if(pidHoldingLock > 0)
!     {
!       /* there is another process holding the lock, so we must abort starting a new postmaster */
!       return pidHoldingLock;
!     }
!   /*no process would block the lock, so we are cleared for starting a new postmaster*/
!   WriteLockFileContents(lockFilePath,lockFileFD,
!                         true,
!                         getpid(),
!                         DataDir,
!                         (long)MyStartTime,
!                         PostPortNumber,
  #ifdef HAVE_UNIX_SOCKETS
!                         (*UnixSocketDir != '\0') ? UnixSocketDir : DEFAULT_PGSOCKET_DIR
  #else
!                          ""
  #endif
!                         );
!   /* There is no need to remove the lock file because the locks synchronize access, not the existence of the file. */
  
!   if(lockFileRetDescriptor != NULL)
!     *lockFileRetDescriptor = lockFileFD;
!   return CreateLockFileNoError;
! }
  
! static void WriteLockFileContents(char *lockFilePath,int lockFileFD,bool isPostmasterFlag,pid_t processPid,char *dataDirectoryPath,long startTime,int portNumber,char * socketDirectoryPath)
! {
!   char writeBuffer[MAXPGPATH * 2 + 256];  
!   snprintf(writeBuffer,sizeof(writeBuffer),"%d\n%s\n%ld\n%d\n%s\n",
!            isPostmasterFlag ? (int) processPid : -((int) processPid),
!            dataDirectoryPath,
!            startTime,
!            portNumber,
!            socketDirectoryPath
!            );
!   errno = 0;
!   if (write(lockFileFD, writeBuffer, strlen(writeBuffer)) != strlen(writeBuffer))
!     {
!       int                     save_errno = errno;
!       unlink(lockFilePath);
!       /* if write didn't set errno, assume problem is no disk space */
!       errno = save_errno ? save_errno : ENOSPC;
!       ereport(FATAL,
!               (errcode_for_file_access(),
!                errmsg("could not write lock file \"%s\": %m", lockFilePath)));
!     }
!   if (pg_fsync(lockFileFD) != 0)
!     {
!       int                     save_errno = errno;
! 
!       unlink(lockFilePath);
!       errno = save_errno;
!       ereport(FATAL,
!               (errcode_for_file_access(),
!                errmsg("could not write lock file \"%s\": %m", lockFilePath)));
!     }
!   return;
! }
  
! /* Called by pg_ctl to determine when the postmaster is shutdown. */
! pid_t GetPIDHoldingDataDirLock(void)
! {
! 	return GetPIDHoldingLock(DataDirLockFileFD,true);
  }
  
+ 
  /*
!  * Called by backends when they startup to signify that the data directory is in use
   */
! void AcquireDataDirLock(void)
  {
!   int success;
!   int exclusiveLockViolatingPID = 0;
!   /* get the read lock */
!   success = AcquireLock(DataDirLockFileFD,false,false); 
!   if(success < 0)
!     {
!       /* Failed to acquire read lock, bomb out */
!       ereport(FATAL,
!               (errmsg("failed to acquire lock on \"%s\": %m",DIRECTORY_LOCK_FILE)));
! 
!     }
!   /* verify that grabbing an exclusive lock would complain that the parent or PROC_ARRAY sibling process would cause exclusive lock acquisition to fail- otherwise a separate postmaster is holding the lock (eliminates a possible race condition when the postmaster spawns a backend, immediately dies and new postmaster takes over) */
!   exclusiveLockViolatingPID = GetPIDHoldingLock(DataDirLockFileFD,true);
!   if(exclusiveLockViolatingPID < 0)
!     {
!       /* error testing for the lock, very unlikely, but fatal */
!       ereport(FATAL,
!               (errmsg("failed to test for lock on \"%s\": %m",DIRECTORY_LOCK_FILE)));
!     }
!   else if(exclusiveLockViolatingPID == 0)
!     {
!       /* the postmaster should be holding the lock- in this case it is not (and this is the only backend running), so don't bother running the backend because the postmaster just died */
!       ereport(FATAL,
!               (errmsg("failed to initialize backend because the postmaster exited")));
!     }
!   else
!     {
!       /* the PID is valid, so we should check that the PID refers either to the postmaster or its children */
!       /* NOTE TO REVIEWER: is this too early to call BackendPidGetProc? */ 
!       PGPROC *violatingProc = NULL;
!       violatingProc = BackendPidGetProc(exclusiveLockViolatingPID);
! 
!       if(exclusiveLockViolatingPID != getppid() && 
!          violatingProc == NULL)
!         {
!           /* the violating lock is neither the postmaster nor a sibling child- data directory conflict detected! */
!           ereport(FATAL,
!                   (errmsg("backend startup race condition detected- another postmaster is running in this data directory")));
!         }
!     }
!   return;
  }
  
  /*
***************
*** 966,977 **** CreateDataDirLockFile(bool amPostmaster)
  void
  CreateSocketLockFile(const char *socketfile, bool amPostmaster)
  {
! 	char		lockfile[MAXPGPATH];
! 
! 	snprintf(lockfile, sizeof(lockfile), "%s.lock", socketfile);
! 	CreateLockFile(lockfile, amPostmaster, false, socketfile);
! 	/* Save name of lockfile for TouchSocketLockFile */
! 	strcpy(socketLockFile, lockfile);
  }
  
  /*
--- 891,939 ----
  void
  CreateSocketLockFile(const char *socketfile, bool amPostmaster)
  {
!   char lockFilePath[MAXPGPATH];
!   CreateLockFileValue error;
! 
!   snprintf(lockFilePath, sizeof(lockFilePath), "%s.lock", socketfile);
! 
!   /* This intentionally leaks the socket file descriptor- we hold onto it so that the lock is held until the process is exited */
!   error = CreateLockFile(lockFilePath, amPostmaster,NULL,false);
!   
!   if(error==CreateLockFileNoError)
!     {
!       return;
!     }
!   else if(error==CreateLockFileFileError)
!     {
!       ereport(FATAL,
!               (errmsg("failed operation on lock file at \"%s\": %m",lockFilePath)));
!     }
!   else if(error==CreateLockFileSharedLockAcquisitionError)
!     {
!       ereport(FATAL,
!               (errmsg("failed to acquire shared lock on file \"%s\": %m",lockFilePath)));
!     }
!   else if(error==CreateLockFileExclusiveLockCheckError)
!     {
!       ereport(FATAL,
!               (errmsg("failed to check for exclusive lock on file \"%s\": %m", lockFilePath)));
!       
!     }
!   else if(error>0)
!     {
!       /* error holds the pid of the conflicting process */
!       ereport(FATAL,
!               (errmsg("another postgresql process with pid %d is bound to the socket file at \"%s\"",error,lockFilePath),
!                errhint("configure a different socket file path in postgresql.conf or kill the conflicting postgresql server")));
!     }
!   else
!     {
!       ereport(FATAL,
!               (errmsg("an unhandled locking error occurred")));
!     }
!   
!   /* Save name of lockfile for TouchSocketLockFile */
!   strcpy(socketLockFile, lockFilePath);
  }
  
  /*
***************
*** 985,1020 **** CreateSocketLockFile(const char *socketfile, bool amPostmaster)
  void
  TouchSocketLockFile(void)
  {
! 	/* Do nothing if we did not create a socket... */
! 	if (socketLockFile[0] != '\0')
! 	{
! 		/*
! 		 * utime() is POSIX standard, utimes() is a common alternative; if we
! 		 * have neither, fall back to actually reading the file (which only
! 		 * sets the access time not mod time, but that should be enough in
! 		 * most cases).  In all paths, we ignore errors.
! 		 */
  #ifdef HAVE_UTIME
! 		utime(socketLockFile, NULL);
! #else							/* !HAVE_UTIME */
  #ifdef HAVE_UTIMES
! 		utimes(socketLockFile, NULL);
! #else							/* !HAVE_UTIMES */
! 		int			fd;
! 		char		buffer[1];
! 
! 		fd = open(socketLockFile, O_RDONLY | PG_BINARY, 0);
! 		if (fd >= 0)
! 		{
! 			read(fd, buffer, sizeof(buffer));
! 			close(fd);
! 		}
  #endif   /* HAVE_UTIMES */
  #endif   /* HAVE_UTIME */
! 	}
  }
  
- 
  /*
   * Add (or replace) a line in the data directory lock file.
   * The given string should not include a trailing newline.
--- 947,980 ----
  void
  TouchSocketLockFile(void)
  {
!   /* Do nothing if we did not create a socket... */
!   if (socketLockFile[0] != '\0')
!     {
!       /*
!        * utime() is POSIX standard, utimes() is a common alternative; if we
!        * have neither, fall back to actually reading the file (which only
!        * sets the access time not mod time, but that should be enough in
!        * most cases).  In all paths, we ignore errors.
!        */
  #ifdef HAVE_UTIME
!       utime(socketLockFile, NULL);
! #else/* !HAVE_UTIME */
  #ifdef HAVE_UTIMES
!       utimes(socketLockFile, NULL);
! #else/* !HAVE_UTIMES */
!       intfd;
!       charbuffer[1];
! 
!       fd = open(socketLockFile, O_RDONLY | PG_BINARY, 0);
!       if (fd >= 0)
!         {
!           read(fd, buffer, sizeof(buffer));
!         }
  #endif   /* HAVE_UTIMES */
  #endif   /* HAVE_UTIME */
!     }
  }
  
  /*
   * Add (or replace) a line in the data directory lock file.
   * The given string should not include a trailing newline.
***************
*** 1030,1043 **** AddToDataDirLockFile(int target_line, const char *str)
  	int			lineno;
  	char	   *ptr;
  	char		buffer[BLCKSZ];
  
! 	fd = open(DIRECTORY_LOCK_FILE, O_RDWR | PG_BINARY, 0);
! 	if (fd < 0)
  	{
  		ereport(LOG,
  				(errcode_for_file_access(),
! 				 errmsg("could not open file \"%s\": %m",
! 						DIRECTORY_LOCK_FILE)));
  		return;
  	}
  	len = read(fd, buffer, sizeof(buffer) - 1);
--- 990,1006 ----
  	int			lineno;
  	char	   *ptr;
  	char		buffer[BLCKSZ];
+         int success;
  
! 	fd = DataDirLockFileFD;
!         /* rewind the file handle to rewrite it */
!         success = lseek(fd,0,SEEK_SET);
! 	if (success < 0)
  	{
  		ereport(LOG,
  				(errcode_for_file_access(),
! 				 errmsg("could not seek lock file \"%s\": %m",
!                                         DIRECTORY_LOCK_FILE)));
  		return;
  	}
  	len = read(fd, buffer, sizeof(buffer) - 1);
***************
*** 1047,1053 **** AddToDataDirLockFile(int target_line, const char *str)
  				(errcode_for_file_access(),
  				 errmsg("could not read from file \"%s\": %m",
  						DIRECTORY_LOCK_FILE)));
- 		close(fd);
  		return;
  	}
  	buffer[len] = '\0';
--- 1010,1015 ----
***************
*** 1061,1067 **** AddToDataDirLockFile(int target_line, const char *str)
  		if ((ptr = strchr(ptr, '\n')) == NULL)
  		{
  			elog(LOG, "bogus data in \"%s\"", DIRECTORY_LOCK_FILE);
- 			close(fd);
  			return;
  		}
  		ptr++;
--- 1023,1028 ----
***************
*** 1088,1094 **** AddToDataDirLockFile(int target_line, const char *str)
  				(errcode_for_file_access(),
  				 errmsg("could not write to file \"%s\": %m",
  						DIRECTORY_LOCK_FILE)));
- 		close(fd);
  		return;
  	}
  	if (pg_fsync(fd) != 0)
--- 1049,1054 ----
***************
*** 1098,1110 **** AddToDataDirLockFile(int target_line, const char *str)
  				 errmsg("could not write to file \"%s\": %m",
  						DIRECTORY_LOCK_FILE)));
  	}
- 	if (close(fd) != 0)
- 	{
- 		ereport(LOG,
- 				(errcode_for_file_access(),
- 				 errmsg("could not write to file \"%s\": %m",
- 						DIRECTORY_LOCK_FILE)));
- 	}
  }
  
  
--- 1058,1063 ----
***************
*** 1300,1302 **** pg_bindtextdomain(const char *domain)
--- 1253,1300 ----
  	}
  #endif
  }
+ 
+ /* We can also offer the option to block until the other postmaster is cleared away using F_SETLKW */
+ static int AcquireLock(int fileDescriptor,bool exclusiveLockFlag,bool waitForLock)
+ {
+   struct flock lock = { 
+     .l_type = exclusiveLockFlag ? F_WRLCK : F_RDLCK,
+     .l_start = 0,
+     .l_whence = SEEK_SET,
+     .l_len = 100 
+   };
+   return fcntl(fileDescriptor , waitForLock ? F_SETLKW : F_SETLK, &lock);
+ }
+ 
+ static int ReleaseLock(int fileDescriptor)
+ {
+   struct flock lock = {
+     .l_type = F_UNLCK,
+     .l_start = 0,
+     .l_whence = SEEK_SET,
+     .l_len = 100
+   };
+   return fcntl(fileDescriptor, F_SETLK, &lock);
+ }
+ 
+ static pid_t GetPIDHoldingLock(int fileDescriptor,bool exclusiveLockFlag)
+ {
+   struct flock lock = {
+     .l_type = exclusiveLockFlag ? F_WRLCK : F_RDLCK,
+     .l_start = 0,
+     .l_whence = SEEK_SET,
+     .l_len = 100,
+     .l_pid = 0
+   };
+   int success;
+ 
+   success = fcntl(fileDescriptor,F_GETLK,&lock);
+   if(success < 0)
+     {
+       return (pid_t)success;
+     }
+   if(lock.l_whence == SEEK_SET)
+     return lock.l_pid;
+   else
+     return -1;
+ }
*** a/src/bin/pg_ctl/pg_ctl.c
--- b/src/bin/pg_ctl/pg_ctl.c
***************
*** 26,31 ****
--- 26,32 ----
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <unistd.h>
+ #include <fcntl.h>
  
  #ifdef HAVE_SYS_RESOURCE_H
  #include <sys/time.h>
***************
*** 271,297 **** get_pgpid(void)
  {
  	FILE	   *pidf;
  	long		pid;
  
  	pidf = fopen(pid_file, "r");
! 	if (pidf == NULL)
! 	{
! 		/* No pid file, not an error on startup */
! 		if (errno == ENOENT)
! 			return 0;
! 		else
! 		{
! 			write_stderr(_("%s: could not open PID file \"%s\": %s\n"),
! 						 progname, pid_file, strerror(errno));
! 			exit(1);
! 		}
! 	}
! 	if (fscanf(pidf, "%ld", &pid) != 1)
! 	{
! 		write_stderr(_("%s: invalid data in PID file \"%s\"\n"),
! 					 progname, pid_file);
! 		exit(1);
! 	}
  	fclose(pidf);
  	return (pgpid_t) pid;
  }
  
--- 272,320 ----
  {
  	FILE	   *pidf;
  	long		pid;
+         struct flock lock = {
+           .l_type =  F_WRLCK,
+           .l_start = 0,
+           .l_whence = SEEK_SET,
+           .l_len = 100,
+           .l_pid = 0
+         };
+         int success;
  
  	pidf = fopen(pid_file, "r");
! 
!         /* Attempt to acquire an exclusive lock. If that fails, we know that an existing backend is still holding a read lock. See src/backend/utils/init/miscinit.c for more details. */
!         if(pidf == NULL)
!           {
!             if(errno == ENOENT)
!               {
!                 /* No lock file found. */
!                 return 0;
!               }
!             else 
!               {
!                 write_stderr(_("%s: could not open PID file \"%s\": %s\n"),
!                              progname,pid_file,strerror(errno));
!                 exit(1);
!               }
!           }
!         success = fcntl(fileno(pidf),F_GETLK,&lock);
  	fclose(pidf);
+         if(success < 0)
+           {
+             /* Failed syscall */
+             write_stderr(_("%s: failed to test lock status: %s"),progname,strerror(errno));
+             exit(1);
+           }
+         if(lock.l_whence == SEEK_SET)
+           /* There is a pid holding a lock. */
+           return lock.l_pid;
+         else if(lock.l_type == F_UNLCK)
+           /* No lock would block exclusive access. */
+           return 0;
+         else
+           return -1;
+ 
  	return (pgpid_t) pid;
  }
  
*** a/src/include/miscadmin.h
--- b/src/include/miscadmin.h
***************
*** 373,379 **** extern char *local_preload_libraries_string;
  #define LOCK_FILE_LINE_LISTEN_ADDR	6
  #define LOCK_FILE_LINE_SHMEM_KEY	7
  
! extern void CreateDataDirLockFile(bool amPostmaster);
  extern void CreateSocketLockFile(const char *socketfile, bool amPostmaster);
  extern void TouchSocketLockFile(void);
  extern void AddToDataDirLockFile(int target_line, const char *str);
--- 373,381 ----
  #define LOCK_FILE_LINE_LISTEN_ADDR	6
  #define LOCK_FILE_LINE_SHMEM_KEY	7
  
! extern void CreateDataDirLockFile(bool amPostmaster,bool blockOptionFlag);
! extern void AcquireDataDirLock(void);
! extern pid_t GetPIDHoldingDataDirLock(void);
  extern void CreateSocketLockFile(const char *socketfile, bool amPostmaster);
  extern void TouchSocketLockFile(void);
  extern void AddToDataDirLockFile(int target_line, const char *str);