PQinSend question

Manfred Spraul <manfred@colorfullife.com> writes:

return false; /* No threading, so we can't be in send() */

Why not? Signal delivery can interrupt send() even with single-threaded
users.

It looks like Bruce left the old logic in place for unthreaded
implementations: we just replace the signal handler during every send().
So there's no need for PQinSend() to do anything useful.

regards, tom lane

Manfred Spraul wrote:

From fe-secure.c:

/*
* Indicates whether the current thread is in send()
* For use by SIGPIPE signal handlers; they should
* ignore SIGPIPE when libpq is in send(). This means
* that the backend has died unexpectedly.
*/
pqbool
PQinSend(void)
{
#ifdef ENABLE_THREAD_SAFETY
return (pthread_getspecific(thread_in_send) /* has it been
set? */ &&
*(char *)pthread_getspecific(thread_in_send)
== 't') ? true : false;
#else
return false; /* No threading, so we can't be in send() */

Why not? Signal delivery can interrupt send() even with single-threaded
users.

[ Sorry I am late replying to this.]

I have added the attached comment to CVS to more clearly describe why we
are returning false from PQinSend().

I really like the openssl interface: what about something like

typedef void (*pgsigpipehandler_t)(bool enable);

void PQregisterSignalCallback(pgsigpipehandler_t new);

The callback is global, and called around the send() calls.
The default handler uses the sigaction code from 7.4. The current
autodetection code is less flexible than a callback, and it's not 100%
backward compatible.

I think I addressed this and it is backward compatible (thread-local
storage), and requires no user application changes.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

Tom Lane wrote:

Manfred Spraul <manfred@colorfullife.com> writes:

return false; /* No threading, so we can't be in send() */

Why not? Signal delivery can interrupt send() even with single-threaded
users.

It looks like Bruce left the old logic in place for unthreaded
implementations: we just replace the signal handler during every send().
So there's no need for PQinSend() to do anything useful.

I have updated the CVS comments to more clearly explain this.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073