Non-volatile variables used for spinlock manipulation
Since SpinLockAcquire() / SpinLockRelease() macros usually reference variables
declared as volatile, I wonder if the following changes should be applied.
--
Antonin Houska
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt
Web: http://www.postgresql-support.de, http://www.cybertec.at
Attachments:
volatile.patchtext/x-diffDownload
diff --git a/src/backend/storage/ipc/shm_mq.c b/src/backend/storage/ipc/shm_mq.c
index 0e60dbc..256d09d 100644
--- a/src/backend/storage/ipc/shm_mq.c
+++ b/src/backend/storage/ipc/shm_mq.c
@@ -195,11 +195,11 @@ shm_mq_set_receiver(shm_mq *mq, PGPROC *proc)
volatile shm_mq *vmq = mq;
PGPROC *sender;
- SpinLockAcquire(&mq->mq_mutex);
+ SpinLockAcquire(&vmq->mq_mutex);
Assert(vmq->mq_receiver == NULL);
vmq->mq_receiver = proc;
sender = vmq->mq_sender;
- SpinLockRelease(&mq->mq_mutex);
+ SpinLockRelease(&vmq->mq_mutex);
if (sender != NULL)
SetLatch(&sender->procLatch);
@@ -214,11 +214,11 @@ shm_mq_set_sender(shm_mq *mq, PGPROC *proc)
volatile shm_mq *vmq = mq;
PGPROC *receiver;
- SpinLockAcquire(&mq->mq_mutex);
+ SpinLockAcquire(&vmq->mq_mutex);
Assert(vmq->mq_sender == NULL);
vmq->mq_sender = proc;
receiver = vmq->mq_receiver;
- SpinLockRelease(&mq->mq_mutex);
+ SpinLockRelease(&vmq->mq_mutex);
if (receiver != NULL)
SetLatch(&receiver->procLatch);
@@ -233,9 +233,9 @@ shm_mq_get_receiver(shm_mq *mq)
volatile shm_mq *vmq = mq;
PGPROC *receiver;
- SpinLockAcquire(&mq->mq_mutex);
+ SpinLockAcquire(&vmq->mq_mutex);
receiver = vmq->mq_receiver;
- SpinLockRelease(&mq->mq_mutex);
+ SpinLockRelease(&vmq->mq_mutex);
return receiver;
}
@@ -249,9 +249,9 @@ shm_mq_get_sender(shm_mq *mq)
volatile shm_mq *vmq = mq;
PGPROC *sender;
- SpinLockAcquire(&mq->mq_mutex);
+ SpinLockAcquire(&vmq->mq_mutex);
sender = vmq->mq_sender;
- SpinLockRelease(&mq->mq_mutex);
+ SpinLockRelease(&vmq->mq_mutex);
return sender;
}
Antonin Houska <ah@cybertec.at> writes:
Since SpinLockAcquire() / SpinLockRelease() macros usually reference variables
declared as volatile, I wonder if the following changes should be applied.
We've been making changes to remove that requirement, so I think that at
least in 9.5/HEAD this isn't an issue anymore.
regards, tom lane
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On 2015-09-04 09:42:20 -0400, Tom Lane wrote:
Antonin Houska <ah@cybertec.at> writes:
Since SpinLockAcquire() / SpinLockRelease() macros usually reference variables
declared as volatile, I wonder if the following changes should be applied.We've been making changes to remove that requirement, so I think that at
least in 9.5/HEAD this isn't an issue anymore.
And even before that the pointer passed to SpinLockAcquire/Release()
didn't have to be volatile. The important thing was that read/writes
that are protected by the spinlock were only done via volatile
variables, to prevent them from being moved outside the critical
section. All the tas()/unlock section already force the pointer to the
lock to be volatile anyway.
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