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Add a default local latch for use in signal handlers.

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To do so, move InitializeLatchSupport() into the new common process
initialization functions, and add a new global variable MyLatch.

MyLatch is usable as soon InitPostmasterChild() has been called
(i.e. very early during startup). Initially it points to a process
local latch that exists in all processes. InitProcess/InitAuxiliaryProcess
then replaces that local latch with PGPROC->procLatch. During shutdown
the reverse happens.

This is primarily advantageous for two reasons: For one it simplifies
dealing with the shared process latch, especially in signal handlers,
because instead of having to check for MyProc, MyLatch can be used
unconditionally. For another, a later patch that makes FEs/BE
communication use latches, now can rely on the existence of a latch,
even before having gone through InitProcess.

Discussion: 20140927191243.GD5423@alap3.anarazel.de
This commit is contained in:
Andres Freund
2015-01-14 18:45:22 +01:00
parent 85a2a8903f
commit 59f71a0d0b
23 changed files with 136 additions and 134 deletions
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12
src/backend/storage/ipc/shm_mq.c
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@@ -827,13 +827,13 @@ shm_mq_send_bytes(shm_mq_handle *mqh, Size nbytes, const void *data,
* at top of loop, because setting an already-set latch is much
* cheaper than setting one that has been reset.
*/
WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0);
WaitLatch(MyLatch, WL_LATCH_SET, 0);
/* An interrupt may have occurred while we were waiting. */
CHECK_FOR_INTERRUPTS();
/* Reset the latch so we don't spin. */
ResetLatch(&MyProc->procLatch);
ResetLatch(MyLatch);
}
else
{
@@ -924,13 +924,13 @@ shm_mq_receive_bytes(shm_mq *mq, Size bytes_needed, bool nowait,
* loop, because setting an already-set latch is much cheaper than
* setting one that has been reset.
*/
WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0);
WaitLatch(MyLatch, WL_LATCH_SET, 0);
/* An interrupt may have occurred while we were waiting. */
CHECK_FOR_INTERRUPTS();
/* Reset the latch so we don't spin. */
ResetLatch(&MyProc->procLatch);
ResetLatch(MyLatch);
}
}
@@ -991,13 +991,13 @@ shm_mq_wait_internal(volatile shm_mq *mq, PGPROC *volatile * ptr,
}
/* Wait to be signalled. */
WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0);
WaitLatch(MyLatch, WL_LATCH_SET, 0);
/* An interrupt may have occurred while we were waiting. */
CHECK_FOR_INTERRUPTS();
/* Reset the latch so we don't spin. */
ResetLatch(&MyProc->procLatch);
ResetLatch(MyLatch);
}
}
PG_CATCH();