Add a default local latch for use in signal handlers.

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: [email protected]

2 files changed, 8 insertions, 8 deletions

diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index cf094187661..48573bef60b 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -292,8 +292,8 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
-	if (set_latch_on_sigusr1 && MyProc != NULL)
-		SetLatch(&MyProc->procLatch);
+	if (set_latch_on_sigusr1)
+		SetLatch(MyLatch);
 
 	latch_sigusr1_handler();
 
diff --git a/src/backend/storage/ipc/shm_mq.c b/src/backend/storage/ipc/shm_mq.c
index 7c41400d216..d42a8d1ae4d 100644
--- a/src/backend/storage/ipc/shm_mq.c
+++ b/src/backend/storage/ipc/shm_mq.c
@@ -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();