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: 20140927191243.GD5423@alap3.anarazel.de

1 files changed, 5 insertions, 8 deletions

diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index 3c9c216c6f1..237be121dd6 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -360,7 +360,7 @@ CheckpointerMain(void)
 		int			rc;
 
 		/* Clear any already-pending wakeups */
-		ResetLatch(&MyProc->procLatch);
+		ResetLatch(MyLatch);
 
 		/*
 		 * Process any requests or signals received recently.
@@ -559,7 +559,7 @@ CheckpointerMain(void)
 			cur_timeout = Min(cur_timeout, XLogArchiveTimeout - elapsed_secs);
 		}
 
-		rc = WaitLatch(&MyProc->procLatch,
+		rc = WaitLatch(MyLatch,
 					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
 					   cur_timeout * 1000L /* convert to ms */ );
 
@@ -832,8 +832,7 @@ ChkptSigHupHandler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_SIGHUP = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -845,8 +844,7 @@ ReqCheckpointHandler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	checkpoint_requested = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -869,8 +867,7 @@ ReqShutdownHandler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	shutdown_requested = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }