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, 4 insertions, 8 deletions

diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index f805368899a..8f743536cff 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -2607,8 +2607,7 @@ die(SIGNAL_ARGS)
 	}
 
 	/* If we're still here, waken anything waiting on the process latch */
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -2649,8 +2648,7 @@ StatementCancelHandler(SIGNAL_ARGS)
 	}
 
 	/* If we're still here, waken anything waiting on the process latch */
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -2675,8 +2673,7 @@ SigHupHandler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_SIGHUP = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -2814,8 +2811,7 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 	 * waiting on that latch, expecting to get interrupted by query cancels et
 	 * al., would also need to set set_latch_on_sigusr1.
 	 */
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }