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

4 files changed, 9 insertions, 12 deletions

diff --git a/src/test/modules/test_shm_mq/setup.c b/src/test/modules/test_shm_mq/setup.c
index b049cff2d05..195099095de 100644
--- a/src/test/modules/test_shm_mq/setup.c
+++ b/src/test/modules/test_shm_mq/setup.c
@@ -285,13 +285,13 @@ wait_for_workers_to_become_ready(worker_state *wstate,
 			}
 
 			/* 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();
diff --git a/src/test/modules/test_shm_mq/test.c b/src/test/modules/test_shm_mq/test.c
index 6428fcf51c4..732376daff2 100644
--- a/src/test/modules/test_shm_mq/test.c
+++ b/src/test/modules/test_shm_mq/test.c
@@ -230,9 +230,9 @@ test_shm_mq_pipelined(PG_FUNCTION_ARGS)
 			 * have read or written data and therefore there may now be work
 			 * for us to do.
 			 */
-			WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0);
+			WaitLatch(MyLatch, WL_LATCH_SET, 0);
 			CHECK_FOR_INTERRUPTS();
-			ResetLatch(&MyProc->procLatch);
+			ResetLatch(MyLatch);
 		}
 	}
 
diff --git a/src/test/modules/test_shm_mq/worker.c b/src/test/modules/test_shm_mq/worker.c
index dec058b55ea..a9d9e0e2552 100644
--- a/src/test/modules/test_shm_mq/worker.c
+++ b/src/test/modules/test_shm_mq/worker.c
@@ -211,8 +211,7 @@ handle_sigterm(SIGNAL_ARGS)
 {
 	int			save_errno = errno;
 
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	if (!proc_exit_inprogress)
 	{
diff --git a/src/test/modules/worker_spi/worker_spi.c b/src/test/modules/worker_spi/worker_spi.c
index ac0f59c9886..94d3857364f 100644
--- a/src/test/modules/worker_spi/worker_spi.c
+++ b/src/test/modules/worker_spi/worker_spi.c
@@ -74,8 +74,7 @@ worker_spi_sigterm(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_sigterm = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -91,8 +90,7 @@ worker_spi_sighup(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_sighup = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -227,10 +225,10 @@ worker_spi_main(Datum main_arg)
 		 * necessary, but is awakened if postmaster dies.  That way the
 		 * background process goes away immediately in an emergency.
 		 */
-		rc = WaitLatch(&MyProc->procLatch,
+		rc = WaitLatch(MyLatch,
 					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
 					   worker_spi_naptime * 1000L);
-		ResetLatch(&MyProc->procLatch);
+		ResetLatch(MyLatch);
 
 		/* emergency bailout if postmaster has died */
 		if (rc & WL_POSTMASTER_DEATH)