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, 0 deletions

diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index b94a94499b7..6e33a172122 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -148,6 +148,7 @@ extern int	max_worker_processes;
 extern PGDLLIMPORT int MyProcPid;
 extern PGDLLIMPORT pg_time_t MyStartTime;
 extern PGDLLIMPORT struct Port *MyProcPort;
+extern PGDLLIMPORT struct Latch *MyLatch;
 extern long MyCancelKey;
 extern int	MyPMChildSlot;
 
@@ -302,6 +303,9 @@ extern void SetCurrentRoleId(Oid roleid, bool is_superuser);
 extern void SetDataDir(const char *dir);
 extern void ChangeToDataDir(void);
 
+extern void SwitchToSharedLatch(void);
+extern void SwitchBackToLocalLatch(void);
+
 /* in utils/misc/superuser.c */
 extern bool superuser(void);	/* current user is superuser */
 extern bool superuser_arg(Oid roleid);	/* given user is superuser */