From: Peter Eisentraut <peter@eisentraut.org>
Date: Mon, 25 Feb 2019 08:24:15 +0000 (+0100)
Subject: Remove volatile from latch API
X-Git-Url: http://git.postgresql.org/gitweb/-?a=commitdiff_plain;h=278584b526d71a3fe86f91be5870f99f38477e27;p=users%2Frhaas%2Fpostgres.git

Remove volatile from latch API

This was no longer useful since the latch functions use memory
barriers already, which are also compiler barriers, and volatile does
not help with cross-process access.

Discussion: https://www.postgresql.org/message-id/flat/20190218202511.qsfpuj5sy4dbezcw%40alap3.anarazel.de#18783c27d73e9e40009c82f6e0df0974
---

diff --git a/src/backend/storage/ipc/latch.c b/src/backend/storage/ipc/latch.c
index 7da337d11f..59fa917ae0 100644
--- a/src/backend/storage/ipc/latch.c
+++ b/src/backend/storage/ipc/latch.c
@@ -225,7 +225,7 @@ InitializeLatchSupport(void)
  * Initialize a process-local latch.
  */
 void
-InitLatch(volatile Latch *latch)
+InitLatch(Latch *latch)
 {
 	latch->is_set = false;
 	latch->owner_pid = MyProcPid;
@@ -257,7 +257,7 @@ InitLatch(volatile Latch *latch)
  * process references to postmaster-private latches or WaitEventSets.
  */
 void
-InitSharedLatch(volatile Latch *latch)
+InitSharedLatch(Latch *latch)
 {
 #ifdef WIN32
 	SECURITY_ATTRIBUTES sa;
@@ -293,7 +293,7 @@ InitSharedLatch(volatile Latch *latch)
  * as shared latches use SIGUSR1 for inter-process communication.
  */
 void
-OwnLatch(volatile Latch *latch)
+OwnLatch(Latch *latch)
 {
 	/* Sanity checks */
 	Assert(latch->is_shared);
@@ -313,7 +313,7 @@ OwnLatch(volatile Latch *latch)
  * Disown a shared latch currently owned by the current process.
  */
 void
-DisownLatch(volatile Latch *latch)
+DisownLatch(Latch *latch)
 {
 	Assert(latch->is_shared);
 	Assert(latch->owner_pid == MyProcPid);
@@ -341,7 +341,7 @@ DisownLatch(volatile Latch *latch)
  * we return all of them in one call, but we will return at least one.
  */
 int
-WaitLatch(volatile Latch *latch, int wakeEvents, long timeout,
+WaitLatch(Latch *latch, int wakeEvents, long timeout,
 		  uint32 wait_event_info)
 {
 	return WaitLatchOrSocket(latch, wakeEvents, PGINVALID_SOCKET, timeout,
@@ -366,7 +366,7 @@ WaitLatch(volatile Latch *latch, int wakeEvents, long timeout,
  * WaitEventSet instead; that's more efficient.
  */
 int
-WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
+WaitLatchOrSocket(Latch *latch, int wakeEvents, pgsocket sock,
 				  long timeout, uint32 wait_event_info)
 {
 	int			ret = 0;
@@ -381,7 +381,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
 
 	if (wakeEvents & WL_LATCH_SET)
 		AddWaitEventToSet(set, WL_LATCH_SET, PGINVALID_SOCKET,
-						  (Latch *) latch, NULL);
+						  latch, NULL);
 
 	/* Postmaster-managed callers must handle postmaster death somehow. */
 	Assert(!IsUnderPostmaster ||
@@ -433,7 +433,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
  * throwing an error is not a good idea.
  */
 void
-SetLatch(volatile Latch *latch)
+SetLatch(Latch *latch)
 {
 #ifndef WIN32
 	pid_t		owner_pid;
@@ -516,7 +516,7 @@ SetLatch(volatile Latch *latch)
  * the latch is set again before the WaitLatch call.
  */
 void
-ResetLatch(volatile Latch *latch)
+ResetLatch(Latch *latch)
 {
 	/* Only the owner should reset the latch */
 	Assert(latch->owner_pid == MyProcPid);
diff --git a/src/include/storage/latch.h b/src/include/storage/latch.h
index 5b48709c8a..fc995819d3 100644
--- a/src/include/storage/latch.h
+++ b/src/include/storage/latch.h
@@ -156,12 +156,12 @@ typedef struct WaitEventSet WaitEventSet;
  * prototypes for functions in latch.c
  */
 extern void InitializeLatchSupport(void);
-extern void InitLatch(volatile Latch *latch);
-extern void InitSharedLatch(volatile Latch *latch);
-extern void OwnLatch(volatile Latch *latch);
-extern void DisownLatch(volatile Latch *latch);
-extern void SetLatch(volatile Latch *latch);
-extern void ResetLatch(volatile Latch *latch);
+extern void InitLatch(Latch *latch);
+extern void InitSharedLatch(Latch *latch);
+extern void OwnLatch(Latch *latch);
+extern void DisownLatch(Latch *latch);
+extern void SetLatch(Latch *latch);
+extern void ResetLatch(Latch *latch);
 
 extern WaitEventSet *CreateWaitEventSet(MemoryContext context, int nevents);
 extern void FreeWaitEventSet(WaitEventSet *set);
@@ -172,9 +172,9 @@ extern void ModifyWaitEvent(WaitEventSet *set, int pos, uint32 events, Latch *la
 extern int WaitEventSetWait(WaitEventSet *set, long timeout,
 				 WaitEvent *occurred_events, int nevents,
 				 uint32 wait_event_info);
-extern int WaitLatch(volatile Latch *latch, int wakeEvents, long timeout,
+extern int WaitLatch(Latch *latch, int wakeEvents, long timeout,
 		  uint32 wait_event_info);
-extern int WaitLatchOrSocket(volatile Latch *latch, int wakeEvents,
+extern int WaitLatchOrSocket(Latch *latch, int wakeEvents,
 				  pgsocket sock, long timeout, uint32 wait_event_info);
 
 /*