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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2001-12-11 02:58:49 +0000 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2001-12-11 02:58:49 +0000 |
| commit | 4433eb1dff36707914081efeaff222f81412d60f (patch) | |
| tree | 2e5d04e18ca0a271623ee4fa15210881a8e219ce /src | |
| parent | 07009651ce4b2cc866171aed32bb67c8c65137ce (diff) | |
| download | postgresql-4433eb1dff36707914081efeaff222f81412d60f.tar.gz postgresql-4433eb1dff36707914081efeaff222f81412d60f.zip | |
Make sure that inlined S_UNLOCK is marked as an update of a 'volatile'
object. This should prevent the compiler from reordering loads and stores
into or out of a critical section.
Diffstat (limited to 'src')
| -rw-r--r-- | src/include/storage/s_lock.h | 11 |
1 files changed, 8 insertions, 3 deletions
diff --git a/src/include/storage/s_lock.h b/src/include/storage/s_lock.h index 166019a6faf..721b488c087 100644 --- a/src/include/storage/s_lock.h +++ b/src/include/storage/s_lock.h @@ -43,6 +43,11 @@ * will "fail" if interrupted. Therefore TAS() should always be invoked * in a retry loop, even if you are certain the lock is free. * + * ANOTHER CAUTION: be sure that TAS() and S_UNLOCK() represent sequence + * points, ie, loads and stores of other values must not be moved across + * a lock or unlock. In most cases it suffices to make the operation be + * done through a "volatile" pointer. + * * On most supported platforms, TAS() uses a tas() function written * in assembly language to execute a hardware atomic-test-and-set * instruction. Equivalent OS-supplied mutex routines could be used too. @@ -58,7 +63,7 @@ * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $Id: s_lock.h,v 1.95 2001/09/29 04:02:26 tgl Exp $ + * $Id: s_lock.h,v 1.96 2001/12/11 02:58:49 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -306,7 +311,7 @@ tas(volatile slock_t *s_lock) do \ {\ __asm__ __volatile__ (" mb \n"); \ - *(lock) = 0; \ + *((volatile slock_t *) (lock)) = 0; \ } while (0) static __inline__ int @@ -500,7 +505,7 @@ extern int tas_sema(volatile slock_t *lock); #endif /* S_LOCK_FREE */ #if !defined(S_UNLOCK) -#define S_UNLOCK(lock) (*(lock) = 0) +#define S_UNLOCK(lock) (*((volatile slock_t *) (lock)) = 0) #endif /* S_UNLOCK */ #if !defined(S_INIT_LOCK) |