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Fix failure in CreateCheckPoint on some Alpha boxes --- it's not OK to

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assume that TAS() will always succeed the first time, even if the lock
is known to be free.  Also, make sure that code will eventually time out
and report a stuck spinlock, rather than looping forever.  Small cleanups
in s_lock.h, too.
This commit is contained in:
Tom Lane
2000-12-29 21:31:21 +00:00
parent 7d363c4c33
commit 7f60b81e1a
4 changed files with 196 additions and 179 deletions
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6
src/backend/storage/buffer/bufmgr.c
View File

@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.100 2000/12/28 13:00:21 vadim Exp $
* $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.101 2000/12/29 21:31:21 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -1987,7 +1987,7 @@ LockBuffer(Buffer buffer, int mode)
while (buf->ri_lock || buf->w_lock)
{
S_UNLOCK(&(buf->cntx_lock));
s_lock_sleep(i++);
S_LOCK_SLEEP(&(buf->cntx_lock), i++);
S_LOCK(&(buf->cntx_lock));
}
(buf->r_locks)++;
@@ -2013,7 +2013,7 @@ LockBuffer(Buffer buffer, int mode)
buf->ri_lock = true;
}
S_UNLOCK(&(buf->cntx_lock));
s_lock_sleep(i++);
S_LOCK_SLEEP(&(buf->cntx_lock), i++);
S_LOCK(&(buf->cntx_lock));
}
buf->w_lock = true;

52
src/backend/storage/buffer/s_lock.c
View File

@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/storage/buffer/Attic/s_lock.c,v 1.27 2000/12/11 00:49:51 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/storage/buffer/Attic/s_lock.c,v 1.28 2000/12/29 21:31:20 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -25,19 +25,21 @@
* number of microseconds to wait. This accomplishes pseudo random back-off.
* Values are not critical but 10 milliseconds is a common platform
* granularity.
* note: total time to cycle through all 16 entries might be about .07 sec.
*
* Total time to cycle through all 20 entries might be about .07 sec,
* so the given value of S_MAX_BUSY results in timeout after ~70 sec.
*/
#define S_NSPINCYCLE 20
#define S_MAX_BUSY 1000 * S_NSPINCYCLE
int s_spincycle[S_NSPINCYCLE] =
{0, 0, 0, 0, 10000, 0, 0, 0, 10000, 0,
{ 0, 0, 0, 0, 10000, 0, 0, 0, 10000, 0,
0, 10000, 0, 0, 10000, 0, 10000, 0, 10000, 10000
};
/*
* s_lock_stuck(lock) - complain about a stuck spinlock
* s_lock_stuck() - complain about a stuck spinlock
*/
static void
s_lock_stuck(volatile slock_t *lock, const char *file, const int line)
@@ -52,13 +54,38 @@ s_lock_stuck(volatile slock_t *lock, const char *file, const int line)
}
/*
* s_lock_sleep() - sleep a pseudo-random amount of time, check for timeout
*
* Normally 'microsec' is 0, specifying to use the next s_spincycle[] value.
* Some callers may pass a nonzero interval, specifying to use exactly that
* delay value rather than a pseudo-random delay.
*/
void
s_lock_sleep(unsigned spin)
s_lock_sleep(unsigned spins, int microsec,
volatile slock_t *lock,
const char *file, const int line)
{
struct timeval delay;
unsigned max_spins;
if (microsec > 0)
{
delay.tv_sec = 0;
delay.tv_usec = microsec;
/* two-minute timeout in this case */
max_spins = 120000000 / microsec;
}
else
{
delay.tv_sec = 0;
delay.tv_usec = s_spincycle[spins % S_NSPINCYCLE];
max_spins = S_MAX_BUSY;
}
if (spins > max_spins)
s_lock_stuck(lock, file, line);
delay.tv_sec = 0;
delay.tv_usec = s_spincycle[spin % S_NSPINCYCLE];
(void) select(0, NULL, NULL, NULL, &delay);
}
@@ -71,14 +98,13 @@ s_lock(volatile slock_t *lock, const char *file, const int line)
{
unsigned spins = 0;
/*
* If you are thinking of changing this code, be careful. This same
* loop logic is used in other places that call TAS() directly.
*/
while (TAS(lock))
{
s_lock_sleep(spins);
if (++spins > S_MAX_BUSY)
{
/* It's been over a minute... */
s_lock_stuck(lock, file, line);
}
s_lock_sleep(spins++, 0, lock, file, line);
}
}