diff options
| -rw-r--r-- | src/backend/storage/lmgr/s_lock.c | 71 |
1 files changed, 53 insertions, 18 deletions
diff --git a/src/backend/storage/lmgr/s_lock.c b/src/backend/storage/lmgr/s_lock.c index ff37daaa251..de6b355aace 100644 --- a/src/backend/storage/lmgr/s_lock.c +++ b/src/backend/storage/lmgr/s_lock.c @@ -9,7 +9,7 @@ * * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/s_lock.c,v 1.14 2003/08/04 15:28:33 tgl Exp $ + * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/s_lock.c,v 1.15 2003/08/06 16:43:43 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -31,7 +31,7 @@ s_lock_stuck(volatile slock_t *lock, const char *file, int line) fprintf(stderr, "\nStuck spinlock (%p) detected at %s:%d.\n", lock, file, line); - abort(); + exit(1); #else elog(PANIC, "stuck spinlock (%p) detected at %s:%d", lock, file, line); @@ -45,35 +45,68 @@ s_lock_stuck(volatile slock_t *lock, const char *file, int line) void s_lock(volatile slock_t *lock, const char *file, int line) { - unsigned spins = 0; - unsigned delays = 0; - struct timeval delay; - /* * We loop tightly for awhile, then delay using select() and try * again. Preferably, "awhile" should be a small multiple of the * maximum time we expect a spinlock to be held. 100 iterations seems - * about right. + * about right. In most multi-CPU scenarios, the spinlock is probably + * held by a process on another CPU and will be released before we + * finish 100 iterations. However, on a uniprocessor, the tight loop + * is just a waste of cycles, so don't iterate thousands of times. + * + * Once we do decide to block, we use randomly increasing select() delays. + * The first delay is 10 msec, then the delay randomly increases to about + * one second, after which we reset to 10 msec and start again. The idea + * here is that in the presence of heavy contention we need to increase + * the delay, else the spinlock holder may never get to run and release + * the lock. (Consider situation where spinlock holder has been nice'd + * down in priority by the scheduler --- it will not get scheduled until + * all would-be acquirers are sleeping, so if we always use a 10-msec + * sleep, there is a real possibility of starvation.) But we can't just + * clamp the delay to an upper bound, else it would take a long time to + * make a reasonable number of tries. * - * We use a 10 millisec select delay because that is the lower limit on - * many platforms. The timeout is figured on this delay only, and so - * the nominal 1 minute is a lower bound. + * We time out and declare error after NUM_DELAYS delays (thus, exactly + * that many tries). With the given settings, this will usually take + * 3 or so minutes. It seems better to fix the total number of tries (and + * thus the probability of unintended failure) than to fix the total time + * spent. + * + * The select() delays are measured in centiseconds (0.01 sec) because + * 10 msec is a common resolution limit at the OS level. */ #define SPINS_PER_DELAY 100 -#define DELAY_MSEC 10 -#define TIMEOUT_MSEC (60 * 1000) +#define NUM_DELAYS 1000 +#define MIN_DELAY_CSEC 1 +#define MAX_DELAY_CSEC 100 + + int spins = 0; + int delays = 0; + int cur_delay = MIN_DELAY_CSEC; + struct timeval delay; while (TAS(lock)) { if (++spins > SPINS_PER_DELAY) { - if (++delays > (TIMEOUT_MSEC / DELAY_MSEC)) + if (++delays > NUM_DELAYS) s_lock_stuck(lock, file, line); - delay.tv_sec = 0; - delay.tv_usec = DELAY_MSEC * 1000; + delay.tv_sec = cur_delay / 100; + delay.tv_usec = (cur_delay % 100) * 10000; (void) select(0, NULL, NULL, NULL, &delay); +#if defined(S_LOCK_TEST) + fprintf(stdout, "*"); fflush(stdout); +#endif + + /* increase delay by a random fraction between 1X and 2X */ + cur_delay += (int) (cur_delay * + (((double) random()) / ((double) MAX_RANDOM_VALUE)) + 0.5); + /* wrap back to minimum delay when max is exceeded */ + if (cur_delay > MAX_DELAY_CSEC) + cur_delay = MIN_DELAY_CSEC; + spins = 0; } } @@ -217,6 +250,8 @@ volatile slock_t test_lock; int main() { + srandom((unsigned int) time(NULL)); + S_INIT_LOCK(&test_lock); if (!S_LOCK_FREE(&test_lock)) @@ -249,9 +284,9 @@ main() return 1; } - printf("S_LOCK_TEST: this will hang for a minute or so and then abort\n"); - printf(" with a 'stuck spinlock' message if S_LOCK()\n"); - printf(" and TAS() are working.\n"); + printf("S_LOCK_TEST: this will print %d stars and then\n", NUM_DELAYS); + printf(" exit with a 'stuck spinlock' message\n"); + printf(" if S_LOCK() and TAS() are working.\n"); fflush(stdout); s_lock(&test_lock, __FILE__, __LINE__); |