diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/storage/lmgr/proc.c | 46 |
1 files changed, 34 insertions, 12 deletions
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ab096ac527..d3631a143b3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -7,7 +7,7 @@ * * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.30 1998/01/28 02:29:29 momjian Exp $ + * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.31 1998/02/19 15:04:45 momjian Exp $ * *------------------------------------------------------------------------- */ @@ -46,7 +46,7 @@ * This is so that we can support more backends. (system-wide semaphore * sets run out pretty fast.) -ay 4/95 * - * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.30 1998/01/28 02:29:29 momjian Exp $ + * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.31 1998/02/19 15:04:45 momjian Exp $ */ #include <sys/time.h> #include <unistd.h> @@ -451,19 +451,42 @@ ProcSleep(PROC_QUEUE *waitQueue, int prio, LOCK *lock) { - int i; + int i = 0; PROC *proc; struct itimerval timeval, dummy; + /* + * If the first entries in the waitQueue have a greater priority than + * we have, we must be a reader, and they must be a writers, and we + * must be here because the current holder is a writer or a + * reader but we don't share shared locks if a writer is waiting. + * We put ourselves after the writers. This way, we have a FIFO, but + * keep the readers together to give them decent priority, and no one + * starves. Because we group all readers together, a non-empty queue + * only has a few possible configurations: + * + * [readers] + * [writers] + * [readers][writers] + * [writers][readers] + * [writers][readers][writers] + * + * In a full queue, we would have a reader holding a lock, then a + * writer gets the lock, then a bunch of readers, made up of readers + * who could not share the first readlock because a writer was waiting, + * and new readers arriving while the writer had the lock. + * + */ proc = (PROC *) MAKE_PTR(waitQueue->links.prev); - for (i = 0; i < waitQueue->size; i++) - { - if (proc->prio >= prio) - proc = (PROC *) MAKE_PTR(proc->links.prev); - else - break; - } + + /* If we are a reader, and they are writers, skip past them */ + while (i++ < waitQueue->size && proc->prio > prio) + proc = (PROC *) MAKE_PTR(proc->links.prev); + + /* The rest of the queue is FIFO, with readers first, writers last */ + while (i++ < waitQueue->size && proc->prio <= prio) + proc = (PROC *) MAKE_PTR(proc->links.prev); MyProc->prio = prio; MyProc->token = token; @@ -596,8 +619,7 @@ ProcLockWakeup(PROC_QUEUE *queue, char *ltable, char *lock) /* * ProcWakeup removes proc from the lock waiting process queue and - * returns the next proc in chain. If a writer just dropped its - * lock and there are several waiting readers, wake them all up. + * returns the next proc in chain. */ proc = ProcWakeup(proc, NO_ERROR); |