Merge changes from Daniel Boulet to avoid waiting for the semaphore lock in
semexit() if there are no undo records to process.
This commit is contained in:
mycroft
parent
181155cde0
commit
af33b8e0c6
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@ -1,4 +1,4 @@
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/* $NetBSD: sysv_sem.c,v 1.13 1994/12/05 06:46:29 mycroft Exp $ */
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/* $NetBSD: sysv_sem.c,v 1.14 1994/12/05 07:22:12 mycroft Exp $ */
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/*
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* Implementation of SVID semaphores
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@ -826,11 +826,6 @@ semexit(p)
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{
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register struct sem_undo *suptr;
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register struct sem_undo **supptr;
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int did_something;
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semwait();
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did_something = 0;
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/*
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* Go through the chain of undo vectors looking for one
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@ -843,8 +838,83 @@ semexit(p)
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break;
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}
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if (suptr == NULL)
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goto unlock;
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/*
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* There are a few possibilities to consider here ...
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*
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* 1) The semaphore facility isn't currently locked. In this case,
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* this call should proceed normally.
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* 2) The semaphore facility is locked by this process (i.e. the one
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* that is exiting). In this case, this call should proceed as
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* usual and the facility should be unlocked at the end of this
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* routine (since the locker is exiting).
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* 3) The semaphore facility is locked by some other process and this
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* process doesn't have an undo structure allocated for it. In this
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* case, this call should proceed normally (i.e. not accomplish
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* anything and, most importantly, not block since that is
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* unnecessary and could result in a LOT of processes blocking in
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* here if the facility is locked for a long time).
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* 4) The semaphore facility is locked by some other process and this
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* process has an undo structure allocated for it. In this case,
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* this call should block until the facility has been unlocked since
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* the holder of the lock may be examining this process's proc entry
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* (the ipcs utility does this when printing out the information
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* from the allocated sem undo elements).
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*
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* This leads to the conclusion that we should not block unless we
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* discover that the someone else has the semaphore facility locked and
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* this process has an undo structure. Let's do that...
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*
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* Note that we do this in a separate pass from the one that processes
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* any existing undo structure since we don't want to risk blocking at
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* that time (it would make the actual unlinking of the element from
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* the chain of allocated undo structures rather messy).
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*/
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/*
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* Does someone else hold the semaphore facility's lock?
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*/
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if (semlock_holder != NULL && semlock_holder != p) {
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/*
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* Yes (i.e. we are in case 3 or 4).
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*
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* If we didn't find an undo record associated with this
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* process than we can just return (i.e. we are in case 3).
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*
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* Note that we know that someone else is holding the lock so
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* we don't even have to see if we're holding it...
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*/
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if (suptr == NULL)
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return;
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/*
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* We are in case 4.
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*
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* Go to sleep as long as someone else is locking the semaphore
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* facility (note that we won't get here if we are holding the
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* lock so we don't need to check for that possibility).
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*/
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while (semlock_holder != NULL)
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sleep((caddr_t)&semlock_holder, (PZERO - 4));
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/*
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* Nobody is holding the facility (i.e. we are now in case 1).
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* We can proceed safely according to the argument outlined
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* above.
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*/
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} else {
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/*
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* No (i.e. we are in case 1 or 2).
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*
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* If there is no undo record, skip to the end and unlock the
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* semaphore facility if necessary.
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*/
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if (suptr == NULL)
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goto unlock;
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}
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#ifdef SEM_DEBUG
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printf("proc @%08x has undo structure with %d entries\n", p,
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@ -877,13 +947,10 @@ semexit(p)
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semaptr->sem_base[semnum].semval);
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#endif
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if (adjval < 0) {
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if (semaptr->sem_base[semnum].semval < -adjval)
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semaptr->sem_base[semnum].semval = 0;
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else
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semaptr->sem_base[semnum].semval +=
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adjval;
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} else
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if (adjval < 0 &&
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semaptr->sem_base[semnum].semval < -adjval)
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semaptr->sem_base[semnum].semval = 0;
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else
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semaptr->sem_base[semnum].semval += adjval;
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#ifdef SEM_WAKEUP
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@ -909,7 +976,7 @@ semexit(p)
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unlock:
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/*
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* If the exiting process is holding the global semaphore facility
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* lock then release it.
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* lock (i.e. we are in case 2) then release it.
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*/
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if (semlock_holder == p) {
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semlock_holder = NULL;
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