nssrwlk.c

来自「支持SSL v2/v3, TLS, PKCS #5, PKCS #7, PKCS」· C语言 代码 · 共 513 行 · 第 1/2 页

#ifdef NSS_RWLOCK_RANK_ORDER_DEBUG
    /*
     * update thread's lock rank
     */
    nssRWLock_UnsetThreadRank(me, rwlock);
#endif
    return;
}

/*
** Write-lock the RWLock.
*/
PR_IMPLEMENT(void)
NSSRWLock_LockWrite(NSSRWLock *rwlock)
{
    PRInt32 lock_acquired = 0;
    PRThread *me = PR_GetCurrentThread();

    PR_Lock(rwlock->rw_lock);
#ifdef NSS_RWLOCK_RANK_ORDER_DEBUG
    /*
     * assert that rank ordering is not violated; the rank of 'rwlock' should
     * be equal to or greater than the highest rank of all the locks held by
     * the thread.
     */
    PR_ASSERT((rwlock->rw_rank == NSS_RWLOCK_RANK_NONE) ||
                    (rwlock->rw_rank >= nssRWLock_GetThreadRank(me)));
#endif
    /*
     * wait if read locked or write locked.
     */
    PR_ASSERT(rwlock->rw_reader_locks >= 0);
    PR_ASSERT(me != NULL);

    UNTIL ( (rwlock->rw_owner == me) ||           /* I own write lock, or */
	   ((rwlock->rw_owner == NULL) &&	  /* no writer   and */
	    (rwlock->rw_reader_locks == 0))) {    /* no readers, either. */

        rwlock->rw_waiting_writers++;
        PR_WaitCondVar(rwlock->rw_writer_waitq, PR_INTERVAL_NO_TIMEOUT);
        rwlock->rw_waiting_writers--;
	PR_ASSERT(rwlock->rw_reader_locks >= 0);
    }

    PR_ASSERT(rwlock->rw_reader_locks == 0);
    /*
     * apply write lock
     */
    rwlock->rw_owner = me;
    rwlock->rw_writer_locks++; 		/* Increment write-lock count */

    PR_Unlock(rwlock->rw_lock);

#ifdef NSS_RWLOCK_RANK_ORDER_DEBUG
    /*
     * update thread's lock rank
     */
    nssRWLock_SetThreadRank(me,rwlock);
#endif
}

/* Unlock a Read lock held on this RW lock.
*/
PR_IMPLEMENT(void)
NSSRWLock_UnlockWrite(NSSRWLock *rwlock)
{
    PRThread *me = PR_GetCurrentThread();

    PR_Lock(rwlock->rw_lock);
    PR_ASSERT(rwlock->rw_owner == me); /* lock must be write-locked by me.  */
    PR_ASSERT(rwlock->rw_writer_locks > 0); /* lock must be write locked */

    if (  rwlock->rw_owner        == me  &&	/* I own it, and            */
          rwlock->rw_writer_locks  > 0   &&	/* I own it, and            */
        --rwlock->rw_writer_locks == 0) {	/* I'm all done with it     */

	rwlock->rw_owner = NULL;		/* I don't own it any more. */

	if (rwlock->rw_reader_locks == 0) { /* no readers, wake up somebody. */
	    /* Give preference to waiting writers. */
	    if (rwlock->rw_waiting_writers > 0) 
		PR_NotifyCondVar(rwlock->rw_writer_waitq);
	    else if (rwlock->rw_waiting_readers > 0)
		PR_NotifyAllCondVar(rwlock->rw_reader_waitq);
	}
    }
    PR_Unlock(rwlock->rw_lock);

#ifdef NSS_RWLOCK_RANK_ORDER_DEBUG
    /*
     * update thread's lock rank
     */
    nssRWLock_UnsetThreadRank(me, rwlock);
#endif
    return;
}

/* This is primarily for debugging, i.e. for inclusion in ASSERT calls. */
PR_IMPLEMENT(PRBool)
NSSRWLock_HaveWriteLock(NSSRWLock *rwlock) {
    PRBool ownWriteLock;
    PRThread *me = PR_GetCurrentThread();

    /* This lock call isn't really necessary.
    ** If this thread is the owner, that fact cannot change during this call,
    ** because this thread is in this call.
    ** If this thread is NOT the owner, the owner could change, but it 
    ** could not become this thread.  
    */
#if UNNECESSARY
    PR_Lock(rwlock->rw_lock);	
#endif
    ownWriteLock = (PRBool)(me == rwlock->rw_owner);
#if UNNECESSARY
    PR_Unlock(rwlock->rw_lock);
#endif
    return ownWriteLock;
}

#ifdef NSS_RWLOCK_RANK_ORDER_DEBUG

/*
 * nssRWLock_SetThreadRank
 *      Set a thread's lock rank, which is the highest of the ranks of all
 *      the locks held by the thread. Pointers to the locks are added to a
 *      per-thread list, which is anchored off a thread-private data key.
 */

static void
nssRWLock_SetThreadRank(PRThread *me, NSSRWLock *rwlock)
{
    thread_rwlock_stack *lock_stack;
    PRStatus rv;

    /*
     * allocated thread-private-data for rwlock list, if not already allocated
     */
    if (!nss_thread_rwlock_initialized) {
        /*
         * allocate tpd, only if not failed already
         */
        if (!nss_thread_rwlock_alloc_failed) {
            if (PR_NewThreadPrivateIndex(&nss_thread_rwlock,
                                        nssRWLock_ReleaseLockStack)
                                                == PR_FAILURE) {
                nss_thread_rwlock_alloc_failed = 1;
                return;
            }
        } else
            return;
    }
    /*
     * allocate a lock stack
     */
    if ((lock_stack = PR_GetThreadPrivate(nss_thread_rwlock)) == NULL) {
        lock_stack = (thread_rwlock_stack *)
                        PR_CALLOC(1 * sizeof(thread_rwlock_stack));
        if (lock_stack) {
            rv = PR_SetThreadPrivate(nss_thread_rwlock, lock_stack);
            if (rv == PR_FAILURE) {
                PR_DELETE(lock_stack);
                nss_thread_rwlock_alloc_failed = 1;
                return;
            }
        } else {
            nss_thread_rwlock_alloc_failed = 1;
            return;
        }
    }
    /*
     * add rwlock to lock stack, if limit is not exceeded
     */
    if (lock_stack) {
        if (lock_stack->trs_index < _NSS_RWLOCK_RANK_ORDER_LIMIT)
            lock_stack->trs_stack[lock_stack->trs_index++] = rwlock;
    }
    nss_thread_rwlock_initialized = 1;
}

static void
nssRWLock_ReleaseLockStack(void *lock_stack)
{
    PR_ASSERT(lock_stack);
    PR_DELETE(lock_stack);
}

/*
 * nssRWLock_GetThreadRank
 *
 *      return thread's lock rank. If thread-private-data for the lock
 *      stack is not allocated, return NSS_RWLOCK_RANK_NONE.
 */

static PRUint32
nssRWLock_GetThreadRank(PRThread *me)
{
    thread_rwlock_stack *lock_stack;

    if (nss_thread_rwlock_initialized) {
        if ((lock_stack = PR_GetThreadPrivate(nss_thread_rwlock)) == NULL)
            return (NSS_RWLOCK_RANK_NONE);
        else
            return(lock_stack->trs_stack[lock_stack->trs_index - 1]->rw_rank);

    } else
            return (NSS_RWLOCK_RANK_NONE);
}

/*
 * nssRWLock_UnsetThreadRank
 *
 *      remove the rwlock from the lock stack. Since locks may not be
 *      unlocked in a FIFO order, the entire lock stack is searched.
 */

static void
nssRWLock_UnsetThreadRank(PRThread *me, NSSRWLock *rwlock)
{
    thread_rwlock_stack *lock_stack;
    int new_index = 0, index, done = 0;

    if (!nss_thread_rwlock_initialized)
        return;

    lock_stack = PR_GetThreadPrivate(nss_thread_rwlock);

    PR_ASSERT(lock_stack != NULL);

    index = lock_stack->trs_index - 1;
    while (index-- >= 0) {
        if ((lock_stack->trs_stack[index] == rwlock) && !done)  {
            /*
             * reset the slot for rwlock
             */
            lock_stack->trs_stack[index] = NULL;
            done = 1;
        }
        /*
         * search for the lowest-numbered empty slot, above which there are
         * no non-empty slots
         */
        if ((lock_stack->trs_stack[index] != NULL) && !new_index)
            new_index = index + 1;
        if (done && new_index)
            break;
    }
    /*
     * set top of stack to highest numbered empty slot
     */
    lock_stack->trs_index = new_index;

}

#endif  /* NSS_RWLOCK_RANK_ORDER_DEBUG */