path: root/nsprpub/pr/src/threads/prrwlock.c

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "primpl.h"

#include <string.h>

#if defined(HPUX) && defined(_PR_PTHREADS)

#include <pthread.h>
#define HAVE_UNIX98_RWLOCK
#define RWLOCK_T pthread_rwlock_t
#define RWLOCK_INIT(lock) pthread_rwlock_init(lock, NULL)
#define RWLOCK_DESTROY(lock) pthread_rwlock_destroy(lock)
#define RWLOCK_RDLOCK(lock) pthread_rwlock_rdlock(lock)
#define RWLOCK_WRLOCK(lock) pthread_rwlock_wrlock(lock)
#define RWLOCK_UNLOCK(lock) pthread_rwlock_unlock(lock)

#elif defined(SOLARIS) && (defined(_PR_PTHREADS) \
        || defined(_PR_GLOBAL_THREADS_ONLY))

#include <synch.h>
#define HAVE_UI_RWLOCK
#define RWLOCK_T rwlock_t
#define RWLOCK_INIT(lock) rwlock_init(lock, USYNC_THREAD, NULL)
#define RWLOCK_DESTROY(lock) rwlock_destroy(lock)
#define RWLOCK_RDLOCK(lock) rw_rdlock(lock)
#define RWLOCK_WRLOCK(lock) rw_wrlock(lock)
#define RWLOCK_UNLOCK(lock) rw_unlock(lock)

#endif

/*
 * Reader-writer lock
 */
struct PRRWLock {
    char            *rw_name;           /* lock name                    */
    PRUint32        rw_rank;            /* rank of the lock             */

#if defined(HAVE_UNIX98_RWLOCK) || defined(HAVE_UI_RWLOCK)
    RWLOCK_T        rw_lock;
#else
    PRLock          *rw_lock;
    PRInt32         rw_lock_cnt;        /* ==  0, if unlocked           */
    /* == -1, if write-locked       */
    /* > 0  , # of read locks       */
    PRUint32        rw_reader_cnt;      /* number of waiting readers    */
    PRUint32        rw_writer_cnt;      /* number of waiting writers    */
    PRCondVar       *rw_reader_waitq;   /* cvar for readers             */
    PRCondVar       *rw_writer_waitq;   /* cvar for writers             */
#ifdef DEBUG
    PRThread        *rw_owner;          /* lock owner for write-lock    */
#endif
#endif
};

#ifdef DEBUG
#define _PR_RWLOCK_RANK_ORDER_DEBUG /* enable deadlock detection using
                                       rank-order for locks
                                    */
#endif

#ifdef _PR_RWLOCK_RANK_ORDER_DEBUG

static PRUintn  pr_thread_rwlock_key;           /* TPD key for lock stack */
static PRUintn  pr_thread_rwlock_alloc_failed;

#define _PR_RWLOCK_RANK_ORDER_LIMIT 10

typedef struct thread_rwlock_stack {
    PRInt32     trs_index;                                  /* top of stack */
    PRRWLock    *trs_stack[_PR_RWLOCK_RANK_ORDER_LIMIT];    /* stack of lock
                                                               pointers */

} thread_rwlock_stack;

static void _PR_SET_THREAD_RWLOCK_RANK(PRRWLock *rwlock);
static PRUint32 _PR_GET_THREAD_RWLOCK_RANK(void);
static void _PR_UNSET_THREAD_RWLOCK_RANK(PRRWLock *rwlock);
static void _PR_RELEASE_LOCK_STACK(void *lock_stack);

#endif

/*
 * Reader/Writer Locks
 */

/*
 * PR_NewRWLock
 *      Create a reader-writer lock, with the given lock rank and lock name
 *
 */

PR_IMPLEMENT(PRRWLock *)
PR_NewRWLock(PRUint32 lock_rank, const char *lock_name)
{
    PRRWLock *rwlock;
#if defined(HAVE_UNIX98_RWLOCK) || defined(HAVE_UI_RWLOCK)
    int err;
#endif

    if (!_pr_initialized) {
        _PR_ImplicitInitialization();
    }

    rwlock = PR_NEWZAP(PRRWLock);
    if (rwlock == NULL) {
        return NULL;
    }

    rwlock->rw_rank = lock_rank;
    if (lock_name != NULL) {
        rwlock->rw_name = (char*) PR_Malloc(strlen(lock_name) + 1);
        if (rwlock->rw_name == NULL) {
            PR_DELETE(rwlock);
            return(NULL);
        }
        strcpy(rwlock->rw_name, lock_name);
    } else {
        rwlock->rw_name = NULL;
    }

#if defined(HAVE_UNIX98_RWLOCK) || defined(HAVE_UI_RWLOCK)
    err = RWLOCK_INIT(&rwlock->rw_lock);
    if (err != 0) {
        PR_SetError(PR_UNKNOWN_ERROR, err);
        PR_Free(rwlock->rw_name);
        PR_DELETE(rwlock);
        return NULL;
    }
    return rwlock;
#else
    rwlock->rw_lock = PR_NewLock();
    if (rwlock->rw_lock == NULL) {
        goto failed;
    }
    rwlock->rw_reader_waitq = PR_NewCondVar(rwlock->rw_lock);
    if (rwlock->rw_reader_waitq == NULL) {
        goto failed;
    }
    rwlock->rw_writer_waitq = PR_NewCondVar(rwlock->rw_lock);
    if (rwlock->rw_writer_waitq == NULL) {
        goto failed;
    }
    rwlock->rw_reader_cnt = 0;
    rwlock->rw_writer_cnt = 0;
    rwlock->rw_lock_cnt = 0;
    return rwlock;

failed:
    if (rwlock->rw_reader_waitq != NULL) {
        PR_DestroyCondVar(rwlock->rw_reader_waitq);
    }
    if (rwlock->rw_lock != NULL) {
        PR_DestroyLock(rwlock->rw_lock);
    }
    PR_Free(rwlock->rw_name);
    PR_DELETE(rwlock);
    return NULL;
#endif
}

/*
** Destroy the given RWLock "lock".
*/
PR_IMPLEMENT(void)
PR_DestroyRWLock(PRRWLock *rwlock)
{
#if defined(HAVE_UNIX98_RWLOCK) || defined(HAVE_UI_RWLOCK)
    int err;
    err = RWLOCK_DESTROY(&rwlock->rw_lock);
    PR_ASSERT(err == 0);
#else
    PR_ASSERT(rwlock->rw_reader_cnt == 0);
    PR_DestroyCondVar(rwlock->rw_reader_waitq);
    PR_DestroyCondVar(rwlock->rw_writer_waitq);
    PR_DestroyLock(rwlock->rw_lock);
#endif
    if (rwlock->rw_name != NULL) {
        PR_Free(rwlock->rw_name);
    }
    PR_DELETE(rwlock);
}

/*
** Read-lock the RWLock.
*/
PR_IMPLEMENT(void)
PR_RWLock_Rlock(PRRWLock *rwlock)
{
#if defined(HAVE_UNIX98_RWLOCK) || defined(HAVE_UI_RWLOCK)
    int err;
#endif

#ifdef _PR_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 == PR_RWLOCK_RANK_NONE) ||
              (rwlock->rw_rank >= _PR_GET_THREAD_RWLOCK_RANK()));
#endif

#if defined(HAVE_UNIX98_RWLOCK) || defined(HAVE_UI_RWLOCK)
    err = RWLOCK_RDLOCK(&rwlock->rw_lock);
    PR_ASSERT(err == 0);
#else
    PR_Lock(rwlock->rw_lock);
    /*
     * wait if write-locked or if a writer is waiting; preference for writers
     */
    while ((rwlock->rw_lock_cnt < 0) ||
           (rwlock->rw_writer_cnt > 0)) {
        rwlock->rw_reader_cnt++;
        PR_WaitCondVar(rwlock->rw_reader_waitq, PR_INTERVAL_NO_TIMEOUT);
        rwlock->rw_reader_cnt--;
    }
    /*
     * Increment read-lock count
     */
    rwlock->rw_lock_cnt++;

    PR_Unlock(rwlock->rw_lock);
#endif

#ifdef _PR_RWLOCK_RANK_ORDER_DEBUG
    /*
     * update thread's lock rank
     */
    if (rwlock->rw_rank != PR_RWLOCK_RANK_NONE) {
        _PR_SET_THREAD_RWLOCK_RANK(rwlock);
    }
#endif
}

/*
** Write-lock the RWLock.
*/
PR_IMPLEMENT(void)
PR_RWLock_Wlock(PRRWLock *rwlock)
{
#if defined(DEBUG)
    PRThread *me = PR_GetCurrentThread();
#endif
#if defined(HAVE_UNIX98_RWLOCK) || defined(HAVE_UI_RWLOCK)
    int err;
#endif

#ifdef _PR_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 == PR_RWLOCK_RANK_NONE) ||
              (rwlock->rw_rank >= _PR_GET_THREAD_RWLOCK_RANK()));
#endif

#if defined(HAVE_UNIX98_RWLOCK) || defined(HAVE_UI_RWLOCK)
    err = RWLOCK_WRLOCK(&rwlock->rw_lock);
    PR_ASSERT(err == 0);
#else
    PR_Lock(rwlock->rw_lock);
    /*
     * wait if read locked
     */
    while (rwlock->rw_lock_cnt != 0) {
        rwlock->rw_writer_cnt++;
        PR_WaitCondVar(rwlock->rw_writer_waitq, PR_INTERVAL_NO_TIMEOUT);
        rwlock->rw_writer_cnt--;
    }
    /*
     * apply write lock
     */
    rwlock->rw_lock_cnt--;
    PR_ASSERT(rwlock->rw_lock_cnt == -1);
#ifdef DEBUG
    PR_ASSERT(me != NULL);
    rwlock->rw_owner = me;
#endif
    PR_Unlock(rwlock->rw_lock);
#endif

#ifdef _PR_RWLOCK_RANK_ORDER_DEBUG
    /*
     * update thread's lock rank
     */
    if (rwlock->rw_rank != PR_RWLOCK_RANK_NONE) {
        _PR_SET_THREAD_RWLOCK_RANK(rwlock);
    }
#endif
}

/*
** Unlock the RW lock.
*/
PR_IMPLEMENT(void)
PR_RWLock_Unlock(PRRWLock *rwlock)
{
#if defined(DEBUG)
    PRThread *me = PR_GetCurrentThread();
#endif
#if defined(HAVE_UNIX98_RWLOCK) || defined(HAVE_UI_RWLOCK)
    int err;
#endif

#if defined(HAVE_UNIX98_RWLOCK) || defined(HAVE_UI_RWLOCK)
    err = RWLOCK_UNLOCK(&rwlock->rw_lock);
    PR_ASSERT(err == 0);
#else
    PR_Lock(rwlock->rw_lock);
    /*
     * lock must be read or write-locked
     */
    PR_ASSERT(rwlock->rw_lock_cnt != 0);
    if (rwlock->rw_lock_cnt > 0) {

        /*
         * decrement read-lock count
         */
        rwlock->rw_lock_cnt--;
        if (rwlock->rw_lock_cnt == 0) {
            /*
             * lock is not read-locked anymore; wakeup a waiting writer
             */
            if (rwlock->rw_writer_cnt > 0) {
                PR_NotifyCondVar(rwlock->rw_writer_waitq);
            }
        }
    } else {
        PR_ASSERT(rwlock->rw_lock_cnt == -1);

        rwlock->rw_lock_cnt = 0;
#ifdef DEBUG
        PR_ASSERT(rwlock->rw_owner == me);
        rwlock->rw_owner = NULL;
#endif
        /*
         * wakeup a writer, if present; preference for writers
         */
        if (rwlock->rw_writer_cnt > 0) {
            PR_NotifyCondVar(rwlock->rw_writer_waitq);
        }
        /*
         * else, wakeup all readers, if any
         */
        else if (rwlock->rw_reader_cnt > 0) {
            PR_NotifyAllCondVar(rwlock->rw_reader_waitq);
        }
    }
    PR_Unlock(rwlock->rw_lock);
#endif

#ifdef _PR_RWLOCK_RANK_ORDER_DEBUG
    /*
     * update thread's lock rank
     */
    if (rwlock->rw_rank != PR_RWLOCK_RANK_NONE) {
        _PR_UNSET_THREAD_RWLOCK_RANK(rwlock);
    }
#endif
    return;
}

#ifndef _PR_RWLOCK_RANK_ORDER_DEBUG

void _PR_InitRWLocks(void) { }

#else

void _PR_InitRWLocks(void)
{
    /*
     * allocated thread-private-data index for rwlock list
     */
    if (PR_NewThreadPrivateIndex(&pr_thread_rwlock_key,
                                 _PR_RELEASE_LOCK_STACK) == PR_FAILURE) {
        pr_thread_rwlock_alloc_failed = 1;
        return;
    }
}

/*
 * _PR_SET_THREAD_RWLOCK_RANK
 *      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
_PR_SET_THREAD_RWLOCK_RANK(PRRWLock *rwlock)
{
    thread_rwlock_stack *lock_stack;
    PRStatus rv;

    /*
     * allocate a lock stack
     */
    if ((lock_stack = PR_GetThreadPrivate(pr_thread_rwlock_key)) == NULL) {
        lock_stack = (thread_rwlock_stack *)
                     PR_CALLOC(1 * sizeof(thread_rwlock_stack));
        if (lock_stack) {
            rv = PR_SetThreadPrivate(pr_thread_rwlock_key, lock_stack);
            if (rv == PR_FAILURE) {
                PR_DELETE(lock_stack);
                pr_thread_rwlock_alloc_failed = 1;
                return;
            }
        } else {
            pr_thread_rwlock_alloc_failed = 1;
            return;
        }
    }
    /*
     * add rwlock to lock stack, if limit is not exceeded
     */
    if (lock_stack) {
        if (lock_stack->trs_index < _PR_RWLOCK_RANK_ORDER_LIMIT) {
            lock_stack->trs_stack[lock_stack->trs_index++] = rwlock;
        }
    }
}

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

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

static PRUint32
_PR_GET_THREAD_RWLOCK_RANK(void)
{
    thread_rwlock_stack *lock_stack;

    lock_stack = PR_GetThreadPrivate(pr_thread_rwlock_key);
    if (lock_stack == NULL || lock_stack->trs_index == 0) {
        return (PR_RWLOCK_RANK_NONE);
    }
    else {
        return(lock_stack->trs_stack[lock_stack->trs_index - 1]->rw_rank);
    }
}

/*
 * _PR_UNSET_THREAD_RWLOCK_RANK
 *
 *      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
_PR_UNSET_THREAD_RWLOCK_RANK(PRRWLock *rwlock)
{
    thread_rwlock_stack *lock_stack;
    int new_index = 0, index, done = 0;

    lock_stack = PR_GetThreadPrivate(pr_thread_rwlock_key);

    PR_ASSERT(lock_stack != NULL);

    for (index = lock_stack->trs_index - 1; index >= 0; index--) {
        if (!done && (lock_stack->trs_stack[index] == rwlock))  {
            /*
             * 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 (!new_index && (lock_stack->trs_stack[index] != NULL)) {
            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  /* _PR_RWLOCK_RANK_ORDER_DEBUG */