DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Header

Mercurial (31ec81b5d7bb)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447
/* 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 "nssrwlk.h"
#include "nspr.h"

PR_BEGIN_EXTERN_C

/*
 * Reader-writer lock
 */
struct nssRWLockStr {
    PZLock *        rw_lock;
    char   *        rw_name;            /* lock name                    */
    PRUint32        rw_rank;            /* rank of the lock             */
    PRInt32         rw_writer_locks;    /* ==  0, if unlocked           */
    PRInt32         rw_reader_locks;    /* ==  0, if unlocked           */
                                        /* > 0  , # of read locks       */
    PRUint32        rw_waiting_readers; /* number of waiting readers    */
    PRUint32        rw_waiting_writers; /* number of waiting writers    */
    PZCondVar *     rw_reader_waitq;    /* cvar for readers             */
    PZCondVar *     rw_writer_waitq;    /* cvar for writers             */
    PRThread  *     rw_owner;           /* lock owner for write-lock    */
                                        /* Non-null if write lock held. */
};

PR_END_EXTERN_C

#include <string.h>

#ifdef DEBUG_RANK_ORDER
#define NSS_RWLOCK_RANK_ORDER_DEBUG /* enable deadlock detection using
                                       rank-order for locks
                                    */
#endif

#ifdef NSS_RWLOCK_RANK_ORDER_DEBUG

static PRUintn  nss_thread_rwlock_initialized;
static PRUintn  nss_thread_rwlock;               /* TPD key for lock stack */
static PRUintn  nss_thread_rwlock_alloc_failed;

#define _NSS_RWLOCK_RANK_ORDER_LIMIT 10

typedef struct thread_rwlock_stack {
    PRInt32     trs_index;                                  /* top of stack */
    NSSRWLock    *trs_stack[_NSS_RWLOCK_RANK_ORDER_LIMIT];  /* stack of lock
                                                               pointers */
} thread_rwlock_stack;

/* forward static declarations. */
static PRUint32 nssRWLock_GetThreadRank(PRThread *me);
static void     nssRWLock_SetThreadRank(PRThread *me, NSSRWLock *rwlock);
static void     nssRWLock_UnsetThreadRank(PRThread *me, NSSRWLock *rwlock);
static void     nssRWLock_ReleaseLockStack(void *lock_stack);

#endif

#define UNTIL(x) while(!(x))

/*
 * Reader/Writer Locks
 */

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

NSSRWLock *
NSSRWLock_New(PRUint32 lock_rank, const char *lock_name)
{
    NSSRWLock *rwlock;

    rwlock = PR_NEWZAP(NSSRWLock);
    if (rwlock == NULL)
        return NULL;

    rwlock->rw_lock = PZ_NewLock(nssILockRWLock);
    if (rwlock->rw_lock == NULL) {
	goto loser;
    }
    rwlock->rw_reader_waitq = PZ_NewCondVar(rwlock->rw_lock);
    if (rwlock->rw_reader_waitq == NULL) {
	goto loser;
    }
    rwlock->rw_writer_waitq = PZ_NewCondVar(rwlock->rw_lock);
    if (rwlock->rw_writer_waitq == NULL) {
	goto loser;
    }
    if (lock_name != NULL) {
        rwlock->rw_name = (char*) PR_Malloc(strlen(lock_name) + 1);
        if (rwlock->rw_name == NULL) {
	    goto loser;
        }
        strcpy(rwlock->rw_name, lock_name);
    } else {
        rwlock->rw_name = NULL;
    }
    rwlock->rw_rank            = lock_rank;
    rwlock->rw_waiting_readers = 0;
    rwlock->rw_waiting_writers = 0;
    rwlock->rw_reader_locks    = 0;
    rwlock->rw_writer_locks    = 0;

    return rwlock;

loser:
    NSSRWLock_Destroy(rwlock);
    return(NULL);
}

/*
** Destroy the given RWLock "lock".
*/
void
NSSRWLock_Destroy(NSSRWLock *rwlock)
{
    PR_ASSERT(rwlock != NULL);
    PR_ASSERT(rwlock->rw_waiting_readers == 0);

    /* XXX Shouldn't we lock the PZLock before destroying this?? */

    if (rwlock->rw_name)
    	PR_Free(rwlock->rw_name);
    if (rwlock->rw_reader_waitq)
    	PZ_DestroyCondVar(rwlock->rw_reader_waitq);
    if (rwlock->rw_writer_waitq)
	PZ_DestroyCondVar(rwlock->rw_writer_waitq);
    if (rwlock->rw_lock)
	PZ_DestroyLock(rwlock->rw_lock);
    PR_DELETE(rwlock);
}

/*
** Read-lock the RWLock.
*/
void
NSSRWLock_LockRead(NSSRWLock *rwlock)
{
    PRThread *me = PR_GetCurrentThread();

    PZ_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 write-locked or if a writer is waiting; preference for writers
     */
    UNTIL ( (rwlock->rw_owner == me) ||		  /* I own it, or        */
	   ((rwlock->rw_owner == NULL) &&	  /* no-one owns it, and */
	    (rwlock->rw_waiting_writers == 0))) { /* no-one is waiting to own */

	rwlock->rw_waiting_readers++;
	PZ_WaitCondVar(rwlock->rw_reader_waitq, PR_INTERVAL_NO_TIMEOUT);
	rwlock->rw_waiting_readers--;
    }
    rwlock->rw_reader_locks++; 		/* Increment read-lock count */

    PZ_Unlock(rwlock->rw_lock);

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

/* Unlock a Read lock held on this RW lock.
*/
void
NSSRWLock_UnlockRead(NSSRWLock *rwlock)
{
    PZ_Lock(rwlock->rw_lock);

    PR_ASSERT(rwlock->rw_reader_locks > 0); /* lock must be read locked */

    if ((  rwlock->rw_reader_locks  > 0)  &&	/* caller isn't screwey */
        (--rwlock->rw_reader_locks == 0)  &&	/* not read locked any more */
	(  rwlock->rw_owner        == NULL) &&	/* not write locked */
	(  rwlock->rw_waiting_writers > 0)) {	/* someone's waiting. */

	PZ_NotifyCondVar(rwlock->rw_writer_waitq); /* wake him up. */
    }

    PZ_Unlock(rwlock->rw_lock);

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

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

    PZ_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++;
        PZ_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 */

    PZ_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.
*/
void
NSSRWLock_UnlockWrite(NSSRWLock *rwlock)
{
    PRThread *me = PR_GetCurrentThread();

    PZ_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. */

	/* Give preference to waiting writers. */
	if (rwlock->rw_waiting_writers > 0) {
	    if (rwlock->rw_reader_locks == 0)
		PZ_NotifyCondVar(rwlock->rw_writer_waitq);
	} else if (rwlock->rw_waiting_readers > 0) {
	    PZ_NotifyAllCondVar(rwlock->rw_reader_waitq);
	}
    }
    PZ_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. */
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
    PZ_Lock(rwlock->rw_lock);	
#endif
    ownWriteLock = (PRBool)(me == rwlock->rw_owner);
#if UNNECESSARY
    PZ_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 */