/* 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 */