The Tor Browser: nsprpub/pr/src/threads/prcmon.c@ca08bd8f51b2 (annotated)

nsprpub/pr/src/threads/prcmon.c@ca08bd8f51b2 (annotated)

nsprpub/pr/src/threads/prcmon.c

Wed, 31 Dec 2014 06:55:46 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:55:46 +0100
changeset 1: ca08bd8f51b2
permissions: -rw-r--r--

Added tag TORBROWSER_REPLICA for changeset 6474c204b198

 /* -*- 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 <stdlib.h>
 #include <stddef.h>
 /* Lock used to lock the monitor cache */
 #ifdef _PR_NO_PREEMPT
 #define _PR_NEW_LOCK_MCACHE()
 #define _PR_DESTROY_LOCK_MCACHE()
 #define _PR_LOCK_MCACHE()
 #define _PR_UNLOCK_MCACHE()
 #else
 #ifdef _PR_LOCAL_THREADS_ONLY
 #define _PR_NEW_LOCK_MCACHE()
 #define _PR_DESTROY_LOCK_MCACHE()
 #define _PR_LOCK_MCACHE() { PRIntn _is; _PR_INTSOFF(_is)
 #define _PR_UNLOCK_MCACHE() _PR_INTSON(_is); }
 #else
 PRLock *_pr_mcacheLock;
 #define _PR_NEW_LOCK_MCACHE() (_pr_mcacheLock = PR_NewLock())
 #define _PR_DESTROY_LOCK_MCACHE()               \
     PR_BEGIN_MACRO                              \
         if (_pr_mcacheLock) {                   \
             PR_DestroyLock(_pr_mcacheLock);     \
             _pr_mcacheLock = NULL;              \
         }                                       \
     PR_END_MACRO
 #define _PR_LOCK_MCACHE() PR_Lock(_pr_mcacheLock)
 #define _PR_UNLOCK_MCACHE() PR_Unlock(_pr_mcacheLock)
 #endif
 #endif
 /************************************************************************/
 typedef struct MonitorCacheEntryStr MonitorCacheEntry;
 struct MonitorCacheEntryStr {
     MonitorCacheEntry*  next;
     void*               address;
     PRMonitor*          mon;
     long                cacheEntryCount;
 };
 /*
 ** An array of MonitorCacheEntry's, plus a pointer to link these
 ** arrays together.
 */
 typedef struct MonitorCacheEntryBlockStr MonitorCacheEntryBlock;
 struct MonitorCacheEntryBlockStr {
     MonitorCacheEntryBlock* next;
     MonitorCacheEntry entries[1];
 };
 static PRUint32 hash_mask;
 static PRUintn num_hash_buckets;
 static PRUintn num_hash_buckets_log2;
 static MonitorCacheEntry **hash_buckets;
 static MonitorCacheEntry *free_entries;
 static PRUintn num_free_entries;
 static PRBool expanding;
 static MonitorCacheEntryBlock *mcache_blocks;
 static void (*OnMonitorRecycle)(void *address);
 #define HASH(address)                               \
     ((PRUint32) ( ((PRUptrdiff)(address) >> 2) ^    \
                   ((PRUptrdiff)(address) >> 10) )   \
      & hash_mask)
 /*
 ** Expand the monitor cache. This grows the hash buckets and allocates a
 ** new chunk of cache entries and throws them on the free list. We keep
 ** as many hash buckets as there are entries.
 **
 ** Because we call malloc and malloc may need the monitor cache, we must
 ** ensure that there are several free monitor cache entries available for
 ** malloc to get. FREE_THRESHOLD is used to prevent monitor cache
 ** starvation during monitor cache expansion.
 */
 #define FREE_THRESHOLD  5
 static PRStatus ExpandMonitorCache(PRUintn new_size_log2)
 {
     MonitorCacheEntry **old_hash_buckets, *p;
     PRUintn i, entries, old_num_hash_buckets, added;
     MonitorCacheEntry **new_hash_buckets;
     MonitorCacheEntryBlock *new_block;
     entries = 1L << new_size_log2;
     /*
     ** Expand the monitor-cache-entry free list
     */
     new_block = (MonitorCacheEntryBlock*)
         PR_CALLOC(sizeof(MonitorCacheEntryBlock)
         + (entries - 1) * sizeof(MonitorCacheEntry));
     if (NULL == new_block) return PR_FAILURE;
     /*
     ** Allocate system monitors for the new monitor cache entries. If we
     ** run out of system monitors, break out of the loop.
     */
     for (i = 0, p = new_block->entries; i < entries; i++, p++) {
         p->mon = PR_NewMonitor();
         if (!p->mon)
             break;
     }
     added = i;
     if (added != entries) {
         MonitorCacheEntryBlock *realloc_block;
         if (added == 0) {
             /* Totally out of system monitors. Lossage abounds */
             PR_DELETE(new_block);
             return PR_FAILURE;
         }
         /*
         ** We were able to allocate some of the system monitors. Use
         ** realloc to shrink down the new_block memory. If that fails,
         ** carry on with the too-large new_block.
         */
         realloc_block = (MonitorCacheEntryBlock*)
             PR_REALLOC(new_block, sizeof(MonitorCacheEntryBlock)
             + (added - 1) * sizeof(MonitorCacheEntry));
         if (realloc_block)
             new_block = realloc_block;
     }
     /*
     ** Now that we have allocated all of the system monitors, build up
     ** the new free list. We can just update the free_list because we own
     ** the mcache-lock and we aren't calling anyone who might want to use
     ** it.
     */
     for (i = 0, p = new_block->entries; i < added - 1; i++, p++)
         p->next = p + 1;
     p->next = free_entries;
     free_entries = new_block->entries;
     num_free_entries += added;
     new_block->next = mcache_blocks;
     mcache_blocks = new_block;
     /* Try to expand the hash table */
     new_hash_buckets = (MonitorCacheEntry**)
         PR_CALLOC(entries * sizeof(MonitorCacheEntry*));
     if (NULL == new_hash_buckets) {
         /*
         ** Partial lossage. In this situation we don't get any more hash
         ** buckets, which just means that the table lookups will take
         ** longer. This is bad, but not fatal
         */
         PR_LOG(_pr_cmon_lm, PR_LOG_WARNING,
                ("unable to grow monitor cache hash buckets"));
         return PR_SUCCESS;
     }
     /*
     ** Compute new hash mask value. This value is used to mask an address
     ** until it's bits are in the right spot for indexing into the hash
     ** table.
     */
     hash_mask = entries - 1;
     /*
     ** Expand the hash table. We have to rehash everything in the old
     ** table into the new table.
     */
     old_hash_buckets = hash_buckets;
     old_num_hash_buckets = num_hash_buckets;
     for (i = 0; i < old_num_hash_buckets; i++) {
         p = old_hash_buckets[i];
         while (p) {
             MonitorCacheEntry *next = p->next;
             /* Hash based on new table size, and then put p in the new table */
             PRUintn hash = HASH(p->address);
             p->next = new_hash_buckets[hash];
             new_hash_buckets[hash] = p;
             p = next;
         }
     }
     /*
     ** Switch over to new hash table and THEN call free of the old
     ** table. Since free might re-enter _pr_mcache_lock, things would
     ** break terribly if it used the old hash table.
     */
     hash_buckets = new_hash_buckets;
     num_hash_buckets = entries;
     num_hash_buckets_log2 = new_size_log2;
     PR_DELETE(old_hash_buckets);
     PR_LOG(_pr_cmon_lm, PR_LOG_NOTICE,
            ("expanded monitor cache to %d (buckets %d)",
             num_free_entries, entries));
     return PR_SUCCESS;
 }  /* ExpandMonitorCache */
 /*
 ** Lookup a monitor cache entry by address. Return a pointer to the
 ** pointer to the monitor cache entry on success, null on failure.
 */
 static MonitorCacheEntry **LookupMonitorCacheEntry(void *address)
 {
     PRUintn hash;
     MonitorCacheEntry **pp, *p;
     hash = HASH(address);
     pp = hash_buckets + hash;
     while ((p = *pp) != 0) {
         if (p->address == address) {
             if (p->cacheEntryCount > 0)
                 return pp;
             return NULL;
         }
         pp = &p->next;
     }
     return NULL;
 }
 /*
 ** Try to create a new cached monitor. If it's already in the cache,
 ** great - return it. Otherwise get a new free cache entry and set it
 ** up. If the cache free space is getting low, expand the cache.
 */
 static PRMonitor *CreateMonitor(void *address)
 {
     PRUintn hash;
     MonitorCacheEntry **pp, *p;
     hash = HASH(address);
     pp = hash_buckets + hash;
     while ((p = *pp) != 0) {
         if (p->address == address) goto gotit;
         pp = &p->next;
     }
     /* Expand the monitor cache if we have run out of free slots in the table */
     if (num_free_entries < FREE_THRESHOLD) {
         /* Expand monitor cache */
         /*
         ** This function is called with the lock held. So what's the 'expanding'
         ** boolean all about? Seems a bit redundant.
         */
         if (!expanding) {
             PRStatus rv;
             expanding = PR_TRUE;
             rv = ExpandMonitorCache(num_hash_buckets_log2 + 1);
             expanding = PR_FALSE;
             if (PR_FAILURE == rv)  return NULL;
             /* redo the hash because it'll be different now */
             hash = HASH(address);
         } else {
             /*
             ** We are in process of expanding and we need a cache
             ** monitor.  Make sure we have enough!
             */
             PR_ASSERT(num_free_entries > 0);
         }
     }
     /* Make a new monitor */
     p = free_entries;
     free_entries = p->next;
     num_free_entries--;
     if (OnMonitorRecycle && p->address)
         OnMonitorRecycle(p->address);
     p->address = address;
     p->next = hash_buckets[hash];
     hash_buckets[hash] = p;
     PR_ASSERT(p->cacheEntryCount == 0);
   gotit:
     p->cacheEntryCount++;
     return p->mon;
 }
 /*
 ** Initialize the monitor cache
 */
 void _PR_InitCMon(void)
 {
     _PR_NEW_LOCK_MCACHE();
     ExpandMonitorCache(3);
 }
 /*
 ** Destroy the monitor cache
 */
 void _PR_CleanupCMon(void)
 {
     _PR_DESTROY_LOCK_MCACHE();
     while (free_entries) {
         PR_DestroyMonitor(free_entries->mon);
         free_entries = free_entries->next;
     }
     num_free_entries = 0;
     while (mcache_blocks) {
         MonitorCacheEntryBlock *block;
         block = mcache_blocks;
         mcache_blocks = block->next;
         PR_DELETE(block);
     }
     PR_DELETE(hash_buckets);
     hash_mask = 0;
     num_hash_buckets = 0;
     num_hash_buckets_log2 = 0;
     expanding = PR_FALSE;
     OnMonitorRecycle = NULL;
 }
 /*
 ** Create monitor for address. Don't enter the monitor while we have the
 ** mcache locked because we might block!
 */
 PR_IMPLEMENT(PRMonitor*) PR_CEnterMonitor(void *address)
 {
     PRMonitor *mon;
     if (!_pr_initialized) _PR_ImplicitInitialization();
     _PR_LOCK_MCACHE();
     mon = CreateMonitor(address);
     _PR_UNLOCK_MCACHE();
     if (!mon) return NULL;
     PR_EnterMonitor(mon);
     return mon;
 }
 PR_IMPLEMENT(PRStatus) PR_CExitMonitor(void *address)
 {
     MonitorCacheEntry **pp, *p;
     PRStatus status = PR_SUCCESS;
     _PR_LOCK_MCACHE();
     pp = LookupMonitorCacheEntry(address);
     if (pp != NULL) {
         p = *pp;
         if (--p->cacheEntryCount == 0) {
             /*
             ** Nobody is using the system monitor. Put it on the cached free
             ** list. We are safe from somebody trying to use it because we
             ** have the mcache locked.
             */
             p->address = 0;             /* defensive move */
             *pp = p->next;              /* unlink from hash_buckets */
             p->next = free_entries;     /* link into free list */
             free_entries = p;
             num_free_entries++;         /* count it as free */
         }
         status = PR_ExitMonitor(p->mon);
     } else {
         status = PR_FAILURE;
     }
     _PR_UNLOCK_MCACHE();
     return status;
 }
 PR_IMPLEMENT(PRStatus) PR_CWait(void *address, PRIntervalTime ticks)
 {
     MonitorCacheEntry **pp;
     PRMonitor *mon;
     _PR_LOCK_MCACHE();
     pp = LookupMonitorCacheEntry(address);
     mon = pp ? ((*pp)->mon) : NULL;
     _PR_UNLOCK_MCACHE();
     if (mon == NULL)
         return PR_FAILURE;
     return PR_Wait(mon, ticks);
 }
 PR_IMPLEMENT(PRStatus) PR_CNotify(void *address)
 {
     MonitorCacheEntry **pp;
     PRMonitor *mon;
     _PR_LOCK_MCACHE();
     pp = LookupMonitorCacheEntry(address);
     mon = pp ? ((*pp)->mon) : NULL;
     _PR_UNLOCK_MCACHE();
     if (mon == NULL)
         return PR_FAILURE;
     return PR_Notify(mon);
 }
 PR_IMPLEMENT(PRStatus) PR_CNotifyAll(void *address)
 {
     MonitorCacheEntry **pp;
     PRMonitor *mon;
     _PR_LOCK_MCACHE();
     pp = LookupMonitorCacheEntry(address);
     mon = pp ? ((*pp)->mon) : NULL;
     _PR_UNLOCK_MCACHE();
     if (mon == NULL)
         return PR_FAILURE;
     return PR_NotifyAll(mon);
 }
 PR_IMPLEMENT(void)
 PR_CSetOnMonitorRecycle(void (*callback)(void *address))
 {
     OnMonitorRecycle = callback;
 }

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nsprpub/pr/src/threads/prcmon.c@ca08bd8f51b2 (annotated)

nsprpub/pr/src/threads/prcmon.c