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wtc%netscape.com 1999-01-28 03:41:08 +00:00
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nsprpub/pr/src/bthreads/btcmon.c
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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
* The contents of this file are subject to the Mozilla Public License
* Version 1.0 (the "MPL"); you may not use this file except in
* compliance with the MPL. You may obtain a copy of the MPL at
* http://www.mozilla.org/MPL/
*
* Software distributed under the MPL is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the MPL
* for the specific language governing rights and limitations under the
* MPL.
*/
#include <kernel/OS.h>
#include "primpl.h"
/*
** Most of this is ripped out of ../threads/prcmon.c
*/
PRLock *_pr_mcacheLock;
#define _PR_NEW_LOCK_MCACHE() (_pr_mcacheLock = PR_NewLock())
#define _PR_LOCK_MCACHE() PR_Lock(_pr_mcacheLock)
#define _PR_UNLOCK_MCACHE() PR_Unlock(_pr_mcacheLock)
typedef struct MonitorCacheEntryStr MonitorCacheEntry;
struct MonitorCacheEntryStr {
MonitorCacheEntry* next;
void* address;
PRMonitor* mon;
long cacheEntryCount;
};
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;
int _pr_mcache_ready;
#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, *new_entries;
entries = 1L << new_size_log2;
/*
** Expand the monitor-cache-entry free list
*/
new_entries = (MonitorCacheEntry*)PR_CALLOC(
entries * sizeof(MonitorCacheEntry));
if (NULL == new_entries) 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, added = 0, p = new_entries; i < entries; i++, p++, added++)
{
p->mon = PR_NewMonitor();
if (!p->mon) break;
}
if (added != entries)
{
if (added == 0)
{
/* Totally out of system monitors. Lossage abounds */
PR_DELETE(new_entries);
return PR_FAILURE;
}
/*
** We were able to allocate some of the system monitors. Use
** realloc to shrink down the new_entries memory
*/
p = (MonitorCacheEntry*)PR_REALLOC(
new_entries, added * sizeof(MonitorCacheEntry));
if (p == 0)
{
/*
** Total lossage. We just leaked a bunch of system monitors
** all over the floor. This should never ever happen.
*/
PR_ASSERT(p != 0);
return PR_FAILURE;
}
}
/*
** 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_entries; i < added - 1; i++, p++) p->next = p + 1;
p->next = free_entries;
free_entries = new_entries;
num_free_entries += added;
/* 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;
else
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--;
p->address = address;
p->next = hash_buckets[hash];
hash_buckets[hash] = p;
PR_ASSERT(p->cacheEntryCount == 0);
gotit:
p->cacheEntryCount++;
return p->mon;
}
/* this is needed by prinit for some reason */
void
_PR_InitCMon (void)
{
_PR_NEW_LOCK_MCACHE();
ExpandMonitorCache(3);
_pr_mcache_ready = 1;
}
/**
** Like PR_EnterMonitor except use the "address" to find a monitor in the
** monitor cache. If successful, returns the PRMonitor now associated
** with "address". Note that you must PR_CExitMonitor the address to
** release the monitor cache entry (otherwise the monitor cache will fill
** up). This call will return NULL if the monitor cache needs to be
** expanded and the system is out of memory.
*/
PR_IMPLEMENT(PRMonitor*)
PR_CEnterMonitor (void *address)
{
PRMonitor *mon;
_PR_LOCK_MCACHE();
mon = CreateMonitor( address );
_PR_UNLOCK_MCACHE();
if( !mon ) return( NULL );
PR_EnterMonitor( mon );
return( mon );
}
/*
** Like PR_ExitMonitor except use the "address" to find a monitor in the
** monitor cache.
*/
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;
}
/*
** Like PR_Wait except use the "address" to find a monitor in the
** monitor cache.
*/
PR_IMPLEMENT(PRStatus)
PR_CWait (void *address, PRIntervalTime timeout)
{
MonitorCacheEntry **pp;
PRMonitor *mon;
_PR_LOCK_MCACHE();
pp = LookupMonitorCacheEntry(address);
mon = pp ? ((*pp)->mon) : NULL;
_PR_UNLOCK_MCACHE();
if (mon == NULL)
return PR_FAILURE;
else
{
return PR_Wait( mon, timeout );
}
}
/*
** Like PR_Notify except use the "address" to find a monitor in the
** monitor cache.
*/
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;
else
{
return PR_Notify(mon);
}
}
/*
** Like PR_NotifyAll except use the "address" to find a monitor in the
** monitor cache.
*/
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;
else
{
return PR_NotifyAll(mon);
}
}