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/* -*- 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
/*
** PR Atomic operations
*/
#include "pratom.h"
#include "primpl.h"
#include <string.h>
/*
* The following is a fallback implementation that emulates
* atomic operations for platforms without atomic operations.
* If a platform has atomic operations, it should define the
* macro _PR_HAVE_ATOMIC_OPS, and the following will not be
* compiled in.
*/
#if !defined(_PR_HAVE_ATOMIC_OPS)
#if defined(_PR_PTHREADS)
/*
* PR_AtomicDecrement() is used in NSPR's thread-specific data
* destructor. Because thread-specific data destructors may be
* invoked after a PR_Cleanup() call, we need an implementation
* of the atomic routines that doesn't need NSPR to be initialized.
*/
/*
* We use a set of locks for all the emulated atomic operations.
* By hashing on the address of the integer to be locked the
* contention between multiple threads should be lessened.
*
* The number of atomic locks can be set by the environment variable
* NSPR_ATOMIC_HASH_LOCKS
*/
/*
* lock counts should be a power of 2
*/
#define DEFAULT_ATOMIC_LOCKS 16 /* should be in sync with the number of initializers
below */
#define MAX_ATOMIC_LOCKS (4 * 1024)
static pthread_mutex_t static_atomic_locks[DEFAULT_ATOMIC_LOCKS] = {
PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER,
PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER,
PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER,
PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER,
PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER,
PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER,
PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER,
PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER
};
#ifdef DEBUG
static PRInt32 static_hash_lock_counts[DEFAULT_ATOMIC_LOCKS];
static PRInt32 *hash_lock_counts = static_hash_lock_counts;
#endif
static PRUint32 num_atomic_locks = DEFAULT_ATOMIC_LOCKS;
static pthread_mutex_t *atomic_locks = static_atomic_locks;
static PRUint32 atomic_hash_mask = DEFAULT_ATOMIC_LOCKS - 1;
#define _PR_HASH_FOR_LOCK(ptr) \
((PRUint32) (((PRUptrdiff) (ptr) >> 2) ^ \
((PRUptrdiff) (ptr) >> 8)) & \
atomic_hash_mask)
void _PR_MD_INIT_ATOMIC()
{
char *eval;
int index;
PR_ASSERT(PR_FloorLog2(MAX_ATOMIC_LOCKS) ==
PR_CeilingLog2(MAX_ATOMIC_LOCKS));
PR_ASSERT(PR_FloorLog2(DEFAULT_ATOMIC_LOCKS) ==
PR_CeilingLog2(DEFAULT_ATOMIC_LOCKS));
if (((eval = getenv("NSPR_ATOMIC_HASH_LOCKS")) != NULL) &&
((num_atomic_locks = atoi(eval)) != DEFAULT_ATOMIC_LOCKS)) {
if (num_atomic_locks > MAX_ATOMIC_LOCKS) {
num_atomic_locks = MAX_ATOMIC_LOCKS;
}
else if (num_atomic_locks < 1) {
num_atomic_locks = 1;
}
else {
num_atomic_locks = PR_FloorLog2(num_atomic_locks);
num_atomic_locks = 1L << num_atomic_locks;
}
atomic_locks = (pthread_mutex_t *) PR_Malloc(sizeof(pthread_mutex_t) *
num_atomic_locks);
if (atomic_locks) {
for (index = 0; index < num_atomic_locks; index++) {
if (pthread_mutex_init(&atomic_locks[index], NULL)) {
PR_DELETE(atomic_locks);
atomic_locks = NULL;
break;
}
}
}
#ifdef DEBUG
if (atomic_locks) {
hash_lock_counts = PR_CALLOC(num_atomic_locks * sizeof(PRInt32));
if (hash_lock_counts == NULL) {
PR_DELETE(atomic_locks);
atomic_locks = NULL;
}
}
#endif
if (atomic_locks == NULL) {
/*
* Use statically allocated locks
*/
atomic_locks = static_atomic_locks;
num_atomic_locks = DEFAULT_ATOMIC_LOCKS;
#ifdef DEBUG
hash_lock_counts = static_hash_lock_counts;
#endif
}
atomic_hash_mask = num_atomic_locks - 1;
}
PR_ASSERT(PR_FloorLog2(num_atomic_locks) ==
PR_CeilingLog2(num_atomic_locks));
}
PRInt32
_PR_MD_ATOMIC_INCREMENT(PRInt32 *val)
{
PRInt32 rv;
PRInt32 idx = _PR_HASH_FOR_LOCK(val);
pthread_mutex_lock(&atomic_locks[idx]);
rv = ++(*val);
#ifdef DEBUG
hash_lock_counts[idx]++;
#endif
pthread_mutex_unlock(&atomic_locks[idx]);
return rv;
}
PRInt32
_PR_MD_ATOMIC_ADD(PRInt32 *ptr, PRInt32 val)
{
PRInt32 rv;
PRInt32 idx = _PR_HASH_FOR_LOCK(ptr);
pthread_mutex_lock(&atomic_locks[idx]);
rv = ((*ptr) += val);
#ifdef DEBUG
hash_lock_counts[idx]++;
#endif
pthread_mutex_unlock(&atomic_locks[idx]);
return rv;
}
PRInt32
_PR_MD_ATOMIC_DECREMENT(PRInt32 *val)
{
PRInt32 rv;
PRInt32 idx = _PR_HASH_FOR_LOCK(val);
pthread_mutex_lock(&atomic_locks[idx]);
rv = --(*val);
#ifdef DEBUG
hash_lock_counts[idx]++;
#endif
pthread_mutex_unlock(&atomic_locks[idx]);
return rv;
}
PRInt32
_PR_MD_ATOMIC_SET(PRInt32 *val, PRInt32 newval)
{
PRInt32 rv;
PRInt32 idx = _PR_HASH_FOR_LOCK(val);
pthread_mutex_lock(&atomic_locks[idx]);
rv = *val;
*val = newval;
#ifdef DEBUG
hash_lock_counts[idx]++;
#endif
pthread_mutex_unlock(&atomic_locks[idx]);
return rv;
}
#else /* _PR_PTHREADS */
/*
* We use a single lock for all the emulated atomic operations.
* The lock contention should be acceptable.
*/
static PRLock *atomic_lock = NULL;
void _PR_MD_INIT_ATOMIC(void)
{
if (atomic_lock == NULL) {
atomic_lock = PR_NewLock();
}
}
PRInt32
_PR_MD_ATOMIC_INCREMENT(PRInt32 *val)
{
PRInt32 rv;
if (!_pr_initialized) {
_PR_ImplicitInitialization();
}
PR_Lock(atomic_lock);
rv = ++(*val);
PR_Unlock(atomic_lock);
return rv;
}
PRInt32
_PR_MD_ATOMIC_ADD(PRInt32 *ptr, PRInt32 val)
{
PRInt32 rv;
if (!_pr_initialized) {
_PR_ImplicitInitialization();
}
PR_Lock(atomic_lock);
rv = ((*ptr) += val);
PR_Unlock(atomic_lock);
return rv;
}
PRInt32
_PR_MD_ATOMIC_DECREMENT(PRInt32 *val)
{
PRInt32 rv;
if (!_pr_initialized) {
_PR_ImplicitInitialization();
}
PR_Lock(atomic_lock);
rv = --(*val);
PR_Unlock(atomic_lock);
return rv;
}
PRInt32
_PR_MD_ATOMIC_SET(PRInt32 *val, PRInt32 newval)
{
PRInt32 rv;
if (!_pr_initialized) {
_PR_ImplicitInitialization();
}
PR_Lock(atomic_lock);
rv = *val;
*val = newval;
PR_Unlock(atomic_lock);
return rv;
}
#endif /* _PR_PTHREADS */
#endif /* !_PR_HAVE_ATOMIC_OPS */
void _PR_InitAtomic(void)
{
_PR_MD_INIT_ATOMIC();
}
PR_IMPLEMENT(PRInt32)
PR_AtomicIncrement(PRInt32 *val)
{
return _PR_MD_ATOMIC_INCREMENT(val);
}
PR_IMPLEMENT(PRInt32)
PR_AtomicDecrement(PRInt32 *val)
{
return _PR_MD_ATOMIC_DECREMENT(val);
}
PR_IMPLEMENT(PRInt32)
PR_AtomicSet(PRInt32 *val, PRInt32 newval)
{
return _PR_MD_ATOMIC_SET(val, newval);
}
PR_IMPLEMENT(PRInt32)
PR_AtomicAdd(PRInt32 *ptr, PRInt32 val)
{
return _PR_MD_ATOMIC_ADD(ptr, val);
}
/*
* For platforms, which don't support the CAS (compare-and-swap) instruction
* (or an equivalent), the stack operations are implemented by use of PRLock
*/
PR_IMPLEMENT(PRStack *)
PR_CreateStack(const char *stack_name)
{
PRStack *stack;
if (!_pr_initialized) {
_PR_ImplicitInitialization();
}
if ((stack = PR_NEW(PRStack)) == NULL) {
return NULL;
}
if (stack_name) {
stack->prstk_name = (char *) PR_Malloc(strlen(stack_name) + 1);
if (stack->prstk_name == NULL) {
PR_DELETE(stack);
return NULL;
}
strcpy(stack->prstk_name, stack_name);
} else {
stack->prstk_name = NULL;
}
#ifndef _PR_HAVE_ATOMIC_CAS
stack->prstk_lock = PR_NewLock();
if (stack->prstk_lock == NULL) {
PR_Free(stack->prstk_name);
PR_DELETE(stack);
return NULL;
}
#endif /* !_PR_HAVE_ATOMIC_CAS */
stack->prstk_head.prstk_elem_next = NULL;
return stack;
}
PR_IMPLEMENT(PRStatus)
PR_DestroyStack(PRStack *stack)
{
if (stack->prstk_head.prstk_elem_next != NULL) {
PR_SetError(PR_INVALID_STATE_ERROR, 0);
return PR_FAILURE;
}
if (stack->prstk_name) {
PR_Free(stack->prstk_name);
}
#ifndef _PR_HAVE_ATOMIC_CAS
PR_DestroyLock(stack->prstk_lock);
#endif /* !_PR_HAVE_ATOMIC_CAS */
PR_DELETE(stack);
return PR_SUCCESS;
}
#ifndef _PR_HAVE_ATOMIC_CAS
PR_IMPLEMENT(void)
PR_StackPush(PRStack *stack, PRStackElem *stack_elem)
{
PR_Lock(stack->prstk_lock);
stack_elem->prstk_elem_next = stack->prstk_head.prstk_elem_next;
stack->prstk_head.prstk_elem_next = stack_elem;
PR_Unlock(stack->prstk_lock);
return;
}
PR_IMPLEMENT(PRStackElem *)
PR_StackPop(PRStack *stack)
{
PRStackElem *element;
PR_Lock(stack->prstk_lock);
element = stack->prstk_head.prstk_elem_next;
if (element != NULL) {
stack->prstk_head.prstk_elem_next = element->prstk_elem_next;
element->prstk_elem_next = NULL; /* debugging aid */
}
PR_Unlock(stack->prstk_lock);
return element;
}
#endif /* !_PR_HAVE_ATOMIC_CAS */