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/*
* Copyright 2024-present MongoDB, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* Note: this file was derived from libbson's bson-atomic.c */
#include "bson/bson.h"
#include "phongo_atomic.h"
#ifdef BSON_OS_UNIX
/* For sched_yield() */
#include <sched.h>
#endif
static void _thrd_yield(void)
{
BSON_IF_WINDOWS(SwitchToThread();)
BSON_IF_POSIX(sched_yield();)
}
/**
* Some platforms do not support compiler intrinsics for atomic operations.
* We emulate that here using a spin lock and regular arithmetic operations
*/
static int8_t gEmulAtomicLock = 0;
static void _lock_emul_atomic(void)
{
int i;
if (phongo_atomic_int8_compare_exchange_weak(&gEmulAtomicLock, 0, 1, phongo_memory_order_acquire) == 0) {
/* Successfully took the spinlock */
return;
}
/* Failed. Try taking ten more times, then begin sleeping. */
for (i = 0; i < 10; ++i) {
if (phongo_atomic_int8_compare_exchange_weak(&gEmulAtomicLock, 0, 1, phongo_memory_order_acquire) == 0) {
/* Succeeded in taking the lock */
return;
}
}
/* Still don't have the lock. Spin and yield */
while (phongo_atomic_int8_compare_exchange_weak(&gEmulAtomicLock, 0, 1, phongo_memory_order_acquire) != 0) {
_thrd_yield();
}
}
static void _unlock_emul_atomic(void)
{
int64_t rv = phongo_atomic_int8_exchange(&gEmulAtomicLock, 0, phongo_memory_order_release);
BSON_ASSERT(rv == 1 && "Released atomic lock while not holding it");
}
int32_t _phongo_emul_atomic_int32_fetch_add(volatile int32_t* p, int32_t n, enum phongo_memory_order _unused)
{
int32_t ret;
BSON_UNUSED(_unused);
_lock_emul_atomic();
ret = *p;
*p += n;
_unlock_emul_atomic();
return ret;
}
int32_t _phongo_emul_atomic_int32_exchange(volatile int32_t* p, int32_t n, enum phongo_memory_order _unused)
{
int32_t ret;
BSON_UNUSED(_unused);
_lock_emul_atomic();
ret = *p;
*p = n;
_unlock_emul_atomic();
return ret;
}
int32_t _phongo_emul_atomic_int32_compare_exchange_strong(
volatile int32_t* p,
int32_t expect_value,
int32_t new_value,
enum phongo_memory_order _unused)
{
int32_t ret;
BSON_UNUSED(_unused);
_lock_emul_atomic();
ret = *p;
if (ret == expect_value) {
*p = new_value;
}
_unlock_emul_atomic();
return ret;
}
int32_t _phongo_emul_atomic_int32_compare_exchange_weak(
volatile int32_t* p,
int32_t expect_value,
int32_t new_value,
enum phongo_memory_order order)
{
/* We're emulating. We can't do a weak version. */
return _phongo_emul_atomic_int32_compare_exchange_strong(p, expect_value, new_value, order);
}

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