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/*
* QemuLockCnt implementation
*
* Copyright Red Hat, Inc. 2017
*
* Author:
* Paolo Bonzini <pbonzini@redhat.com>
*/
#include "qemu/osdep.h"
#include "qemu/thread.h"
#include "qemu/atomic.h"
void qemu_lockcnt_init(QemuLockCnt *lockcnt)
{
qemu_mutex_init(&lockcnt->mutex);
lockcnt->count = 0;
}
void qemu_lockcnt_destroy(QemuLockCnt *lockcnt)
{
qemu_mutex_destroy(&lockcnt->mutex);
}
void qemu_lockcnt_inc(QemuLockCnt *lockcnt)
{
int old;
for (;;) {
old = atomic_read(&lockcnt->count);
if (old == 0) {
qemu_lockcnt_lock(lockcnt);
qemu_lockcnt_inc_and_unlock(lockcnt);
return;
} else {
if (atomic_cmpxchg(&lockcnt->count, old, old + 1) == old) {
return;
}
}
}
}
void qemu_lockcnt_dec(QemuLockCnt *lockcnt)
{
atomic_dec(&lockcnt->count);
}
/* Decrement a counter, and return locked if it is decremented to zero.
* It is impossible for the counter to become nonzero while the mutex
* is taken.
*/
bool qemu_lockcnt_dec_and_lock(QemuLockCnt *lockcnt)
{
int val = atomic_read(&lockcnt->count);
while (val > 1) {
int old = atomic_cmpxchg(&lockcnt->count, val, val - 1);
if (old != val) {
val = old;
continue;
}
return false;
}
qemu_lockcnt_lock(lockcnt);
if (atomic_fetch_dec(&lockcnt->count) == 1) {
return true;
}
qemu_lockcnt_unlock(lockcnt);
return false;
}
/* Decrement a counter and return locked if it is decremented to zero.
* Otherwise do nothing.
*
* It is impossible for the counter to become nonzero while the mutex
* is taken.
*/
bool qemu_lockcnt_dec_if_lock(QemuLockCnt *lockcnt)
{
/* No need for acquire semantics if we return false. */
int val = atomic_read(&lockcnt->count);
if (val > 1) {
return false;
}
qemu_lockcnt_lock(lockcnt);
if (atomic_fetch_dec(&lockcnt->count) == 1) {
return true;
}
qemu_lockcnt_inc_and_unlock(lockcnt);
return false;
}
void qemu_lockcnt_lock(QemuLockCnt *lockcnt)
{
qemu_mutex_lock(&lockcnt->mutex);
}
void qemu_lockcnt_inc_and_unlock(QemuLockCnt *lockcnt)
{
atomic_inc(&lockcnt->count);
qemu_mutex_unlock(&lockcnt->mutex);
}
void qemu_lockcnt_unlock(QemuLockCnt *lockcnt)
{
qemu_mutex_unlock(&lockcnt->mutex);
}
unsigned qemu_lockcnt_count(QemuLockCnt *lockcnt)
{
return atomic_read(&lockcnt->count);
}
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