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/*
* Wrappers around Linux futex syscall and similar
*
* Copyright Red Hat, Inc. 2017
*
* Author:
* Paolo Bonzini <pbonzini@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*
*/
/*
* Note that a wake-up can also be caused by common futex usage patterns in
* unrelated code that happened to have previously used the futex word's
* memory location (e.g., typical futex-based implementations of Pthreads
* mutexes can cause this under some conditions). Therefore, qemu_futex_wait()
* callers should always conservatively assume that it is a spurious wake-up,
* and use the futex word's value (i.e., the user-space synchronization scheme)
* to decide whether to continue to block or not.
*/
#ifndef QEMU_FUTEX_H
#define QEMU_FUTEX_H
#define HAVE_FUTEX
#ifdef CONFIG_LINUX
#include <sys/syscall.h>
#include <linux/futex.h>
#define qemu_futex(...) syscall(__NR_futex, __VA_ARGS__)
static inline void qemu_futex_wake_all(void *f)
{
qemu_futex(f, FUTEX_WAKE, INT_MAX, NULL, NULL, 0);
}
static inline void qemu_futex_wake_single(void *f)
{
qemu_futex(f, FUTEX_WAKE, 1, NULL, NULL, 0);
}
static inline void qemu_futex_wait(void *f, unsigned val)
{
while (qemu_futex(f, FUTEX_WAIT, (int) val, NULL, NULL, 0)) {
switch (errno) {
case EWOULDBLOCK:
return;
case EINTR:
break; /* get out of switch and retry */
default:
abort();
}
}
}
#elif defined(CONFIG_WIN32)
#include <synchapi.h>
static inline void qemu_futex_wake_all(void *f)
{
WakeByAddressAll(f);
}
static inline void qemu_futex_wake_single(void *f)
{
WakeByAddressSingle(f);
}
static inline void qemu_futex_wait(void *f, unsigned val)
{
WaitOnAddress(f, &val, sizeof(val), INFINITE);
}
#else
#undef HAVE_FUTEX
#endif
#endif /* QEMU_FUTEX_H */
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