1 /*
2 * Wrappers around Linux futex syscall and similar
3 *
4 * Copyright Red Hat, Inc. 2017
5 *
6 * Author:
7 * Paolo Bonzini <pbonzini@redhat.com>
8 *
9 * This work is licensed under the terms of the GNU GPL, version 2 or later.
10 * See the COPYING file in the top-level directory.
11 *
12 */
13
14 /*
15 * Note that a wake-up can also be caused by common futex usage patterns in
16 * unrelated code that happened to have previously used the futex word's
17 * memory location (e.g., typical futex-based implementations of Pthreads
18 * mutexes can cause this under some conditions). Therefore, qemu_futex_wait()
19 * callers should always conservatively assume that it is a spurious wake-up,
20 * and use the futex word's value (i.e., the user-space synchronization scheme)
21 * to decide whether to continue to block or not.
22 */
23
24 #ifndef QEMU_FUTEX_H
25 #define QEMU_FUTEX_H
26
27 #define HAVE_FUTEX
28
29 #ifdef CONFIG_LINUX
30 #include <sys/syscall.h>
31 #include <linux/futex.h>
32
33 #define qemu_futex(...) syscall(__NR_futex, __VA_ARGS__)
34
qemu_futex_wake_all(void * f)35 static inline void qemu_futex_wake_all(void *f)
36 {
37 qemu_futex(f, FUTEX_WAKE, INT_MAX, NULL, NULL, 0);
38 }
39
qemu_futex_wake_single(void * f)40 static inline void qemu_futex_wake_single(void *f)
41 {
42 qemu_futex(f, FUTEX_WAKE, 1, NULL, NULL, 0);
43 }
44
qemu_futex_wait(void * f,unsigned val)45 static inline void qemu_futex_wait(void *f, unsigned val)
46 {
47 while (qemu_futex(f, FUTEX_WAIT, (int) val, NULL, NULL, 0)) {
48 switch (errno) {
49 case EWOULDBLOCK:
50 return;
51 case EINTR:
52 break; /* get out of switch and retry */
53 default:
54 abort();
55 }
56 }
57 }
58 #elif defined(CONFIG_WIN32)
59 #include <synchapi.h>
60
qemu_futex_wake_all(void * f)61 static inline void qemu_futex_wake_all(void *f)
62 {
63 WakeByAddressAll(f);
64 }
65
qemu_futex_wake_single(void * f)66 static inline void qemu_futex_wake_single(void *f)
67 {
68 WakeByAddressSingle(f);
69 }
70
qemu_futex_wait(void * f,unsigned val)71 static inline void qemu_futex_wait(void *f, unsigned val)
72 {
73 WaitOnAddress(f, &val, sizeof(val), INFINITE);
74 }
75 #else
76 #undef HAVE_FUTEX
77 #endif
78
79 #endif /* QEMU_FUTEX_H */
80