| 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 | |
| 35 | static inline void qemu_futex_wake_all(void *f) |
| 36 | { |
| 37 | qemu_futex(f, FUTEX_WAKE, INT_MAX, NULL, NULL, 0); |
| 38 | } |
| 39 | |
| 40 | static inline void qemu_futex_wake_single(void *f) |
| 41 | { |
| 42 | qemu_futex(f, FUTEX_WAKE, 1, NULL, NULL, 0); |
| 43 | } |
| 44 | |
| 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 | |
| 61 | static inline void qemu_futex_wake_all(void *f) |
| 62 | { |
| 63 | WakeByAddressAll(f); |
| 64 | } |
| 65 | |
| 66 | static inline void qemu_futex_wake_single(void *f) |
| 67 | { |
| 68 | WakeByAddressSingle(f); |
| 69 | } |
| 70 | |
| 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 */ |