1 /* Copyright (c) 2009, Google Inc.
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31 * This file is a Linux-specific part of spinlock_internal.cc
38 #include "base/linux_syscall_support.h"
42 #define FUTEX_PRIVATE_FLAG 128
44 static bool have_futex;
45 static int futex_private_flag = FUTEX_PRIVATE_FLAG;
48 static struct InitModule {
51 // futexes are ints, so we can use them only when
52 // that's the same size as the lockword_ in SpinLock.
54 // ARM linux doesn't support sys_futex1(void*, int, int, struct timespec*);
57 have_futex = (sizeof (Atomic32) == sizeof (int) &&
58 sys_futex(&x, FUTEX_WAKE, 1, 0) >= 0);
61 sys_futex(&x, FUTEX_WAKE | futex_private_flag, 1, 0) < 0) {
62 futex_private_flag = 0;
67 } // anonymous namespace
73 void SpinLockDelay(volatile Atomic32 *w, int32 value, int loop) {
75 int save_errno = errno;
79 tm.tv_nsec = base::internal::SuggestedDelayNS(loop);
81 tm.tv_nsec = 2000001; // above 2ms so linux 2.4 doesn't spin
84 tm.tv_nsec *= 16; // increase the delay; we expect explicit wakeups
85 sys_futex(reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
86 FUTEX_WAIT | futex_private_flag,
87 value, reinterpret_cast<struct kernel_timespec *>(&tm));
95 void SpinLockWake(volatile Atomic32 *w, bool all) {
97 sys_futex(reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
98 FUTEX_WAKE | futex_private_flag, all? INT_MAX : 1, 0);
102 } // namespace internal