diff options
Diffstat (limited to 'absl/synchronization/internal/futex.h')
-rw-r--r-- | absl/synchronization/internal/futex.h | 70 |
1 files changed, 47 insertions, 23 deletions
diff --git a/absl/synchronization/internal/futex.h b/absl/synchronization/internal/futex.h index 9cf9841d..62bb40f7 100644 --- a/absl/synchronization/internal/futex.h +++ b/absl/synchronization/internal/futex.h @@ -16,9 +16,7 @@ #include "absl/base/config.h" -#ifdef _WIN32 -#include <windows.h> -#else +#ifndef _WIN32 #include <sys/time.h> #include <unistd.h> #endif @@ -85,34 +83,60 @@ namespace synchronization_internal { class FutexImpl { public: - static int WaitUntil(std::atomic<int32_t> *v, int32_t val, + // Atomically check that `*v == val`, and if it is, then sleep until the + // timeout `t` has been reached, or until woken by `Wake()`. + static int WaitUntil(std::atomic<int32_t>* v, int32_t val, KernelTimeout t) { - long err = 0; // NOLINT(runtime/int) - if (t.has_timeout()) { - // https://locklessinc.com/articles/futex_cheat_sheet/ - // Unlike FUTEX_WAIT, FUTEX_WAIT_BITSET uses absolute time. - struct timespec abs_timeout = t.MakeAbsTimespec(); - // Atomically check that the futex value is still 0, and if it - // is, sleep until abs_timeout or until woken by FUTEX_WAKE. - err = syscall( - SYS_futex, reinterpret_cast<int32_t *>(v), - FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME, val, - &abs_timeout, nullptr, FUTEX_BITSET_MATCH_ANY); + if (!t.has_timeout()) { + return Wait(v, val); + } else if (t.is_absolute_timeout()) { + auto abs_timespec = t.MakeAbsTimespec(); + return WaitAbsoluteTimeout(v, val, &abs_timespec); } else { - // Atomically check that the futex value is still 0, and if it - // is, sleep until woken by FUTEX_WAKE. - err = syscall(SYS_futex, reinterpret_cast<int32_t *>(v), - FUTEX_WAIT | FUTEX_PRIVATE_FLAG, val, nullptr); + auto rel_timespec = t.MakeRelativeTimespec(); + return WaitRelativeTimeout(v, val, &rel_timespec); } - if (ABSL_PREDICT_FALSE(err != 0)) { + } + + // Atomically check that `*v == val`, and if it is, then sleep until the until + // woken by `Wake()`. + static int Wait(std::atomic<int32_t>* v, int32_t val) { + return WaitAbsoluteTimeout(v, val, nullptr); + } + + // Atomically check that `*v == val`, and if it is, then sleep until + // CLOCK_REALTIME reaches `*abs_timeout`, or until woken by `Wake()`. + static int WaitAbsoluteTimeout(std::atomic<int32_t>* v, int32_t val, + const struct timespec* abs_timeout) { + // https://locklessinc.com/articles/futex_cheat_sheet/ + // Unlike FUTEX_WAIT, FUTEX_WAIT_BITSET uses absolute time. + auto err = + syscall(SYS_futex, reinterpret_cast<int32_t*>(v), + FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME, + val, abs_timeout, nullptr, FUTEX_BITSET_MATCH_ANY); + if (err != 0) { + return -errno; + } + return 0; + } + + // Atomically check that `*v == val`, and if it is, then sleep until + // `*rel_timeout` has elapsed, or until woken by `Wake()`. + static int WaitRelativeTimeout(std::atomic<int32_t>* v, int32_t val, + const struct timespec* rel_timeout) { + // Atomically check that the futex value is still 0, and if it + // is, sleep until abs_timeout or until woken by FUTEX_WAKE. + auto err = syscall(SYS_futex, reinterpret_cast<int32_t*>(v), + FUTEX_PRIVATE_FLAG, val, rel_timeout); + if (err != 0) { return -errno; } return 0; } - static int Wake(std::atomic<int32_t> *v, int32_t count) { - // NOLINTNEXTLINE(runtime/int) - long err = syscall(SYS_futex, reinterpret_cast<int32_t*>(v), + // Wakes at most `count` waiters that have entered the sleep state on `v`. + static int Wake(std::atomic<int32_t>* v, int32_t count) { + auto err = syscall(SYS_futex, reinterpret_cast<int32_t*>(v), FUTEX_WAKE | FUTEX_PRIVATE_FLAG, count); if (ABSL_PREDICT_FALSE(err < 0)) { return -errno; |