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Diffstat (limited to 'absl/synchronization/internal/waiter.cc')
-rw-r--r--absl/synchronization/internal/waiter.cc73
1 files changed, 47 insertions, 26 deletions
diff --git a/absl/synchronization/internal/waiter.cc b/absl/synchronization/internal/waiter.cc
index cd16c788..db1b54f6 100644
--- a/absl/synchronization/internal/waiter.cc
+++ b/absl/synchronization/internal/waiter.cc
@@ -39,10 +39,12 @@
#include <atomic>
#include <cassert>
+#include <cstdint>
#include "absl/base/internal/malloc_extension.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/base/internal/thread_identity.h"
+#include "absl/base/optimization.h"
#include "absl/synchronization/internal/kernel_timeout.h"
namespace absl {
@@ -82,6 +84,42 @@ static void MaybeBecomeIdle() {
#define FUTEX_BITSET_MATCH_ANY 0xFFFFFFFF
#endif
#endif
+class Futex {
+ public:
+ static int WaitUntil(std::atomic<int32_t> *v, int32_t val,
+ KernelTimeout t) {
+ int err = 0;
+ 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);
+ } 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);
+ }
+ if (err != 0) {
+ err = -errno;
+ }
+ return err;
+ }
+
+ static int Wake(std::atomic<int32_t> *v, int32_t count) {
+ int err = syscall(SYS_futex, reinterpret_cast<int32_t *>(v),
+ FUTEX_WAKE | FUTEX_PRIVATE_FLAG, count);
+ if (ABSL_PREDICT_FALSE(err < 0)) {
+ err = -errno;
+ }
+ return err;
+ }
+};
void Waiter::Init() {
futex_.store(0, std::memory_order_relaxed);
@@ -91,7 +129,7 @@ bool Waiter::Wait(KernelTimeout t) {
// Loop until we can atomically decrement futex from a positive
// value, waiting on a futex while we believe it is zero.
while (true) {
- int x = futex_.load(std::memory_order_relaxed);
+ int32_t x = futex_.load(std::memory_order_relaxed);
if (x != 0) {
if (!futex_.compare_exchange_weak(x, x - 1,
std::memory_order_acquire,
@@ -101,30 +139,14 @@ bool Waiter::Wait(KernelTimeout t) {
return true; // Consumed a wakeup, we are done.
}
- int err = 0;
- 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<int *>(&futex_),
- FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME, 0,
- &abs_timeout, nullptr, FUTEX_BITSET_MATCH_ANY);
- } 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<int *>(&futex_),
- FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, nullptr);
- }
+ const int err = Futex::WaitUntil(&futex_, 0, t);
if (err != 0) {
- if (errno == EINTR || errno == EWOULDBLOCK) {
+ if (err == -EINTR || err == -EWOULDBLOCK) {
// Do nothing, the loop will retry.
- } else if (errno == ETIMEDOUT) {
- return false; // Timeout.
+ } else if (err == -ETIMEDOUT) {
+ return false;
} else {
- ABSL_RAW_LOG(FATAL, "Futex operation failed with errno %d\n", errno);
+ ABSL_RAW_LOG(FATAL, "Futex operation failed with error %d\n", err);
}
}
@@ -141,10 +163,9 @@ void Waiter::Post() {
void Waiter::Poke() {
// Wake one thread waiting on the futex.
- int err = syscall(SYS_futex, reinterpret_cast<int *>(&futex_),
- FUTEX_WAKE | FUTEX_PRIVATE_FLAG, 1);
- if (err < 0) {
- ABSL_RAW_LOG(FATAL, "FUTEX_WAKE failed with errno %d\n", errno);
+ const int err = Futex::Wake(&futex_, 1);
+ if (ABSL_PREDICT_FALSE(err < 0)) {
+ ABSL_RAW_LOG(FATAL, "Futex operation failed with error %d\n", err);
}
}