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-rw-r--r--absl/synchronization/internal/futex.h70
-rw-r--r--absl/synchronization/internal/waiter.cc106
-rw-r--r--absl/synchronization/internal/waiter.h3
-rw-r--r--absl/synchronization/mutex.cc45
4 files changed, 47 insertions, 177 deletions
diff --git a/absl/synchronization/internal/futex.h b/absl/synchronization/internal/futex.h
index 62bb40f7..9cf9841d 100644
--- a/absl/synchronization/internal/futex.h
+++ b/absl/synchronization/internal/futex.h
@@ -16,7 +16,9 @@
#include "absl/base/config.h"
-#ifndef _WIN32
+#ifdef _WIN32
+#include <windows.h>
+#else
#include <sys/time.h>
#include <unistd.h>
#endif
@@ -83,60 +85,34 @@ namespace synchronization_internal {
class FutexImpl {
public:
- // 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,
+ static int WaitUntil(std::atomic<int32_t> *v, int32_t val,
KernelTimeout t) {
- 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);
+ 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);
} else {
- auto rel_timespec = t.MakeRelativeTimespec();
- return WaitRelativeTimeout(v, val, &rel_timespec);
+ // 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);
}
- }
-
- // 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) {
+ if (ABSL_PREDICT_FALSE(err != 0)) {
return -errno;
}
return 0;
}
- // 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),
+ static int Wake(std::atomic<int32_t> *v, int32_t count) {
+ // NOLINTNEXTLINE(runtime/int)
+ long err = syscall(SYS_futex, reinterpret_cast<int32_t*>(v),
FUTEX_WAKE | FUTEX_PRIVATE_FLAG, count);
if (ABSL_PREDICT_FALSE(err < 0)) {
return -errno;
diff --git a/absl/synchronization/internal/waiter.cc b/absl/synchronization/internal/waiter.cc
index 4eee1298..f2051d67 100644
--- a/absl/synchronization/internal/waiter.cc
+++ b/absl/synchronization/internal/waiter.cc
@@ -67,74 +67,11 @@ static void MaybeBecomeIdle() {
#if ABSL_WAITER_MODE == ABSL_WAITER_MODE_FUTEX
-Waiter::Waiter() : futex_(0) {}
-
-bool Waiter::WaitAbsoluteTimeout(KernelTimeout t) {
- // Loop until we can atomically decrement futex from a positive
- // value, waiting on a futex while we believe it is zero.
- // Note that, since the thread ticker is just reset, we don't need to check
- // whether the thread is idle on the very first pass of the loop.
- bool first_pass = true;
-
- while (true) {
- int32_t x = futex_.load(std::memory_order_relaxed);
- while (x != 0) {
- if (!futex_.compare_exchange_weak(x, x - 1,
- std::memory_order_acquire,
- std::memory_order_relaxed)) {
- continue; // Raced with someone, retry.
- }
- return true; // Consumed a wakeup, we are done.
- }
-
- if (!first_pass) MaybeBecomeIdle();
- auto abs_timeout = t.MakeAbsTimespec();
- const int err = Futex::WaitAbsoluteTimeout(&futex_, 0, &abs_timeout);
- if (err != 0) {
- if (err == -EINTR || err == -EWOULDBLOCK) {
- // Do nothing, the loop will retry.
- } else if (err == -ETIMEDOUT) {
- return false;
- } else {
- ABSL_RAW_LOG(FATAL, "Futex operation failed with error %d\n", err);
- }
- }
- first_pass = false;
- }
-}
-
-#ifdef CLOCK_MONOTONIC
-
-// Subtracts the timespec `sub` from `in` if the result would not be negative,
-// and returns true. Returns false if the result would be negative, and leaves
-// `in` unchanged.
-static bool TimespecSubtract(struct timespec& in, const struct timespec& sub) {
- if (in.tv_sec < sub.tv_sec) {
- return false;
- }
- if (in.tv_nsec < sub.tv_nsec) {
- if (in.tv_sec == sub.tv_sec) {
- return false;
- }
- // Borrow from tv_sec.
- in.tv_sec -= 1;
- in.tv_nsec += 1'000'000'000;
- }
- in.tv_sec -= sub.tv_sec;
- in.tv_nsec -= sub.tv_nsec;
- return true;
+Waiter::Waiter() {
+ futex_.store(0, std::memory_order_relaxed);
}
-// On some platforms a background thread periodically calls `Poke()` to briefly
-// wake waiter threads so that they may call `MaybeBecomeIdle()`. This means
-// that `WaitRelativeTimeout()` differs slightly from `WaitAbsoluteTimeout()`
-// because it must adjust the timeout by the amount of time that it has already
-// slept.
-bool Waiter::WaitRelativeTimeout(KernelTimeout t) {
- struct timespec start;
- ABSL_RAW_CHECK(clock_gettime(CLOCK_MONOTONIC, &start) == 0,
- "clock_gettime() failed");
-
+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.
// Note that, since the thread ticker is just reset, we don't need to check
@@ -152,24 +89,8 @@ bool Waiter::WaitRelativeTimeout(KernelTimeout t) {
return true; // Consumed a wakeup, we are done.
}
- auto relative_timeout = t.MakeRelativeTimespec();
- if (!first_pass) {
- MaybeBecomeIdle();
-
- // Adjust relative_timeout for `Poke()`s.
- struct timespec now;
- ABSL_RAW_CHECK(clock_gettime(CLOCK_MONOTONIC, &now) == 0,
- "clock_gettime() failed");
- // If TimespecSubstract(now, start) returns false, then the clock isn't
- // truly monotonic.
- if (TimespecSubtract(now, start)) {
- if (!TimespecSubtract(relative_timeout, now)) {
- return false; // Timeout.
- }
- }
- }
-
- const int err = Futex::WaitRelativeTimeout(&futex_, 0, &relative_timeout);
+ if (!first_pass) MaybeBecomeIdle();
+ const int err = Futex::WaitUntil(&futex_, 0, t);
if (err != 0) {
if (err == -EINTR || err == -EWOULDBLOCK) {
// Do nothing, the loop will retry.
@@ -183,23 +104,6 @@ bool Waiter::WaitRelativeTimeout(KernelTimeout t) {
}
}
-#else // CLOCK_MONOTONIC
-
-// No support for CLOCK_MONOTONIC.
-// KernelTimeout will automatically convert to an absolute timeout.
-bool Waiter::WaitRelativeTimeout(KernelTimeout t) {
- return WaitAbsoluteTimeout(t);
-}
-
-#endif // CLOCK_MONOTONIC
-
-bool Waiter::Wait(KernelTimeout t) {
- if (t.is_absolute_timeout()) {
- return WaitAbsoluteTimeout(t);
- }
- return WaitRelativeTimeout(t);
-}
-
void Waiter::Post() {
if (futex_.fetch_add(1, std::memory_order_release) == 0) {
// We incremented from 0, need to wake a potential waiter.
diff --git a/absl/synchronization/internal/waiter.h b/absl/synchronization/internal/waiter.h
index c206cc3f..b8adfeb5 100644
--- a/absl/synchronization/internal/waiter.h
+++ b/absl/synchronization/internal/waiter.h
@@ -110,9 +110,6 @@ class Waiter {
~Waiter() = delete;
#if ABSL_WAITER_MODE == ABSL_WAITER_MODE_FUTEX
- bool WaitAbsoluteTimeout(KernelTimeout t);
- bool WaitRelativeTimeout(KernelTimeout t);
-
// Futexes are defined by specification to be 32-bits.
// Thus std::atomic<int32_t> must be just an int32_t with lockfree methods.
std::atomic<int32_t> futex_;
diff --git a/absl/synchronization/mutex.cc b/absl/synchronization/mutex.cc
index a8911614..ef6d063e 100644
--- a/absl/synchronization/mutex.cc
+++ b/absl/synchronization/mutex.cc
@@ -635,6 +635,21 @@ void Mutex::InternalAttemptToUseMutexInFatalSignalHandler() {
std::memory_order_release);
}
+// --------------------------time support
+
+// Return the current time plus the timeout. Use the same clock as
+// PerThreadSem::Wait() for consistency. Unfortunately, we don't have
+// such a choice when a deadline is given directly.
+static absl::Time DeadlineFromTimeout(absl::Duration timeout) {
+#ifndef _WIN32
+ struct timeval tv;
+ gettimeofday(&tv, nullptr);
+ return absl::TimeFromTimeval(tv) + timeout;
+#else
+ return absl::Now() + timeout;
+#endif
+}
+
// --------------------------Mutexes
// In the layout below, the msb of the bottom byte is currently unused. Also,
@@ -1534,13 +1549,7 @@ void Mutex::LockWhen(const Condition &cond) {
}
bool Mutex::LockWhenWithTimeout(const Condition &cond, absl::Duration timeout) {
- ABSL_TSAN_MUTEX_PRE_LOCK(this, 0);
- GraphId id = DebugOnlyDeadlockCheck(this);
- bool res = LockSlowWithDeadline(kExclusive, &cond,
- KernelTimeout(timeout), 0);
- DebugOnlyLockEnter(this, id);
- ABSL_TSAN_MUTEX_POST_LOCK(this, 0, 0);
- return res;
+ return LockWhenWithDeadline(cond, DeadlineFromTimeout(timeout));
}
bool Mutex::LockWhenWithDeadline(const Condition &cond, absl::Time deadline) {
@@ -1563,12 +1572,7 @@ void Mutex::ReaderLockWhen(const Condition &cond) {
bool Mutex::ReaderLockWhenWithTimeout(const Condition &cond,
absl::Duration timeout) {
- ABSL_TSAN_MUTEX_PRE_LOCK(this, __tsan_mutex_read_lock);
- GraphId id = DebugOnlyDeadlockCheck(this);
- bool res = LockSlowWithDeadline(kShared, &cond, KernelTimeout(timeout), 0);
- DebugOnlyLockEnter(this, id);
- ABSL_TSAN_MUTEX_POST_LOCK(this, __tsan_mutex_read_lock, 0);
- return res;
+ return ReaderLockWhenWithDeadline(cond, DeadlineFromTimeout(timeout));
}
bool Mutex::ReaderLockWhenWithDeadline(const Condition &cond,
@@ -1593,18 +1597,7 @@ void Mutex::Await(const Condition &cond) {
}
bool Mutex::AwaitWithTimeout(const Condition &cond, absl::Duration timeout) {
- if (cond.Eval()) { // condition already true; nothing to do
- if (kDebugMode) {
- this->AssertReaderHeld();
- }
- return true;
- }
-
- KernelTimeout t{timeout};
- bool res = this->AwaitCommon(cond, t);
- ABSL_RAW_CHECK(res || t.has_timeout(),
- "condition untrue on return from Await");
- return res;
+ return AwaitWithDeadline(cond, DeadlineFromTimeout(timeout));
}
bool Mutex::AwaitWithDeadline(const Condition &cond, absl::Time deadline) {
@@ -2670,7 +2663,7 @@ bool CondVar::WaitCommon(Mutex *mutex, KernelTimeout t) {
}
bool CondVar::WaitWithTimeout(Mutex *mu, absl::Duration timeout) {
- return WaitCommon(mu, KernelTimeout(timeout));
+ return WaitWithDeadline(mu, DeadlineFromTimeout(timeout));
}
bool CondVar::WaitWithDeadline(Mutex *mu, absl::Time deadline) {
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-22 08:57:14 +0000