--- /dev/null
+/*
+ * Copyright 2013 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <folly/detail/Futex.h>
+
+namespace folly { namespace detail {
+
+/* see Futex.h */
+FutexResult futexErrnoToFutexResult(int returnVal, int futexErrno) {
+ if (returnVal == 0) {
+ return FutexResult::AWOKEN;
+ }
+ switch(futexErrno) {
+ case ETIMEDOUT:
+ return FutexResult::TIMEDOUT;
+ case EINTR:
+ return FutexResult::INTERRUPTED;
+ case EWOULDBLOCK:
+ return FutexResult::VALUE_CHANGED;
+ default:
+ assert(false);
+ /* Shouldn't reach here. Just return one of the FutexResults */
+ return FutexResult::VALUE_CHANGED;
+ }
+}
+
+}}
#pragma once
#include <atomic>
+#include <chrono>
#include <limits>
#include <assert.h>
#include <errno.h>
#include <unistd.h>
#include <boost/noncopyable.hpp>
+using std::chrono::steady_clock;
+using std::chrono::system_clock;
+using std::chrono::time_point;
+
namespace folly { namespace detail {
+enum class FutexResult {
+ VALUE_CHANGED, /* Futex value didn't match expected */
+ AWOKEN, /* futex wait matched with a futex wake */
+ INTERRUPTED, /* Spurious wake-up or signal caused futex wait failure */
+ TIMEDOUT
+};
+
+/* Converts return value and errno from a futex syscall to a FutexResult */
+FutexResult futexErrnoToFutexResult(int returnVal, int futexErrno);
+
/**
* Futex is an atomic 32 bit unsigned integer that provides access to the
* futex() syscall on that value. It is templated in such a way that it
* other return (signal, this->load() != expected, or spurious wakeup). */
bool futexWait(uint32_t expected, uint32_t waitMask = -1);
+ /** Similar to futexWait but also accepts a timeout that gives the time until
+ * when the call can block (time is the absolute time i.e time since epoch).
+ * Allowed clock types: std::chrono::system_clock, std::chrono::steady_clock.
+ * Returns one of FutexResult values.
+ *
+ * NOTE: On some systems steady_clock is just an alias for system_clock,
+ * and is not actually steady.*/
+ template <class Clock, class Duration = typename Clock::duration>
+ FutexResult futexWaitUntil(uint32_t expected,
+ const time_point<Clock, Duration>& absTime,
+ uint32_t waitMask = -1);
+
/** Wakens up to count waiters where (waitMask & wakeMask) != 0,
* returning the number of awoken threads. */
int futexWake(int count = std::numeric_limits<int>::max(),
uint32_t wakeMask = -1);
+
+ private:
+
+ /** Futex wait implemented via syscall SYS_futex. absTimeout gives
+ * time till when the wait can block. If it is nullptr the call will
+ * block until a matching futex wake is received. extraOpFlags can be
+ * used to specify addtional flags to add to the futex operation (by
+ * default only FUTEX_WAIT_BITSET and FUTEX_PRIVATE_FLAG are included).
+ * Returns 0 on success or -1 on error, with errno set to one of the
+ * values listed in futex(2). */
+ int futexWaitImpl(uint32_t expected,
+ const struct timespec* absTimeout,
+ int extraOpFlags,
+ uint32_t waitMask);
};
+template <>
+inline int
+Futex<std::atomic>::futexWaitImpl(uint32_t expected,
+ const struct timespec* absTimeout,
+ int extraOpFlags,
+ uint32_t waitMask) {
+ assert(sizeof(*this) == sizeof(int));
+
+ /* Unlike FUTEX_WAIT, FUTEX_WAIT_BITSET requires an absolute timeout
+ * value - http://locklessinc.com/articles/futex_cheat_sheet/ */
+ int rv = syscall(
+ SYS_futex,
+ this, /* addr1 */
+ FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG | extraOpFlags, /* op */
+ expected, /* val */
+ absTimeout, /* timeout */
+ nullptr, /* addr2 */
+ waitMask); /* val3 */
+
+ assert(rv == 0 ||
+ errno == EWOULDBLOCK ||
+ errno == EINTR ||
+ (absTimeout != nullptr && errno == ETIMEDOUT));
+
+ return rv;
+}
+
template <>
inline bool Futex<std::atomic>::futexWait(uint32_t expected,
uint32_t waitMask) {
- assert(sizeof(*this) == sizeof(int));
- int rv = syscall(SYS_futex,
- this, /* addr1 */
- FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG, /* op */
- expected, /* val */
- nullptr, /* timeout */
- nullptr, /* addr2 */
- waitMask); /* val3 */
- assert(rv == 0 || (errno == EWOULDBLOCK || errno == EINTR));
- return rv == 0;
+ return futexWaitImpl(expected, nullptr, 0 /* extraOpFlags */, waitMask) == 0;
}
template <>
return rv;
}
+/* Convert std::chrono::time_point to struct timespec */
+template <class Clock, class Duration = typename Clock::Duration>
+struct timespec timePointToTimeSpec(const time_point<Clock, Duration>& tp) {
+ using std::chrono::nanoseconds;
+ using std::chrono::seconds;
+ using std::chrono::duration_cast;
+
+ struct timespec ts;
+ auto duration = tp.time_since_epoch();
+ auto secs = duration_cast<seconds>(duration);
+ auto nanos = duration_cast<nanoseconds>(duration - secs);
+ ts.tv_sec = secs.count();
+ ts.tv_nsec = nanos.count();
+ return ts;
+}
+
+template <template<typename> class Atom> template<class Clock, class Duration>
+inline FutexResult
+Futex<Atom>::futexWaitUntil(
+ uint32_t expected,
+ const time_point<Clock, Duration>& absTime,
+ uint32_t waitMask) {
+
+ static_assert(std::is_same<Clock,system_clock>::value ||
+ std::is_same<Clock,steady_clock>::value,
+ "Only std::system_clock or std::steady_clock supported");
+
+ struct timespec absTimeSpec = timePointToTimeSpec(absTime);
+ int extraOpFlags = 0;
+
+ /* We must use FUTEX_CLOCK_REALTIME flag if we are getting the time_point
+ * from the system clock (CLOCK_REALTIME). This check also works correctly for
+ * broken glibc in which steady_clock is a typedef to system_clock.*/
+ if (std::is_same<Clock,system_clock>::value) {
+ extraOpFlags = FUTEX_CLOCK_REALTIME;
+ } else {
+ assert(Clock::is_steady);
+ }
+
+ const int rv = futexWaitImpl(expected, &absTimeSpec, extraOpFlags, waitMask);
+ return futexErrnoToFutexResult(rv, errno);
+}
+
}}
sem_post(sched->sems_[sched->scheduler_(sched->sems_.size())]);
}
+int
+DeterministicSchedule::getRandNumber(int n) {
+ if (tls_sched) {
+ return tls_sched->scheduler_(n);
+ }
+ return std::rand() % n;
+}
+
sem_t*
DeterministicSchedule::beforeThreadCreate() {
sem_t* s = new sem_t;
return rv;
}
+FutexResult futexWaitUntilImpl(Futex<DeterministicAtomic>* futex,
+ uint32_t expected, uint32_t waitMask) {
+ if (futex == nullptr) {
+ return FutexResult::VALUE_CHANGED;
+ }
+
+ bool rv = false;
+ int futexErrno = 0;
+
+ DeterministicSchedule::beforeSharedAccess();
+ futexLock.lock();
+ if (futex->data == expected) {
+ auto& queue = futexQueues[futex];
+ queue.push_back(std::make_pair(waitMask, &rv));
+ auto ours = queue.end();
+ ours--;
+ while (!rv) {
+ futexLock.unlock();
+ DeterministicSchedule::afterSharedAccess();
+ DeterministicSchedule::beforeSharedAccess();
+ futexLock.lock();
+
+ // Simulate spurious wake-ups, timeouts each time with
+ // a 10% probability
+ if (DeterministicSchedule::getRandNumber(100) < 10) {
+ queue.erase(ours);
+ if (queue.empty()) {
+ futexQueues.erase(futex);
+ }
+ rv = false;
+ // Simulate ETIMEDOUT 90% of the time and other failures
+ // remaining time
+ futexErrno =
+ DeterministicSchedule::getRandNumber(100) >= 10 ? ETIMEDOUT : EINTR;
+ break;
+ }
+ }
+ }
+ futexLock.unlock();
+ DeterministicSchedule::afterSharedAccess();
+ return futexErrnoToFutexResult(rv ? 0 : -1, futexErrno);
+}
+
template<>
int Futex<DeterministicAtomic>::futexWake(int count, uint32_t wakeMask) {
int rv = 0;
/** Calls sem_wait(sem) as part of a deterministic schedule. */
static void wait(sem_t* sem);
+ /** Used scheduler_ to get a random number b/w [0, n). If tls_sched is
+ * not set-up it falls back to std::rand() */
+ static int getRandNumber(int n);
+
private:
static __thread sem_t* tls_sem;
static __thread DeterministicSchedule* tls_sched;
bool Futex<test::DeterministicAtomic>::futexWait(uint32_t expected,
uint32_t waitMask);
+/// This function ignores the time bound, and instead pseudo-randomly chooses
+/// whether the timeout was reached. To do otherwise would not be deterministic.
+FutexResult futexWaitUntilImpl(Futex<test::DeterministicAtomic> *futex,
+ uint32_t expected, uint32_t waitMask);
+
+template<> template<class Clock, class Duration>
+FutexResult
+Futex<test::DeterministicAtomic>::futexWaitUntil(
+ uint32_t expected,
+ const time_point<Clock, Duration>& absTimeUnused,
+ uint32_t waitMask) {
+ return futexWaitUntilImpl(this, expected, waitMask);
+}
+
template<>
int Futex<test::DeterministicAtomic>::futexWake(int count, uint32_t wakeMask);
#include "folly/detail/Futex.h"
#include "folly/test/DeterministicSchedule.h"
+#include <chrono>
#include <thread>
#include <gflags/gflags.h>
#include <gtest/gtest.h>
+#include <common/logging/logging.h>
+#include <time.h>
using namespace folly::detail;
using namespace folly::test;
+using namespace std::chrono;
typedef DeterministicSchedule DSched;
DSched::join(thr);
}
+template<template<typename> class Atom>
+void run_wait_until_tests();
+
+template <typename Clock>
+void stdAtomicWaitUntilTests() {
+ Futex<std::atomic> f(0);
+
+ auto thrA = DSched::thread([&]{
+ while (true) {
+ typename Clock::time_point nowPlus2s = Clock::now() + seconds(2);
+ auto res = f.futexWaitUntil(0, nowPlus2s);
+ EXPECT_TRUE(res == FutexResult::TIMEDOUT || res == FutexResult::AWOKEN);
+ if (res == FutexResult::AWOKEN) {
+ break;
+ }
+ }
+ });
+
+ while (f.futexWake() != 1) {
+ std::this_thread::yield();
+ }
+
+ DSched::join(thrA);
+
+ auto start = Clock::now();
+ EXPECT_EQ(f.futexWaitUntil(0, start + milliseconds(100)),
+ FutexResult::TIMEDOUT);
+ LOG(INFO) << "Futex wait timed out after waiting for "
+ << duration_cast<milliseconds>(Clock::now() - start).count()
+ << "ms";
+}
+
+template <typename Clock>
+void deterministicAtomicWaitUntilTests() {
+ Futex<DeterministicAtomic> f(0);
+
+ // Futex wait must eventually fail with either FutexResult::TIMEDOUT or
+ // FutexResult::INTERRUPTED
+ auto res = f.futexWaitUntil(0, Clock::now() + milliseconds(100));
+ EXPECT_TRUE(res == FutexResult::TIMEDOUT || res == FutexResult::INTERRUPTED);
+}
+
+template <>
+void run_wait_until_tests<std::atomic>() {
+ stdAtomicWaitUntilTests<system_clock>();
+ stdAtomicWaitUntilTests<steady_clock>();
+}
+
+template <>
+void run_wait_until_tests<DeterministicAtomic>() {
+ deterministicAtomicWaitUntilTests<system_clock>();
+ deterministicAtomicWaitUntilTests<steady_clock>();
+}
+
+uint64_t diff(uint64_t a, uint64_t b) {
+ return a > b ? a - b : b - a;
+}
+
+void run_system_clock_test() {
+ /* Test to verify that system_clock uses clock_gettime(CLOCK_REALTIME, ...)
+ * for the time_points */
+ struct timespec ts;
+ const int maxIters = 1000;
+ int iter = 0;
+ uint64_t delta = 10000000 /* 10 ms */;
+
+ /** The following loop is only to make the test more robust in the presence of
+ * clock adjustments that can occur. We just run the loop maxIter times and
+ * expect with very high probability that there will be atleast one iteration
+ * of the test during which clock adjustments > delta have not occurred. */
+ while (iter < maxIters) {
+ uint64_t a = duration_cast<nanoseconds>(system_clock::now()
+ .time_since_epoch()).count();
+
+ clock_gettime(CLOCK_REALTIME, &ts);
+ uint64_t b = ts.tv_sec * 1000000000ULL + ts.tv_nsec;
+
+ uint64_t c = duration_cast<nanoseconds>(system_clock::now()
+ .time_since_epoch()).count();
+
+ if (diff(a, b) <= delta &&
+ diff(b, c) <= delta &&
+ diff(a, c) <= 2 * delta) {
+ /* Success! system_clock uses CLOCK_REALTIME for time_points */
+ break;
+ }
+ iter++;
+ }
+ EXPECT_TRUE(iter < maxIters);
+}
+
+void run_steady_clock_test() {
+ /* Test to verify that steady_clock uses clock_gettime(CLOCK_MONOTONIC, ...)
+ * for the time_points */
+ EXPECT_TRUE(steady_clock::is_steady);
+
+ uint64_t A = duration_cast<nanoseconds>(steady_clock::now()
+ .time_since_epoch()).count();
+
+ struct timespec ts;
+ clock_gettime(CLOCK_MONOTONIC, &ts);
+ uint64_t B = ts.tv_sec * 1000000000ULL + ts.tv_nsec;
+
+ uint64_t C = duration_cast<nanoseconds>(steady_clock::now()
+ .time_since_epoch()).count();
+ EXPECT_TRUE(A <= B && B <= C);
+}
+
+TEST(Futex, clock_source) {
+ run_system_clock_test();
+
+ /* On some systems steady_clock is just an alias for system_clock. So,
+ * we must skip run_steady_clock_test if the two clocks are the same. */
+ if (!std::is_same<system_clock,steady_clock>::value) {
+ run_steady_clock_test();
+ }
+}
TEST(Futex, basic_live) {
run_basic_tests<std::atomic>();
+ run_wait_until_tests<std::atomic>();
}
TEST(Futex, basic_deterministic) {
DSched sched(DSched::uniform(0));
run_basic_tests<DeterministicAtomic>();
+ run_wait_until_tests<DeterministicAtomic>();
}
int main(int argc, char ** argv) {
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