tvl-depot/absl/synchronization/mutex.h

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// Copyright 2017 The Abseil Authors.
//
// 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.
//
// -----------------------------------------------------------------------------
// mutex.h
// -----------------------------------------------------------------------------
//
// This header file defines a `Mutex` -- a mutually exclusive lock -- and the
// most common type of synchronization primitive for facilitating locks on
// shared resources. A mutex is used to prevent multiple threads from accessing
// and/or writing to a shared resource concurrently.
//
// Unlike a `std::mutex`, the Abseil `Mutex` provides the following additional
// features:
// * Conditional predicates intrinsic to the `Mutex` object
Export of internal Abseil changes. -- 898e99cae89ca4cc27f86f719148f020d521dd58 by Abseil Team <absl-team@google.com>: Update comment. PiperOrigin-RevId: 204323401 -- b9d14db8b8a9dfb0e1cfb5967aaa0de1c4e94c42 by Abseil Team <absl-team@google.com>: Internal change PiperOrigin-RevId: 204178059 -- f3b5a667611a588aa06fea9168e997ef5cffa7ac by Abseil Team <absl-team@google.com>: Fix a potential reinterpret_cast compile error in absl::InlinedVector The current code will trigger a reinterpret_cast error enhanced by llvm r336738. PiperOrigin-RevId: 204131536 -- cc87d7a8302ad4471c1a25781d6ec19c2ce1524e by Abseil Team <absl-team@google.com>: Internal change. PiperOrigin-RevId: 203979040 -- bc5cae3cfc72af1d3e786d5a3b59a47e205afec9 by Gennadiy Rozental <rogeeff@google.com>: Internal: add internal logging hooks PiperOrigin-RevId: 203850605 -- 503655c248f557f677c920078613522b010e73c8 by Derek Mauro <dmauro@google.com>: Cleanup stacktrace_config.h Instead of listing the platforms that aren't supported, list the ones we do support, and fallback to stacktrace_unimplemented-inl.inc at the end. Previously any platform that wasn't listed gets "#error Not supported yet". GitHub issue #135 PiperOrigin-RevId: 203823079 -- cb69925c4cacc14558cf103a09f218c37f466a16 by Abseil Team <absl-team@google.com>: Fix a minor typo in absl::variant documentation. PiperOrigin-RevId: 203679877 -- 23a0e4db10039011fa5fd879fb73d2f2bbd17301 by Abseil Team <absl-team@google.com>: Format .bzl files with buildifier PiperOrigin-RevId: 203461813 -- 1ad02616bdb715dfdc7f1a73313e383f4ededa03 by Abseil Team <absl-team@google.com>: Make the absl::SleepFor() tests treat any successful retry within a 48x deadline as a total success, thereby reducing flakiness. PiperOrigin-RevId: 203401603 -- b3dccbbc6563ea0173527076a3fff21433d48f47 by Abseil Team <absl-team@google.com>: Replace config_setting.values{"compiler"} with config_setting.flag_values{"@bazel_tools//tools/cpp:compiler"} Due to changes in Bazel we need to change the way "compiler" is specified in config_setting. This will not change the behavior of the config_setting itself. PiperOrigin-RevId: 203345693 -- 170f1692537460a4ba1756d34852275899c2339b by Matt Armstrong <marmstrong@google.com>: Address test flakiness in the TimeoutTest. The basic idea is to loop forever until the expected scheduling delays are observed (within reasonable bounds), and only then assert the other invariants. PiperOrigin-RevId: 203188162 GitOrigin-RevId: 898e99cae89ca4cc27f86f719148f020d521dd58 Change-Id: Ie853ec050afa3a04c519393afe666bc03e11dc87
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// * Shared/reader locks, in addition to standard exclusive/writer locks
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// * Deadlock detection and debug support.
//
// The following helper classes are also defined within this file:
//
// MutexLock - An RAII wrapper to acquire and release a `Mutex` for exclusive/
// write access within the current scope.
// ReaderMutexLock
// - An RAII wrapper to acquire and release a `Mutex` for shared/read
// access within the current scope.
//
// WriterMutexLock
// - Alias for `MutexLock` above, designed for use in distinguishing
// reader and writer locks within code.
//
// In addition to simple mutex locks, this file also defines ways to perform
// locking under certain conditions.
//
// Condition - (Preferred) Used to wait for a particular predicate that
// depends on state protected by the `Mutex` to become true.
// CondVar - A lower-level variant of `Condition` that relies on
// application code to explicitly signal the `CondVar` when
// a condition has been met.
//
// See below for more information on using `Condition` or `CondVar`.
//
// Mutexes and mutex behavior can be quite complicated. The information within
// this header file is limited, as a result. Please consult the Mutex guide for
// more complete information and examples.
#ifndef ABSL_SYNCHRONIZATION_MUTEX_H_
#define ABSL_SYNCHRONIZATION_MUTEX_H_
#include <atomic>
#include <cstdint>
#include <string>
#include "absl/base/internal/identity.h"
#include "absl/base/internal/low_level_alloc.h"
#include "absl/base/internal/thread_identity.h"
#include "absl/base/internal/tsan_mutex_interface.h"
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#include "absl/base/port.h"
#include "absl/base/thread_annotations.h"
#include "absl/synchronization/internal/kernel_timeout.h"
#include "absl/synchronization/internal/per_thread_sem.h"
#include "absl/time/time.h"
// Decide if we should use the non-production implementation because
// the production implementation hasn't been fully ported yet.
#ifdef ABSL_INTERNAL_USE_NONPROD_MUTEX
#error ABSL_INTERNAL_USE_NONPROD_MUTEX cannot be directly set
#elif defined(ABSL_LOW_LEVEL_ALLOC_MISSING)
#define ABSL_INTERNAL_USE_NONPROD_MUTEX 1
#include "absl/synchronization/internal/mutex_nonprod.inc"
#endif
namespace absl {
class Condition;
Changes imported from Abseil "staging" branch: - b527a3e4b36b644ac424e3c525b1cd393f6f6c40 Fix some typos in the usage examples by Jorg Brown <jorg@google.com> - 82be4a9adf3bb0ddafc0d46274969c99afffe870 Fix typo in optional.h comment. by Abseil Team <absl-team@google.com> - d6ee63bf8fc51fba074c23b33cebc28c808d7f07 Remove internal-only identifiers from code. by Daniel Katz <katzdm@google.com> - f9c3ad2f0d73f53b21603638af8b4bed636e79f4 Use easier understandable names for absl::StartsWith and ... by Abseil Team <absl-team@google.com> - 7c16c14fefee89c927b8789d6043c4691bcffc9b Add -Wno-missing-prototypes back to the LLVM copts. by Derek Mauro <dmauro@google.com> - 2f4b7d2e50c7023240242f1e15db60ccd7e8768d IWYU | absl/strings by Juemin Yang <jueminyang@google.com> - a99cbcc1daa34a2d6a2bb26de275e05173cc77e9 IWYU | absl/type by Juemin Yang <jueminyang@google.com> - 12e1146d0fc76c071d7e0ebaabb62f0a984fae66 Use LLVM_FLAGS and LLVM_TEST_FLAGS when --compiler=llvm. by Derek Mauro <dmauro@google.com> - cd6bea616abda558d0bace5bd77455662a233688 IWYU | absl/debugging by Juemin Yang <jueminyang@google.com> - d9a7382e59d46a8581b6b7a31cd5a48bb89326e9 IWYU | absl/synchronization by Juemin Yang <jueminyang@google.com> - 07ec7d6d5a4a666f4183c5d0ed9c342baa7b24bc IWYU | absl/numeric by Juemin Yang <jueminyang@google.com> - 12bfe40051f4270f8707e191af5652f83f2f750c Remove the RoundTrip{Float,Double}ToBuffer routines from ... by Jorg Brown <jorg@google.com> - eeb4fd67c9d97f66cb9475c3c5e51ab132f1c810 Adds conversion functions for converting between absl/tim... by Greg Miller <jgm@google.com> - 59a2108d05d4ea85dc5cc11e49b2cd2335d4295a Change Substitute to use %.6g formatting rather than 15/1... by Jorg Brown <jorg@google.com> - 394becb48e0fcd161642cdaac5120d32567e0ef8 IWYU | absl/meta by Juemin Yang <jueminyang@google.com> - 1e5da6e8da336699b2469dcf6dda025b9b0ec4c9 Rewrite atomic_hook.h to not use std::atomic<T*> under Wi... by Greg Falcon <gfalcon@google.com> GitOrigin-RevId: b527a3e4b36b644ac424e3c525b1cd393f6f6c40 Change-Id: I14e331d91c956ef045ac7927091a9f179716de0c
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struct SynchWaitParams;
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// -----------------------------------------------------------------------------
// Mutex
// -----------------------------------------------------------------------------
//
// A `Mutex` is a non-reentrant (aka non-recursive) Mutually Exclusive lock
// on some resource, typically a variable or data structure with associated
// invariants. Proper usage of mutexes prevents concurrent access by different
// threads to the same resource.
//
// A `Mutex` has two basic operations: `Mutex::Lock()` and `Mutex::Unlock()`.
// The `Lock()` operation *acquires* a `Mutex` (in a state known as an
// *exclusive* -- or write -- lock), while the `Unlock()` operation *releases* a
// Mutex. During the span of time between the Lock() and Unlock() operations,
// a mutex is said to be *held*. By design all mutexes support exclusive/write
// locks, as this is the most common way to use a mutex.
//
// The `Mutex` state machine for basic lock/unlock operations is quite simple:
//
// | | Lock() | Unlock() |
// |----------------+------------+----------|
// | Free | Exclusive | invalid |
// | Exclusive | blocks | Free |
//
// Attempts to `Unlock()` must originate from the thread that performed the
// corresponding `Lock()` operation.
//
// An "invalid" operation is disallowed by the API. The `Mutex` implementation
// is allowed to do anything on an invalid call, including but not limited to
// crashing with a useful error message, silently succeeding, or corrupting
// data structures. In debug mode, the implementation attempts to crash with a
// useful error message.
//
// `Mutex` is not guaranteed to be "fair" in prioritizing waiting threads; it
// is, however, approximately fair over long periods, and starvation-free for
// threads at the same priority.
//
// The lock/unlock primitives are now annotated with lock annotations
// defined in (base/thread_annotations.h). When writing multi-threaded code,
// you should use lock annotations whenever possible to document your lock
// synchronization policy. Besides acting as documentation, these annotations
// also help compilers or static analysis tools to identify and warn about
// issues that could potentially result in race conditions and deadlocks.
//
// For more information about the lock annotations, please see
// [Thread Safety Analysis](http://clang.llvm.org/docs/ThreadSafetyAnalysis.html)
// in the Clang documentation.
//
// See also `MutexLock`, below, for scoped `Mutex` acquisition.
class LOCKABLE Mutex {
public:
Mutex();
~Mutex();
// Mutex::Lock()
//
// Blocks the calling thread, if necessary, until this `Mutex` is free, and
// then acquires it exclusively. (This lock is also known as a "write lock.")
void Lock() EXCLUSIVE_LOCK_FUNCTION();
// Mutex::Unlock()
//
// Releases this `Mutex` and returns it from the exclusive/write state to the
// free state. Caller must hold the `Mutex` exclusively.
void Unlock() UNLOCK_FUNCTION();
// Mutex::TryLock()
//
// If the mutex can be acquired without blocking, does so exclusively and
// returns `true`. Otherwise, returns `false`. Returns `true` with high
// probability if the `Mutex` was free.
bool TryLock() EXCLUSIVE_TRYLOCK_FUNCTION(true);
// Mutex::AssertHeld()
//
// Return immediately if this thread holds the `Mutex` exclusively (in write
// mode). Otherwise, may report an error (typically by crashing with a
// diagnostic), or may return immediately.
void AssertHeld() const ASSERT_EXCLUSIVE_LOCK();
// ---------------------------------------------------------------------------
// Reader-Writer Locking
// ---------------------------------------------------------------------------
// A Mutex can also be used as a starvation-free reader-writer lock.
// Neither read-locks nor write-locks are reentrant/recursive to avoid
// potential client programming errors.
//
// The Mutex API provides `Writer*()` aliases for the existing `Lock()`,
// `Unlock()` and `TryLock()` methods for use within applications mixing
// reader/writer locks. Using `Reader*()` and `Writer*()` operations in this
// manner can make locking behavior clearer when mixing read and write modes.
//
// Introducing reader locks necessarily complicates the `Mutex` state
// machine somewhat. The table below illustrates the allowed state transitions
// of a mutex in such cases. Note that ReaderLock() may block even if the lock
// is held in shared mode; this occurs when another thread is blocked on a
// call to WriterLock().
//
// ---------------------------------------------------------------------------
// Operation: WriterLock() Unlock() ReaderLock() ReaderUnlock()
// ---------------------------------------------------------------------------
// State
// ---------------------------------------------------------------------------
// Free Exclusive invalid Shared(1) invalid
// Shared(1) blocks invalid Shared(2) or blocks Free
// Shared(n) n>1 blocks invalid Shared(n+1) or blocks Shared(n-1)
// Exclusive blocks Free blocks invalid
// ---------------------------------------------------------------------------
//
// In comments below, "shared" refers to a state of Shared(n) for any n > 0.
// Mutex::ReaderLock()
//
// Blocks the calling thread, if necessary, until this `Mutex` is either free,
// or in shared mode, and then acquires a share of it. Note that
// `ReaderLock()` will block if some other thread has an exclusive/writer lock
// on the mutex.
void ReaderLock() SHARED_LOCK_FUNCTION();
// Mutex::ReaderUnlock()
//
// Releases a read share of this `Mutex`. `ReaderUnlock` may return a mutex to
// the free state if this thread holds the last reader lock on the mutex. Note
// that you cannot call `ReaderUnlock()` on a mutex held in write mode.
void ReaderUnlock() UNLOCK_FUNCTION();
// Mutex::ReaderTryLock()
//
// If the mutex can be acquired without blocking, acquires this mutex for
// shared access and returns `true`. Otherwise, returns `false`. Returns
// `true` with high probability if the `Mutex` was free or shared.
bool ReaderTryLock() SHARED_TRYLOCK_FUNCTION(true);
// Mutex::AssertReaderHeld()
//
// Returns immediately if this thread holds the `Mutex` in at least shared
// mode (read mode). Otherwise, may report an error (typically by
// crashing with a diagnostic), or may return immediately.
void AssertReaderHeld() const ASSERT_SHARED_LOCK();
// Mutex::WriterLock()
// Mutex::WriterUnlock()
// Mutex::WriterTryLock()
//
// Aliases for `Mutex::Lock()`, `Mutex::Unlock()`, and `Mutex::TryLock()`.
//
// These methods may be used (along with the complementary `Reader*()`
// methods) to distingish simple exclusive `Mutex` usage (`Lock()`,
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// etc.) from reader/writer lock usage.
void WriterLock() EXCLUSIVE_LOCK_FUNCTION() { this->Lock(); }
void WriterUnlock() UNLOCK_FUNCTION() { this->Unlock(); }
bool WriterTryLock() EXCLUSIVE_TRYLOCK_FUNCTION(true) {
return this->TryLock();
}
// ---------------------------------------------------------------------------
// Conditional Critical Regions
// ---------------------------------------------------------------------------
// Conditional usage of a `Mutex` can occur using two distinct paradigms:
//
// * Use of `Mutex` member functions with `Condition` objects.
// * Use of the separate `CondVar` abstraction.
//
// In general, prefer use of `Condition` and the `Mutex` member functions
// listed below over `CondVar`. When there are multiple threads waiting on
// distinctly different conditions, however, a battery of `CondVar`s may be
// more efficient. This section discusses use of `Condition` objects.
//
// `Mutex` contains member functions for performing lock operations only under
// certain conditions, of class `Condition`. For correctness, the `Condition`
// must return a boolean that is a pure function, only of state protected by
// the `Mutex`. The condition must be invariant w.r.t. environmental state
// such as thread, cpu id, or time, and must be `noexcept`. The condition will
// always be invoked with the mutex held in at least read mode, so you should
// not block it for long periods or sleep it on a timer.
//
// Since a condition must not depend directly on the current time, use
// `*WithTimeout()` member function variants to make your condition
// effectively true after a given duration, or `*WithDeadline()` variants to
// make your condition effectively true after a given time.
//
// The condition function should have no side-effects aside from debug
// logging; as a special exception, the function may acquire other mutexes
// provided it releases all those that it acquires. (This exception was
// required to allow logging.)
// Mutex::Await()
//
// Unlocks this `Mutex` and blocks until simultaneously both `cond` is `true`
// and this `Mutex` can be reacquired, then reacquires this `Mutex` in the
// same mode in which it was previously held. If the condition is initially
// `true`, `Await()` *may* skip the release/re-acquire step.
//
// `Await()` requires that this thread holds this `Mutex` in some mode.
void Await(const Condition &cond);
// Mutex::LockWhen()
// Mutex::ReaderLockWhen()
// Mutex::WriterLockWhen()
//
Export of internal Abseil changes. -- 898e99cae89ca4cc27f86f719148f020d521dd58 by Abseil Team <absl-team@google.com>: Update comment. PiperOrigin-RevId: 204323401 -- b9d14db8b8a9dfb0e1cfb5967aaa0de1c4e94c42 by Abseil Team <absl-team@google.com>: Internal change PiperOrigin-RevId: 204178059 -- f3b5a667611a588aa06fea9168e997ef5cffa7ac by Abseil Team <absl-team@google.com>: Fix a potential reinterpret_cast compile error in absl::InlinedVector The current code will trigger a reinterpret_cast error enhanced by llvm r336738. PiperOrigin-RevId: 204131536 -- cc87d7a8302ad4471c1a25781d6ec19c2ce1524e by Abseil Team <absl-team@google.com>: Internal change. PiperOrigin-RevId: 203979040 -- bc5cae3cfc72af1d3e786d5a3b59a47e205afec9 by Gennadiy Rozental <rogeeff@google.com>: Internal: add internal logging hooks PiperOrigin-RevId: 203850605 -- 503655c248f557f677c920078613522b010e73c8 by Derek Mauro <dmauro@google.com>: Cleanup stacktrace_config.h Instead of listing the platforms that aren't supported, list the ones we do support, and fallback to stacktrace_unimplemented-inl.inc at the end. Previously any platform that wasn't listed gets "#error Not supported yet". GitHub issue #135 PiperOrigin-RevId: 203823079 -- cb69925c4cacc14558cf103a09f218c37f466a16 by Abseil Team <absl-team@google.com>: Fix a minor typo in absl::variant documentation. PiperOrigin-RevId: 203679877 -- 23a0e4db10039011fa5fd879fb73d2f2bbd17301 by Abseil Team <absl-team@google.com>: Format .bzl files with buildifier PiperOrigin-RevId: 203461813 -- 1ad02616bdb715dfdc7f1a73313e383f4ededa03 by Abseil Team <absl-team@google.com>: Make the absl::SleepFor() tests treat any successful retry within a 48x deadline as a total success, thereby reducing flakiness. PiperOrigin-RevId: 203401603 -- b3dccbbc6563ea0173527076a3fff21433d48f47 by Abseil Team <absl-team@google.com>: Replace config_setting.values{"compiler"} with config_setting.flag_values{"@bazel_tools//tools/cpp:compiler"} Due to changes in Bazel we need to change the way "compiler" is specified in config_setting. This will not change the behavior of the config_setting itself. PiperOrigin-RevId: 203345693 -- 170f1692537460a4ba1756d34852275899c2339b by Matt Armstrong <marmstrong@google.com>: Address test flakiness in the TimeoutTest. The basic idea is to loop forever until the expected scheduling delays are observed (within reasonable bounds), and only then assert the other invariants. PiperOrigin-RevId: 203188162 GitOrigin-RevId: 898e99cae89ca4cc27f86f719148f020d521dd58 Change-Id: Ie853ec050afa3a04c519393afe666bc03e11dc87
2018-07-12 19:34:29 +02:00
// Blocks until simultaneously both `cond` is `true` and this `Mutex` can
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// be acquired, then atomically acquires this `Mutex`. `LockWhen()` is
// logically equivalent to `*Lock(); Await();` though they may have different
// performance characteristics.
void LockWhen(const Condition &cond) EXCLUSIVE_LOCK_FUNCTION();
void ReaderLockWhen(const Condition &cond) SHARED_LOCK_FUNCTION();
void WriterLockWhen(const Condition &cond) EXCLUSIVE_LOCK_FUNCTION() {
this->LockWhen(cond);
}
// ---------------------------------------------------------------------------
// Mutex Variants with Timeouts/Deadlines
// ---------------------------------------------------------------------------
// Mutex::AwaitWithTimeout()
// Mutex::AwaitWithDeadline()
//
// If `cond` is initially true, do nothing, or act as though `cond` is
// initially false.
//
// If `cond` is initially false, unlock this `Mutex` and block until
// simultaneously:
// - either `cond` is true or the {timeout has expired, deadline has passed}
// and
// - this `Mutex` can be reacquired,
// then reacquire this `Mutex` in the same mode in which it was previously
// held, returning `true` iff `cond` is `true` on return.
//
// Deadlines in the past are equivalent to an immediate deadline.
// Negative timeouts are equivalent to a zero timeout.
//
// This method requires that this thread holds this `Mutex` in some mode.
bool AwaitWithTimeout(const Condition &cond, absl::Duration timeout);
bool AwaitWithDeadline(const Condition &cond, absl::Time deadline);
// Mutex::LockWhenWithTimeout()
// Mutex::ReaderLockWhenWithTimeout()
// Mutex::WriterLockWhenWithTimeout()
//
// Blocks until simultaneously both:
// - either `cond` is `true` or the timeout has expired, and
// - this `Mutex` can be acquired,
// then atomically acquires this `Mutex`, returning `true` iff `cond` is
// `true` on return.
//
// Negative timeouts are equivalent to a zero timeout.
bool LockWhenWithTimeout(const Condition &cond, absl::Duration timeout)
EXCLUSIVE_LOCK_FUNCTION();
bool ReaderLockWhenWithTimeout(const Condition &cond, absl::Duration timeout)
SHARED_LOCK_FUNCTION();
bool WriterLockWhenWithTimeout(const Condition &cond, absl::Duration timeout)
EXCLUSIVE_LOCK_FUNCTION() {
return this->LockWhenWithTimeout(cond, timeout);
}
// Mutex::LockWhenWithDeadline()
// Mutex::ReaderLockWhenWithDeadline()
// Mutex::WriterLockWhenWithDeadline()
//
// Blocks until simultaneously both:
// - either `cond` is `true` or the deadline has been passed, and
// - this `Mutex` can be acquired,
// then atomically acquires this Mutex, returning `true` iff `cond` is `true`
// on return.
//
// Deadlines in the past are equivalent to an immediate deadline.
bool LockWhenWithDeadline(const Condition &cond, absl::Time deadline)
EXCLUSIVE_LOCK_FUNCTION();
bool ReaderLockWhenWithDeadline(const Condition &cond, absl::Time deadline)
SHARED_LOCK_FUNCTION();
bool WriterLockWhenWithDeadline(const Condition &cond, absl::Time deadline)
EXCLUSIVE_LOCK_FUNCTION() {
return this->LockWhenWithDeadline(cond, deadline);
}
// ---------------------------------------------------------------------------
// Debug Support: Invariant Checking, Deadlock Detection, Logging.
// ---------------------------------------------------------------------------
// Mutex::EnableInvariantDebugging()
//
// If `invariant`!=null and if invariant debugging has been enabled globally,
// cause `(*invariant)(arg)` to be called at moments when the invariant for
// this `Mutex` should hold (for example: just after acquire, just before
// release).
//
// The routine `invariant` should have no side-effects since it is not
// guaranteed how many times it will be called; it should check the invariant
// and crash if it does not hold. Enabling global invariant debugging may
// substantially reduce `Mutex` performance; it should be set only for
// non-production runs. Optimization options may also disable invariant
// checks.
void EnableInvariantDebugging(void (*invariant)(void *), void *arg);
// Mutex::EnableDebugLog()
//
// Cause all subsequent uses of this `Mutex` to be logged via
// `ABSL_RAW_LOG(INFO)`. Log entries are tagged with `name` if no previous
// call to `EnableInvariantDebugging()` or `EnableDebugLog()` has been made.
//
// Note: This method substantially reduces `Mutex` performance.
void EnableDebugLog(const char *name);
// Deadlock detection
// Mutex::ForgetDeadlockInfo()
//
// Forget any deadlock-detection information previously gathered
// about this `Mutex`. Call this method in debug mode when the lock ordering
// of a `Mutex` changes.
void ForgetDeadlockInfo();
// Mutex::AssertNotHeld()
//
// Return immediately if this thread does not hold this `Mutex` in any
// mode; otherwise, may report an error (typically by crashing with a
// diagnostic), or may return immediately.
//
// Currently this check is performed only if all of:
// - in debug mode
// - SetMutexDeadlockDetectionMode() has been set to kReport or kAbort
// - number of locks concurrently held by this thread is not large.
// are true.
void AssertNotHeld() const;
// Special cases.
// A `MuHow` is a constant that indicates how a lock should be acquired.
// Internal implementation detail. Clients should ignore.
typedef const struct MuHowS *MuHow;
// Mutex::InternalAttemptToUseMutexInFatalSignalHandler()
//
// Causes the `Mutex` implementation to prepare itself for re-entry caused by
// future use of `Mutex` within a fatal signal handler. This method is
// intended for use only for last-ditch attempts to log crash information.
// It does not guarantee that attempts to use Mutexes within the handler will
// not deadlock; it merely makes other faults less likely.
//
// WARNING: This routine must be invoked from a signal handler, and the
// signal handler must either loop forever or terminate the process.
// Attempts to return from (or `longjmp` out of) the signal handler once this
// call has been made may cause arbitrary program behaviour including
// crashes and deadlocks.
static void InternalAttemptToUseMutexInFatalSignalHandler();
private:
#ifdef ABSL_INTERNAL_USE_NONPROD_MUTEX
friend class CondVar;
synchronization_internal::MutexImpl *impl() { return impl_.get(); }
synchronization_internal::SynchronizationStorage<
synchronization_internal::MutexImpl>
impl_;
#else
std::atomic<intptr_t> mu_; // The Mutex state.
// Post()/Wait() versus associated PerThreadSem; in class for required
// friendship with PerThreadSem.
static inline void IncrementSynchSem(Mutex *mu,
base_internal::PerThreadSynch *w);
static inline bool DecrementSynchSem(
Mutex *mu, base_internal::PerThreadSynch *w,
synchronization_internal::KernelTimeout t);
// slow path acquire
void LockSlowLoop(SynchWaitParams *waitp, int flags);
// wrappers around LockSlowLoop()
bool LockSlowWithDeadline(MuHow how, const Condition *cond,
synchronization_internal::KernelTimeout t,
int flags);
void LockSlow(MuHow how, const Condition *cond,
int flags) ABSL_ATTRIBUTE_COLD;
// slow path release
void UnlockSlow(SynchWaitParams *waitp) ABSL_ATTRIBUTE_COLD;
// Common code between Await() and AwaitWithTimeout/Deadline()
bool AwaitCommon(const Condition &cond,
synchronization_internal::KernelTimeout t);
// Attempt to remove thread s from queue.
void TryRemove(base_internal::PerThreadSynch *s);
// Block a thread on mutex.
void Block(base_internal::PerThreadSynch *s);
// Wake a thread; return successor.
base_internal::PerThreadSynch *Wakeup(base_internal::PerThreadSynch *w);
friend class CondVar; // for access to Trans()/Fer().
void Trans(MuHow how); // used for CondVar->Mutex transfer
void Fer(
base_internal::PerThreadSynch *w); // used for CondVar->Mutex transfer
#endif
// Catch the error of writing Mutex when intending MutexLock.
Mutex(const volatile Mutex * /*ignored*/) {} // NOLINT(runtime/explicit)
Mutex(const Mutex&) = delete;
Mutex& operator=(const Mutex&) = delete;
};
// -----------------------------------------------------------------------------
// Mutex RAII Wrappers
// -----------------------------------------------------------------------------
// MutexLock
//
// `MutexLock` is a helper class, which acquires and releases a `Mutex` via
// RAII.
//
// Example:
//
// Class Foo {
//
// Foo::Bar* Baz() {
// MutexLock l(&lock_);
// ...
// return bar;
// }
//
// private:
// Mutex lock_;
// };
class SCOPED_LOCKABLE MutexLock {
public:
explicit MutexLock(Mutex *mu) EXCLUSIVE_LOCK_FUNCTION(mu) : mu_(mu) {
this->mu_->Lock();
}
MutexLock(const MutexLock &) = delete; // NOLINT(runtime/mutex)
MutexLock(MutexLock&&) = delete; // NOLINT(runtime/mutex)
MutexLock& operator=(const MutexLock&) = delete;
MutexLock& operator=(MutexLock&&) = delete;
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~MutexLock() UNLOCK_FUNCTION() { this->mu_->Unlock(); }
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private:
Mutex *const mu_;
};
// ReaderMutexLock
//
// The `ReaderMutexLock` is a helper class, like `MutexLock`, which acquires and
// releases a shared lock on a `Mutex` via RAII.
class SCOPED_LOCKABLE ReaderMutexLock {
public:
explicit ReaderMutexLock(Mutex *mu) SHARED_LOCK_FUNCTION(mu)
: mu_(mu) {
mu->ReaderLock();
}
ReaderMutexLock(const ReaderMutexLock&) = delete;
ReaderMutexLock(ReaderMutexLock&&) = delete;
ReaderMutexLock& operator=(const ReaderMutexLock&) = delete;
ReaderMutexLock& operator=(ReaderMutexLock&&) = delete;
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~ReaderMutexLock() UNLOCK_FUNCTION() {
this->mu_->ReaderUnlock();
}
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private:
Mutex *const mu_;
};
// WriterMutexLock
//
// The `WriterMutexLock` is a helper class, like `MutexLock`, which acquires and
// releases a write (exclusive) lock on a `Mutex` via RAII.
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class SCOPED_LOCKABLE WriterMutexLock {
public:
explicit WriterMutexLock(Mutex *mu) EXCLUSIVE_LOCK_FUNCTION(mu)
: mu_(mu) {
mu->WriterLock();
}
WriterMutexLock(const WriterMutexLock&) = delete;
WriterMutexLock(WriterMutexLock&&) = delete;
WriterMutexLock& operator=(const WriterMutexLock&) = delete;
WriterMutexLock& operator=(WriterMutexLock&&) = delete;
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~WriterMutexLock() UNLOCK_FUNCTION() {
this->mu_->WriterUnlock();
}
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private:
Mutex *const mu_;
};
// -----------------------------------------------------------------------------
// Condition
// -----------------------------------------------------------------------------
//
// As noted above, `Mutex` contains a number of member functions which take a
// `Condition` as a argument; clients can wait for conditions to become `true`
// before attempting to acquire the mutex. These sections are known as
// "condition critical" sections. To use a `Condition`, you simply need to
// construct it, and use within an appropriate `Mutex` member function;
// everything else in the `Condition` class is an implementation detail.
//
// A `Condition` is specified as a function pointer which returns a boolean.
// `Condition` functions should be pure functions -- their results should depend
// only on passed arguments, should not consult any external state (such as
// clocks), and should have no side-effects, aside from debug logging. Any
// objects that the function may access should be limited to those which are
// constant while the mutex is blocked on the condition (e.g. a stack variable),
// or objects of state protected explicitly by the mutex.
//
// No matter which construction is used for `Condition`, the underlying
// function pointer / functor / callable must not throw any
// exceptions. Correctness of `Mutex` / `Condition` is not guaranteed in
// the face of a throwing `Condition`. (When Abseil is allowed to depend
// on C++17, these function pointers will be explicitly marked
// `noexcept`; until then this requirement cannot be enforced in the
// type system.)
//
// Note: to use a `Condition`, you need only construct it and pass it within the
// appropriate `Mutex' member function, such as `Mutex::Await()`.
//
// Example:
//
// // assume count_ is not internal reference count
// int count_ GUARDED_BY(mu_);
//
// mu_.LockWhen(Condition(+[](int* count) { return *count == 0; },
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// &count_));
//
// When multiple threads are waiting on exactly the same condition, make sure
// that they are constructed with the same parameters (same pointer to function
// + arg, or same pointer to object + method), so that the mutex implementation
// can avoid redundantly evaluating the same condition for each thread.
class Condition {
public:
// A Condition that returns the result of "(*func)(arg)"
Condition(bool (*func)(void *), void *arg);
// Templated version for people who are averse to casts.
//
// To use a lambda, prepend it with unary plus, which converts the lambda
// into a function pointer:
// Condition(+[](T* t) { return ...; }, arg).
//
// Note: lambdas in this case must contain no bound variables.
//
// See class comment for performance advice.
template<typename T>
Condition(bool (*func)(T *), T *arg);
// Templated version for invoking a method that returns a `bool`.
//
// `Condition(object, &Class::Method)` constructs a `Condition` that evaluates
// `object->Method()`.
//
// Implementation Note: `absl::internal::identity` is used to allow methods to
// come from base classes. A simpler signature like
// `Condition(T*, bool (T::*)())` does not suffice.
template<typename T>
Condition(T *object, bool (absl::internal::identity<T>::type::* method)());
// Same as above, for const members
template<typename T>
Condition(const T *object,
bool (absl::internal::identity<T>::type::* method)() const);
// A Condition that returns the value of `*cond`
explicit Condition(const bool *cond);
// Templated version for invoking a functor that returns a `bool`.
// This approach accepts pointers to non-mutable lambdas, `std::function`,
// the result of` std::bind` and user-defined functors that define
// `bool F::operator()() const`.
//
// Example:
//
// auto reached = [this, current]() {
// mu_.AssertReaderHeld(); // For annotalysis.
// return processed_ >= current;
// };
// mu_.Await(Condition(&reached));
// See class comment for performance advice. In particular, if there
// might be more than one waiter for the same condition, make sure
// that all waiters construct the condition with the same pointers.
// Implementation note: The second template parameter ensures that this
// constructor doesn't participate in overload resolution if T doesn't have
// `bool operator() const`.
template <typename T, typename E = decltype(
static_cast<bool (T::*)() const>(&T::operator()))>
explicit Condition(const T *obj)
: Condition(obj, static_cast<bool (T::*)() const>(&T::operator())) {}
// A Condition that always returns `true`.
static const Condition kTrue;
// Evaluates the condition.
bool Eval() const;
// Returns `true` if the two conditions are guaranteed to return the same
// value if evaluated at the same time, `false` if the evaluation *may* return
// different results.
//
// Two `Condition` values are guaranteed equal if both their `func` and `arg`
// components are the same. A null pointer is equivalent to a `true`
// condition.
static bool GuaranteedEqual(const Condition *a, const Condition *b);
private:
typedef bool (*InternalFunctionType)(void * arg);
typedef bool (Condition::*InternalMethodType)();
typedef bool (*InternalMethodCallerType)(void * arg,
InternalMethodType internal_method);
bool (*eval_)(const Condition*); // Actual evaluator
InternalFunctionType function_; // function taking pointer returning bool
InternalMethodType method_; // method returning bool
void *arg_; // arg of function_ or object of method_
Condition(); // null constructor used only to create kTrue
// Various functions eval_ can point to:
static bool CallVoidPtrFunction(const Condition*);
template <typename T> static bool CastAndCallFunction(const Condition* c);
template <typename T> static bool CastAndCallMethod(const Condition* c);
};
// -----------------------------------------------------------------------------
// CondVar
// -----------------------------------------------------------------------------
//
// A condition variable, reflecting state evaluated separately outside of the
// `Mutex` object, which can be signaled to wake callers.
// This class is not normally needed; use `Mutex` member functions such as
// `Mutex::Await()` and intrinsic `Condition` abstractions. In rare cases
// with many threads and many conditions, `CondVar` may be faster.
//
// The implementation may deliver signals to any condition variable at
// any time, even when no call to `Signal()` or `SignalAll()` is made; as a
// result, upon being awoken, you must check the logical condition you have
// been waiting upon.
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//
// Examples:
//
// Usage for a thread waiting for some condition C protected by mutex mu:
// mu.Lock();
// while (!C) { cv->Wait(&mu); } // releases and reacquires mu
// // C holds; process data
// mu.Unlock();
//
// Usage to wake T is:
// mu.Lock();
// // process data, possibly establishing C
// if (C) { cv->Signal(); }
// mu.Unlock();
//
// If C may be useful to more than one waiter, use `SignalAll()` instead of
// `Signal()`.
//
// With this implementation it is efficient to use `Signal()/SignalAll()` inside
// the locked region; this usage can make reasoning about your program easier.
//
class CondVar {
public:
CondVar();
~CondVar();
// CondVar::Wait()
//
// Atomically releases a `Mutex` and blocks on this condition variable.
// Waits until awakened by a call to `Signal()` or `SignalAll()` (or a
// spurious wakeup), then reacquires the `Mutex` and returns.
//
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// Requires and ensures that the current thread holds the `Mutex`.
void Wait(Mutex *mu);
// CondVar::WaitWithTimeout()
//
// Atomically releases a `Mutex` and blocks on this condition variable.
// Waits until awakened by a call to `Signal()` or `SignalAll()` (or a
// spurious wakeup), or until the timeout has expired, then reacquires
// the `Mutex` and returns.
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//
// Returns true if the timeout has expired without this `CondVar`
// being signalled in any manner. If both the timeout has expired
// and this `CondVar` has been signalled, the implementation is free
// to return `true` or `false`.
//
// Requires and ensures that the current thread holds the `Mutex`.
bool WaitWithTimeout(Mutex *mu, absl::Duration timeout);
// CondVar::WaitWithDeadline()
//
// Atomically releases a `Mutex` and blocks on this condition variable.
// Waits until awakened by a call to `Signal()` or `SignalAll()` (or a
// spurious wakeup), or until the deadline has passed, then reacquires
// the `Mutex` and returns.
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//
// Deadlines in the past are equivalent to an immediate deadline.
//
// Returns true if the deadline has passed without this `CondVar`
// being signalled in any manner. If both the deadline has passed
// and this `CondVar` has been signalled, the implementation is free
// to return `true` or `false`.
//
// Requires and ensures that the current thread holds the `Mutex`.
bool WaitWithDeadline(Mutex *mu, absl::Time deadline);
// CondVar::Signal()
//
// Signal this `CondVar`; wake at least one waiter if one exists.
void Signal();
// CondVar::SignalAll()
//
// Signal this `CondVar`; wake all waiters.
void SignalAll();
// CondVar::EnableDebugLog()
//
// Causes all subsequent uses of this `CondVar` to be logged via
// `ABSL_RAW_LOG(INFO)`. Log entries are tagged with `name` if `name != 0`.
// Note: this method substantially reduces `CondVar` performance.
void EnableDebugLog(const char *name);
private:
#ifdef ABSL_INTERNAL_USE_NONPROD_MUTEX
synchronization_internal::CondVarImpl *impl() { return impl_.get(); }
synchronization_internal::SynchronizationStorage<
synchronization_internal::CondVarImpl>
impl_;
#else
bool WaitCommon(Mutex *mutex, synchronization_internal::KernelTimeout t);
void Remove(base_internal::PerThreadSynch *s);
void Wakeup(base_internal::PerThreadSynch *w);
std::atomic<intptr_t> cv_; // Condition variable state.
#endif
CondVar(const CondVar&) = delete;
CondVar& operator=(const CondVar&) = delete;
};
// Variants of MutexLock.
//
// If you find yourself using one of these, consider instead using
// Mutex::Unlock() and/or if-statements for clarity.
// MutexLockMaybe
//
// MutexLockMaybe is like MutexLock, but is a no-op when mu is null.
class SCOPED_LOCKABLE MutexLockMaybe {
public:
explicit MutexLockMaybe(Mutex *mu) EXCLUSIVE_LOCK_FUNCTION(mu)
: mu_(mu) { if (this->mu_ != nullptr) { this->mu_->Lock(); } }
~MutexLockMaybe() UNLOCK_FUNCTION() {
if (this->mu_ != nullptr) { this->mu_->Unlock(); }
}
private:
Mutex *const mu_;
MutexLockMaybe(const MutexLockMaybe&) = delete;
MutexLockMaybe(MutexLockMaybe&&) = delete;
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MutexLockMaybe& operator=(const MutexLockMaybe&) = delete;
MutexLockMaybe& operator=(MutexLockMaybe&&) = delete;
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};
// ReleasableMutexLock
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//
// ReleasableMutexLock is like MutexLock, but permits `Release()` of its
// mutex before destruction. `Release()` may be called at most once.
class SCOPED_LOCKABLE ReleasableMutexLock {
public:
explicit ReleasableMutexLock(Mutex *mu) EXCLUSIVE_LOCK_FUNCTION(mu)
: mu_(mu) {
this->mu_->Lock();
}
~ReleasableMutexLock() UNLOCK_FUNCTION() {
if (this->mu_ != nullptr) { this->mu_->Unlock(); }
}
void Release() UNLOCK_FUNCTION();
private:
Mutex *mu_;
ReleasableMutexLock(const ReleasableMutexLock&) = delete;
ReleasableMutexLock(ReleasableMutexLock&&) = delete;
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ReleasableMutexLock& operator=(const ReleasableMutexLock&) = delete;
ReleasableMutexLock& operator=(ReleasableMutexLock&&) = delete;
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};
#ifdef ABSL_INTERNAL_USE_NONPROD_MUTEX
#else
inline Mutex::Mutex() : mu_(0) {
ABSL_TSAN_MUTEX_CREATE(this, __tsan_mutex_not_static);
}
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inline CondVar::CondVar() : cv_(0) {}
#endif
// static
template <typename T>
bool Condition::CastAndCallMethod(const Condition *c) {
typedef bool (T::*MemberType)();
MemberType rm = reinterpret_cast<MemberType>(c->method_);
T *x = static_cast<T *>(c->arg_);
return (x->*rm)();
}
// static
template <typename T>
bool Condition::CastAndCallFunction(const Condition *c) {
typedef bool (*FuncType)(T *);
FuncType fn = reinterpret_cast<FuncType>(c->function_);
T *x = static_cast<T *>(c->arg_);
return (*fn)(x);
}
template <typename T>
inline Condition::Condition(bool (*func)(T *), T *arg)
: eval_(&CastAndCallFunction<T>),
function_(reinterpret_cast<InternalFunctionType>(func)),
method_(nullptr),
arg_(const_cast<void *>(static_cast<const void *>(arg))) {}
template <typename T>
inline Condition::Condition(T *object,
bool (absl::internal::identity<T>::type::*method)())
: eval_(&CastAndCallMethod<T>),
function_(nullptr),
method_(reinterpret_cast<InternalMethodType>(method)),
arg_(object) {}
template <typename T>
inline Condition::Condition(const T *object,
bool (absl::internal::identity<T>::type::*method)()
const)
: eval_(&CastAndCallMethod<T>),
function_(nullptr),
method_(reinterpret_cast<InternalMethodType>(method)),
arg_(reinterpret_cast<void *>(const_cast<T *>(object))) {}
// Register a hook for profiling support.
//
// The function pointer registered here will be called whenever a mutex is
// contended. The callback is given the absl/base/cycleclock.h timestamp when
// waiting began.
//
// Calls to this function do not race or block, but there is no ordering
// guaranteed between calls to this function and call to the provided hook.
// In particular, the previously registered hook may still be called for some
// time after this function returns.
void RegisterMutexProfiler(void (*fn)(int64_t wait_timestamp));
// Register a hook for Mutex tracing.
//
// The function pointer registered here will be called whenever a mutex is
// contended. The callback is given an opaque handle to the contended mutex,
// an event name, and the number of wait cycles (as measured by
// //absl/base/internal/cycleclock.h, and which may not be real
// "cycle" counts.)
//
// The only event name currently sent is "slow release".
//
// This has the same memory ordering concerns as RegisterMutexProfiler() above.
void RegisterMutexTracer(void (*fn)(const char *msg, const void *obj,
int64_t wait_cycles));
// TODO(gfalcon): Combine RegisterMutexProfiler() and RegisterMutexTracer()
// into a single interface, since they are only ever called in pairs.
// Register a hook for CondVar tracing.
//
// The function pointer registered here will be called here on various CondVar
// events. The callback is given an opaque handle to the CondVar object and
// a std::string identifying the event. This is thread-safe, but only a single
// tracer can be registered.
//
// Events that can be sent are "Wait", "Unwait", "Signal wakeup", and
// "SignalAll wakeup".
//
// This has the same memory ordering concerns as RegisterMutexProfiler() above.
void RegisterCondVarTracer(void (*fn)(const char *msg, const void *cv));
// Register a hook for symbolizing stack traces in deadlock detector reports.
//
// 'pc' is the program counter being symbolized, 'out' is the buffer to write
// into, and 'out_size' is the size of the buffer. This function can return
// false if symbolizing failed, or true if a null-terminated symbol was written
// to 'out.'
//
// This has the same memory ordering concerns as RegisterMutexProfiler() above.
//
// DEPRECATED: The default symbolizer function is absl::Symbolize() and the
// ability to register a different hook for symbolizing stack traces will be
// removed on or after 2023-05-01.
ABSL_DEPRECATED("absl::RegisterSymbolizer() is deprecated and will be removed "
"on or after 2023-05-01")
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void RegisterSymbolizer(bool (*fn)(const void *pc, char *out, int out_size));
// EnableMutexInvariantDebugging()
//
// Enable or disable global support for Mutex invariant debugging. If enabled,
// then invariant predicates can be registered per-Mutex for debug checking.
// See Mutex::EnableInvariantDebugging().
void EnableMutexInvariantDebugging(bool enabled);
// When in debug mode, and when the feature has been enabled globally, the
// implementation will keep track of lock ordering and complain (or optionally
// crash) if a cycle is detected in the acquired-before graph.
// Possible modes of operation for the deadlock detector in debug mode.
enum class OnDeadlockCycle {
kIgnore, // Neither report on nor attempt to track cycles in lock ordering
kReport, // Report lock cycles to stderr when detected
kAbort, // Report lock cycles to stderr when detected, then abort
};
// SetMutexDeadlockDetectionMode()
//
// Enable or disable global support for detection of potential deadlocks
// due to Mutex lock ordering inversions. When set to 'kIgnore', tracking of
// lock ordering is disabled. Otherwise, in debug builds, a lock ordering graph
// will be maintained internally, and detected cycles will be reported in
// the manner chosen here.
void SetMutexDeadlockDetectionMode(OnDeadlockCycle mode);
} // namespace absl
// In some build configurations we pass --detect-odr-violations to the
// gold linker. This causes it to flag weak symbol overrides as ODR
// violations. Because ODR only applies to C++ and not C,
// --detect-odr-violations ignores symbols not mangled with C++ names.
// By changing our extension points to be extern "C", we dodge this
// check.
extern "C" {
void AbslInternalMutexYield();
} // extern "C"
#endif // ABSL_SYNCHRONIZATION_MUTEX_H_