Repo created

TMessagesProj/jni/voip/webrtc/rtc_base/synchronization/mutex.h

@@ -0,0 +1,73 @@
+/*
+ *  Copyright 2020 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef RTC_BASE_SYNCHRONIZATION_MUTEX_H_
+#define RTC_BASE_SYNCHRONIZATION_MUTEX_H_
+
+#include <atomic>
+
+#include "absl/base/attributes.h"
+#include "absl/base/const_init.h"
+#include "rtc_base/checks.h"
+#include "rtc_base/thread_annotations.h"
+
+#if defined(WEBRTC_ABSL_MUTEX)
+#include "rtc_base/synchronization/mutex_abseil.h"  // nogncheck
+#elif defined(WEBRTC_WIN)
+#include "rtc_base/synchronization/mutex_critical_section.h"
+#elif defined(WEBRTC_POSIX)
+#include "rtc_base/synchronization/mutex_pthread.h"
+#else
+#error Unsupported platform.
+#endif
+
+namespace webrtc {
+
+// The Mutex guarantees exclusive access and aims to follow Abseil semantics
+// (i.e. non-reentrant etc).
+class RTC_LOCKABLE Mutex final {
+ public:
+  Mutex() = default;
+  Mutex(const Mutex&) = delete;
+  Mutex& operator=(const Mutex&) = delete;
+
+  void Lock() RTC_EXCLUSIVE_LOCK_FUNCTION() { impl_.Lock(); }
+  ABSL_MUST_USE_RESULT bool TryLock() RTC_EXCLUSIVE_TRYLOCK_FUNCTION(true) {
+    return impl_.TryLock();
+  }
+  // Return immediately if this thread holds the mutex, or RTC_DCHECK_IS_ON==0.
+  // Otherwise, may report an error (typically by crashing with a diagnostic),
+  // or may return immediately.
+  void AssertHeld() const RTC_ASSERT_EXCLUSIVE_LOCK() { impl_.AssertHeld(); }
+  void Unlock() RTC_UNLOCK_FUNCTION() { impl_.Unlock(); }
+
+ private:
+  MutexImpl impl_;
+};
+
+// MutexLock, for serializing execution through a scope.
+class RTC_SCOPED_LOCKABLE MutexLock final {
+ public:
+  MutexLock(const MutexLock&) = delete;
+  MutexLock& operator=(const MutexLock&) = delete;
+
+  explicit MutexLock(Mutex* mutex) RTC_EXCLUSIVE_LOCK_FUNCTION(mutex)
+      : mutex_(mutex) {
+    mutex->Lock();
+  }
+  ~MutexLock() RTC_UNLOCK_FUNCTION() { mutex_->Unlock(); }
+
+ private:
+  Mutex* mutex_;
+};
+
+}  // namespace webrtc
+
+#endif  // RTC_BASE_SYNCHRONIZATION_MUTEX_H_

TMessagesProj/jni/voip/webrtc/rtc_base/synchronization/mutex_abseil.h

@@ -0,0 +1,43 @@
+/*
+ *  Copyright 2020 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef RTC_BASE_SYNCHRONIZATION_MUTEX_ABSEIL_H_
+#define RTC_BASE_SYNCHRONIZATION_MUTEX_ABSEIL_H_
+
+#include "absl/base/attributes.h"
+#include "absl/synchronization/mutex.h"
+#include "rtc_base/thread_annotations.h"
+
+namespace webrtc {
+
+class RTC_LOCKABLE MutexImpl final {
+ public:
+  MutexImpl() = default;
+  MutexImpl(const MutexImpl&) = delete;
+  MutexImpl& operator=(const MutexImpl&) = delete;
+
+  void Lock() RTC_EXCLUSIVE_LOCK_FUNCTION() { mutex_.Lock(); }
+  ABSL_MUST_USE_RESULT bool TryLock() RTC_EXCLUSIVE_TRYLOCK_FUNCTION(true) {
+    return mutex_.TryLock();
+  }
+  void AssertHeld() const RTC_ASSERT_EXCLUSIVE_LOCK() {
+#if RTC_DCHECK_IS_ON
+    mutex_.AssertHeld();
+#endif
+  }
+  void Unlock() RTC_UNLOCK_FUNCTION() { mutex_.Unlock(); }
+
+ private:
+  absl::Mutex mutex_;
+};
+
+}  // namespace webrtc
+
+#endif  // RTC_BASE_SYNCHRONIZATION_MUTEX_ABSEIL_H_

TMessagesProj/jni/voip/webrtc/rtc_base/synchronization/mutex_critical_section.h

@@ -0,0 +1,56 @@
+/*
+ *  Copyright 2020 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef RTC_BASE_SYNCHRONIZATION_MUTEX_CRITICAL_SECTION_H_
+#define RTC_BASE_SYNCHRONIZATION_MUTEX_CRITICAL_SECTION_H_
+
+#if defined(WEBRTC_WIN)
+// clang-format off
+// clang formating would change include order.
+
+// Include winsock2.h before including <windows.h> to maintain consistency with
+// win32.h. To include win32.h directly, it must be broken out into its own
+// build target.
+#include <winsock2.h>
+#include <windows.h>
+#include <sal.h>  // must come after windows headers.
+// clang-format on
+
+#include "absl/base/attributes.h"
+#include "rtc_base/thread_annotations.h"
+
+namespace webrtc {
+
+class RTC_LOCKABLE MutexImpl final {
+ public:
+  MutexImpl() { InitializeCriticalSection(&critical_section_); }
+  MutexImpl(const MutexImpl&) = delete;
+  MutexImpl& operator=(const MutexImpl&) = delete;
+  ~MutexImpl() { DeleteCriticalSection(&critical_section_); }
+
+  void Lock() RTC_EXCLUSIVE_LOCK_FUNCTION() {
+    EnterCriticalSection(&critical_section_);
+  }
+  ABSL_MUST_USE_RESULT bool TryLock() RTC_EXCLUSIVE_TRYLOCK_FUNCTION(true) {
+    return TryEnterCriticalSection(&critical_section_) != FALSE;
+  }
+  void AssertHeld() const RTC_ASSERT_EXCLUSIVE_LOCK() {}
+  void Unlock() RTC_UNLOCK_FUNCTION() {
+    LeaveCriticalSection(&critical_section_);
+  }
+
+ private:
+  CRITICAL_SECTION critical_section_;
+};
+
+}  // namespace webrtc
+
+#endif  // #if defined(WEBRTC_WIN)
+#endif  // RTC_BASE_SYNCHRONIZATION_MUTEX_CRITICAL_SECTION_H_

TMessagesProj/jni/voip/webrtc/rtc_base/synchronization/mutex_pthread.h

@@ -0,0 +1,101 @@
+/*
+ *  Copyright 2020 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef RTC_BASE_SYNCHRONIZATION_MUTEX_PTHREAD_H_
+#define RTC_BASE_SYNCHRONIZATION_MUTEX_PTHREAD_H_
+
+#if defined(WEBRTC_POSIX)
+
+#include <pthread.h>
+#if defined(WEBRTC_MAC)
+#include <pthread_spis.h>
+#endif
+
+#include "absl/base/attributes.h"
+#include "rtc_base/system/no_unique_address.h"
+#include "rtc_base/thread_annotations.h"
+
+namespace webrtc {
+
+class RTC_LOCKABLE MutexImpl final {
+ public:
+  MutexImpl() {
+    pthread_mutexattr_t mutex_attribute;
+    pthread_mutexattr_init(&mutex_attribute);
+#if defined(WEBRTC_MAC)
+    pthread_mutexattr_setpolicy_np(&mutex_attribute,
+                                   _PTHREAD_MUTEX_POLICY_FIRSTFIT);
+#endif
+    pthread_mutex_init(&mutex_, &mutex_attribute);
+    pthread_mutexattr_destroy(&mutex_attribute);
+  }
+  MutexImpl(const MutexImpl&) = delete;
+  MutexImpl& operator=(const MutexImpl&) = delete;
+  ~MutexImpl() { pthread_mutex_destroy(&mutex_); }
+
+  void Lock() RTC_EXCLUSIVE_LOCK_FUNCTION() {
+    pthread_mutex_lock(&mutex_);
+    owner_.SetOwner();
+  }
+  ABSL_MUST_USE_RESULT bool TryLock() RTC_EXCLUSIVE_TRYLOCK_FUNCTION(true) {
+    if (pthread_mutex_trylock(&mutex_) != 0) {
+      return false;
+    }
+    owner_.SetOwner();
+    return true;
+  }
+  void AssertHeld() const RTC_ASSERT_EXCLUSIVE_LOCK() { owner_.AssertOwned(); }
+  void Unlock() RTC_UNLOCK_FUNCTION() {
+    owner_.ClearOwner();
+    pthread_mutex_unlock(&mutex_);
+  }
+
+ private:
+  class OwnerRecord {
+   public:
+#if !RTC_DCHECK_IS_ON
+    void SetOwner() {}
+    void ClearOwner() {}
+    void AssertOwned() const {}
+#else
+    void SetOwner() {
+      latest_owner_ = pthread_self();
+      is_owned_ = true;
+    }
+    void ClearOwner() { is_owned_ = false; }
+    void AssertOwned() const {
+      RTC_CHECK(is_owned_);
+      RTC_CHECK(pthread_equal(latest_owner_, pthread_self()));
+    }
+
+   private:
+    // Use two separate primitive types, rather than absl::optional, since the
+    // data race described below might invalidate absl::optional invariants.
+    bool is_owned_ = false;
+    pthread_t latest_owner_ = pthread_self();
+#endif
+  };
+
+  pthread_mutex_t mutex_;
+  // This record is modified only with the mutex held, and hence, calls to
+  // AssertHeld where mutex is held are race-free and will always succeed.
+  //
+  // The failure case is more subtle: If AssertHeld is called from some thread
+  // not holding the mutex, and RTC_DCHECK_IS_ON==1, we have a data race. It is
+  // highly likely that the calling thread will see `is_owned_` false or
+  // `latest_owner_` different from itself, and crash. But it may fail to crash,
+  // and invoke some other undefined behavior (still, this race can happen only
+  // when RTC_DCHECK_IS_ON==1).
+  RTC_NO_UNIQUE_ADDRESS OwnerRecord owner_;
+};
+
+}  // namespace webrtc
+#endif  // #if defined(WEBRTC_POSIX)
+#endif  // RTC_BASE_SYNCHRONIZATION_MUTEX_PTHREAD_H_

TMessagesProj/jni/voip/webrtc/rtc_base/synchronization/sequence_checker_internal.cc

@@ -0,0 +1,86 @@
+/*
+ *  Copyright 2019 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#include "rtc_base/synchronization/sequence_checker_internal.h"
+
+#include <string>
+
+#include "rtc_base/checks.h"
+#include "rtc_base/strings/string_builder.h"
+
+namespace webrtc {
+namespace webrtc_sequence_checker_internal {
+
+SequenceCheckerImpl::SequenceCheckerImpl(bool attach_to_current_thread)
+    : attached_(attach_to_current_thread),
+      valid_thread_(rtc::CurrentThreadRef()),
+      valid_queue_(TaskQueueBase::Current()) {}
+
+SequenceCheckerImpl::SequenceCheckerImpl(TaskQueueBase* attached_queue)
+    : attached_(attached_queue != nullptr),
+      valid_thread_(rtc::PlatformThreadRef()),
+      valid_queue_(attached_queue) {}
+
+bool SequenceCheckerImpl::IsCurrent() const {
+  const TaskQueueBase* const current_queue = TaskQueueBase::Current();
+  const rtc::PlatformThreadRef current_thread = rtc::CurrentThreadRef();
+  MutexLock scoped_lock(&lock_);
+  if (!attached_) {  // Previously detached.
+    attached_ = true;
+    valid_thread_ = current_thread;
+    valid_queue_ = current_queue;
+    return true;
+  }
+  if (valid_queue_) {
+    return valid_queue_ == current_queue;
+  }
+  return rtc::IsThreadRefEqual(valid_thread_, current_thread);
+}
+
+void SequenceCheckerImpl::Detach() {
+  MutexLock scoped_lock(&lock_);
+  attached_ = false;
+  // We don't need to touch the other members here, they will be
+  // reset on the next call to IsCurrent().
+}
+
+#if RTC_DCHECK_IS_ON
+std::string SequenceCheckerImpl::ExpectationToString() const {
+  const TaskQueueBase* const current_queue = TaskQueueBase::Current();
+  const rtc::PlatformThreadRef current_thread = rtc::CurrentThreadRef();
+  MutexLock scoped_lock(&lock_);
+  if (!attached_)
+    return "Checker currently not attached.";
+
+  // The format of the string is meant to compliment the one we have inside of
+  // FatalLog() (checks.cc).  Example:
+  //
+  // # Expected: TQ: 0x0 SysQ: 0x7fff69541330 Thread: 0x11dcf6dc0
+  // # Actual:   TQ: 0x7fa8f0604190 SysQ: 0x7fa8f0604a30 Thread: 0x700006f1a000
+  // TaskQueue doesn't match
+
+  rtc::StringBuilder message;
+  message.AppendFormat(
+      "# Expected: TQ: %p Thread: %p\n"
+      "# Actual:   TQ: %p Thread: %p\n",
+      valid_queue_, reinterpret_cast<const void*>(valid_thread_), current_queue,
+      reinterpret_cast<const void*>(current_thread));
+
+  if ((valid_queue_ || current_queue) && valid_queue_ != current_queue) {
+    message << "TaskQueue doesn't match\n";
+  } else if (!rtc::IsThreadRefEqual(valid_thread_, current_thread)) {
+    message << "Threads don't match\n";
+  }
+
+  return message.Release();
+}
+#endif  // RTC_DCHECK_IS_ON
+
+}  // namespace webrtc_sequence_checker_internal
+}  // namespace webrtc

TMessagesProj/jni/voip/webrtc/rtc_base/synchronization/sequence_checker_internal.h

@@ -0,0 +1,90 @@
+/*
+ *  Copyright 2020 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#ifndef RTC_BASE_SYNCHRONIZATION_SEQUENCE_CHECKER_INTERNAL_H_
+#define RTC_BASE_SYNCHRONIZATION_SEQUENCE_CHECKER_INTERNAL_H_
+
+#include <string>
+#include <type_traits>
+
+#include "api/task_queue/task_queue_base.h"
+#include "rtc_base/platform_thread_types.h"
+#include "rtc_base/synchronization/mutex.h"
+#include "rtc_base/system/rtc_export.h"
+#include "rtc_base/thread_annotations.h"
+
+namespace webrtc {
+namespace webrtc_sequence_checker_internal {
+
+// Real implementation of SequenceChecker, for use in debug mode, or
+// for temporary use in release mode (e.g. to RTC_CHECK on a threading issue
+// seen only in the wild).
+//
+// Note: You should almost always use the SequenceChecker class to get the
+// right version for your build configuration.
+class RTC_EXPORT SequenceCheckerImpl {
+ public:
+  explicit SequenceCheckerImpl(bool attach_to_current_thread);
+  explicit SequenceCheckerImpl(TaskQueueBase* attached_queue);
+  ~SequenceCheckerImpl() = default;
+
+  bool IsCurrent() const;
+  // Changes the task queue or thread that is checked for in IsCurrent. This can
+  // be useful when an object may be created on one task queue / thread and then
+  // used exclusively on another thread.
+  void Detach();
+
+  // Returns a string that is formatted to match with the error string printed
+  // by RTC_CHECK() when a condition is not met.
+  // This is used in conjunction with the RTC_DCHECK_RUN_ON() macro.
+  std::string ExpectationToString() const;
+
+ private:
+  mutable Mutex lock_;
+  // These are mutable so that IsCurrent can set them.
+  mutable bool attached_ RTC_GUARDED_BY(lock_);
+  mutable rtc::PlatformThreadRef valid_thread_ RTC_GUARDED_BY(lock_);
+  mutable const TaskQueueBase* valid_queue_ RTC_GUARDED_BY(lock_);
+};
+
+// Do nothing implementation, for use in release mode.
+//
+// Note: You should almost always use the SequenceChecker class to get the
+// right version for your build configuration.
+class SequenceCheckerDoNothing {
+ public:
+  explicit SequenceCheckerDoNothing(bool attach_to_current_thread) {}
+  explicit SequenceCheckerDoNothing(TaskQueueBase* attached_queue) {}
+  bool IsCurrent() const { return true; }
+  void Detach() {}
+};
+
+template <typename ThreadLikeObject>
+std::enable_if_t<std::is_base_of_v<SequenceCheckerImpl, ThreadLikeObject>,
+                 std::string>
+ExpectationToString(const ThreadLikeObject* checker) {
+#if RTC_DCHECK_IS_ON
+  return checker->ExpectationToString();
+#else
+  return std::string();
+#endif
+}
+
+// Catch-all implementation for types other than explicitly supported above.
+template <typename ThreadLikeObject>
+std::enable_if_t<!std::is_base_of_v<SequenceCheckerImpl, ThreadLikeObject>,
+                 std::string>
+ExpectationToString(const ThreadLikeObject*) {
+  return std::string();
+}
+
+}  // namespace webrtc_sequence_checker_internal
+}  // namespace webrtc
+
+#endif  // RTC_BASE_SYNCHRONIZATION_SEQUENCE_CHECKER_INTERNAL_H_

TMessagesProj/jni/voip/webrtc/rtc_base/synchronization/yield.cc

@@ -0,0 +1,36 @@
+/*
+ *  Copyright 2020 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "rtc_base/synchronization/yield.h"
+
+#if defined(WEBRTC_WIN)
+#include <windows.h>
+#else
+#include <sched.h>
+#include <time.h>
+#endif
+
+namespace webrtc {
+
+void YieldCurrentThread() {
+  // TODO(bugs.webrtc.org/11634): use dedicated OS functionality instead of
+  // sleep for yielding.
+#if defined(WEBRTC_WIN)
+  ::Sleep(0);
+#elif defined(WEBRTC_MAC) && defined(RTC_USE_NATIVE_MUTEX_ON_MAC) && \
+    !RTC_USE_NATIVE_MUTEX_ON_MAC
+  sched_yield();
+#else
+  static const struct timespec ts_null = {0};
+  nanosleep(&ts_null, nullptr);
+#endif
+}
+
+}  // namespace webrtc

TMessagesProj/jni/voip/webrtc/rtc_base/synchronization/yield.h

@@ -0,0 +1,20 @@
+/*
+ *  Copyright 2020 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#ifndef RTC_BASE_SYNCHRONIZATION_YIELD_H_
+#define RTC_BASE_SYNCHRONIZATION_YIELD_H_
+
+namespace webrtc {
+
+// Request rescheduling of threads.
+void YieldCurrentThread();
+
+}  // namespace webrtc
+
+#endif  // RTC_BASE_SYNCHRONIZATION_YIELD_H_

TMessagesProj/jni/voip/webrtc/rtc_base/synchronization/yield_policy.cc

@@ -0,0 +1,82 @@
+/*
+ *  Copyright 2019 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#include "rtc_base/synchronization/yield_policy.h"
+
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+#include "rtc_base/checks.h"
+#if !defined(ABSL_HAVE_THREAD_LOCAL) && defined(WEBRTC_POSIX)
+#include <pthread.h>
+#endif
+
+namespace rtc {
+namespace {
+
+#if defined(ABSL_HAVE_THREAD_LOCAL)
+
+ABSL_CONST_INIT thread_local YieldInterface* current_yield_policy = nullptr;
+
+YieldInterface* GetCurrentYieldPolicy() {
+  return current_yield_policy;
+}
+
+void SetCurrentYieldPolicy(YieldInterface* ptr) {
+  current_yield_policy = ptr;
+}
+
+#elif defined(WEBRTC_POSIX)
+
+// Emscripten does not support the C++11 thread_local keyword but does support
+// the pthread thread-local storage API.
+// https://github.com/emscripten-core/emscripten/issues/3502
+
+ABSL_CONST_INIT pthread_key_t g_current_yield_policy_tls = 0;
+
+void InitializeTls() {
+  RTC_CHECK_EQ(pthread_key_create(&g_current_yield_policy_tls, nullptr), 0);
+}
+
+pthread_key_t GetCurrentYieldPolicyTls() {
+  static pthread_once_t init_once = PTHREAD_ONCE_INIT;
+  RTC_CHECK_EQ(pthread_once(&init_once, &InitializeTls), 0);
+  return g_current_yield_policy_tls;
+}
+
+YieldInterface* GetCurrentYieldPolicy() {
+  return static_cast<YieldInterface*>(
+      pthread_getspecific(GetCurrentYieldPolicyTls()));
+}
+
+void SetCurrentYieldPolicy(YieldInterface* ptr) {
+  pthread_setspecific(GetCurrentYieldPolicyTls(), ptr);
+}
+
+#else
+#error Unsupported platform
+#endif
+
+}  // namespace
+
+ScopedYieldPolicy::ScopedYieldPolicy(YieldInterface* policy)
+    : previous_(GetCurrentYieldPolicy()) {
+  SetCurrentYieldPolicy(policy);
+}
+
+ScopedYieldPolicy::~ScopedYieldPolicy() {
+  SetCurrentYieldPolicy(previous_);
+}
+
+void ScopedYieldPolicy::YieldExecution() {
+  YieldInterface* current = GetCurrentYieldPolicy();
+  if (current)
+    current->YieldExecution();
+}
+
+}  // namespace rtc

TMessagesProj/jni/voip/webrtc/rtc_base/synchronization/yield_policy.h

@@ -0,0 +1,38 @@
+/*
+ *  Copyright 2019 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#ifndef RTC_BASE_SYNCHRONIZATION_YIELD_POLICY_H_
+#define RTC_BASE_SYNCHRONIZATION_YIELD_POLICY_H_
+
+namespace rtc {
+class YieldInterface {
+ public:
+  virtual ~YieldInterface() = default;
+  virtual void YieldExecution() = 0;
+};
+
+// Sets the current thread-local yield policy while it's in scope and reverts
+// to the previous policy when it leaves the scope.
+class ScopedYieldPolicy final {
+ public:
+  explicit ScopedYieldPolicy(YieldInterface* policy);
+  ScopedYieldPolicy(const ScopedYieldPolicy&) = delete;
+  ScopedYieldPolicy& operator=(const ScopedYieldPolicy&) = delete;
+  ~ScopedYieldPolicy();
+  // Will yield as specified by the currently active thread-local yield policy
+  // (which by default is a no-op).
+  static void YieldExecution();
+
+ private:
+  YieldInterface* const previous_;
+};
+
+}  // namespace rtc
+
+#endif  // RTC_BASE_SYNCHRONIZATION_YIELD_POLICY_H_