thread.h

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// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#ifndef FLUTTER_IMPELLER_BASE_THREAD_H_
#define FLUTTER_IMPELLER_BASE_THREAD_H_
 
#include <chrono>
#include <condition_variable>
#include <functional>
#include <memory>
#include <mutex>
#include <thread>
 
#include "flutter/fml/synchronization/shared_mutex.h"
#include "impeller/base/thread_safety.h"
 
namespace impeller {
 
class ConditionVariable;
 
class IPLR_CAPABILITY("mutex") Mutex {
 public:
  Mutex() = default;
 
  ~Mutex() = default;
 
  void Lock() IPLR_ACQUIRE() { mutex_.lock(); }
 
  void Unlock() IPLR_RELEASE() { mutex_.unlock(); }
 
 private:
  friend class ConditionVariable;
 
  std::mutex mutex_;
 
  Mutex(const Mutex&) = delete;
 
  Mutex(Mutex&&) = delete;
 
  Mutex& operator=(const Mutex&) = delete;
 
  Mutex& operator=(Mutex&&) = delete;
};
 
class IPLR_CAPABILITY("mutex") RWMutex {
 public:
  RWMutex()
      : mutex_(std::unique_ptr<fml::SharedMutex>(fml::SharedMutex::Create())) {}
 
  ~RWMutex() = default;
 
  void LockWriter() IPLR_ACQUIRE() { mutex_->Lock(); }
 
  void UnlockWriter() IPLR_RELEASE() { mutex_->Unlock(); }
 
  void LockReader() IPLR_ACQUIRE_SHARED() { mutex_->LockShared(); }
 
  void UnlockReader() IPLR_RELEASE_SHARED() { mutex_->UnlockShared(); }
 
 private:
  std::unique_ptr<fml::SharedMutex> mutex_;
 
  RWMutex(const RWMutex&) = delete;
 
  RWMutex(RWMutex&&) = delete;
 
  RWMutex& operator=(const RWMutex&) = delete;
 
  RWMutex& operator=(RWMutex&&) = delete;
};
 
class IPLR_SCOPED_CAPABILITY Lock {
 public:
  explicit Lock(Mutex& mutex) IPLR_ACQUIRE(mutex) : mutex_(mutex) {
    mutex_.Lock();
  }
 
  ~Lock() IPLR_RELEASE() { mutex_.Unlock(); }
 
 private:
  Mutex& mutex_;
 
  Lock(const Lock&) = delete;
 
  Lock(Lock&&) = delete;
 
  Lock& operator=(const Lock&) = delete;
 
  Lock& operator=(Lock&&) = delete;
};
 
class IPLR_SCOPED_CAPABILITY ReaderLock {
 public:
  explicit ReaderLock(RWMutex& mutex) IPLR_ACQUIRE_SHARED(mutex)
      : mutex_(mutex) {
    mutex_.LockReader();
  }
 
  ~ReaderLock() IPLR_RELEASE() { mutex_.UnlockReader(); }
 
 private:
  RWMutex& mutex_;
 
  ReaderLock(const ReaderLock&) = delete;
 
  ReaderLock(ReaderLock&&) = delete;
 
  ReaderLock& operator=(const ReaderLock&) = delete;
 
  ReaderLock& operator=(ReaderLock&&) = delete;
};
 
class IPLR_SCOPED_CAPABILITY WriterLock {
 public:
  explicit WriterLock(RWMutex& mutex) IPLR_ACQUIRE(mutex) : mutex_(mutex) {
    mutex_.LockWriter();
  }
 
  ~WriterLock() IPLR_RELEASE() { mutex_.UnlockWriter(); }
 
 private:
  RWMutex& mutex_;
 
  WriterLock(const WriterLock&) = delete;
 
  WriterLock(WriterLock&&) = delete;
 
  WriterLock& operator=(const WriterLock&) = delete;
 
  WriterLock& operator=(WriterLock&&) = delete;
};
 
//------------------------------------------------------------------------------
/// @brief      A condition variable exactly similar to the one in libcxx with
///             two major differences:
///
///             * On the Wait, WaitFor, and WaitUntil calls, static analysis
///               annotation are respected.
///             * There is no ability to wait on a condition variable and also
///               be susceptible to spurious wakes. This is because the
///               predicate is mandatory.
///
class ConditionVariable {
 public:
  ConditionVariable() = default;
 
  ~ConditionVariable() = default;
 
  ConditionVariable(const ConditionVariable&) = delete;
 
  ConditionVariable& operator=(const ConditionVariable&) = delete;
 
  void NotifyOne() { cv_.notify_one(); }
 
  void NotifyAll() { cv_.notify_all(); }
 
  using Predicate = std::function<bool()>;
 
  //----------------------------------------------------------------------------
  /// @brief      Atomically unlocks the mutex and waits on the condition
  ///             variable up to a specified time point. Lock will be reacquired
  ///             when the wait exits. Spurious wakes may happen before the time
  ///             point is reached. In such cases the predicate is invoked and
  ///             it must return `false` for the wait to continue. The predicate
  ///             will be invoked with the mutex locked.
  ///
  /// @note       Since the predicate is invoked with the mutex locked, if it
  ///             accesses other guarded resources, the predicate itself must be
  ///             decorated with the IPLR_REQUIRES directive. For instance,
  ///
  ///             ```c++
  ///                [] () IPLR_REQUIRES(mutex) {
  ///                return my_guarded_resource.should_stop_waiting;
  ///              }
  ///              ```
  ///
  /// @param      mutex                The mutex.
  /// @param[in]  time_point           The time point to wait to.
  /// @param[in]  should_stop_waiting  The predicate invoked on spurious wakes.
  ///                                  Must return false for the wait to
  ///                                  continue.
  ///
  /// @tparam     Clock                The clock type.
  /// @tparam     Duration             The duration type.
  ///
  /// @return     The value of the predicate at the end of the wait.
  ///
  template <class Clock, class Duration>
  bool WaitUntil(Mutex& mutex,
                 const std::chrono::time_point<Clock, Duration>& time_point,
                 const Predicate& should_stop_waiting) IPLR_REQUIRES(mutex) {
    std::unique_lock lock(mutex.mutex_, std::adopt_lock);
    const auto result = cv_.wait_until(lock, time_point, should_stop_waiting);
    lock.release();
    return result;
  }
 
  //----------------------------------------------------------------------------
  /// @brief      Atomically unlocks the mutex and waits on the condition
  ///             variable for a designated duration. Lock will be reacquired
  ///             when the wait exits. Spurious wakes may happen before the time
  ///             point is reached. In such cases the predicate is invoked and
  ///             it must return `false` for the wait to continue. The predicate
  ///             will be invoked with the mutex locked.
  ///
  /// @note       Since the predicate is invoked with the mutex locked, if it
  ///             accesses other guarded resources, the predicate itself must be
  ///             decorated with the IPLR_REQUIRES directive. For instance,
  ///
  ///             ```c++
  ///                [] () IPLR_REQUIRES(mutex) {
  ///                return my_guarded_resource.should_stop_waiting;
  ///              }
  ///              ```
  ///
  /// @param      mutex                The mutex.
  /// @param[in]  duration             The duration to wait for.
  /// @param[in]  should_stop_waiting  The predicate invoked on spurious wakes.
  ///                                  Must return false for the wait to
  ///                                  continue.
  ///
  /// @tparam     Representation       The duration representation type.
  /// @tparam     Period               The duration period type.
  ///
  /// @return     The value of the predicate at the end of the wait.
  ///
  template <class Representation, class Period>
  bool WaitFor(Mutex& mutex,
               const std::chrono::duration<Representation, Period>& duration,
               const Predicate& should_stop_waiting) IPLR_REQUIRES(mutex) {
    return WaitUntil(mutex, std::chrono::steady_clock::now() + duration,
                     should_stop_waiting);
  }
 
  //----------------------------------------------------------------------------
  /// @brief      Atomically unlocks the mutex and waits on the condition
  ///             variable indefinitely till the predicate determines that the
  ///             wait must end. Lock will be reacquired when the wait exits.
  ///             Spurious wakes may happen before the time point is reached. In
  ///             such cases the predicate is invoked and it must return `false`
  ///             for the wait to continue. The predicate will be invoked with
  ///             the mutex locked.
  ///
  /// @note       Since the predicate is invoked with the mutex locked, if it
  ///             accesses other guarded resources, the predicate itself must be
  ///             decorated with the IPLR_REQUIRES directive. For instance,
  ///
  ///             ```c++
  ///                [] () IPLR_REQUIRES(mutex) {
  ///                return my_guarded_resource.should_stop_waiting;
  ///              }
  ///              ```
  ///
  /// @param      mutex                The mutex
  /// @param[in]  should_stop_waiting  The should stop waiting
  ///
  void Wait(Mutex& mutex, const Predicate& should_stop_waiting)
      IPLR_REQUIRES(mutex) {
    std::unique_lock lock(mutex.mutex_, std::adopt_lock);
    cv_.wait(lock, should_stop_waiting);
    lock.release();
  }
 
 private:
  std::condition_variable cv_;
};
 
}  // namespace impeller
 
#endif  // FLUTTER_IMPELLER_BASE_THREAD_H_