text: // Copyright (c) 2011 The Chromium 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 BASE_SYNCHRONIZATION_LOCK_IMPL_H_
  #define BASE_SYNCHRONIZATION_LOCK_IMPL_H_
  
  #include "base/base_export.h"
  #include "base/logging.h"
  #include "base/macros.h"
  #include "base/thread_annotations.h"
  #include "build/build_config.h"
  
  #if defined(OS_WIN)
  #include "base/win/windows_types.h"
  #elif defined(OS_POSIX) || defined(OS_FUCHSIA)
  #include <errno.h>
  #include <pthread.h>
  #include <string.h>
  #include <ostream>
  #endif
  
  namespace base {
  namespace internal {
  
  // This class implements the underlying platform-specific spin-lock mechanism
  // used for the Lock class.  Most users should not use LockImpl directly, but
  // should instead use Lock.
  class BASE_EXPORT LockImpl {
   public:
  #if defined(OS_WIN)
    using NativeHandle = CHROME_SRWLOCK;
  #elif defined(OS_POSIX) || defined(OS_FUCHSIA)
    using NativeHandle = pthread_mutex_t;
  #endif
  
    LockImpl();
    ~LockImpl();
  
    // If the lock is not held, take it and return true.  If the lock is already
    // held by something else, immediately return false.
    bool Try();
  
    // Take the lock, blocking until it is available if necessary.
    void Lock();
  
    // Release the lock.  This must only be called by the lock's holder: after
    // a successful call to Try, or a call to Lock.
    inline void Unlock();
  
    // Return the native underlying lock.
    // TODO(awalker): refactor lock and condition variables so that this is
    // unnecessary.
    NativeHandle* native_handle() { return &native_handle_; }
  
  #if defined(OS_POSIX) || defined(OS_FUCHSIA)
    // Whether this lock will attempt to use priority inheritance.
    static bool PriorityInheritanceAvailable();
  #endif
  
   private:
    NativeHandle native_handle_;
  
    DISALLOW_COPY_AND_ASSIGN(LockImpl);
  };
  
  #if defined(OS_WIN)
  void LockImpl::Unlock() {
    ::ReleaseSRWLockExclusive(reinterpret_cast<PSRWLOCK>(&native_handle_));
  }
  #elif defined(OS_POSIX) || defined(OS_FUCHSIA)
  void LockImpl::Unlock() {
    int rv = pthread_mutex_unlock(&native_handle_);
    DCHECK_EQ(rv, 0) << ". " << strerror(rv);
  }
  #endif
  
  // This is an implementation used for AutoLock templated on the lock type.
  template <class LockType>
  class SCOPED_LOCKABLE BasicAutoLock {
   public:
    struct AlreadyAcquired {};
  
    explicit BasicAutoLock(LockType& lock) EXCLUSIVE_LOCK_FUNCTION(lock)
        : lock_(lock) {
      lock_.Acquire();
    }
  
    BasicAutoLock(LockType& lock, const AlreadyAcquired&)
        EXCLUSIVE_LOCKS_REQUIRED(lock)
        : lock_(lock) {
      lock_.AssertAcquired();
    }
  
    ~BasicAutoLock() UNLOCK_FUNCTION() {
      lock_.AssertAcquired();
      lock_.Release();
    }
  
   private:
    LockType& lock_;
    DISALLOW_COPY_AND_ASSIGN(BasicAutoLock);
  };
  
  // This is an implementation used for AutoUnlock templated on the lock type.
  template <class LockType>
  class BasicAutoUnlock {
   public:
    explicit BasicAutoUnlock(LockType& lock) : lock_(lock) {
      // We require our caller to have the lock.
      lock_.AssertAcquired();
      lock_.Release();
    }
  
    ~BasicAutoUnlock() { lock_.Acquire(); }
  
   private:
    LockType& lock_;
    DISALLOW_COPY_AND_ASSIGN(BasicAutoUnlock);
  };
  
  // This is an implementation used for AutoLockMaybe templated on the lock type.
  template <class LockType>
  class SCOPED_LOCKABLE BasicAutoLockMaybe {
   public:
    explicit BasicAutoLockMaybe(LockType* lock) EXCLUSIVE_LOCK_FUNCTION(lock)
        : lock_(lock) {
      if (lock_)
        lock_->Acquire();
    }
  
    ~BasicAutoLockMaybe() UNLOCK_FUNCTION() {
      if (lock_) {
        lock_->AssertAcquired();
        lock_->Release();
      }
    }
  
   private:
    LockType* const lock_;
    DISALLOW_COPY_AND_ASSIGN(BasicAutoLockMaybe);
  };
  
  // This is an implementation used for ReleasableAutoLock templated on the lock
  // type.
  template <class LockType>
  class SCOPED_LOCKABLE BasicReleasableAutoLock {
   public:
    explicit BasicReleasableAutoLock(LockType* lock) EXCLUSIVE_LOCK_FUNCTION(lock)
        : lock_(lock) {
      DCHECK(lock_);
      lock_->Acquire();
    }
  
    ~BasicReleasableAutoLock() UNLOCK_FUNCTION() {
      if (lock_) {
        lock_->AssertAcquired();
        lock_->Release();
      }
    }
  
    void Release() UNLOCK_FUNCTION() {
      DCHECK(lock_);
      lock_->AssertAcquired();
      lock_->Release();
      lock_ = nullptr;
    }
  
   private:
    LockType* lock_;
    DISALLOW_COPY_AND_ASSIGN(BasicReleasableAutoLock);
  };
  
  }  // namespace internal
  }  // namespace base
  
  #endif  // BASE_SYNCHRONIZATION_LOCK_IMPL_H_
  