condition_variable.h

// Copyright 2015 The Cobalt Authors. All Rights Reserved.
//
// 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.

// Module Overview: Starboard Condition Variable module
//
// Defines an interface for condition variables.

#ifndef STARBOARD_CONDITION_VARIABLE_H_
#define STARBOARD_CONDITION_VARIABLE_H_

#include "starboard/export.h"
#include "starboard/mutex.h"
#include "starboard/time.h"
#include "starboard/types.h"

#ifdef __cplusplus
extern "C" {
#endif

// Max size of the SbConditionVariable type.
#define SB_CONDITION_VARIABLE_MAX_SIZE 80

// An opaque handle to a condition variable type with
// reserved memory buffer of size SB_CONDITION_VARIABLE_MAX_SIZE and
// aligned at void pointer type.
typedef union SbConditionVariable {
  // Reserved memory in which the implementation should map its
  // native condition variable type.
  uint8_t condition_buffer[SB_CONDITION_VARIABLE_MAX_SIZE];

  // Guarantees alignment of the type to a void pointer.
  void* ptr;
} SbConditionVariable;

#ifdef __cplusplus
#define SB_CONDITION_VARIABLE_INITIALIZER \
  {}
#else
#define SB_CONDITION_VARIABLE_INITIALIZER \
  { 0 }
#endif

// Enumeration of possible results from waiting on a condvar.
typedef enum SbConditionVariableResult {
  // The wait completed because the condition variable was signaled.
  kSbConditionVariableSignaled,

  // The wait completed because it timed out, and was not signaled.
  kSbConditionVariableTimedOut,

  // The wait failed, either because a parameter wasn't valid, or the condition
  // variable has already been destroyed, or something similar.
  kSbConditionVariableFailed,
} SbConditionVariableResult;

// Returns whether the given result is a success.
static SB_C_INLINE bool SbConditionVariableIsSignaled(
    SbConditionVariableResult result) {
  return result == kSbConditionVariableSignaled;
}

// Creates a new condition variable to work with |opt_mutex|, which may be null,
// placing the newly created condition variable in |out_condition|.
//
// The return value indicates whether the condition variable could be created.
SB_EXPORT bool SbConditionVariableCreate(SbConditionVariable* out_condition,
                                         SbMutex* opt_mutex);

// Destroys the specified SbConditionVariable. The return value indicates
// whether the destruction was successful. The behavior is undefined if other
// threads are currently waiting on this condition variable.
//
// |condition|: The SbConditionVariable to be destroyed. This invalidates the
// condition variable.
SB_EXPORT bool SbConditionVariableDestroy(SbConditionVariable* condition);

// Waits for |condition|, releasing the held lock |mutex|, blocking
// indefinitely, and returning the result. Behavior is undefined if |mutex| is
// not held.
SB_EXPORT SbConditionVariableResult
SbConditionVariableWait(SbConditionVariable* condition, SbMutex* mutex);

// Waits for |condition|, releasing the held lock |mutex|, blocking up to
// |timeout_duration|, and returning the acquisition result. Behavior is
// undefined if |mutex| is not held.
//
// |timeout_duration|: The maximum amount of time that function should wait
// for |condition|. If the |timeout_duration| value is less than or equal to
// zero, the function returns as quickly as possible with a
// kSbConditionVariableTimedOut result.
SB_EXPORT SbConditionVariableResult
SbConditionVariableWaitTimed(SbConditionVariable* condition,
                             SbMutex* mutex,
                             SbTime timeout_duration);

// Broadcasts to all current waiters of |condition| to stop waiting. This
// function wakes all of the threads waiting on |condition| while
// SbConditionVariableSignal wakes a single thread.
//
// |condition|: The condition that should no longer be waited for.
SB_EXPORT bool SbConditionVariableBroadcast(SbConditionVariable* condition);

// Signals the next waiter of |condition| to stop waiting. This function wakes
// a single thread waiting on |condition| while SbConditionVariableBroadcast
// wakes all threads waiting on it.
//
// |condition|: The condition that the waiter should stop waiting for.
SB_EXPORT bool SbConditionVariableSignal(SbConditionVariable* condition);

#ifdef __cplusplus
}  // extern "C"
#endif

#endif  // STARBOARD_CONDITION_VARIABLE_H_