| /****************************************************************************** |
| * |
| * Copyright (C) 2014 Google, Inc. |
| * |
| * 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. |
| * |
| ******************************************************************************/ |
| |
| #pragma once |
| |
| #include <stdbool.h> |
| |
| struct semaphore_t; |
| typedef struct semaphore_t semaphore_t; |
| |
| // Creates a new semaphore with an initial value of |value|. |
| // Returns NULL on failure. The returned object must be released |
| // with |semaphore_free|. |
| semaphore_t* semaphore_new(unsigned int value); |
| |
| // Frees a semaphore allocated with |semaphore_new|. |semaphore| may |
| // be NULL. |
| void semaphore_free(semaphore_t* semaphore); |
| |
| // Decrements the value of |semaphore|. If it is 0, this call blocks until |
| // it becomes non-zero. |semaphore| may not be NULL. |
| void semaphore_wait(semaphore_t* semaphore); |
| |
| // Tries to decrement the value of |semaphore|. Returns true if the value was |
| // decremented, false if the value was 0. This function never blocks. |
| // |semaphore| may not be NULL. |
| bool semaphore_try_wait(semaphore_t* semaphore); |
| |
| // Increments the value of |semaphore|. |semaphore| may not be NULL. |
| void semaphore_post(semaphore_t* semaphore); |
| |
| // Returns a file descriptor representing this semaphore. The caller may |
| // only perform one operation on the file descriptor: select(2). If |select| |
| // indicates the fd is readable, the caller may call |semaphore_wait| |
| // without blocking. If select indicates the fd is writable, the caller may |
| // call |semaphore_post| without blocking. Note that there may be a race |
| // condition between calling |select| and |semaphore_wait| or |semaphore_post| |
| // which results in blocking behaviour. |
| // |
| // The caller must not close the returned file descriptor. |semaphore| may not |
| // be NULL. |
| int semaphore_get_fd(const semaphore_t* semaphore); |