1 /****************************************************************************** 2 * 3 * Copyright (C) 2014 Google, Inc. 4 * 5 * Licensed under the Apache License, Version 2.0 (the "License"); 6 * you may not use this file except in compliance with the License. 7 * You may obtain a copy of the License at: 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 * 17 ******************************************************************************/ 18 19 #pragma once 20 21 #include <stdbool.h> 22 23 struct semaphore_t; 24 typedef struct semaphore_t semaphore_t; 25 26 // Creates a new semaphore with an initial value of |value|. 27 // Returns NULL on failure. The returned object must be released 28 // with |semaphore_free|. 29 semaphore_t* semaphore_new(unsigned int value); 30 31 // Frees a semaphore allocated with |semaphore_new|. |semaphore| may 32 // be NULL. 33 void semaphore_free(semaphore_t* semaphore); 34 35 // Decrements the value of |semaphore|. If it is 0, this call blocks until 36 // it becomes non-zero. |semaphore| may not be NULL. 37 void semaphore_wait(semaphore_t* semaphore); 38 39 // Tries to decrement the value of |semaphore|. Returns true if the value was 40 // decremented, false if the value was 0. This function never blocks. 41 // |semaphore| may not be NULL. 42 bool semaphore_try_wait(semaphore_t* semaphore); 43 44 // Increments the value of |semaphore|. |semaphore| may not be NULL. 45 void semaphore_post(semaphore_t* semaphore); 46 47 // Returns a file descriptor representing this semaphore. The caller may 48 // only perform one operation on the file descriptor: select(2). If |select| 49 // indicates the fd is readable, the caller may call |semaphore_wait| 50 // without blocking. If select indicates the fd is writable, the caller may 51 // call |semaphore_post| without blocking. Note that there may be a race 52 // condition between calling |select| and |semaphore_wait| or |semaphore_post| 53 // which results in blocking behaviour. 54 // 55 // The caller must not close the returned file descriptor. |semaphore| may not 56 // be NULL. 57 int semaphore_get_fd(const semaphore_t* semaphore); 58
