1a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati/****************************************************************************** 2a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * 3a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * Copyright (C) 2014 Google, Inc. 4a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * 5a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * Licensed under the Apache License, Version 2.0 (the "License"); 6a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * you may not use this file except in compliance with the License. 7a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * You may obtain a copy of the License at: 8a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * 9a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * http://www.apache.org/licenses/LICENSE-2.0 10a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * 11a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * Unless required by applicable law or agreed to in writing, software 12a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * distributed under the License is distributed on an "AS IS" BASIS, 13a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * See the License for the specific language governing permissions and 15a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * limitations under the License. 16a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati * 17a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati ******************************************************************************/ 18a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati 19c11b407e78d96e05b0991bbe6dfde0d7eb5349b5Sharvil Nanavati#pragma once 20c11b407e78d96e05b0991bbe6dfde0d7eb5349b5Sharvil Nanavati 21a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati#include <stdbool.h> 22a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati 23c11b407e78d96e05b0991bbe6dfde0d7eb5349b5Sharvil Nanavatistruct semaphore_t; 24c11b407e78d96e05b0991bbe6dfde0d7eb5349b5Sharvil Nanavatitypedef struct semaphore_t semaphore_t; 25c11b407e78d96e05b0991bbe6dfde0d7eb5349b5Sharvil Nanavati 26a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati// Creates a new semaphore with an initial value of |value|. 27a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati// Returns NULL on failure. The returned object must be released 28a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati// with |semaphore_free|. 29c11b407e78d96e05b0991bbe6dfde0d7eb5349b5Sharvil Nanavatisemaphore_t *semaphore_new(unsigned int value); 30a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati 31a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati// Frees a semaphore allocated with |semaphore_new|. |semaphore| may 32a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati// be NULL. 33c11b407e78d96e05b0991bbe6dfde0d7eb5349b5Sharvil Nanavativoid semaphore_free(semaphore_t *semaphore); 34c11b407e78d96e05b0991bbe6dfde0d7eb5349b5Sharvil Nanavati 35a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati// Decrements the value of |semaphore|. If it is 0, this call blocks until 36a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati// it becomes non-zero. |semaphore| may not be NULL. 37c11b407e78d96e05b0991bbe6dfde0d7eb5349b5Sharvil Nanavativoid semaphore_wait(semaphore_t *semaphore); 38a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati 39a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati// Tries to decrement the value of |semaphore|. Returns true if the value was 40a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati// decremented, false if the value was 0. This function never blocks. |semaphore| 41a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati// may not be NULL. 42a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavatibool semaphore_try_wait(semaphore_t *semaphore); 43a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati 44a3164c9b0b2da60509f16bcbc23c36e30d3df862Sharvil Nanavati// Increments the value of |semaphore|. |semaphore| may not be NULL. 45c11b407e78d96e05b0991bbe6dfde0d7eb5349b5Sharvil Nanavativoid semaphore_post(semaphore_t *semaphore); 46f4013f29e38095abd556e23742ef713840f2f903Sharvil Nanavati 47f4013f29e38095abd556e23742ef713840f2f903Sharvil Nanavati// Returns a file descriptor representing this semaphore. The caller may 48f4013f29e38095abd556e23742ef713840f2f903Sharvil Nanavati// only perform one operation on the file descriptor: select(2). If |select| 49f4013f29e38095abd556e23742ef713840f2f903Sharvil Nanavati// indicates the fd is readable, the caller may call |semaphore_wait| 50f4013f29e38095abd556e23742ef713840f2f903Sharvil Nanavati// without blocking. If select indicates the fd is writable, the caller may 51f4013f29e38095abd556e23742ef713840f2f903Sharvil Nanavati// call |semaphore_post| without blocking. Note that there may be a race 52f4013f29e38095abd556e23742ef713840f2f903Sharvil Nanavati// condition between calling |select| and |semaphore_wait| or |semaphore_post| 53f4013f29e38095abd556e23742ef713840f2f903Sharvil Nanavati// which results in blocking behaviour. 54f4013f29e38095abd556e23742ef713840f2f903Sharvil Nanavati// 55f4013f29e38095abd556e23742ef713840f2f903Sharvil Nanavati// The caller must not close the returned file descriptor. |semaphore| may not 56f4013f29e38095abd556e23742ef713840f2f903Sharvil Nanavati// be NULL. 57f4013f29e38095abd556e23742ef713840f2f903Sharvil Nanavatiint semaphore_get_fd(const semaphore_t *semaphore); 58