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58 lines
2.3 KiB
58 lines
2.3 KiB
/******************************************************************************
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*
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* Copyright 2014 Google, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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******************************************************************************/
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#pragma once
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#include <stdbool.h>
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struct semaphore_t;
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typedef struct semaphore_t semaphore_t;
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// Creates a new semaphore with an initial value of |value|.
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// Returns NULL on failure. The returned object must be released
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// with |semaphore_free|.
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semaphore_t* semaphore_new(unsigned int value);
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// Frees a semaphore allocated with |semaphore_new|. |semaphore| may
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// be NULL.
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void semaphore_free(semaphore_t* semaphore);
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// Decrements the value of |semaphore|. If it is 0, this call blocks until
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// it becomes non-zero. |semaphore| may not be NULL.
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void semaphore_wait(semaphore_t* semaphore);
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// Tries to decrement the value of |semaphore|. Returns true if the value was
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// decremented, false if the value was 0. This function never blocks.
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// |semaphore| may not be NULL.
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bool semaphore_try_wait(semaphore_t* semaphore);
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// Increments the value of |semaphore|. |semaphore| may not be NULL.
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void semaphore_post(semaphore_t* semaphore);
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// Returns a file descriptor representing this semaphore. The caller may
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// only perform one operation on the file descriptor: select(2). If |select|
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// indicates the fd is readable, the caller may call |semaphore_wait|
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// without blocking. If select indicates the fd is writable, the caller may
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// call |semaphore_post| without blocking. Note that there may be a race
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// condition between calling |select| and |semaphore_wait| or |semaphore_post|
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// which results in blocking behaviour.
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//
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// The caller must not close the returned file descriptor. |semaphore| may not
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// be NULL.
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int semaphore_get_fd(const semaphore_t* semaphore);
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