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+/*
+ * Copyright (c) 2008-2011 Apple Inc. All rights reserved.
+ *
+ * @APPLE_APACHE_LICENSE_HEADER_START@
+ *
+ * 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.
+ *
+ * @APPLE_APACHE_LICENSE_HEADER_END@
+ */
+
+#ifndef __DISPATCH_SEMAPHORE__
+#define __DISPATCH_SEMAPHORE__
+
+#ifndef __DISPATCH_INDIRECT__
+#error "Please #include <dispatch/dispatch.h> instead of this file directly."
+#include <dispatch/base.h> // for HeaderDoc
+#endif
+
+/*!
+ * @typedef dispatch_semaphore_t
+ *
+ * @abstract
+ * A counting semaphore.
+ */
+DISPATCH_DECL(dispatch_semaphore);
+
+__BEGIN_DECLS
+
+/*!
+ * @function dispatch_semaphore_create
+ *
+ * @abstract
+ * Creates new counting semaphore with an initial value.
+ *
+ * @discussion
+ * Passing zero for the value is useful for when two threads need to reconcile
+ * the completion of a particular event. Passing a value greather than zero is
+ * useful for managing a finite pool of resources, where the pool size is equal
+ * to the value.
+ *
+ * @param value
+ * The starting value for the semaphore. Passing a value less than zero will
+ * cause NULL to be returned.
+ *
+ * @result
+ * The newly created semaphore, or NULL on failure.
+ */
+__OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
+DISPATCH_EXPORT DISPATCH_MALLOC DISPATCH_WARN_RESULT DISPATCH_NOTHROW
+dispatch_semaphore_t
+dispatch_semaphore_create(long value);
+
+/*!
+ * @function dispatch_semaphore_wait
+ *
+ * @abstract
+ * Wait (decrement) for a semaphore.
+ *
+ * @discussion
+ * Decrement the counting semaphore. If the resulting value is less than zero,
+ * this function waits in FIFO order for a signal to occur before returning.
+ *
+ * @param dsema
+ * The semaphore. The result of passing NULL in this parameter is undefined.
+ *
+ * @param timeout
+ * When to timeout (see dispatch_time). As a convenience, there are the
+ * DISPATCH_TIME_NOW and DISPATCH_TIME_FOREVER constants.
+ *
+ * @result
+ * Returns zero on success, or non-zero if the timeout occurred.
+ */
+__OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
+DISPATCH_EXPORT DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
+long
+dispatch_semaphore_wait(dispatch_semaphore_t dsema, dispatch_time_t timeout);
+
+/*!
+ * @function dispatch_semaphore_signal
+ *
+ * @abstract
+ * Signal (increment) a semaphore.
+ *
+ * @discussion
+ * Increment the counting semaphore. If the previous value was less than zero,
+ * this function wakes a waiting thread before returning.
+ *
+ * @param dsema The counting semaphore.
+ * The result of passing NULL in this parameter is undefined.
+ *
+ * @result
+ * This function returns non-zero if a thread is woken. Otherwise, zero is
+ * returned.
+ */
+__OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
+DISPATCH_EXPORT DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
+long
+dispatch_semaphore_signal(dispatch_semaphore_t dsema);
+
+__END_DECLS
+
+#endif /* __DISPATCH_SEMAPHORE__ */