libdispatch-187.5.tar.gz

[apple/libdispatch.git] / dispatch / once.h

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+/*
+ * Copyright (c) 2008-2010 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_ONCE__
+#define __DISPATCH_ONCE__
+
+#ifndef __DISPATCH_INDIRECT__
+#error "Please #include <dispatch/dispatch.h> instead of this file directly."
+#include <dispatch/base.h> // for HeaderDoc
+#endif
+
+__BEGIN_DECLS
+
+/*!
+ * @typedef dispatch_once_t
+ *
+ * @abstract
+ * A predicate for use with dispatch_once(). It must be initialized to zero.
+ * Note: static and global variables default to zero.
+ */
+typedef long dispatch_once_t;
+
+/*!
+ * @function dispatch_once
+ *
+ * @abstract
+ * Execute a block once and only once.
+ *
+ * @param predicate
+ * A pointer to a dispatch_once_t that is used to test whether the block has
+ * completed or not.
+ *
+ * @param block
+ * The block to execute once.
+ *
+ * @discussion
+ * Always call dispatch_once() before using or testing any variables that are
+ * initialized by the block.
+ */
+#ifdef __BLOCKS__
+__OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
+DISPATCH_EXPORT DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
+void
+dispatch_once(dispatch_once_t *predicate, dispatch_block_t block);
+
+DISPATCH_INLINE DISPATCH_ALWAYS_INLINE DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
+void
+_dispatch_once(dispatch_once_t *predicate, dispatch_block_t block)
+{
+       if (DISPATCH_EXPECT(*predicate, ~0l) != ~0l) {
+               dispatch_once(predicate, block);
+       }
+}
+#undef dispatch_once
+#define dispatch_once _dispatch_once
+#endif
+
+__OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
+DISPATCH_EXPORT DISPATCH_NONNULL1 DISPATCH_NONNULL3 DISPATCH_NOTHROW
+void
+dispatch_once_f(dispatch_once_t *predicate, void *context,
+               dispatch_function_t function);
+
+DISPATCH_INLINE DISPATCH_ALWAYS_INLINE DISPATCH_NONNULL1 DISPATCH_NONNULL3
+DISPATCH_NOTHROW
+void
+_dispatch_once_f(dispatch_once_t *predicate, void *context,
+               dispatch_function_t function)
+{
+       if (DISPATCH_EXPECT(*predicate, ~0l) != ~0l) {
+               dispatch_once_f(predicate, context, function);
+       }
+}
+#undef dispatch_once_f
+#define dispatch_once_f _dispatch_once_f
+
+__END_DECLS
+
+#endif