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	1	/*
	2	* Copyright (c) 2008-2010 Apple Inc. All rights reserved.
	3	*
	4	* @APPLE_APACHE_LICENSE_HEADER_START@
	5	*
	6	* Licensed under the Apache License, Version 2.0 (the "License");
	7	* you may not use this file except in compliance with the License.
	8	* You may obtain a copy of the License at
	9	*
	10	* http://www.apache.org/licenses/LICENSE-2.0
	11	*
	12	* Unless required by applicable law or agreed to in writing, software
	13	* distributed under the License is distributed on an "AS IS" BASIS,
	14	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	15	* See the License for the specific language governing permissions and
	16	* limitations under the License.
	17	*
	18	* @APPLE_APACHE_LICENSE_HEADER_END@
	19	*/
	20
	21	#ifndef __DISPATCH_ONCE__
	22	#define __DISPATCH_ONCE__
	23
	24	#ifndef __DISPATCH_INDIRECT__
	25	#error "Please #include <dispatch/dispatch.h> instead of this file directly."
	26	#include <dispatch/base.h> // for HeaderDoc
	27	#endif
	28
	29	DISPATCH_ASSUME_NONNULL_BEGIN
	30
	31	__BEGIN_DECLS
	32
	33	/*!
	34	* @typedef dispatch_once_t
	35	*
	36	* @abstract
	37	* A predicate for use with dispatch_once(). It must be initialized to zero.
	38	* Note: static and global variables default to zero.
	39	*/
	40	DISPATCH_SWIFT3_UNAVAILABLE("Use lazily initialized globals instead")
	41	typedef long dispatch_once_t;
	42
	43	#if defined(__x86_64__) \|\| defined(__i386__) \|\| defined(__s390x__)
	44	#define DISPATCH_ONCE_INLINE_FASTPATH 1
	45	#elif defined(__APPLE__)
	46	#define DISPATCH_ONCE_INLINE_FASTPATH 1
	47	#else
	48	#define DISPATCH_ONCE_INLINE_FASTPATH 0
	49	#endif
	50
	51	/*!
	52	* @function dispatch_once
	53	*
	54	* @abstract
	55	* Execute a block once and only once.
	56	*
	57	* @param predicate
	58	* A pointer to a dispatch_once_t that is used to test whether the block has
	59	* completed or not.
	60	*
	61	* @param block
	62	* The block to execute once.
	63	*
	64	* @discussion
	65	* Always call dispatch_once() before using or testing any variables that are
	66	* initialized by the block.
	67	*/
	68	#ifdef __BLOCKS__
	69	API_AVAILABLE(macos(10.6), ios(4.0))
	70	DISPATCH_EXPORT DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
	71	DISPATCH_SWIFT3_UNAVAILABLE("Use lazily initialized globals instead")
	72	void
	73	dispatch_once(dispatch_once_t *predicate,
	74	DISPATCH_NOESCAPE dispatch_block_t block);
	75
	76	#if DISPATCH_ONCE_INLINE_FASTPATH
	77	DISPATCH_INLINE DISPATCH_ALWAYS_INLINE DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
	78	DISPATCH_SWIFT3_UNAVAILABLE("Use lazily initialized globals instead")
	79	void
	80	_dispatch_once(dispatch_once_t *predicate,
	81	DISPATCH_NOESCAPE dispatch_block_t block)
	82	{
	83	if (DISPATCH_EXPECT(*predicate, ~0l) != ~0l) {
	84	dispatch_once(predicate, block);
	85	} else {
	86	dispatch_compiler_barrier();
	87	}
	88	DISPATCH_COMPILER_CAN_ASSUME(*predicate == ~0l);
	89	}
	90	#undef dispatch_once
	91	#define dispatch_once _dispatch_once
	92	#endif
	93	#endif // DISPATCH_ONCE_INLINE_FASTPATH
	94
	95	API_AVAILABLE(macos(10.6), ios(4.0))
	96	DISPATCH_EXPORT DISPATCH_NONNULL1 DISPATCH_NONNULL3 DISPATCH_NOTHROW
	97	DISPATCH_SWIFT3_UNAVAILABLE("Use lazily initialized globals instead")
	98	void
	99	dispatch_once_f(dispatch_once_t predicate, void _Nullable context,
	100	dispatch_function_t function);
	101
	102	#if DISPATCH_ONCE_INLINE_FASTPATH
	103	DISPATCH_INLINE DISPATCH_ALWAYS_INLINE DISPATCH_NONNULL1 DISPATCH_NONNULL3
	104	DISPATCH_NOTHROW
	105	DISPATCH_SWIFT3_UNAVAILABLE("Use lazily initialized globals instead")
	106	void
	107	_dispatch_once_f(dispatch_once_t predicate, void _Nullable context,
	108	dispatch_function_t function)
	109	{
	110	if (DISPATCH_EXPECT(*predicate, ~0l) != ~0l) {
	111	dispatch_once_f(predicate, context, function);
	112	} else {
	113	dispatch_compiler_barrier();
	114	}
	115	DISPATCH_COMPILER_CAN_ASSUME(*predicate == ~0l);
	116	}
	117	#undef dispatch_once_f
	118	#define dispatch_once_f _dispatch_once_f
	119	#endif // DISPATCH_ONCE_INLINE_FASTPATH
	120
	121	__END_DECLS
	122
	123	DISPATCH_ASSUME_NONNULL_END
	124
	125	#endif