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46 lines
887 B
46 lines
887 B
6 years ago
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/*
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6 years ago
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* Copyright (c) Facebook, Inc. and its affiliates.
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6 years ago
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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#import <Foundation/Foundation.h>
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@interface A : NSObject
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@property(strong) void (^block)(void);
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@end
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@implementation A
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+ (instancetype)autoUpdating {
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static A* a;
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dispatch_once_t onceToken;
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dispatch_once(&onceToken, ^{
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a = [self alloc];
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a.block = ^{
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};
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});
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return a;
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}
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static void dispatch_once2(dispatch_once_t* predicate, dispatch_block_t block);
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+ (instancetype)autoUpdating2 {
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static A* a;
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dispatch_once_t onceToken;
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dispatch_once2(&onceToken, ^{
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a = [self alloc];
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a.block = ^{
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};
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});
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return a;
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}
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@end
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int main() {
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A* a = [A autoUpdating];
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A* a2 = [A autoUpdating2];
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a.block();
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a2.block(); // NPE here since dispatch_once2 is skipped
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}
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