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[Objective-C] Cancellable dispatch after

#ifndef dispatch_cancellable_block_h
#define dispatch_cancellable_block_h

#import <Foundation/Foundation.h>

typedef void(^dispatch_cancelable_block_t)(BOOL cancel);

NS_INLINE dispatch_cancelable_block_t dispatch_after_delay(NSTimeInterval delay, dispatch_block_t block) {
    if (block == nil) {
        return nil;
    // First we have to create a new dispatch_cancelable_block_t and we also need to copy the block given (if you want more explanations about the __block storage type, read this: https://developer.apple.com/library/ios/documentation/cocoa/conceptual/Blocks/Articles/bxVariables.html#//apple_ref/doc/uid/TP40007502-CH6-SW6
    __block dispatch_cancelable_block_t cancelableBlock = nil;
    __block dispatch_block_t originalBlock = [block copy];
    // This block will be executed in NOW() + delay
    dispatch_cancelable_block_t delayBlock = ^(BOOL cancel){
        if (cancel == NO && originalBlock) {
        // We don't want to hold any objects in the memory
        originalBlock = nil;
    cancelableBlock = [delayBlock copy];
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, delay * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
        // We are now in the future (NOW() + delay). It means the block hasn't been canceled so we can execute it
        if (cancelableBlock) {
            cancelableBlock = nil;
    return cancelableBlock;

NS_INLINE void cancel_block(dispatch_cancelable_block_t block) {
    if (block == nil) {
    block = nil;

#endif /* dispatch_cancellable_block_h */

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