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    <p>My project did evolve significantly since I've asked this question.</p> <p>From the structural point of view, I can't say much interesting about asynchronous operations: in my project they are all based on dispatch_async and the most valuable functionality is implemented with intensive usage of blocks (mainly: yielding operations themselves to the blocks they execute, allows to control a flow of these operations).</p> <p>The more interesting thing to note here is the code I currently use for synchronous (or "forced-synchronous") operations - though their usage should be avoided in real apps, they are still applicable in unit tests: one example is a need to straighten the curly asynchronous flow of asynchronous net request to test its result in place, in the context of unit test case. </p> <p>Though I am posting this as an answer to my non-specific question I would still really like to see any authoritative answer about whether my SASyncOperation is good enough for forced-sync operations (in the sense I've described it in this question) or maybe it could be improved more.</p> <p><a href="https://github.com/stanislaw/SACompositeOperations/blob/master/SACompositeOperations/SASyncOperation.m" rel="nofollow">SASyncOperation</a> as it currently written</p> <ul> <li>Does not block main thread if it is run on main thread.</li> <li>Does not produce excessive CPU polling as simple approaches with <em>while(!completed){};</em> do.</li> </ul> <p>This is the most important part of the code:</p> <pre><code>#import "SASyncOperation.h" @interface SASyncOperation () { BOOL _isOnMainThread; dispatch_semaphore_t _semaphore; } @end @implementation SASyncOperation // … - (void)start { _semaphore = dispatch_semaphore_create(0); _operation(self); if (_finished) return; if ((_isOnMainThread = [NSThread isMainThread])) { while (dispatch_semaphore_wait(_semaphore, DISPATCH_TIME_NOW)) { CFRunLoopRunInMode(kCFRunLoopDefaultMode, [[NSDate distantFuture] timeIntervalSinceNow], NO); } } else { dispatch_semaphore_wait(_semaphore, DISPATCH_TIME_FOREVER); } _finished = YES; } - (void)run:(^(void)(SASyncOperation *)block { _operation = [block copy]; [self start]; } - (void)finish { _finished = YES; dispatch_semaphore_signal(_semaphore); if (_isOnMainThread) { dispatch_async(dispatch_get_main_queue(), ^{ CFRunLoopStop(CFRunLoopGetMain()); }); } } // … @end </code></pre> <p>This is how SASyncOperation should be used:</p> <pre><code>SASyncOperation *syncOperation = [[SASyncOperation alloc] init]; [syncOperation run:^(SASyncOperation *so) { doSomeThingMultiQueuedPossiblyMultiblockedAndAsynchronous(^{ soOver = YES; [so finish]; }); }]; // &lt;- (*) // (*) The flow will be stopped at this point waiting when 'so' operation will finish itself </code></pre>
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    1. POThe most common and right pattern for performing synchronous tasks, asynchronous tasks to create a composite operation
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    1. USStanislav Pankevich
    1. USStanislav Pankevich
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    1. POThe most common and right pattern for performing synchronous tasks, asynchronous tasks to create a composite operation
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