Open Radar

 
Summary:

The documentation for NSOperation fails to explain that when Operation 2 is dependent on Operation 1, Operation 2 will not begin to execute until the completion block for Operation 1 has finished executing.

Steps to Reproduce:

1. Execute the following code:

    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    
    NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{ NSLog(@"Operation 1 work!"); }];
    [op1 setCompletionBlock:^{ sleep(5); NSLog(@"Operation 1 done!"); }];
    
    NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{ NSLog(@"Operation 2 work!"); }];
    [op2 setCompletionBlock:^{ NSLog(@"Operation 2 done!"); }];
    
    [op2 addDependency:op1];
    
    [queue addOperation:op1];
    [queue addOperation:op2];

Expected Results:

According to the documentation:

"The completion block you provide is executed when the value returned by the isFinished method changes to YES."
"An operation object does not clear a dependency until the value at the isFinished key path changes to YES."

I would expect both the completionBlock of op1 and op2 to execute simultaneously, when the operation is completed.

Actual Results:

The second operation, op2, does not execute until both op1 is marked as finished *and* its completion block finishes executing. Something not explained in the documentation.

Regression:

N/A

Notes:

N/A