Re: Async NSURLConnection and blocks (was: Running NSURLConnection from within an NSOperation?)
Re: Async NSURLConnection and blocks (was: Running NSURLConnection from within an NSOperation?)
- Subject: Re: Async NSURLConnection and blocks (was: Running NSURLConnection from within an NSOperation?)
- From: John Heitmann <email@hidden>
- Date: Mon, 21 Jun 2010 13:37:01 -0700
Thanks for the response. There is definitely a lot of goofiness in that code. I started from the apple xml performance demo, which had run-loop code that led me to believe that I had to run the NSURLConnection run loop in a thread. It's great that that's not the case (I re-read the example[1] and the only reason they have it is to do some blocking). I can drop all block use except the completion block, which should be a really nice cleanup.
I'll play around with the autorelease pool. The apple example had manual autorelease pool management during parsing. I'm going to just drop that entirely since I don't think my app is _that_ performance sensitive.
The odd init-at-a-distance code was because I originally had the connection start upon init, which meant that I had a chicken and egg problem wrt initializing the handler (with a completion block that needed the connection) and the connection (which needed the handler). Now that start is manually run I can clean that up too. Thanks again,
John
[1] http://developer.apple.com/iphone/library/samplecode/XMLPerformance/Listings/Classes_LibXMLParser_m.html#//apple_ref/doc/uid/DTS40008094-Classes_LibXMLParser_m-DontLinkElementID_10
On Jun 21, 2010, at 10:48 AM, Kevin Wojniak wrote:
> NSURLConnection already does its work asynchronously, there is no need to run it on a separate thread. However if you still want to, you should use [NSRunLoop currentRunLoop], which returns the run loop associated with that thread.
>
> In your code you are not creating your objects properly. You should use the form [[Class alloc] init] then operate on that object:
>
>> NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:urlRequest delegate:handler startImmediately:NO];
>
>
> Also I don't believe you need to create the autorelease pool. I think GCD does it for you.
>
> Lastly, you should run the thread's run loop until your delegate method gets called indicating the NSURLConnection is done.
>
>
>
> On Jun 20, 2010, at 1:42 PM, John Heitmann wrote:
>
>>
>> On Feb 9, 2010, at 3:01 PM, Keith Duncan wrote:
>>
>>> ...you should create a 'concurrent' NSOperation as described in the documentation, and schedule your NSURLConnection on +[NSRunLoop mainRunLoop]. This will allow your NSOperation -start method to exit immediately and the thread to return to the pool.
>>
>> I had a working async NSURLConnection scheme where I initialized the connection in a new thread and pumped its run loop manually on that thread until I saw the delegate set a completion flag. I thought I'd convert it to blocks since it cleans up some ugly code there. I'm 95% of the way there and things look good, but there are some lingering problems in my code that I don't understand. The above tip helped with one of my problems: the automatic block thread didn't pump the NSURLConnection run loop, so I scheduled the connection in the main run loop like Keith suggested and things worked. My first question is: doesn't this block the main loop with io? I have another version which uses a block to manually pump, but then this ties up an automatic block thread, which are supposed to be short-lived. Is it really a good practice to drive the NSURLConnection from the main loop?
>>
>> My second question is: How do I memory manage the autorelease pool that the delegate uses? Here's a rough idea of what I have now:
>>
>> dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
>> dispatch_async(queue, ^{
>> __block NSAutoreleasePool *autoReleasePool = [[NSAutoreleasePool alloc] init];
>> NSURLConnection *connection = [NSURLConnection alloc];
>> ResponseHandler *handler = [ResponseHandler alloc];
>>
>> [handler initWithDelegate:delegate
>> completionBlock:^{dispatch_async(queue, ^{
>> [connection release];
>> [handler release];
>> [autoReleasePool release];
>> [delegate release];
>> });}];
>>
>> [connection initWithRequest:urlRequest delegate:handler startImmediately:NO];
>> [connection scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
>> [connection start];
>> });
>>
>> ResponseHandler is pretty simple. It processes the data and calls the completionBlock when done. With that code I get "attempt to pop an unknown autorelease pool". When I drop the release altogether the error goes away, but that seems like a leak.
>>
>> John_______________________________________________
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