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POCFReadStreamRead blocking forever under iOS 7
 

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    <p>I'm seeing an issue wherein <code>CFReadStreamRead</code>, as part of a streamed file upload, <em>never</em> returns.</p> <p>This <em>seems</em> to happen only on iOS7 — and far more often when debugging against a physical device than in the simulator — or at least, it's far more evident there.</p> <p>We have an HTTP (or HTTPS, the problem occurs either way, with a locally-hosted or remote server) <code>POST</code> of a file, via straight-line, blocking (non-event-driven) CFNetwork calls. It's a necessity of the C code calling this handler; there's no provision for callbacks.</p> <p>That's well and good, the network calls are happening in background threads and/or via async dispatch.</p> <p>The network code in question boils down to (removing error handling for brevity):</p> <pre><code>CFReadStreamRef upload = CFReadStreamCreateWithFile( kCFAllocatorDefault, upload_file_url); CFRelease(upload_file_url); CFReadStreamOpen(upload); CFReadStreamRef myReadStream = CFReadStreamCreateForStreamedHTTPRequest( kCFAllocatorDefault, myRequest, upload); CFReadStreamOpen(myReadStream); CFIndex numBytesRead = CFReadStreamRead(myReadStream, buf, sizeof(buf)); // etc. </code></pre> <p>On its own, this code wants to hang immediately under iOS7. If I add a loop with some calls to <code>usleep</code> before it (checking <code>CFReadStreamHasBytesAvailable</code> along the way), it will <em>almost</em> always succeed. Every few hundred tries, it will still fail, never returning. Again, the main thread is unaffected.</p> <p>I'd hoped the GM would clear up this behavior, but it's still present. </p> <p>Adding a runloop/callback method to watch for bytes-available events has no effect - when the call hangs, no events are seen, either.</p> <p>Any suggestions as to why this is happening, or how it can be prevented? Anyone else seeing different <code>CFReadStream</code> behavior under iOS 7?</p>
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    1. COI have similar issue: server hangs and client never get HTTP answer if client runs under iOS 7. Was fine with iOS 3-4-5-6. Client uses NSUrlConnection. Anyone: please share your observations.
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      1. USrjobidon
    2. COThere are valid and documented reasons why the function will block. So, first question: are you sure the file has not been read completely and it blocks somewhere in the middle? Secondly, are you sure the file has been opened successfully?
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    3. COCertain of both of those things, and fully expecting the function to block when it needs to. And yes, the (omitted) error handling checks that the file has been opened properly.
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