CFReadStreamRead blocking forever under iOS 7 - ios

Question

I'm seeing an issue wherein CFReadStreamRead, as part of a streamed file upload, never returns.
This seems 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.
We have an HTTP (or HTTPS, the problem occurs either way, with a locally-hosted or remote server) POST 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.
That's well and good, the network calls are happening in background threads and/or via async dispatch.
The network code in question boils down to (removing error handling for brevity):
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.
On its own, this code wants to hang immediately under iOS7. If I add a loop with some calls to usleep before it (checking CFReadStreamHasBytesAvailable along the way), it will almost always succeed. Every few hundred tries, it will still fail, never returning. Again, the main thread is unaffected.
I'd hoped the GM would clear up this behavior, but it's still present.
Adding a runloop/callback method to watch for bytes-available events has no effect - when the call hangs, no events are seen, either.
Any suggestions as to why this is happening, or how it can be prevented? Anyone else seeing different CFReadStream behavior under iOS 7?

Answer 1

I've try such nasty workaround and it works for me, problem is that I'm requesting delta values from server, so if something goes wrong I'm just fetching new delta value with, in general case it will not work (in logs I see that timeout kicks in sometimes). At least this prevents form permanent thread blocking and gives a chance to handle somehow this problem:
NSInteger readStreamReadWorkaround(CFReadStreamRef readStrem, UInt8 *buffer, CFIndex bufferLength) {
static dispatch_once_t onceToken;
static BOOL isProblematicOs = YES;
dispatch_once(&onceToken, ^{
isProblematicOs = [[UIDevice currentDevice].systemName compare: #"7.0" options: NSNumericSearch]!=NSOrderedAscending;
});
NSInteger readBytesCount = -2;
if (isProblematicOs) {
CFStreamStatus sStatus = CFReadStreamGetStatus(readStrem);
NSDate *date = [NSDate date];
while (YES) {
if(CFReadStreamHasBytesAvailable(readStrem)) {
readBytesCount = CFReadStreamRead(readStrem, buffer, bufferLength);
break;
}
sStatus = CFReadStreamGetStatus(readStrem);
if (sStatus!=kCFStreamStatusOpen && sStatus !=kCFStreamStatusAtEnd
|| [date timeIntervalSinceNow]<-15.0) {
break;
}
usleep(50000);
}
} else {
readBytesCount = CFReadStreamRead(readStrem, buffer, sizeof(buffer));
}
return readBytesCount;
}
I don't like this solution but so far I don't see an alternative.