purgeIdleCellConnections - ios

Question

About the "duplicate" state of this question:
This question here was asked in Nov 2012, it contains a detailed description of the problem and has 3 answers.
The question referred to as "original" was asked in Feb 2013 (3 month after this "duplicate"), has no detailed description and only 2 answers. The best of its two answers is just a link-only-answer.
Why do I get this message in my console?:
purgeIdleCellConnections: found one to purge conn = (some object-ID)
When my App starts I send a message to my server. I do this with this lines of code:
#implementation AppStatus {
NSMutableData* activeDownload;
NSURLConnection* Connection;
}
- (id) init {
self = [super init];
if (self) {
activeDownload = nil;
Connection = nil;
}
return self;
}
- (void)sendStatus:(NSString*)url {
NSString* escaped = [url stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
NSURLConnection* conn =[[NSURLConnection alloc] initWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:escaped]] delegate:self];
Connection = conn;
NSLog(#"%s Connection=%#",__PRETTY_FUNCTION__,Connection);
}
In the same file I have this delegate-methods:
- (void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)data {
NSLog(#"%s connection=%#",__PRETTY_FUNCTION__,connection);
[activeDownload appendData:data];
}
- (void)connection:(NSURLConnection*)connection didFailWithError:(NSError*)error {
NSLog(#"%s connection=%#",__PRETTY_FUNCTION__,connection);
activeDownload = nil;
Connection = nil;
//do nothing else; just ignore the error
}
- (void)connectionDidFinishLoading:(NSURLConnection*)connection {
NSLog(#"%s Connection=%#",__PRETTY_FUNCTION__,Connection);
NSString* answer = [[NSString alloc] initWithData:activeDownload encoding:NSUTF8StringEncoding];
//do something usefull with the server's answer
activeDownload = nil;
Connection = nil;
}
When i run this app on a real device (not on the simulator), I get this messages in the console:
2012-11-22 20:41:51.309 BookMan[376:907] -[AppStatus sendStatus:] Connection=<NSURLConnection: 0x1dd7ff40>
2012-11-22 20:41:51.929 BookMan[376:907] -[AppStatus connection:didReceiveData:] Connection=<NSURLConnection: 0x1dd7ff40>
2012-11-22 20:41:51.935 BookMan[376:907] -[AppStatus connectionDidFinishLoading:] Connection=<NSURLConnection: 0x1dd7ff40>
purgeIdleCellConnections: found one to purge conn = 0x1dd8ff60
The purgeIdleCellConnections-message apears about 4 or 5 seconds after the connectionDidFinishLoading-message.
As you can see, the object-number of the purgeIdleCellConnections-message is not the same as the number of the connection I did create and use in my app.
Maybe IMPORTANT: I do get this message only when I run the App on a real device (iPhone 4 with iOS 6.0.1). This device uses a 3G-connection, not a WIFI-connection. At the moment I have no WIFI-network to test if this happens on a WIFI-connection too.
I do not get this message when I run the App on the simulator.
When I change the method sendStatus: to this:
- (void)sendStatus:(NSString*)url {
NSString* escaped = [url stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
//NSURLConnection* conn =[[NSURLConnection alloc] initWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:escaped]] delegate:self];
//Connection = conn;
NSLog(#"%s Connection=%#",__PRETTY_FUNCTION__,Connection);
}
I get this output in the console:
2012-11-22 20:45:11.927 BookMan[391:907] -[AppStatus sendStatus:] Connection=(null)
I do not get the purgeIdleCellConnections-message when I do not create a connection.
So what does this message mean and why do I get it?:
purgeIdleCellConnections: found one to purge conn = (some object-ID)

Answer 1

It means that, a connection which has been idle for too long has got its TCP connection closed. This is a basic mechanism, and it's log shouldn't bother you as Apple states on Technical QA1774, it's a debug message that has been, erroneously, left enabled.
This log is, indeed, only shown when WWAN connections are purged.

Answer 2

Yes this the OS closing active connections over cellular data i.e 3G only. You shouldn't see this using a Wifi connection. It would seem that the OS purging the connections adds a bit of time to send data request to a server.

Answer 3

When on the device connected to cellular network, I have observed this debug message coming out of the iOS 6.0 SDK. Timing-wise I find it correlates to 'active' AJAX calls being terminated in my app. However it is very difficult to prove anything since this only occurs when rendering the web page in a UIWebView. I am just saying I don't think the messages are benign. I think they might indicate a bug in the Apple framework that is overly aggressive in terminating connections. It is hard to get instrumentation on the javascript running inside the UIWebView that makes the AJAX calls, so it is all highly speculative at this time.