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My app calls a method to each of its plugins, and each plugin is assigned it’s own thread to execute this method in. So 8-9 threads are created instantly and each plugin’s code is going on at once. Each plugin is sent 2 objects, which it can then access and call methods from (one object is General/NSUserDefaults).

So when this is all going on, sometimes I will get random errors, and sometimes it works perfectly fine. The errors are always the same few, and many times it has something to do with the General/NSTask I am running (I have a few methods that call General/NSTask).

One random error is this: * General/NSTimer discarding exception ‘General/NSInvalidArgumentException’ (reason ** -General/[NSCFDictionary setObject:forKey:]: attempt to insert nil value’) that raised during firing of timer with target 5126d80 and selector ‘runPrimaryTask:’ but where I think this is happening I check for nil strings everywhere… and since it only happens randomly, with exact same test data, it’s hard to debug.

The documentation at file:///Developer/Documentation/Cocoa/Conceptual/Multithreading/Tasks/foundation.html says that General/NSTask is generally thread-unsafe. Is there any work around for this? Would this be causing the random errors? Would I need to use General/NSLock’s each time each plugin accesses one of the objects it is sent that is shared?

The General/NSTask’s I use repeatedly call a Perl script that does simple regex (i.e. strip html). But I do use General/NSTask’s for parsing HTML, and those have not had problems (but they aren’t called repeatedly).


Yes, you will most likely need to synchronize access to your shared objects if they not currently thread safe.

Use the debugger, Luke!

You say you don’t know where the exception is being thrown. Put a breakpoint on -General/[NSException raise] and find out. That way you’ll get a lot more information and won’t have to be guessing about what’s going wrong.

I’ve been testing this like crazy, and when I call the function for the first time when the app launches, it always works perfectly. But as I keep calling it in same process, it starts to get more and more errors. But if I relaunch the app and start over, it works fine. It’s really starting to get to me… I’m slowly starting to find where a few of the errors are being generated from but still don’t why because first time it runs, it works perfectly. —- General/NSUserDefaults isn’t thread safe, you’ll have to guard all usage of it.

I’ve figured it out. And I’ve learned a lot better how to catch exceptions. After implementing General/NSLock and NS_DURING/NS_HANDLER/NS_ENDHANDLER I’ve made it much more stable. Also, calling General/NSTask’s launch and waitUntilExit using performSelectorOnMainThread… fixed some other crashing I had too. Weird.