In my app I have to launch background processes (bundled within my app's
Resources folder) to do some things, and I launch them with NSTask. Every now
and then I get a crash report which shows NSTask throws some fatal exception
which is not caught by a wrapping @try block.
For example:
@try {
NSString * taskPath = [[[NSBundle mainBundle] resourcePath]
stringByAppendingPathComponent:@"mytask"];
task = [[NSTask alloc] init];
task.launchPath = taskPath;
task.arguments = @[aUUIDString];
[task launch];
}
@catch (NSException * e) {
...
}
And it crashes:
Exception Type: EXC_BREAKPOINT (SIGTRAP)
Exception Codes: 0x0000000000000002, 0x0000000000000000
*** NSTask: Task create for path
'/Applications/App.app/Contents/Resources/mytask' failed: 22, "Invalid
argument". Terminating temporary process.
*** multi-threaded process forked ***
Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0 com.apple.Foundation 0x978142d8
___NEW_PROCESS_COULD_NOT_BE_EXECD___ + 7
1 com.apple.Foundation 0x976d2e16 -[NSConcreteTask
launchWithDictionary:] + 4698
2 com.apple.Foundation 0x97744447 -[NSConcreteTask launch] + 40
What I can't figure out is what the error message means. I imagine it's coming
from a call to exec(), but which argument is invalid is beyond me. The path to
the task is correct. If the task wasn't in the app bundle, it'd be seriously
broken, but also if I try to replicate it by using a bad path, it does crash
this way, it simply throws a normal exception which is caught. The arguments I
pass to the task are always simple trivial strings, nothing wacky.
Looking around the open source code for exec(), it appears EINVAL (22) can be
returned if the task was exec()'d when not called from a vfork()'d process,
with the comment /* If we're not in vfork, don't permit a mutithreaded task to
exec */ which seems to line up with the *** multi-threaded process forked ***
line in the crash log… trouble is I have no idea what this ultimately means to
me. Seems like an OS bug?
So:
- It crashes instead of throwing an exception — not exactly friendly.
- It crashes *very rarely* (I've never seen it personally.)
- It's not just one task, it can happen with any of the tasks in the bundle.
- Seems to only have happened on 10.8.2 so far.
Any ideas?
--
Seth Willits
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