random crash in ios6 after app launched - ios6

Question

We're getting a random crash in iOS6, here's the crash stack we're getting:
0 libobjc.A.dylib 0x399d75b0 objc_msgSend + 15
1 CoreFoundation 0x31c945de ___CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 14
2 CoreFoundation 0x31c94290 ___CFRunLoopDoTimer + 272
3 CoreFoundation 0x31c92f00 ___CFRunLoopRun + 1232
4 CoreFoundation 0x31c05ebc CFRunLoopRunSpecific + 351
5 CoreFoundation 0x31c05d48 CFRunLoopRunInMode + 103
6 GraphicsServices 0x357dc2ea GSEventRunModal + 71
7 UIKit 0x33b1b300 UIApplicationMain + 1119
8 21 0x00224e96 _main(main.m:27)
9 libdyld.dylib 0x39e13b20 _start
SEGV_ACCERR
We checked the corresponding logs, the crash just happened quite after app launched.
The code is a little complicated. Briefly, here just start a timer for net task when app not launched over.
(void)startTimeOutDetect{
execOnMainThread(^{
#synchronized(self){
[NSObject cancelPreviousPerformRequestsWithTarget:self selector:#selector(handleSyncTimeOut) object:nil];
[self performSelector:#selector(handleSyncTimeOut) withObject:nil afterDelay:70.f];
}
});
}
(void)cancelTimeOutDetect{
execOnMainThread(^{
#synchronized(self){
[NSObject cancelPreviousPerformRequestsWithTarget:self selector:#selector(handleSyncTimeOut) object:nil];
}
});
}