Deallocated instance exception with threads

I've a problem with an app for Mac that I'm writing in Objective-c. I've this situation:

1. In main thread (GUI):

ftEngine = [[FileT alloc] init];
[ftEngine setParameters:searchWord selectedEngine:[[pbEngines selectedItem] title] actualPage:0];
NSThread* thFileT = [[NSThread alloc] initWithTarget:ftEngine selector:@selector(setTotalResult) object:nil]; [thFileT start];

1. In child (ftEngine previous declared):

-(void)setTotalResult {
    NSError* nsError = nil;
    NSURL* urlCompleteUrl = [NSURL URLWithString:m_completeSearchWord];
}

m_completeSearchWord is initialized by setParameters function previously utilized.

And now.. my problem is: When thread is started, it call setTotalResult function and i'll get an exception when I try to use m_completeSearchWord.

It's strange becacuse开发者_StackOverflow社区 if I don't use a thread, all works correctly!

Exception is:

2011-09-08 23:24:06.731 GUI[12935:1a07] *** -[CFString respondsToSelector:]: message sent to deallocated instance 0x1003cc650

It sounds like you may not have retained m_completeSearchWord correctly when you initialized it. Add the body of -setParameters if you want help confirming that.

When calling selectors in a new thread, make sure that the selector has been properly wrapped with an autorelease pool :

-(void) setTotalResult {
    NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
    ...
    [pool release];
}

I see all manner of memory related issues when I forget to add the pool and your error definitely rings a bell.