gistfile1.txt

    - (void)saveSomethingToDisk
{
    NSString* cachesPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    NSString* someFile = [cachesPath stringByAppendingFormat:@"somefile"];
    NSData* data = [NSData dataWithContentsOfFile:[[NSBundle mainBundle]  pathForResource:@"apple_rainbow_logo" ofType:@"jpg"]];
    
    @try
    {
        [NSKeyedArchiver archiveRootObject:data toFile:someFile];
    }
    @catch (NSException *exception)
    {
        NSLog(@"Got an exception");
    }
    @finally
    {
        NSLog(@"written");
    }
    

}


for (int i = 0; i < 100; i++)
    {
        if (i%2==0)
        {
            NSLog(@"main thread");
            [self saveSomethingToDisk];
        }
        else
        {
            NSLog(@"background");
            [self performSelectorInBackground:@selector(saveSomethingToDisk) withObject:nil];
        }
    }