问调试NSOperationQueue阻塞

EN

__block NSMutableArray *collectionOfCourses = [[NSMutableArray alloc] initWithCapacity:[[self courses] count]];

/* Create a filename.  Use our title and set it to lowercase */
NSURL *ourFileURL = [aURL URLByAppendingPathComponent:[[self title] lowercaseString]];
ourFileURL = [ourFileURL URLByAppendingPathExtension:@"js"];

for (Course *aCourse in [self courses]) {
       [[self opQueue] addOperationWithBlock:^{
       NSArray *arrayForOneCourse = [aCourse arrayAndWriteToFileURL:aURL fileFormat:format];
   [collectionOfCourses addObject:arrayForOneCourse];
    }];
}