在《Core Data Programming Guide》文档的Concurrency with Core Data这一章节中提到了“Use Thread Confinement to Support Concurrency”，这里的“Thread”还包含serial operation queue和dispatch queue。
我目前的理解是MOC会负责对PSC进行加锁解锁，这些动作需要保证有序地得到执行，如果两个thread同时访问一份context，尤其是其中一个进行写操作，另一个进行读操作，就很容易发生死锁：
- (void)runSave
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
NSManagedObjectContext *moc = appDelegate.managedObjectContext;
if (moc) {
for (int j = 0; j < 10000; ++j) {
NSString *threadPtr = [NSString stringWithFormat:@"%p", [NSThread currentThread]];
[_threadDict setObject:@"Running Thread" forKey:threadPtr];
People *people = [NSEntityDescription insertNewObjectForEntityForName:@"People" inManagedObjectContext:moc];
people.name = @"noname";
}
NSLog(@"**********IN SAVE %@", [NSThread currentThread]);
NSError *error = nil;
if ([moc save:&error]) {
;
}
NSLog(@"**********OUT SAVE %@", [NSThread currentThread]);
}
});
}
- (void)runFetch
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
NSManagedObjectContext *moc = appDelegate.managedObjectContext;
if (moc) {
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:[NSEntityDescription entityForName:@"People" inManagedObjectContext:moc]];
NSLog(@"~~~~~~~~~~IN FETCH %@", [NSThread currentThread]);
NSError *error = NULL;
NSArray *array = [moc executeFetchRequest:fetchRequest error:&error];
if (array) {
;
}
NSLog(@"~~~~~~~~~~OUT FETCH %@", [NSThread currentThread]);
}
});
}
死锁的表现为：
