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再看Core Data中PSC陷入死鎖的問題
在《Core Data Programming Guide》文檔的Concurrency with Core Data這一章節中提到了“Use Thread Confinement to Support Concurrency”，這裏的“Thread”還包含serial operation queue和dispatch queue。
我目前的理解是MOC會負責對PSC進行加鎖解鎖，這些動作需要保證有序地得到執行，如果兩個thread同時訪問一份context，尤其是其中一個進行寫操作，另一個進行讀操作，就很容易發生死鎖：
- (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]);
}
});
}
死鎖的表現為：
最後更新：2017-04-03 14:53:58