Asynchronously save up the parent-child chain of NSManagedObjectContexts to disk

asyncsave.m

- (BOOL)saveToDiskAndShouldWait:(BOOL)wait {
    __block BOOL success = NO;
    // Give self time to save
    [self performBlockAndWait:^{
        success = [self saveOrLogError];
    }];
    NSManagedObjectContext *parent = [self parentContext];
    if (parent) {
        if (wait) {
            [parent performBlockAndWait:^{
                [parent saveToDiskAndShouldWait:wait];
            }];
        } else {
            [parent performBlock:^{
                [parent saveToDiskAndShouldWait:wait];
            }];
        }
    }

    return success;
}

Posting here to remember. I wrote this method to be able to pass -saveContext messages up the parent-child chain of NSManagedObjectContexts, up to the final one which was a background context. This unloads disk IO off of the main thread.

If wait is NO, then the message to save recurses up the chain, but the caller returns to its execution context. -performBlock and -performBlockAndWait execute in the callee's thread of execution.

Based on Marcus Zarra's implementation of -(void)saveContext:(BOOL)wait, from Core Data 2nd Edition, p96. The implementation above improves upon this idea by not needing to care about how many parents a given context has, and can effectively do asynchronous saves all the way up the stack.