Fix: check if authCallback is running on a background queue

[ricardopereira]

#531

• interacting with certain frameworks like UIKit, we need to ensure that all calls happen from the main thread.

[mattheworiordan]

@ricardopereira does this PR fix #531?

[ricardopereira]

@mattheworiordan Yes. I reproduced the issue and now it's working.

[ricardopereira]

BTW, for the record:

@implementation AppDelegate {
    ARTClientOptions *_clientOptions;
    ARTRealtime *_client;
}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    _clientOptions = [[ARTClientOptions alloc] init];
    _clientOptions.authCallback = ^(ARTTokenParams *params, void(^callback)(id<ARTTokenDetailsCompatible>, NSError*)) {
        callback(nil, [NSError errorWithDomain:@"localhost" code:0 userInfo:nil]);
    };
    _client = [[ARTRealtime alloc] initWithOptions:_clientOptions];
    [_client.connection on:^(ARTConnectionStateChange *stateChange) {
        NSLog(@"%@", stateChange);
    }];
    return YES;
}

@end

The callback(nil, [NSError errorWithDomain:@"localhost" code:0 userInfo:nil]); was not called.

[tcard]

I'm not sure this solves the problem as generally as it could. What's so special about authCallback? Shouldn't this be done deeper, like at the ARTHttp level? Or all the places where the CFRunLoopPerformBlock thing is used?

[ricardopereira]

I'm not sure this solves the problem as generally as it could.

You're right.

What's so special about authCallback?

I don't have an answer. What I know is that the application:didFinishLaunchingWithOptions is running in the main queue and you can test it quite easily (just create a UIView and present it... it works). I debug it line by line and the only case where the execution transitions to a background queue is when the HTTP request is made. The completion is called in the background. Maybe because the authCallback is created in the main queue.

@tcard After I opened the PR I started thinking on generalising the solution. I though checking every callback that is accessible by the user (like, authCallback, state changes, publish message callback) and add the code to execute the callback on the main queue if needed. What do you think?

[tcard]

I though checking every callback that is accessible by the user (like, authCallback, state changes, publish message callback) and add the code to execute the callback on the main queue if needed. What do you think?

Sure, sounds better to me. Although honestly I'm flying a bit blind here, I don't really know how GCD works, etc. so you'll probably know better.

Just please let's avoid duplicating code as we do here, we can put this if-else logic in a generic function that takes a block.

[tcard]

@ricardopereira Is there anything missing here?

[ricardopereira]

@tcard No, it's done.

[tcard]

@ricardopereira Cool, thanks. I still don't get what's special about authCallback, but well...

[ricardopereira]

@tcard I explained here.