Check whether or not the current thread is the main thread

Question

Is there any way to check whether or not the current thread is the main thread in Objective-C?

I want to do something like this.

  - (void)someMethod         


        

Answer 1

let isOnMainQueue = (dispatch_queue_get_label(dispatch_get_main_queue()) == dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL))

check this answer from https://stackoverflow.com/a/34685535/1530581

Answer 2

UPDATE: seems that is not correct solution, according to queue.h header as mentioned @demosten

The first thought was brought to me, when I was needed this functionality was the line:

dispatch_get_main_queue() == dispatch_get_current_queue();

And had looked to the accepted solution:

[NSThread isMainThread];

mine solution 2.5 times faster.

PS And yes, I'd checked, it works for all threads

Answer 3

In Swift3

if Thread.isMainThread {
    print("Main Thread")
}

Answer 4

If you want to know whether or not you're on the main thread, you can simply use the debugger. Set a breakpoint at the line you're interested in, and when your program reaches it, call this:

(lldb) thread info

This will display information about the thread you're on:

(lldb) thread info thread #1: tid = 0xe8ad0, 0x00000001083515a0 MyApp`MyApp.ViewController.sliderMoved (sender=0x00007fd221486340, self=0x00007fd22161c1a0)(ObjectiveC.UISlider) -> () + 112 at ViewController.swift:20, queue = 'com.apple.main-thread', stop reason = breakpoint 2.1

If the value for queue is com.apple.main-thread, then you're on the main thread.

Answer 5

If you want a method to be executed on the main thread, you can:

- (void)someMethod
{
    dispatch_block_t block = ^{
        // Code for the method goes here
    };

    if ([NSThread isMainThread])
    {
        block();
    }
    else
    {
        dispatch_async(dispatch_get_main_queue(), block);
    }
}

Answer 6

void ensureOnMainQueue(void (^block)(void)) {

    if ([[NSOperationQueue currentQueue] isEqual:[NSOperationQueue mainQueue]]) {

        block();

    } else {

        [[NSOperationQueue mainQueue] addOperationWithBlock:^{

            block();

        }];

    }

}

note that i check the operation queue, not the thread, as this is a more safer approach