Check whether or not the current thread is the main thread

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
{
if (IS_THIS_MAIN_THREAD?) {
NSLog(@"ok. this is main thread.");
} else {
NSLog(@"don't call this method from other thread!");
}
}

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);
}
}

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.

**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

Two ways. From @rano's answer,

[[NSThread currentThread] isMainThread] ? NSLog(@"MAIN THREAD") : NSLog(@"NOT MAIN THREAD");

Also,

[[NSThread mainThread] isEqual:[NSThread currentThread]] ? NSLog(@"MAIN THREAD") : NSLog(@"NOT MAIN THREAD");

For Monotouch / Xamarin iOS you can perform the check in this way:

if (NSThread.Current.IsMainThread)
{
DoSomething();
}
else
{
BeginInvokeOnMainThread(() => DoSomething());
}

Swift Version

- - - -

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

**In Swift3**

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

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

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The following pattern will assure a method is executed on the main thread:

- (void)yourMethod {
// make sure this runs on the main thread
if (![NSThread isMainThread]) {
[self performSelectorOnMainThread:_cmd/*@selector(yourMethod)*/
withObject:nil
waitUntilDone:YES];
return;
}
// put your code for yourMethod here
}