Check whether or not the current thread is the main thread

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

Have a look at the [`NSThread` API documentation][1].

There are methods like

`- (BOOL)isMainThread`

`+ (BOOL)isMainThread`

and `+ (NSThread *)mainThread`


[1]:

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## Details ##

- Swift 5.1, Xcode 11.3.1

## Solution 1. Detect any queue ##

[Get current DispatchQueue?][1]

## Solution 2. Detect only main queue ##

import Foundation

extension DispatchQueue {

private struct QueueReference { weak var queue: DispatchQueue? }

private static let key: DispatchSpecificKey<QueueReference> = {
let key = DispatchSpecificKey<QueueReference>()
let queue = DispatchQueue.main
queue.setSpecific(key: key, value: QueueReference(queue: queue))
return key
}()

static var isRunningOnMainQueue: Bool { getSpecific(key: key)?.queue == .main }
}

## Usage ##

if DispatchQueue.isRunningOnMainQueue { ... }

## Sample ##

func test(queue: DispatchQueue) {
queue.async {
print("--------------------------------------------------------")
print("queue label: \(queue.label)")
print("is running on main queue: \(DispatchQueue.isRunningOnMainQueue)")
}
}

test(queue: DispatchQueue.main)
sleep(1)
test(queue: DispatchQueue.global(qos: .background))
sleep(1)
test(queue: DispatchQueue.global(qos: .unspecified))

## Result (log) ##

--------------------------------------------------------
queue label: com.apple.root.background-qos
is running on main queue: false
--------------------------------------------------------
queue label: com.apple.root.default-qos
is running on main queue: false
--------------------------------------------------------
queue label: com.apple.main-thread
is running on main queue: true

[1]:

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Here is a way to detect what the current queue is
extension DispatchQueue {
//Label of the current dispatch queue.
static var currentQueueLabel: String { String(cString: __dispatch_queue_get_label(nil)) }

/// Whether the current queue is a `NSBackgroundActivityScheduler` task.
static var isCurrentQueueNSBackgroundActivitySchedulerQueue: Bool { currentQueueLabel.hasPrefix("com.apple.xpc.activity.") }

/// Whether the current queue is a `Main` task.
static var isCurrentQueueMainQueue: Bool { currentQueueLabel.hasPrefix("com.apple.main-thread") }
}