po [NSThread currentThread]

Question

When I do po [NSThread currentThread], I got

{name = (null), num = 4}

When I look to the left I see:

Looks like it's Thread number 6, not 4. Also what properties do we need to call to get that thread numbers anyway?

[NSThread currentThread].number? Doesn't exist though.

Answer 1

Thread numbers are meaningless, pretty much.

The thread instance, though, is a singleton per thread. You could use the NSThread's address, by coincidence. Better, still, would be to dip down to the mach_* API and grab the thread ID from that API.

[NSThread currentThread] is about as unique of a number as you'll get. If the thread terminates and then a new thread is created, you might see the same address vended. The mach APIs will vend something just about as unique, really.

What are you trying to do?

Answer 2

For Swift 5: It's a private variable, but accessible directly using keypath:

Thread.current.value(forKeyPath: "private.seqNum")!