Because when the main thread is completed the worker thread continues to run.

On Tuesday, 27 October 2020 at 00:46:48 UTC, Marcone wrote:
> Because when the main thread is completed the worker thread continues to run.

Please provide a code example. It's much easier to reason about.

Are you creating a thread from a thread and want the 2nd spawned thread to be terminated when the 1st thread terminates?

You could tell your thread via a shared variable that main has ended:

import std.stdio;
import std.concurrency;
import core.thread;

shared bool end = false;

void thread ()
{
	for (;;)
	{
		Thread.sleep (500.msecs);
		synchronized
		{
			if (end) break;
		}
	}
	writeln ("thread ends");
}

void main ()
{
	spawn (&thread);
	Thread.sleep (3.seconds);
	writeln ("main ends");
	synchronized
	{
		end = true;
	}
}

or you could use the fact, that receiveTimeout throws an exception, when main ends (although I don't know if this is the intended behaviour; the manual just says that it throws an exception when the sending thread was terminated):

import std.stdio;
import std.concurrency;
import core.thread;

void thread ()
{
	for (;;)
	{
		try
		{
			receiveTimeout (500.msecs);
		}
		catch (Throwable)
		{
			break;
		}

	}
	writeln ("thread ends");
}

void main ()
{
	auto tid = spawn (&thread);
	Thread.sleep (3.seconds);
	writeln ("main ends");
}

On Tuesday, 27 October 2020 at 08:33:36 UTC, Johann Lermer wrote:
> or you could use the fact, that receiveTimeout throws an exception, when main ends (although I don't know if this is the intended behaviour; the manual just says that it throws an exception when the sending thread was terminated):

If you're receiving you can listen for an OwnerTerminated message.

bool shouldExit = receiveTimeout((-1).seconds,
    (OwnerTerminated o) {}
);

https://run.dlang.io/is/2t50yS

I want to use isDaemon to automatic stop worker thread if ownner thread is finished

On Tuesday, 27 October 2020 at 11:36:42 UTC, Marcone wrote:
> I want to use isDaemon to automatic stop worker thread if ownner thread is finished

Terminating threads without properly unwinding the stack is generally a very bad idea. Most importantly the destructors of stucts on the stack won't run which can cause problems like locks not being released.

This isn't specific to D either. For example Raymond Chen writes about the TerminateThread function in Windows here:
https://devblogs.microsoft.com/oldnewthing/20150814-00/?p=91811

You should signal the thread somehow that it's time to stop working

On Tuesday, 27 October 2020 at 12:16:01 UTC, Rene Zwanenburg wrote:
> On Tuesday, 27 October 2020 at 11:36:42 UTC, Marcone wrote:
>> I want to use isDaemon to automatic stop worker thread if ownner thread is finished
>
> Terminating threads without properly unwinding the stack is generally a very bad idea. Most importantly the destructors of stucts on the stack won't run which can cause problems like locks not being released.
>
> This isn't specific to D either. For example Raymond Chen writes about the TerminateThread function in Windows here:
> https://devblogs.microsoft.com/oldnewthing/20150814-00/?p=91811
>
> You should signal the thread somehow that it's time to stop working

isDaemon: A daemon thread is automatically terminated when all non-daemon threads have terminated.