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Re: Seeking Thread join / waitpid equivalent.



I have just found this rather ugly code in the tftp_server.c


So it kills the tftp server thread...
       cyg_thread_kill(server->thread_handle);

whangs the priority of the thread it killed as high as possible.
       cyg_thread_set_priority(server->thread_handle, 0);

Waits a random period for it to die
        cyg_thread_delay(1);  // Make sure it gets to die...

Deletes the thread...
        if (cyg_thread_delete(server->thread_handle)) {

If deleting the thread actually worked...

            // Success shutting down the thread
Frees the memory associated with the thread..
            free(server);  // Give up memory
            return 1;
        }
Else ... we have a memory leak.

See why I'm looking for a cleaner way to do this?


On Fri, 27 Aug 2004, John Carter wrote:



Yes and no. What the guy was trying to do via a thread destructor would have been much more simply achieved via a thread.join in a reaper thread.

thread_join(thread);
cyg_thread_delete(thread.handle);
free(thread.stack);

	void
	thread_entry_function(cyg_addrword_t data)
	{
	    struct myThreadType *thread = (struct myThreadType*)data;
	    (*thread->entry_function)(thread->data);
	    cyg_semaphore_post(&thread->death_semaphore);
	}


	void
	thread_join(struct myThreadType *thread)
	{
	    cyg_semaphore_wait(&thread->death_semaphore);
	}



So if you are doing something like..

thread_join(  &thread);
cyg_thread_delete( thread.handle);

unless the thread doing the join is of lower priority than the
exiting thread there exists a narrow gap between the post and the end
of cyg_thread_exit during which cyg_thread_delete can fail.

ie. Fundamentally _any_ userland fix to this problem is not going to
work.

The only hack I can think of is to use something like your thread
join, do the delete, test the result, if it failed sleep for a period,
repeat with exponential fall off on the sleep period.

Ugly ugly ugly.





John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

The universe is absolutely plastered with the dashed lines exactly one
space long.




John Carter Phone : (64)(3) 358 6639 Tait Electronics Fax : (64)(3) 359 4632 PO Box 1645 Christchurch Email : john.carter@tait.co.nz New Zealand

The universe is absolutely plastered with the dashed lines exactly one
space long.

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