issue with ServerSocket::accept

Fri May 14 20:18:00 GMT 2004

Bryce McKinlay wrote:
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>>> Well maybe accept doesn't return when the socket is closed. Perhaps 
>> each thread entering ServerSocket.accept() should put itself on a 
>> list of blocked acceptors. Then when close() is called each thread 
>> on the list is interrupted...
>>>> The threads would have to synchronize when adding themselves to the 
> list. Are multiple threads allowed to call accept() on the same 
> socket? If that is not valid, then the implementation ought to be 
> pretty simple - we can just add a thread field to each socket. We just 
> have to watch out for race conditions in the signaling mechanism.
>It is my understanding that multiple threads can be in accept() on the 
same socket. When a connection arrives, the OS chooses one of waiting 
threads and its accept() returns. That is not to say that it is 
necessarily a good idea, but I think it is legal.
The accepting thread synchronizes on putting itself on the list and 
taking itself off after the accept(2) returns. The closing thread does 
the close(2) and interrupting the accepting threads in a block 
synchronized on the same list.
By the time that the accepting thread leaves the synchronized block 
taking itself off the list, it will either have succeeded or been 
interrupted. But it will never have been interrupted after leaving the 
second synchronized block.
At least that's how I see it.
David Daney