UNIX Sockets, unlink() and accept()

I am using UNIX sockets for some interprocess communication. I have a
thread in the server blocking on accept().

What I wanted to do was to be able, from another thread (perhaps even
another process) to tell the server to cleanly terminate. I was
figuring that I could do this by unlink()ing the socket; I figured that
this would cause accept() to terminate with an error.

However, this is not the case; apparently, since the server still has
the open socket to the inode, the inode is not cleaned up and the server
continues to wait. Thus, the blocked thread will block forever (until I
Ctrl-C it).

Is there a better way to do this?

If it happens to matter, I am using Linux 2.4.x.

Russ Lewis

Russ Lewis <spamhole-2001-07-(E-Mail Removed)> wrote in message news:<I_BWa.278$(E-Mail Removed)>...
> I am using UNIX sockets for some interprocess communication. I have a
> thread in the server blocking on accept().
>
> What I wanted to do was to be able, from another thread (perhaps even
> another process) to tell the server to cleanly terminate. I was
> figuring that I could do this by unlink()ing the socket; I figured that
> this would cause accept() to terminate with an error.
>
> However, this is not the case; apparently, since the server still has
> the open socket to the inode, the inode is not cleaned up and the server
> continues to wait. Thus, the blocked thread will block forever (until I
> Ctrl-C it).
>
> Is there a better way to do this?
>
> If it happens to matter, I am using Linux 2.4.x.
>
> Russ Lewis


Correct; according to the man page, the socket remains open and
available for use until the last process using it closes it.

Solution: write a signal handler for either HUP or USR1 to close the
socket and terminate. Install the signal handler after you create the
socket, then send that signal to the process/thread to cleanly
terminate. The signal handler will be executed even if the process is
blocking on read.

man setsigaction for more info.

-t.