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Re^4: share socket connections amongst multiple threads?

by Elijah (Hermit)
on Jul 09, 2005 at 04:30 UTC ( #473640=note: print w/replies, xml ) Need Help??

in reply to Re^3: share socket connections amongst multiple threads?
in thread share socket connections amongst multiple threads?

It seems I have not been clear enough. When the server accept()'s a connection I add the connection id to a hash so I will have a list of connection id's. Now when any data from any connection comes into the server I need the server to turn around and send that data out to all connections. This does work somewhat but the problem is that when the first user connects the thread is spawned and only ever sees itself. When the second one connects the thread is spawned and the id is added to the hash along with the first and now the second sees itself and the first. The third connects and sees itself and 1 and 2. However 1 cannot see 2 or 3 and 2 cannot see 3. This is because I can not share this list/hash with each thread.
Does this give you a better idea of what I am talking about now?
  • Comment on Re^4: share socket connections amongst multiple threads?

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Re^5: share socket connections amongst multiple threads?
by BrowserUk (Patriarch) on Jul 09, 2005 at 05:04 UTC
    When the server accept()'s a connection I add the connection id to a hash ...

    What do you mean by "connection id"?

    My assumption is that you mean an IO::Socket::INET handle. This is a blessed ref:

    use IO::Socket::Inet;; $sock = IO::Socket::INET->new( PeerAddr => '', PeerPort => 'http(80)', Proto => 't +cp' );; print $sock;; IO::Socket::INET=GLOB(0x1a05ec0)

    which, for very good reason, you cannot put into a shared hash.

    Basically, the methods that are attached to a blessed object like IO::Socket::INET=GLOB(0x1a05ec0) are tied to the thread in which the object handle (a GLOB in this case) is instantiated. So, if you share that object with another thread and that other thread attempts to call a method upon it, it will try to invoke code from the other thread. That cannot work, which is why Perl stops you from trying to do that.

    There are two approached to solving this problem that I am aware of:

  • The first is "tried and tested", and is the method I described above. Each thread has a Thread::Queue associated with it and when it receives a message it posts a copy to each of the other threads and they send it to the client who's thread they are handling.

    This is easier to arrange by having a "controller" thread that also has a queue and each client forwards a copy of data it receives to the contoller via it's queue and it forwards it to each of the other clients.

  • The second is a little harder to explain, and whilst it has worked for me, is not (I believe) an officially sanctioned technique. That of re-blessing the handle into each thread that needs it.

    Again, this works best if a central controller thread is given access to handles from each of the client handles and it reblesses them. The clients would then forward their messages to the controller and it would forward them (directly) to the clients via the reblessed handles. This still leaves the problem of conveying those handles from the clients to the controller. Not insurmountable, but requires some jiggery pokery.

    All in all, the queues method is probably easier.

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