Fwd: Re: [Jython-users] Multiple instances of embedded Jython Interpreter

[Ype K. <yk...@xs...>]

My reply to Adrian:

>Date: Tue, 26 Jun 2001 13:58:19 +0100
>To: "Adrian St. John" <as...@pa...>
>From: Ype Kingma <yk...@xs...>
>Subject: Re: [Jython-users] Multiple instances of embedded Jython Interpreter
>Cc:
>Bcc:
>X-Attachments:
>
>Adrian,
>
>you wrote:
>>Hi,
>>
>>Does anyone know how difficult it is to get multiple embedded Jython
>>interpreters running in the same Java process in separate threads?
>
>It's easy, you can do it from jython and from java, your choice.
>
>>I'm writing a multi-user game engine using Jython as the interactive
>>programming environment. Each interpreter instance has its stdout/stderr
>>redirected to a network connection.
>>
>>The problems I seem to have are:
>>
>>stdout/stderr for all instances get redirected to the last one set.
>
>Stdout/stderr are 'one per process'. You'll have to use your own
>output functions (or methods) in your threads. You can use
>the thread identity provided by Jython to select a network
>connection in your output functions.
>
>You could even replace
>sys.stdout and sys.stderr by objects doing precisely that,
>(make sure to synchronize though, see below).
>Have a look at console.py in the jython distribution for
>an example of stream redirection.
>
>Of the top of my head:
>
>import thread
>
>def threadIdentity():
>    return thread.currentThread() # or something like this, see the python docs.
>
>import threading
>
>class OutputRedirectByThread:
>     def __init__(self):
>          self.networkStreamByThread = {}
>          self.sema = threading.semaphore() # might not be needed
>
>     def startRedirectingThreadOutput(networkOutputStream):
>          self.networkStreamdByThread[threadIdentity()] = networkOutputStream
>
>     def write(self, s):
>          self.sema.acquire()
>          try: self.networkStreamByThread[threadIdentity()].write(s)
>          finally: self.sema.release()
>
>     def flush(self):
>          self.sema.acquire()
>          try: self.networkStreamByThread[threadIdentity()].flush()
>          finally: self.sema.release()
>
>Create an object of this class, use it to replace sys.stdout and/or
>sys.stderr, and call startRedirectingThreadOutput() just before invoking
>the interpreter in the thread.
>
>Also you'll probably need stdin from the network connection too,
>so a more elaborate design with stdin/stdout/stderr per thread
>might be better.
>
>>If I try to 'set' a variable in one interpreter from another, the
>>variable gets lost.
>
>Variables in module scope are 'one per process', because modules
>are 'one per process'. If you change these, the changes are visible
>in other threads. You'll probably need the threading module
>to synchronize access to these.
>Local function variables are 'one per thread', and invisible to
>other threads.
>
>>Thanks in advance,
>
>My pleasure,
>
>Ype Kingma