Threading Pool Event()

[Cliff Wells]

On Fri, 2003-07-18 at 18:29, Graeme Matthew wrote:
> ok still a bit confused sorry .... first attempt at a thread pool
> 
> Am I correct in saying that each thread runs in a continious loop

Yes.

> each thread calls queue.get. The get method will block and not return
> anything until an item is placed into it. When an item is placed into
> it, one of the threads will get assinged a job i.e the first one that
> happens to be in use during the cycle ?

I think you have the idea, but I'm not sure (your terminology escapes me
a bit toward the end).  What happens is each thread blocks waiting for
something to be placed on the queue.  When something is put on the
queue, one of the available threads (i.e. one that is blocking on
queue.get() rather than processing a job).  Only a single thread will be
woken for each item that is put on the queue.  It isn't knowable which
thread that will be.

> The job is returned to the thread, it runs with the job and does all
> the processing then returns and calls queue.get again and waits for a
> job to become available ?

Yes.

> When placing a job via Queue.put() one must acquire a lock place it
> and then release it

No.  The locking semantics are internal to the Queue object.  Do not
concern yourself with it.  It simply works.  Do not attempt to put locks
around it.

> Am i aslo correct in saying that queue is actually doing the blocking
> and controls which thread gets the job ?

In a sense (that is, for practical purposes).  How it is done internally
by the interpreter isn't important.

> Lastly, sorry for all the questions, surely the CPU usage is the same
> when the queue is waiting for jobs and when the threads are polling as
> theyre all in one process anyway

The threads are asleep while waiting.  They don't consume any CPU.  The
queue doesn't "wait" for jobs (that is, it doesn't loop, poll or
otherwise consume any CPU time), when you call queue.put() it is a
method call on an object, not a thread.

> Am i getting this or am i way off :-)

Just a little way off ;)

Regards,

Cliff

-- 
My only regret is that I ever was born
                               -Swans