Re: Thread Pool versus Dedicated Threads

James Kanze <>
Thu, 14 Aug 2008 01:20:17 -0700 (PDT)
On Aug 14, 8:20 am, ??? <> wrote:

Recently I had a new coworker. There is some dispute between us.

The last company he worked for has a special networking
programming model. They split the business logic into
different modules, and have a dedicated thread for the each
module. Modules exchanged info through a in-memory message

In my opinion, such a model means very complicated
asynchronous interaction between module.

If there's common data, there's always a more or less
complicated asynchronous interaction between modules. The
dedicated thread model normally reduces the "common data" to
just the message queue, which makes things significantly

A simple function call between modules would require a timer
to avoid waiting for answer forever. And if a module was
blocked by IO (such as db query), other modules depends on
would have to wait for it.

Yup. That's the downside. The single, dedicated thread is (or
can be) a bottleneck. Of course, such bottlenecks can occur
anyway; if your manipulating a shared resource, for example,
which needs locking.

For example, if module A want to query db, it would

1. save states in a list
2 .sending a message to db-adapter module (a thread dedicated for db
3. start a timer
4. if response message arrived on time, retrieve states from the
list, and go on
5. if timer fires, log an error message and cancel the operation ??
send an error notify to user??

I'd put the time-out in the DB adapter module. Other than this:
what's the difference between putting the request in a single
block and posting it to the message queue, and passing the
information as arguments to a function?

My new coworker had written 300,000 lines of code in this
model and claimed this is the most simple way to write a
network application. He said we could implement a message
queue in half-a day and message would make interface much more

It's typically easier to get the code right using the message
queue, but it's not a silver bullet. You can still end up with
deadlocks. But you're much less likely to have problems due to
two threads accessing the same data without sufficient

I think if module interact with each other through function
calls and a thread/process pool model would be more easier, in
which each thread/ process has no dedicated job but handle
whatever the master thread give it.

A "thread/process pool model" doesn't mean anything. I'm not
sure what real alternative you're suggesting. Most places I've
worked at use a thread per client connection; on receiving a
request, the thread either grabs whatever locks it needs and
does the work, or forwards it to the dedicated thread (which
then doesn't need any locks, because it is the only thread which
accesses the information). Both models work. Which one is
better depends on the application.

James Kanze (GABI Software)
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