[Haskell-cafe] Concurrency best practices?

Jesper Louis Andersen jesper.louis.andersen at gmail.com
Sat Feb 5 13:56:50 CET 2011

On Sat, Feb 5, 2011 at 10:46, wren ng thornton <wren at freegeek.org> wrote:

> Sometimes I need those threads to do some IO like printing logging info.

Logging is easy, especially if you don't mind a performance hit.
Create an STM.TChan and throw each log message on it. Have a separate
forkIO'ed process that reads off log messages and prints them. The
model one step up is to generalize the logger so it forwards log
messages to handlers. This way you can do logging to stdout, binary
serialized logging to disk, logging to memory ring buffers, logging to
databases and so on. This generalized model is used a lot in Erlang.

The price however, is that you may be running into a bottleneck upon
entering messages on the TChan because sadly I can't remember if it is
asynchronous or synchronous when you add messages to it. It won't work
for general IO either (Though perhaps it is a Writer monad).


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