It is very OS dependant. For example on Linux creating a new process is not more expensive that creating threads (after all internally creating process and thread is almost same thing for Linux). Nor it takes more memory because of copy on write. Perfomance is not necessary better with threads because they have overhead or synchronization and locking which separate processes do not have.

Add to this that some OS don't have good threads implementation yet (STABLE branch of FreeBSD comes to my mind) and Perl's support for them is still very experimental (even in 5.8.0).

--
Ilya Martynov, ilya@iponweb.net
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