[M3devel] dynamic chose between user/kernel threads?

[Olaf Wagner]

If I remember correctly, until Antony Hosking provided the PThreads
implementation, M3 only used its own user-level threads on all
POSIX platforms (but not on Windows). The ability to use system
pthread libraries has been added rather late.

(M3's) user level threads are extremely fast and use little resources
(configurable stack sizes). External system threads have a little
more overhead due to the extra user/kernel mode switches for all
scheduling related activies. They have got the advantage that they
can be used for scaling across multiple processors (which wasn't
possible with M3 on Unix until recently).

I agree that these days kernel threads should be the default, as they
are available on almost every system and usually reasonably stable
and fast (which was not so when M3 was created). Nonetheless M3's
user level threads can have advantages for certain uses and should
not be discarded, as they have proven to be mature and useful.

Olaf
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