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Date: Mon, 27 Nov 2000 17:10:31 -0500
From: David Petrou <dpetrou@cs.cmu.edu>
To: freebsd-questions@freebsd.org, freebsd-hackers@freebsd.org
Subject: thread model questions
Message-ID: <20001127171031.D417@auchroisk.pdl.cs.cmu.edu>
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hi.  i've searched the handbook, tutorial, FAQ, and parts of the
mailing list archives but haven't found direct answers to the
following questions.  i hope you don't mind answering them for me; it
will save me a lot of time looking through the code, and / or writing
test cases:

let's say i'm running 4.x-stable.

1. if i use the pthreads interface, is each thread a process that
   happens to share the same addr space (like linux), or are all the
   threads part of the same single process (same PID)?

2. is the threading preemptive?  or do i have to explicitly yield?

3. if preemptive, does that occur at user-level, or by the kernel?
   (and how costly is it?)

4. if one thread makes a system call that could block for some time,
   will another thread be automatically chosen?  or will the whole
   collection of threads sleep until the call returns?

5. if i signal a particular thread, is the signal delivered to one
   thread or to all the threads in the process?

6. if a thread or process (terminology sucks) enters the kernel, can
   the scheduler preempt it and select another thread / process to
   run?  (q.v., what many people call having kernel threads.)  or will
   that process / thread dominate the system until it voluntarily
   relinquishes the processor?

7. are there other threads interfaces besides pthreads that i should
   be aware of?  what are the differences?  e.g., assuming freebsd
   supports a clone()-like interface, do some threads packages use it
   while others do as much as they can without kernel support?

i'm probably forgetting some questions, but these are the bulk.  i'm
just wondering what the current thread model is as i contemplate
moving my development to FreeBSD.

thanks,
david

p.s.: please include me in any responses as i'm not subscribed to
FreeBSD lists at the moment.


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