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Date: Fri, 20 Feb 2004 10:02:01 -0500 (EST)
From: Daniel Eischen <eischen@vigrid.com>
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To: Dag-Erling =?iso-8859-1?q?Sm=F8rgrav?= <des@des.no>
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Subject: Re: cross-thread locking
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On Fri, 20 Feb 2004, Dag-Erling [iso-8859-1] Sm=F8rgrav wrote:

> - What happens when a thread locks a mutex and then starts another
>   thread?  Does the new thread in any way inherit the lock, or will it
>   have to acquire its own?

No, it doesn't inherit any locks.

> - What about spin locks?  Are there any semantic differences between
>   mutexes and spin locks in POSIX, or are spin locks simply mutexes
>   that spin instead of sleeping?

POSIX differentiates between spinlocks and mutexes, and that is
why there is a pthread_spinlock_t instead of using pthread_mutex_t
for both lock operations.  I believe the implementation is allowed
to spin indefinitely or schedule another thread if the lock is
busy.

I can't find a rationale for spinlocks; I _thought_ there was
one in some draft of the spec that I had read.  I wouldn't
really advocate using spinlocks due to possible priority
inversion problems and wasting cycles.

--=20
Dan Eischen