Clarification: Acquiring a mutex when a read write lock is held

Julian Elischer julian at
Wed Apr 22 15:05:28 UTC 2015

On 4/21/15 6:30 PM, Dheeraj Kandula wrote:
> Hey All,
>         Can you clarify the following
> I have a read write lock locked. Next I want to acquire a mutex when the
> read write lock is held. Is this allowed or not. As far as I can understand
> from the "FreeBSD Kernel Developers Handbook" this operation is allowed in
> FreeBSD9.0, 10.0 and further.
> But the read write lock cannot be held while sleeping. Doesn't this
> contradict the above statement, as a thread will go to sleep if can't
> acquire the mutex when another thread holds the mutex.
> Hence what sleep are we referring here. Is this sleep(unbounded sleep) or

look at

      man 9 locking

for an overview.

> the bounded sleep.
> Dheeraj
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