Re: [Boost-users] [Thread] why isn't it possible to acquire 2 different upgrade_lock from 2 different threads?

Subject: Re: [Boost-users] [Thread] why isn't it possible to acquire 2 different upgrade_lock from 2 different threads?
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2014-03-27 11:39:23

AMDG

On 03/27/2014 01:21 AM, Elad Moshe wrote:
> Hi,
> this is my first post here so please bare with me :) .
> I recently used upgrade_lock to try access a shared resource from 2
> different threads.
> I noticed that once the first thread acquired its upgrade_lock the second
> thread was blacked
> until the first thread unlock it.
> can someone please explain me the logic behind this behavior?
> isn't an upgrade lock just a shared_lock that can be upgraded to
> unique_lock?
> why not let both threads acquire it just like shared_lock until, and if,
> they decide to upgrade it to unique_lock?
> 

If both threads tried to upgrade, you would have a deadlock.

In Christ,
Steven Watanabe