Re: [Boost-bugs] [Boost C++ Libraries] #5516: Upgrade lock is not acquired when previous upgrade lock releases if another read lock is present

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #5516: Upgrade lock is not acquired when previous upgrade lock releases if another read lock is present
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-12-09 18:04:16

#5516: Upgrade lock is not acquired when previous upgrade lock releases if another
read lock is present
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  Reporter:  fred@…                 |       Owner:  viboes  
      Type:  Support Requests       |      Status:  assigned
 Milestone:  To Be Determined       |   Component:  thread  
   Version:  Boost 1.42.0           |    Severity:  Problem 
Resolution:                         |    Keywords:          
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Comment (by viboes):

 Coming back to you example

 m1 - Trying to take an shared lock
 m1 - Took a shared lock
 m2 - Trying to take an upgradable lock
 m2 - Took an upgradable lock
 m3 - Trying to take an upgradable lock
 m2 - Released an upgradable lock
 m3 - Took an upgradable lock
 m3 - Releasing locks
 m1 - Released the lock


 Whether these sequence appear before or after in the trace are irrelevant.

 m3 - Took an upgradable lock
 m3 - Releasing locks

 m1 - Released the lock

 It is up to the scheduler to execute m1 or m3, as both are active threads,
 no one is blocking for the other. Note that m1 had already a shared lock,
 so it can continue to be executed independently of whether m3 takes the
 upgrade lock.

 The following sequence could also be possible

 m3 - Took an upgradable lock
 m1 - Released the lock
 m3 - Releasing locks

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5516#comment:6>
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