Re: [Boost-users] interprocess_condition::wait(scoped_lock<interprocess_upgradable_lock> &) missing

Subject: Re: [Boost-users] interprocess_condition::wait(scoped_lock<interprocess_upgradable_lock> &) missing
From: John Ky (newhoggy_at_[hidden])
Date: 2011-02-03 22:30:23

Thanks Howard for the very well written response.  I appreciate the effort.

I will definitely look at this condition_variable_any class.  It is a good
design and I want to stay close to the standard as well.

Cheers,

-John

On 4 February 2011 13:05, Howard Hinnant <howard.hinnant_at_[hidden]> wrote:

> On Feb 3, 2011, at 8:14 PM, John Ky wrote:
>
> > It would be nice to have a condition_variable_any that supports any kind
> of lock.
> >
> > It's probably okay if there were a condition_variable_* class for each
> lock type as well.  Or did you mean something like
> condition_variable_any<Mutex>?
>
> A condition_variable_any<Mutex> is counter-productive.  What you really
> need is:
>
> class condition_variable_any
> {
> public:
>    condition_variable_any();
>    ~condition_variable_any();
>
>    condition_variable_any(const condition_variable_any&) = delete;
>    condition_variable_any& operator=(const condition_variable_any&) =
> delete;
>
>    void notify_one();
>    void notify_all();
>
>    template <class Lock>
>        void wait(Lock& lock);
>    template <class Lock, class Predicate>
>        void wait(Lock& lock, Predicate pred);
>
>    template <class Lock, class Clock, class Duration>
>        cv_status
>        wait_until(Lock& lock,
>                   const chrono::time_point<Clock, Duration>& abs_time);
>
>    template <class Lock, class Clock, class Duration, class Predicate>
>        bool
>        wait_until(Lock& lock,
>                   const chrono::time_point<Clock, Duration>& abs_time,
>                   Predicate pred);
>
>    template <class Lock, class Rep, class Period>
>        cv_status
>        wait_for(Lock& lock,
>                 const chrono::duration<Rep, Period>& rel_time);
>
>    template <class Lock, class Rep, class Period, class Predicate>
>        bool
>        wait_for(Lock& lock,
>                 const chrono::duration<Rep, Period>& rel_time,
>                 Predicate pred);
> };
>
> I.e. only the wait functions are templated on the lock.  This allows one cv
> to be waited on by two different kinds of locks at the same time.  For
> example one thread could wait on the thread with a shared_lock while another
> thread waited on the same cv with a unique_lock (but using the same
> underlying shared_mutex):
>
> shared_mutex mut;
> condition_variable_any cv;
>
> void wait_in_shared_ownership_mode()
> {
>    shared_lock<shared_mutex> shared_lk(mut);
>    // mut is now shared-locked
>    // ...
>    while (not_ready_for_shared_to_proceed())
>        cv.wait(shared_lk);  // shared-lock released while waiting
>    // mut is now shared-locked
>    // ...
> }   // mut is now unlocked
>
> void wait_in_unique_ownership_mode()
> {
>    unique_lock<shared_mutex> lk(mut);
>    // mut is now unique-locked
>    // ...
>    while (not_ready_for_unique_to_proceed())
>        cv.wait(lk);  // unique-lock released while waiting
>    // mut is now unique-locked
>    // ...
> }   // mut is now unlocked
>
> A third thread could change either the not_ready_for_shared_to_proceed
> predicate, the not_ready_for_unique_to_proceed predicate, or both, and then
> cv.notify_all().  This is very powerful stuff when you need it (most of the
> time condition_variable and mutex are all you need).
>
> In this set condition_variable_any and unique_lock are in C++0x.  I hope to
> propose shared_lock and shared_mutex for tr2 and ultimately c++1x.  Field
> experience here (good or bad) would help.  Here is a tutorial and
> implementation of the shared and upgrade mutexes and locks:
>
> http://home.roadrunner.com/~hinnant/mutexes/locking.html
>
> Here is an implementation of condition_variable_any:
>
> http://llvm.org/svn/llvm-project/libcxx/trunk/include/condition_variable
>
> -Howard
>
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