[boost] [thread] Request review of new synchronisation object, boost::permit<>

Subject: [boost] [thread] Request review of new synchronisation object, boost::permit<>
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2014-05-03 17:13:31

Dear Boost,

Review and commentary upon a proposed new Boost object, 
boost::permit<> is invited. A quick description of their purpose:

"Permits come in two variants, consuming and non-consuming. There is 
always a one-to-one relationship between the granting of a permit and 
the receiving of that permit, the only difference with the 
non-consuming variant is that the permit is automatically regranted 
as soon as it is consumed. This leads to the only API difference to 
condition variables: permit<consuming=true> provides notify_one() but 
not notify_all(), whilst permit<consuming=false> provides neither and 
you will have to use grant() and revoke() instead. When deciding to 
substitute permits for condition variables, you will need to decide 
carefully which kind of permit is the correct substitute."

"Permit objects are actually very similar to a void promise/future 
i.e. they act as a reusable promise/future pair but without 
transporting any value or exception state, just the permission to 
proceed. This is due to their original design intention, which was as 
a promise/future equivalent for C11 (see below for their history, and 
note that the original C API is available in the boost::c_permit 
namespace and documentation can be found at 
https://ci.nedprod.com/job/Boost.Thread%20Build%20Documentation/lastSu
ccessfulBuild/artifact/boost-trunk/boost/thread/permit/latex/pthread_p
ermit_reference.pdf). As such, they can be very useful for situations 
where a promise/future is too heavy (permits can spin instead of 
sleep, plus they need not be repeatedly constructed and destructed)."

There is lots more detail at their documentation page: 
https://ci.nedprod.com/job/Boost.Thread%20Build%20Documentation/Boost.
Thread_Documentation/libs/thread/doc/html/thread/synchronization/permi
t_ref.html

Source code of Permit containing fork of Boost.Thread:

https://github.com/ned14/thread/tree/permit_object

They come with a functional and load soak test suite. They work on 
Windows, Linux, FreeBSD and I believe OS X.

Any other questions do ask.

Niall

-- 
Currently unemployed and looking for work in Ireland.
Work Portfolio: http://careers.stackoverflow.com/nialldouglas/