Turns out that one of our WorkQueue integration tests was relying on the
incorrect runFor() behavior that we just fixed, so the test broke. Now that
runFor() doesn't wait around for work to be posted, use an explicit wait loop
instead.
To support this, add LLCond::get(functor), where functor must accept a const
reference to the stored data. This new get() returns whatever the functor
returns, allowing a caller to peek at the stored data.
Also use universal references for all remaining LLCond functor arguments.
Its previous behavior, returning a const reference without locking, was wrong:
it could return a reference to an object in an inconsistent state if it was
concurrently being modified on another thread.
Locking the mutex and returning a copy by value is the correct behavior.
Specifically:
LLCoros::Mutex means boost::fibers::mutex
LLCoros::LockType means std::unique_lock<boost::fibers::mutex>
LLCoros::ConditionVariable means boost::fibers::condition_variable
LLCoros::cv_status means boost::fibers::cv_status
So as not to drag in all of boost::fibers::mutex.hpp or condition_variable.hpp
for each consumer of llcoros.h, instead #define LLCOROS_MUTEX_HEADER and
LLCOROS_CONDVAR_HEADER. Those who need them can #include the relevant macro.
Update llcond.h and llthreadsafequeue.h accordingly.
Nat Goodspeed