This will make easy to track compatibility with a certain DB structure across different flavors of YACReader. It will only change when the DB structure changes.
This member function does not affect the logical state of the class.
Making std::condition_variable and std::mutex data members mutable is
idiomatic as these classes are thread-safe synchronization primitives.
The C++ standard specifies `std::condition_variable::wait(lock, pred)`
as equivalent to `while (!pred()) wait(lock);`. It is implemented
exactly so in libstdc++, libc++ and MSVC.
This function is called only from ~ConcurrentQueue(). joinAll() is not
thread-safe and it cannot be called earlier without introducing a null
state. Moving the function's implementation into the definition of
~ConcurrentQueue() makes the code clearer. Removing joinAll() also
allows to establish and document invariants for two data members.
Assert consistency between jobsLeft and _queue in ~ConcurrentQueue().
ConcurrentQueue is currently used only by two classes and a test, but
modifying concurrent_queue.h requires recompiling 30 source files. None
of the member functions is so lightweight as to make it worth inlining.
An alternative to `@note ConcurrentQueue is unable to execute jobs if
@p threadCount == 0.` is `assert(threadCount != 0);`. But this would
force classes that contain a ConcurrentQueue data member to always start
a thread, even if they detect at runtime that they are never going to
enqueue a job.
Add Job type alias to avoid repeating the type.
Use default member initializers instead of the member initializer list
to make it clear [to the reader of the header] that no data member is
left uninitialized.
* threadCount argument: int => std::size_t to avoid implicit casting;
* eliminate temporary empty std::thread objects;
* replace a trivial lambda with a function pointer and its argument;
* get rid of the unused dedicated loop counter.
