Commit 1f11959 allowed modifying the "quit" attribute from any thread,
and thus the assertion may fail spuriously. This assertion is too
strict for the relaxed use of "quit". Let's remove it and move the
"quit" check to before the SockedMonitor::Dispatch() call.
Simply set the "quit" flag and wake up the thread. This works even if
we're inside this thread. Setting "quit" to a new value without mutex
protection is usually not safe, but good enough here.
Instead of creating a new eventfd for each DeferredMonitor instance,
reuse EventLoop's eventfd, and add a std::list to EventLoop that
manages the list of pending DeferredMonitors. This std::list is
protected by the same mutex as the "calls" list.
The bottom line is: reduced overhead because the per-instance eventfd
was eliminated, slightly added overhead due to Mutex usage (but
negligible), and we're thread-safe now.
This subsystem is now good enough to replace EventLoop::AddCall().
This change adds two configuration options:
--with-eventloop=[glib|internal|auto]
--with-pollmethod=[epoll|auto]
First allows switching between GLib event loop and internal one.
Second chooses backend to use for internal event loop.
Conditional compilation symbols are changed accordingly.
Additional helper macro MPD_OPTIONAL_FUNC_NODEF is added as well.
