The motivating use case is being able to "time out" certain operations
(by adding a timed callback which will force the termination of the
loop), but the design is flexible enough to accomodate other use cases
as well (e.g. running a periodic task in the background).
The implementation builds on the existing "pending callback" mechanism,
by associating a time point with each callback -- every time the loop
wakes up, it runs all of the callbacks which are past their point, and
it also makes sure to sleep only until the next callback is scheduled to
run.
I've done some renaming as names like "TriggerPendingCallbacks" were no
longer accurate -- the function may no longer cause any callbacks to be
called (it may just cause the main loop thread to recalculate the time
it wants to sleep).
This will be used as a replacement for selecting over a pipe fd, which
does not work on windows. The posix implementation still uses a pipe
under the hood, while the windows version uses windows event handles.
The idea is that, instead of writing to a pipe, one just inserts a
callback, which does whatever you wanted to do after the bytes come out
the read end of the pipe.
Differential Revision: https://reviews.llvm.org/D131160
This patch switches the MainLoop class to use the WSAEventSelect
mechanism to wait for multiple sockets to become readable. The
motivation for doing that is that this allows us to wait for other kinds
of events as well (as long as they can be converted to WSAEvents). This
will allow us to avoid (abstract away) pipe-based multiplexing
mechanisms in the generic code, since pipes cannot be combined with
sockets on windows.
Since the windows implementation will now look completely different than
the posix (file descriptor-based) implementations, I have split the
MainLoop class into two (MainLoopPosix and MainLoopWindows), with the
common code going into MainLoopBase.
Differential Revision: https://reviews.llvm.org/D131159
