Allow sockets and other handles to be conditionally driven by an I/O notifier.

[lithdew]

This is just an idea so far, though the idea is that for each exposed syscall (e.g. read()), there would be two variants: Socket.read(buf: []u8) !usize, and Socket.readAsync(buf: []u8) callconv(.Async) !usize.

Another method would be exposed, which is Socket.wait(.{ .read = ?, .write = ? }) callconv(.Async) void which allows users to manually await until a read/write-readiness notification is provided by an I/O notifier for a given file handle.

Calling Socket.read(...) will return immediately if the syscall cannot immediately be completed, and thus may be driven by Socket.wait(.{ .read = true }). Calling Socket.readAsync(...) will automatically retry the syscall, which is done by awaiting for readiness notifications from an I/O notifier via Socket.wait(.{ .read = true }).

Exposing these two variants also allows for Socket's in pike to be used in blocking mode (e.g. read() / write() may be called directly, blocking the current thread until said read() / write() is completed).