This is the local socket for windows, analogous to AF_UNIX.
`Efl_Net_Socket_Windows` is the base class doing `ReadFile()` and
`WriteFile()` using overlapped I/O, as well as the close procedure
(`FlushFileBuffers()`, `DisconnectNamedPipe()` and
`CloseHandle()`). These are done on top of an existing HANDLE that is
set by `Efl_Net_Dialer_Windows` (from `CreateFile()`) or
`Efl_Net_Server_Windows` (from `CreateNamedPipe()`).
The overlapped I/O will return immediately, either with operation
completed or `ERROR_IO_PENDING`, which means the kernel will execute
that asynchronously and will later `SetEvent(overlapped.hEvent)` which
is an event we wait on our main loop. That `overlapped` handle must
exist during the call lifetime, thus cannot be bound to `pd`, as we
may call `CancelIo()` but there is no guarantee the memory won't be
touched, in that case we keep the overlapped around, but without an
associated object.
Windows provides no notification "can read without blocking" or
non-blocking calls that returns partial data. The way to go is to use
these overlapped I/O, with an initial `ReadFile()` to an internal
buffer, once that operation finishes, we callback the user to says
there is something to read (`efl_io_reader_can_read_set()`) and wait
until `efl_io_reader_read()` is called to consume the available data,
then `ReadFile()` is called again to read more data to the same
internal buffer.
Likewise, there is no "can write without blocking" or non-blocking
calls that sends only partial data. The way to go is to get user bytes
in `efl_io_writer_write()` and copy them in an internal buffer, then
call `WriteFile()` on that and inform the user nothing else can be
written until that operation completes
(`efl_io_writer_can_write_set()`).
This is cumbersome since we say we "sent" stuff when we actually
didn't, it's still in our internal buffer (`pd->send.bytes`), but
nonetheless the kernel and the other peer may be adding even more
buffers, in this case we need to do a best effort to get it
delivery. A particular case is troublesome: `write() -> close()`, this
may result in `WriteFile()` pending, in this case we wait using
`GetOverlappedResult()`, *this is nasty and may block*, but it's the
only way I see to cope with such common use case.
Other operations, like ongoing `ReadFile()` or `ConnectNamedPipe()`
will be canceled using `CancelIo()`.
Q: Why no I/O Completion Port (IOCP) was used? Why no
CreateThreadpoolIo()? These perform much better!
A: These will call back from secondary threads, but in EFL we must
report back to the user in order to process incoming data or get
more data to send. That is, we serialize everything to the main
thread, making it impossible to use the benefits of IOCP and
similar such as CreateThreadpoolIo(). Since we'd need to wakeup the
main thread anyways, using `OVERLAPPED.hEvent` with
`ecore_main_win32_handler_add()` does the job as we expect.
Thanks to Vincent Torri (vtorri) for his help getting this code done
with an example on how to do the NamedPipe handling on Windows.
Vincent Torri
Mike Blumenkrantz
Cedric Bail
Carsten Haitzler
Gustavo Sverzut Barbieri