Redesign TIdTCPClient connect with timeout without extra thread...

[gec75]

I have an application where I need a very short connect timeout.
Then I just saw that Indy starts a new thread for this connect ...!?
I took the time to implement a version based on non blocking connect and select... see attached patch.
The idea is to split TIdSocketHandle.Connect into GStack.Connect (which starts an non-blocking connect) and later UpdateBinding.
The code in TIdIOHandlerStack.ConnectClient just starts connect then waits with select (write) and then decides to UpdateBinding or raise exception.
I also added the TIdSocketListWindows.SelectWrite... why was it not yet included??
It's just a prof of concept code, no AntiFreeze and no posix variant.

indy_asyc_connect.patch

[rlebeau]

Duplicate of #3

I have added your patch to that ticket so it is not lost. Might get some useful tidbits from it.

I already have some code written for this feature (ultimately using a non-blocking connect() and handling the timeout via select()/epoll(), similarly to how you suggest, but taking a very different approach to the implementation to lessen changes to the existing interface). That code hasn't been finished or even checked in yet.

Also, not every platform supports non-blocking sockets to begin with, so the connect thread can't be eliminated completely, but certainly avoided whenever possible. The code I have queries the stack if non-blocking is supported, and if so then does the non-blocking connect(), otherwise uses the connect thread as before.