It's not the way VNC hooks itself to the video driver, it's the way VNC responds to the Service Control Manager's SERVICE_CONTROL_SHUTDOWN message - in that we don't. VNC (correctly) dies as soon as the service shutdown message is given. But there's a difference between stopping and shutting down, and we can leverage that to try and remedy this issue.
Here's the relevant bits from the VNCService.cpp file: 1019 case SERVICE_CONTROL_STOP: 1020 // STOP : The service must stop 1021 g_srvstatus.dwCurrentState = SERVICE_STOP_PENDING; 1022 ServiceStop(); 1023 break; And we do not assert that we are interested in SERVICE_ACCEPT_SHUTDOWN in the next function: 1052 g_srvstatus.dwControlsAccepted = SERVICE_ACCEPT_STOP; Remedies? VNC must tell the SCM that it is interested in SERVICE_ACCEPT_SHUTDOWN. This will postpone VNC's exit until after the services that do not assert this flag, but since VNC has no other service dependencies, it will be asked to go down as soon as the other services handlers have been called. We simply ignore the message and set a dwWaitHint of five seconds and keep the dwCheckpoint flag incrementing to ensure that we are not killed. To ensure that the box goes down fairly promptly, VNC must watch if another process (best bet: csrss.exe) from the current desktop dies, or hook into the desktop logoff sequence. Once the trigger has been given, it's time to go down. And we need a watchdog - if the shutdown hasn't occurred in say 20 seconds (roughly the time the NT lets services live for without killing them), VNC re-enters the land of the living by completely ignoring the SERVICE_CONTROL_SHUTDOWN message. This makes the VNC process unkillable if it survives the SCM trying to kill it, and it's the bane of all system administrators everywhere. A potential problem is if the solution gets too complex. The more complex it is to cover off all the corner situations, the harder it'll be to make it reliable and robust. Andrew -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Keith Hall Sent: Wednesday, 6 March 2002 8:14 PM To: '[EMAIL PROTECTED]' Subject: RE: shutdown gotcha with Win32 host [snip] Naturally it would be nice for someone to have a real good think about the way VNC hooks into the display driver (reason I've been told that it can't be done easily) and ensure that it cannot be shut down until almost the last thing before reboot. --------------------------------------------------------------------- To unsubscribe, mail [EMAIL PROTECTED] with the line: 'unsubscribe vnc-list' in the message BODY See also: http://www.uk.research.att.com/vnc/intouch.html ---------------------------------------------------------------------
