Windows 95 LPT Contention Handler

The role of the Windows 95 LPT contention handler (VPD) is to manage contention for LPT ports by VMs.

A VM is automatically granted port access if the port is not currently owned by another VM or VxD.

If there is a VxD owner, VPD sends it RESOURCE_STEAL_REQUEST. If this request succeeds, the port is assigned to the VM. Otherwise, the request fails and is reported to the user with a dialog message.

When a VxD or another VM attempts to steal a VM-owned port, VPD responds as follows:

• Warn: VPD displays a dialog box asking if the port should be assigned to the requesting VxD or VM.
• Fail: If the request is made by a VM, port access is silently trapped. If the request is made by a VxD, the acquire or steal call fails.
• Idle: The port is reassigned automatically if the port has been idle longer for a time-out period specified in Control Panel. Otherwise, the acquire/release request fails for a VxD, or port access is silently trapped for a VM. This is the default setting, with a default time-out period of 2 seconds.