CODEWITHSUNDEEP
c++windowsserial-portusb
Martze
Martze

Reputation: 921

Modify time until DBT_DEVICEREMOVECOMPLETE is sent

Is there a way to trigger the USB Device Discovery of Windows, such that removed devices are detected faster?

I have a USB Serial modem that I unplug (the USB plug, not the serial one). I want to detect the DBT_DEVICEREMOVECOMPLETE event which is sent as soon as the unplugging is detected (That's what I assume). The detection of the Event works as desired, it is sent sometimes 1s after removal, sometimes several minutes after removal.

Is there a way to decrease the refresh interval, or another way to make this event getting sent faster?

Upvotes: 0

Views: 198

Answers (1)

srdjan.veljkovic
srdjan.veljkovic

Reputation: 2548

Well, the problem here is that DBT_DEVICEREMOVECOMPLETE is sent after Windows decides it has detected the removal, and you can't influence that, at least not in the general case. There are various things that make Windows do this faster or slower (type of device, current "data flow" with the device, the device itself), and it also varies between OS versions. What I found helps to some degree in some of cases is to remove, from the Registry, references to USB devices that were plugged into that USB port before (there are various utilities for this).

At the extreme, since this is a Windows Broadcast message (non-queued), there will not be another one sent in until the previous is processed. Thus, you may not receive it at all! To solve that, keep message handling fast and simple and don't set a breakpoint there while debugging.

Also, having a separate Windows and Thread for the specific purpose of handling USB device arrival/removal notifications may help.

But, from my experience, polling will not help, as the main problems seems to be in the criteria Windows uses to detect the removal. The time from that event until you receive the message is small. Of course, in your case this may not be true - to find out, use a tool like SysInternals Process Monitor. Depending on what you see going on there, there may be something you can do to make it faster.

Upvotes: 1

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