Windows: Does something temporarily grab the com ports on startup?

Posted by Tim on Stack Overflow See other posts from Stack Overflow or by Tim
Published on 2010-04-29T14:20:00Z Indexed on 2010/04/30 13:27 UTC
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c#

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wpf

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exception

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comports

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startup

I have a WPF/C# app that is launched as part of the "Startup" group on a Windows Embedded Standard machine. One of the first things the app does (in its static App() method) is create a new SerialPort object for COM1. COM1 is a hardwired serial port, not a USB virtual port or anything like that.

My problem is that every so often (maybe 1 out of 12) on startup, I get an exception: System.UnauthorizedAccessException: Access to the port 'COM1' is denied.

There are no other applications using this port. Also, when I relaunch the app following this error, it grabs the port just fine. It's as if the com port isn't ready/set up for my app sometimes.

I'm clueless on this one! Any insight is appreciated!

UPDATE: I added a call to SerialPort.GetPortNames() and printout all available ports before attempting to open the port. In the failure case COM1 is indeed THERE! So, it's not that the port isn't ready. It looks like something in Windows is actually grabbing the port temporarily and blocking me.

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