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<P ALIGN=CENTER><EM>Posted by <STRONG><A HREF="mailto:kraus@proxima.de">J黵gen Kraus</A></STRONG> on <STRONG>4/24/98 11:39a.m.</STRONG>, in response to <A HREF="read.cgi-read=10301.htm" tppabs="http://www.codeguru.com/mfc_bbs/read.cgi?read=10301">Serial Port Programming Questions</A>, posted by D.Lewis on 4/24/98 4:39a.m.</EM></P>
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<P>Oops, that's a bunch of questions ... ;-)
<P>Well, let's have a look at them:
<P>>Is overlapped I/O (FILE_FLAG_OVERLAPPED) required for serial port programming?
<BR>>If not, what are the benfits of using it?
<P>It is not required, but very useful, as non-overlapped I/O is basically blocking the calling thread... and serial timeouts can be long...
<P>>If non-overlapped I?O is used, what happens if a thread is trying to read the >comm device while another trhead is trying to write to it?
<P>I just can guess, because I always ensure to avoid this by using synchronisation mechanisms as e.g. critical sections, but it'll give you something like 'ERROR_ACCESS_DENIED'
<P>>IWhat is the benefit of using a thread versus a timer event if all that is >required is to read the serial port device?
<P>Hmm, i think you mean something like 'polling' when you mention timers, and that's from the stone age of computing... by using a thread, you can wait for I/O completion not eating CPU time
<P>>How can the thread that is reading datat from the serial port communicate and >synchronize with the main process?
<BR>>Is global data available to both the main process and the thread?
<BR>They can use a shared buffer (synchronize access to it!). Threads run in the same address space as the process (= thread) that created them. Thus all process-global data is available to all threads.
<P>>Is data local to the thread available to the main process?
<BR>Definitely no.
<P>>What is the best way to share memory between a thread and the main process?
<BR>see above...
<P>Hope this helps,
<P>J黵gen
<P>
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