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Subject: Interference between instances on MS-Windows
Date: Thu, 5 Jul 2007 10:10:36 -0400
Message-ID: <FF8482A96323694490C194BABEAC24A0012364D9@Email.cbord.com>
From: "Bob McConnell" <rvm AT CBORD DOT com>
To: <cygwin AT cygwin DOT com>
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Good morning,

I have a POS emulation program written in C. It uses two threads, two
condition variables and a mutex. One thread receives from a serial port,
the other sends. The condition variables and mutex are used to create a
message queue between the two threads to pass received ACK/NAK to the
sending thread with an adjustable timeout (using code from somebody's
ex2.c I got via Google). Outgoing messages are read from a file and
responses are written into a second file. Outgoing messages average 54
bytes with 39 byte responses.

This program will send 2000 transactions in about 12 minutes at 9600
bps. This is what I normally expect. However, if I open a second
instance of bash, then run this program in both shells driving two
serial ports, it takes 24 minutes for them both to send the same 2000
transactions. I expected them to complete in the same 12 minutes. It is
as if there is some resource limitation that only one process can run at
a time. The only external resource they share is the input file which
they both open read-only.

Is this a known issue? Is there any way to prevent the two instances
from interfering with each other?

  CYGWIN_NT-5.0 1.5.24(0.156/4/2) 2007-01-31 10:57
  Win2K SP4
  P4 3.0GHz, 1 GB RAM

Thank you,

Bob McConnell
Principal Communications Programmer
The CBORD Group, Inc.
61 Brown Road
Ithaca NY, 14850
Phone 607 257-2410
FAX 607 257-1902
Email rvm AT cbord DOT com
Web www.cbord.com

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