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I have to concurrently run TCL and Python scripts which access the same files. I have decided to restrict each program so that they have exclusive write access to exactly one file. Each program has read access to all files (say two programs and two files). I don't care about dirty reads (ie reading a partially finished write). I just want to know what will happen in the following two cases:

  1. a programs tries to open a file for writing when another program has it open for reading.

  2. a program tries to open a file for reading while another program has it open for writing.

I guess I am concerned that the write will fail if the other program has the file open (even if it is only open in read mode). I am running in windows with a single Python thread and a TCL program called from Python on subprocess.

Donal Fellows
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user442920
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    Quoting [this answer](http://stackoverflow.com/a/2751750/1595865): "Some filesystems (e.g. NTFS) allow the level of locking to be specified, to allow for example concurrent readers, but no writers" – loopbackbee Oct 21 '13 at 15:16
  • Thanks goncalopp. I tested it and it looks like python will write when TCL is open for reading. Now I will test the other ways. Okay, tested both ways and TCL can write when python is open for reading. Reads don't work when Python has the file open for writing. This is fine. – user442920 Oct 21 '13 at 15:31
  • That's great! If you have the time, consider documenting your findings in an answer, so other people can benefit from them – loopbackbee Oct 21 '13 at 16:12

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I tested writes and reads with Python and TCL and it looks like python will write when TCL has a file open for reading. TCL can write when python has a file open for reading.

user442920
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