Unlinking Files on Windows

This page describes what happens when Python's 'os.unlink(f)' is called on Windows.

File opened using Python's "open"

If the file f itself or any hardlinked copy of f has been opened for reading by another process using Python's 'open()', then calling 'os.unlink(f)' or 'os.rename(f, ..)' will raise

WindowsError: [Error 32] The process cannot access the file because it is being used by another process: <f>

This could be fixed in Microsoft's C runtime implementation by patching the file open.c (VC8):

diff --git a/open.c b/open.c --- a/open.c +++ b/open.c @@ -395,6 +395,9 @@

        *punlock_flag = 1;

   if (osplatform == VER_PLATFORM_WIN32_NT )

       fileshare  |= FILE_SHARE_DELETE;

   /*
    * try to open/create the file
    */

and then making sure Python would use that modified C runtime. Python's 'open' would then behave like Mercurial's 'posixfile'.

File opened using Mercurial's "posixfile"

If the file f has been opened for reading by another process with 'posixfile(f)', calling 'os.rename(f, ..)' succeeds.

Calling unlink will send that file into a "scheduled delete" state.

Scheduled delete has the following characteristics:

(a) the entry in the directory for f is still kept

(b) calling 'fd = posixfile(f, 'w')' will raise 'IOError: [Errno 13] <f>: Access is denied'

(d) calling 'os.lstat(f)' will raise 'WindowsError: [Error 5] Access is denied: <f>'

(e) calling 'os.path.exists(f)' returns False

Scheduled delete is left as soon as the other process closes the file.