#pragma section-numbers 2

<<Include(A:dev)>>

= 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`'
 .(c) calling '`os.rename(f, f+'.foo')`' will raise '`WindowsError: [Error 5] 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.

== See also ==

 * Bts:issue2524: "update loses working copy files on Windows for open files"
 * Bts:issue2543: "os.unlink deletes wrong file on windows share served by Samba"
 * [[http://mercurial.markmail.org/thread/t5ecar6sn3ekifo6|How Mercurial could be made working with Virus Scanners on Windows]]
 * [[https://boostgsoc13.github.io/boost.afio/doc/html/afio/FAQ/deleting_open_files.html|"I thought on Windows it is impossible to delete a file which is still open for use. How does AFIO achieve this?"]]

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CategoryInternals