view tests/test-flags.t @ 26375:3686fa2b8eee

windows: insert file positioning call between reads and writes

fopen() and fdopen() have a unique-to-Windows requirement that
transitions between read and write operations in files opened
in modes r+, w+, and a+ perform a file positioning call
(fsetpos, fseek, or rewind) in between. While the MSDN docs don't
say what will happen if this is not done, observations reveal
that Python raises an IOError with errno 0. Furthermore, I
/think/ this behavior isn't deterministic. But I can reproduce
it reliably with subsequent patches applied that open revlogs
in a+ mode and perform both reads and writes.

This patch introduces a proxy class for file handles opened
in r+, w+, and a+ mode on Windows. The class intercepts calls
and audits whether a file positioning function has been called
between read and write operations. If not, a dummy, no-op seek
to the current file position is performed. This appears to be
sufficient to "trick" Windows into allowing transitions between
read and writes without raising errors.

#require execbit

  $ umask 027

  $ hg init test1
  $ cd test1
  $ touch a b
  $ hg add a b
  $ hg ci -m "added a b"

  $ cd ..
  $ hg clone test1 test3
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg init test2
  $ cd test2
  $ hg pull ../test1
  pulling from ../test1
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 2 changes to 2 files
  (run 'hg update' to get a working copy)
  $ hg co
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ chmod +x a
  $ hg ci -m "chmod +x a"

the changelog should mention file a:

  $ hg tip --template '{files}\n'
  a

  $ cd ../test1
  $ echo 123 >>a
  $ hg ci -m "a updated"

  $ hg pull ../test2
  pulling from ../test2
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files (+1 heads)
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg heads
  changeset:   2:7f4313b42a34
  tag:         tip
  parent:      0:22a449e20da5
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     chmod +x a
  
  changeset:   1:c6ecefc45368
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     a updated
  
  $ hg history
  changeset:   2:7f4313b42a34
  tag:         tip
  parent:      0:22a449e20da5
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     chmod +x a
  
  changeset:   1:c6ecefc45368
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     a updated
  
  changeset:   0:22a449e20da5
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     added a b
  

  $ hg -v merge
  resolving manifests
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat a
  123
  $ [ -x a ]

  $ cd ../test3
  $ echo 123 >>b
  $ hg ci -m "b updated"

  $ hg pull ../test2
  pulling from ../test2
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files (+1 heads)
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg heads
  changeset:   2:7f4313b42a34
  tag:         tip
  parent:      0:22a449e20da5
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     chmod +x a
  
  changeset:   1:dc57ead75f79
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     b updated
  
  $ hg history
  changeset:   2:7f4313b42a34
  tag:         tip
  parent:      0:22a449e20da5
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     chmod +x a
  
  changeset:   1:dc57ead75f79
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     b updated
  
  changeset:   0:22a449e20da5
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     added a b
  

  $ hg -v merge
  resolving manifests
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ ls -l ../test[123]/a > foo
  $ cut -b 1-10 < foo
  -rwxr-x---
  -rwxr-x---
  -rwxr-x---

  $ hg debugindex a
     rev    offset  length  ..... linkrev nodeid       p1           p2 (re)
       0         0       0  .....       0 b80de5d13875 000000000000 000000000000 (re)
  $ hg debugindex -R ../test2 a
     rev    offset  length  ..... linkrev nodeid       p1           p2 (re)
       0         0       0  .....       0 b80de5d13875 000000000000 000000000000 (re)
  $ hg debugindex -R ../test1 a
     rev    offset  length  ..... linkrev nodeid       p1           p2 (re)
       0         0       0  .....       0 b80de5d13875 000000000000 000000000000 (re)
       1         0       5  .....       1 7fe919cc0336 b80de5d13875 000000000000 (re)

  $ cd ..