posix: always seek to EOF when opening a file in append mode
Python 3 already does this, so skip it there.
Consider the program:
#include <stdio.h>
int main() {
FILE *f = fopen("narf", "w");
fprintf(f, "narf\n");
fclose(f);
f = fopen("narf", "a");
printf("%ld\n", ftell(f));
fprintf(f, "troz\n");
printf("%ld\n", ftell(f));
return 0;
}
on macOS, FreeBSD, and Linux with glibc, this program prints
5
10
but on musl libc (Alpine Linux and probably others) this prints
0
10
By my reading of
https://pubs.opengroup.org/onlinepubs/
009695399/functions/fopen.html
this is technically correct, specifically:
> Opening a file with append mode (a as the first character in the
> mode argument) shall cause all subsequent writes to the file to be
> forced to the then current end-of-file, regardless of intervening
> calls to fseek().
in other words, the file position doesn't really matter in append-mode
files, and we can't depend on it being at all meaningful unless we
perform a seek() before tell() after open(..., 'a'). Experimentally
after a .write() we can do a .tell() and it'll always be reasonable,
but I'm unclear from reading the specification if that's a smart thing
to rely on. This matches what we do on Windows and what Python 3 does
for free, so let's just be consistent. Thanks to Yuya for the idea.
================================
Test corner case around bookmark
================================
This test file is meant to gather test around bookmark that are specific
enough to not find a place elsewhere.
Test bookmark/changelog race condition
======================================
The data from the bookmark file are filtered to only contains bookmark with
node known to the changelog. If the cache invalidation between these two bits
goes wrong, bookmark can be dropped.
global setup
------------
$ cat >> $HGRCPATH << EOF
> [ui]
> ssh = "$PYTHON" "$TESTDIR/dummyssh"
> [server]
> concurrent-push-mode=check-related
> EOF
Setup
-----
initial repository setup
$ hg init bookrace-server
$ cd bookrace-server
$ echo a > a
$ hg add a
$ hg commit -m root
$ echo a >> a
$ hg bookmark book-A
$ hg commit -m A0
$ hg up 'desc(root)'
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(leaving bookmark book-A)
$ echo b > b
$ hg add b
$ hg bookmark book-B
$ hg commit -m B0
created new head
$ hg up null
0 files updated, 0 files merged, 2 files removed, 0 files unresolved
(leaving bookmark book-B)
$ hg phase --public --rev 'all()'
$ hg log -G
o changeset: 2:c79985706978
| bookmark: book-B
| tag: tip
| parent: 0:6569b5a81c7e
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: B0
|
| o changeset: 1:39c28d785860
|/ bookmark: book-A
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: A0
|
o changeset: 0:6569b5a81c7e
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: root
$ hg book
book-A 1:39c28d785860
book-B 2:c79985706978
$ cd ..
Add new changeset on each bookmark in distinct clones
$ hg clone ssh://user@dummy/bookrace-server client-A
requesting all changes
adding changesets
adding manifests
adding file changes
added 3 changesets with 3 changes to 2 files (+1 heads)
new changesets 6569b5a81c7e:c79985706978
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg -R client-A update book-A
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
(activating bookmark book-A)
$ echo a >> client-A/a
$ hg -R client-A commit -m A1
$ hg clone ssh://user@dummy/bookrace-server client-B
requesting all changes
adding changesets
adding manifests
adding file changes
added 3 changesets with 3 changes to 2 files (+1 heads)
new changesets 6569b5a81c7e:c79985706978
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg -R client-B update book-B
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
(activating bookmark book-B)
$ echo b >> client-B/b
$ hg -R client-B commit -m B1
extension to reproduce the race
-------------------------------
If two process are pushing we want to make sure the following happens:
* process A read changelog
* process B to its full push
* process A read bookmarks
* process A proceed with rest of the push
We build a server side extension for this purpose
$ cat > bookrace.py << EOF
> import os
> import time
> import atexit
> from mercurial import error, extensions, bookmarks
>
> def wait(repo):
> if not os.path.exists('push-A-started'):
> assert repo._currentlock(repo._lockref) is None
> assert repo._currentlock(repo._wlockref) is None
> print('setting raced push up')
> with open('push-A-started', 'w'):
> pass
> clock = 300
> while not os.path.exists('push-B-done'):
> clock -= 1
> if clock <= 0:
> raise error.Abort("race scenario timed out")
> time.sleep(0.1)
>
> def reposetup(ui, repo):
> class racedrepo(repo.__class__):
> @property
> def _bookmarks(self):
> wait(self)
> return super(racedrepo, self)._bookmarks
> repo.__class__ = racedrepo
>
> def e():
> with open('push-A-done', 'w'):
> pass
> atexit.register(e)
> EOF
Actual test
-----------
Start the raced push.
$ cat >> bookrace-server/.hg/hgrc << EOF
> [extensions]
> bookrace=$TESTTMP/bookrace.py
> EOF
$ hg push -R client-A -r book-A >push-output.txt 2>&1 &
Wait up to 30 seconds for that push to start.
$ clock=30
$ while [ ! -f push-A-started ] && [ $clock -gt 0 ] ; do
> clock=`expr $clock - 1`
> sleep 1
> done
Do the other push.
$ cat >> bookrace-server/.hg/hgrc << EOF
> [extensions]
> bookrace=!
> EOF
$ hg push -R client-B -r book-B
pushing to ssh://user@dummy/bookrace-server
searching for changes
remote: adding changesets
remote: adding manifests
remote: adding file changes
remote: added 1 changesets with 1 changes to 1 files
updating bookmark book-B
Signal the raced put that we are done (it waits up to 30 seconds).
$ touch push-B-done
Wait for the raced push to finish (with the remaning of the initial 30 seconds).
$ while [ ! -f push-A-done ] && [ $clock -gt 0 ] ; do
> clock=`expr $clock - 1`
> sleep 1
> done
Check raced push output.
$ cat push-output.txt
pushing to ssh://user@dummy/bookrace-server
searching for changes
remote: setting raced push up
remote: adding changesets
remote: adding manifests
remote: adding file changes
remote: added 1 changesets with 1 changes to 1 files
updating bookmark book-A
Check result of the push.
$ hg -R bookrace-server log -G
o changeset: 4:9ce3b28c16de
| bookmark: book-A
| tag: tip
| parent: 1:39c28d785860
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: A1
|
| o changeset: 3:f26c3b5167d1
| | bookmark: book-B (false !)
| | user: test
| | date: Thu Jan 01 00:00:00 1970 +0000
| | summary: B1
| |
| o changeset: 2:c79985706978
| | parent: 0:6569b5a81c7e
| | user: test
| | date: Thu Jan 01 00:00:00 1970 +0000
| | summary: B0
| |
o | changeset: 1:39c28d785860
|/ user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: A0
|
o changeset: 0:6569b5a81c7e
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: root
$ hg -R bookrace-server book
book-A 4:9ce3b28c16de
book-B 3:f26c3b5167d1 (false !)