revlog: automatically read from opened file handles
The revlog reading code commonly opens a new file handle for
reading on demand. There is support for passing a file handle
to revlog.revision(). But it is marked as an internal argument.
When revlogs are written, we write() data as it is available. But
we don't flush() data until all revisions are written.
Putting these two traits together, it is possible for an in-process
revlog reader during active writes to trigger the opening of a new
file handle on a file with unflushed writes. The reader won't have
access to all "available" revlog data (as it hasn't been flushed).
And with the introduction of the previous patch, this can lead to
the revlog raising an error due to a partial read.
I witnessed this behavior when applying changegroup data (via
`hg pull`) before issue6006 was fixed via different means. Having
this and the previous patch in play would have helped cause errors
earlier rather than manifesting as hash verification failures.
While this has been a long-standing issue, I believe the relatively
new delta computation code has tickled it into being more common.
This is because the new delta computation code will compute deltas
in more scenarios. This can lead to revlog reading. While the delta
computation code is probably supposed to reuse file handles, it
appears it isn't doing so in all circumstances.
But the issue runs deeper than that. Theoretically, any code can
access revision data during revlog writes. It appears we were just
getting lucky that it wasn't. (The "add revision callback" passed to
addgroup() provides an avenue to do this.)
If I changed the revlog's behavior to not cache the full revision
text or to clear caches after revision insertion during addgroup(),
I was able to produce crashes 100% of the time when writing changelog
revisions. This is because changelog's add revision callback attempts
to resolve the revision data to access the changed files list. And
without the revision's fulltext being cached, we performed a revlog
read, which required opening a new file handle. This attempted to read
unflushed data, leading to a partial read and a crash.
This commit teaches the revlog to store the file handles used for
writing multiple revisions during addgroup(). It also teaches the
code for resolving a file handle when reading to use these handles,
if available. This ensures that *any* reads (regardless of their
source) use the active writing file handles, if available. These
file handles have access to the unflushed data because they wrote it.
This allows reads to complete without issue.
Differential Revision: https://phab.mercurial-scm.org/D5267
# Here we create a simple DAG which has just enough of the required
# topology to test all the bisection status labels:
#
# 13--14
# /
# 0--1--2--3---------9--10--11--12
# \ /
# 4--5--6--7--8
$ hg init
$ echo '0' >a
$ hg add a
$ hg ci -u test -d '0 0' -m '0'
$ echo '1' >a
$ hg ci -u test -d '1 0' -m '1'
branch 2-3
$ echo '2' >b
$ hg add b
$ hg ci -u test -d '2 0' -m '2'
$ echo '3' >b
$ hg ci -u test -d '3 0' -m '3'
branch 4-8
$ hg up -r 1
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo '4' >c
$ hg add c
$ hg ci -u test -d '4 0' -m '4'
created new head
$ echo '5' >c
$ hg ci -u test -d '5 0' -m '5'
$ echo '6' >c
$ hg ci -u test -d '6 0' -m '6'
$ echo '7' >c
$ hg ci -u test -d '7 0' -m '7'
$ echo '8' >c
$ hg ci -u test -d '8 0' -m '8'
merge
$ hg merge -r 3
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg ci -u test -d '9 0' -m '9=8+3'
$ echo '10' >a
$ hg ci -u test -d '10 0' -m '10'
$ echo '11' >a
$ hg ci -u test -d '11 0' -m '11'
$ echo '12' >a
$ hg ci -u test -d '12 0' -m '12'
unrelated branch
$ hg up -r 3
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo '13' >d
$ hg add d
$ hg ci -u test -d '13 0' -m '13'
created new head
$ echo '14' >d
$ hg ci -u test -d '14 0' -m '14'
mark changesets
$ hg bisect --reset
$ hg bisect --good 4
$ hg bisect --good 6
$ hg bisect --bad 12
Testing changeset 9:2197c557e14c (6 changesets remaining, ~2 tests)
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg bisect --bad 10
Testing changeset 8:e74a86251f58 (4 changesets remaining, ~2 tests)
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg bisect --skip 7
Testing changeset 8:e74a86251f58 (4 changesets remaining, ~2 tests)
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
test template
$ hg log --template '{rev}:{node|short} {bisect}\n'
14:cbf2f3105bbf
13:e07efca37c43
12:98c6b56349c0 bad
11:03f491376e63 bad (implicit)
10:c012b15e2409 bad
9:2197c557e14c untested
8:e74a86251f58 untested
7:a5f87041c899 skipped
6:7d997bedcd8d good
5:2dd1875f1028 good (implicit)
4:2a1daef14cd4 good
3:8417d459b90c ignored
2:e1355ee1f23e ignored
1:ce7c85e06a9f good (implicit)
0:b4e73ffab476 good (implicit)
$ hg log --template '{bisect|shortbisect} {rev}:{node|short}\n'
14:cbf2f3105bbf
13:e07efca37c43
B 12:98c6b56349c0
B 11:03f491376e63
B 10:c012b15e2409
U 9:2197c557e14c
U 8:e74a86251f58
S 7:a5f87041c899
G 6:7d997bedcd8d
G 5:2dd1875f1028
G 4:2a1daef14cd4
I 3:8417d459b90c
I 2:e1355ee1f23e
G 1:ce7c85e06a9f
G 0:b4e73ffab476
test style
$ hg log --style bisect
changeset: 14:cbf2f3105bbf
bisect:
tag: tip
user: test
date: Thu Jan 01 00:00:14 1970 +0000
summary: 14
changeset: 13:e07efca37c43
bisect:
parent: 3:8417d459b90c
user: test
date: Thu Jan 01 00:00:13 1970 +0000
summary: 13
changeset: 12:98c6b56349c0
bisect: bad
user: test
date: Thu Jan 01 00:00:12 1970 +0000
summary: 12
changeset: 11:03f491376e63
bisect: bad (implicit)
user: test
date: Thu Jan 01 00:00:11 1970 +0000
summary: 11
changeset: 10:c012b15e2409
bisect: bad
user: test
date: Thu Jan 01 00:00:10 1970 +0000
summary: 10
changeset: 9:2197c557e14c
bisect: untested
parent: 8:e74a86251f58
parent: 3:8417d459b90c
user: test
date: Thu Jan 01 00:00:09 1970 +0000
summary: 9=8+3
changeset: 8:e74a86251f58
bisect: untested
user: test
date: Thu Jan 01 00:00:08 1970 +0000
summary: 8
changeset: 7:a5f87041c899
bisect: skipped
user: test
date: Thu Jan 01 00:00:07 1970 +0000
summary: 7
changeset: 6:7d997bedcd8d
bisect: good
user: test
date: Thu Jan 01 00:00:06 1970 +0000
summary: 6
changeset: 5:2dd1875f1028
bisect: good (implicit)
user: test
date: Thu Jan 01 00:00:05 1970 +0000
summary: 5
changeset: 4:2a1daef14cd4
bisect: good
parent: 1:ce7c85e06a9f
user: test
date: Thu Jan 01 00:00:04 1970 +0000
summary: 4
changeset: 3:8417d459b90c
bisect: ignored
user: test
date: Thu Jan 01 00:00:03 1970 +0000
summary: 3
changeset: 2:e1355ee1f23e
bisect: ignored
user: test
date: Thu Jan 01 00:00:02 1970 +0000
summary: 2
changeset: 1:ce7c85e06a9f
bisect: good (implicit)
user: test
date: Thu Jan 01 00:00:01 1970 +0000
summary: 1
changeset: 0:b4e73ffab476
bisect: good (implicit)
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 0
$ hg log --quiet --style bisect
14:cbf2f3105bbf
13:e07efca37c43
B 12:98c6b56349c0
B 11:03f491376e63
B 10:c012b15e2409
U 9:2197c557e14c
U 8:e74a86251f58
S 7:a5f87041c899
G 6:7d997bedcd8d
G 5:2dd1875f1028
G 4:2a1daef14cd4
I 3:8417d459b90c
I 2:e1355ee1f23e
G 1:ce7c85e06a9f
G 0:b4e73ffab476
$ hg --config extensions.color= --color=debug log --quiet --style bisect
[log.bisect| ] 14:cbf2f3105bbf
[log.bisect| ] 13:e07efca37c43
[log.bisect bisect.bad|B] 12:98c6b56349c0
[log.bisect bisect.bad|B] 11:03f491376e63
[log.bisect bisect.bad|B] 10:c012b15e2409
[log.bisect bisect.untested|U] 9:2197c557e14c
[log.bisect bisect.untested|U] 8:e74a86251f58
[log.bisect bisect.skipped|S] 7:a5f87041c899
[log.bisect bisect.good|G] 6:7d997bedcd8d
[log.bisect bisect.good|G] 5:2dd1875f1028
[log.bisect bisect.good|G] 4:2a1daef14cd4
[log.bisect bisect.ignored|I] 3:8417d459b90c
[log.bisect bisect.ignored|I] 2:e1355ee1f23e
[log.bisect bisect.good|G] 1:ce7c85e06a9f
[log.bisect bisect.good|G] 0:b4e73ffab476