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
$ HGMERGE=true; export HGMERGE
$ hg init r1
$ cd r1
$ echo a > a
$ hg addremove
adding a
$ hg commit -m "1"
$ hg clone . ../r2
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd ../r2
$ hg up
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo abc > a
$ hg diff --nodates
diff -r c19d34741b0a a
--- a/a
+++ b/a
@@ -1,1 +1,1 @@
-a
+abc
$ cd ../r1
$ echo b > b
$ echo a2 > a
$ hg addremove
adding b
$ hg commit -m "2"
$ cd ../r2
$ hg -q pull ../r1
$ hg status
M a
$ hg parents
changeset: 0:c19d34741b0a
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 1
$ hg --debug up
searching for copies back to rev 1
unmatched files in other:
b
resolving manifests
branchmerge: False, force: False, partial: False
ancestor: c19d34741b0a, local: c19d34741b0a+, remote: 1e71731e6fbb
preserving a for resolve of a
b: remote created -> g
getting b
a: versions differ -> m (premerge)
picked tool 'true' for a (binary False symlink False changedelete False)
merging a
my a@c19d34741b0a+ other a@1e71731e6fbb ancestor a@c19d34741b0a
a: versions differ -> m (merge)
picked tool 'true' for a (binary False symlink False changedelete False)
my a@c19d34741b0a+ other a@1e71731e6fbb ancestor a@c19d34741b0a
launching merge tool: true *$TESTTMP/r2/a* * * (glob)
merge tool returned: 0
1 files updated, 1 files merged, 0 files removed, 0 files unresolved
$ hg parents
changeset: 1:1e71731e6fbb
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 2
$ hg --debug up 0
starting 4 threads for background file closing (?)
searching for copies back to rev 0
unmatched files in local (from topological common ancestor):
b
resolving manifests
branchmerge: False, force: False, partial: False
ancestor: 1e71731e6fbb, local: 1e71731e6fbb+, remote: c19d34741b0a
preserving a for resolve of a
b: other deleted -> r
removing b
starting 4 threads for background file closing (?)
a: versions differ -> m (premerge)
picked tool 'true' for a (binary False symlink False changedelete False)
merging a
my a@1e71731e6fbb+ other a@c19d34741b0a ancestor a@1e71731e6fbb
a: versions differ -> m (merge)
picked tool 'true' for a (binary False symlink False changedelete False)
my a@1e71731e6fbb+ other a@c19d34741b0a ancestor a@1e71731e6fbb
launching merge tool: true *$TESTTMP/r2/a* * * (glob)
merge tool returned: 0
0 files updated, 1 files merged, 1 files removed, 0 files unresolved
$ hg parents
changeset: 0:c19d34741b0a
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 1
$ hg --debug up
searching for copies back to rev 1
unmatched files in other:
b
resolving manifests
branchmerge: False, force: False, partial: False
ancestor: c19d34741b0a, local: c19d34741b0a+, remote: 1e71731e6fbb
preserving a for resolve of a
b: remote created -> g
getting b
a: versions differ -> m (premerge)
picked tool 'true' for a (binary False symlink False changedelete False)
merging a
my a@c19d34741b0a+ other a@1e71731e6fbb ancestor a@c19d34741b0a
a: versions differ -> m (merge)
picked tool 'true' for a (binary False symlink False changedelete False)
my a@c19d34741b0a+ other a@1e71731e6fbb ancestor a@c19d34741b0a
launching merge tool: true *$TESTTMP/r2/a* * * (glob)
merge tool returned: 0
1 files updated, 1 files merged, 0 files removed, 0 files unresolved
$ hg parents
changeset: 1:1e71731e6fbb
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 2
$ hg -v history
changeset: 1:1e71731e6fbb
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
files: a b
description:
2
changeset: 0:c19d34741b0a
user: test
date: Thu Jan 01 00:00:00 1970 +0000
files: a
description:
1
$ hg diff --nodates
diff -r 1e71731e6fbb a
--- a/a
+++ b/a
@@ -1,1 +1,1 @@
-a2
+abc
create a second head
$ cd ../r1
$ hg up 0
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo b2 > b
$ echo a3 > a
$ hg addremove
adding b
$ hg commit -m "3"
created new head
$ cd ../r2
$ hg -q pull ../r1
$ hg status
M a
$ hg parents
changeset: 1:1e71731e6fbb
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 2
$ hg --debug up
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
updated to "1e71731e6fbb: 2"
1 other heads for branch "default"
test conflicting untracked files
$ hg up -qC 0
$ echo untracked > b
$ hg st
? b
$ hg up 1
b: untracked file differs
abort: untracked files in working directory differ from files in requested revision
[255]
$ rm b
test conflicting untracked ignored file
$ hg up -qC 0
$ echo ignored > .hgignore
$ hg add .hgignore
$ hg ci -m 'add .hgignore'
created new head
$ echo ignored > ignored
$ hg add ignored
$ hg ci -m 'add ignored file'
$ hg up -q 'desc("add .hgignore")'
$ echo untracked > ignored
$ hg st
$ hg up 'desc("add ignored file")'
ignored: untracked file differs
abort: untracked files in working directory differ from files in requested revision
[255]
test a local add
$ cd ..
$ hg init a
$ hg init b
$ echo a > a/a
$ echo a > b/a
$ hg --cwd a commit -A -m a
adding a
$ cd b
$ hg add a
$ hg pull -u ../a
pulling from ../a
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
new changesets cb9a9f314b8b
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg st
test updating backwards through a rename
$ hg mv a b
$ hg ci -m b
$ echo b > b
$ hg up -q 0
$ hg st
M a
$ hg diff --nodates
diff -r cb9a9f314b8b a
--- a/a
+++ b/a
@@ -1,1 +1,1 @@
-a
+b
test for superfluous filemerge of clean files renamed in the past
$ hg up -qC tip
$ echo c > c
$ hg add c
$ hg up -qt:fail 0
$ cd ..