revlog: test possible read race condition with splitting

This is currently working fine, but could break with another approach (for
example, with the one we are about to use in the next changesets…)

So we make sure the case is covered.

tests/test-transaction-rollback-on-revlog-split.t

@@ -1,335 +1,394 b''
 Test correctness of revlog inline -> non-inline transition
 ----------------------------------------------------------
 
 Helper extension to intercept renames and kill process
 
   $ cat > $TESTTMP/intercept_before_rename.py << EOF
   > import os
   > import signal
   > from mercurial import extensions, util
   > 
   > def extsetup(ui):
   >     def close(orig, *args, **kwargs):
   >         path = util.normpath(args[0]._atomictempfile__name)
   >         if path.endswith(b'/.hg/store/data/file.i'):
   >             os.kill(os.getpid(), signal.SIGKILL)
   >         return orig(*args, **kwargs)
   >     extensions.wrapfunction(util.atomictempfile, 'close', close)
   > EOF
 
   $ cat > $TESTTMP/intercept_after_rename.py << EOF
   > import os
   > import signal
   > from mercurial import extensions, util
   > 
   > def extsetup(ui):
   >     def close(orig, *args, **kwargs):
   >         path = util.normpath(args[0]._atomictempfile__name)
   >         r = orig(*args, **kwargs)
   >         if path.endswith(b'/.hg/store/data/file.i'):
   >             os.kill(os.getpid(), signal.SIGKILL)
   >         return r
   >     extensions.wrapfunction(util.atomictempfile, 'close', close)
   > EOF
 
   $ cat > $TESTTMP/killme.py << EOF
   > import os
   > import signal
   > 
   > def killme(ui, repo, hooktype, **kwargs):
   >     os.kill(os.getpid(), signal.SIGKILL)
   > EOF
 
+  $ cat > $TESTTMP/reader_wait_split.py << EOF
+  > import os
+  > import signal
+  > from mercurial import extensions, revlog, testing
+  > def _wait_post_load(orig, self, *args, **kwargs):
+  >     wait = b'data/file' in self.radix
+  >     if wait:
+  >         testing.wait_file(b"$TESTTMP/writer-revlog-split")
+  >     r = orig(self, *args, **kwargs)
+  >     if wait:
+  >         testing.write_file(b"$TESTTMP/reader-index-read")
+  >         testing.wait_file(b"$TESTTMP/writer-revlog-unsplit")
+  >     return r
+  > 
+  > def extsetup(ui):
+  >     extensions.wrapfunction(revlog.revlog, '_loadindex', _wait_post_load)
+  > EOF
+
 setup a repository for tests
 ----------------------------
 
   $ cat >> $HGRCPATH << EOF
   > [format]
   > revlog-compression=none
   > EOF
 
   $ hg init troffset-computation
   $ cd troffset-computation
   $ printf '%20d' '1' > file
   $ hg commit -Aqma
   $ printf '%1024d' '1' > file
   $ hg commit -Aqmb
   $ printf '%20d' '1' > file
   $ hg commit -Aqmc
   $ dd if=/dev/zero of=file bs=1k count=128 > /dev/null 2>&1
   $ hg commit -AqmD
 
 Reference size:
   $ f -s file
   file: size=131072
   $ f -s .hg/store/data/file*
   .hg/store/data/file.d: size=132139
   .hg/store/data/file.i: size=256
 
   $ cd ..
 
 
 Test a hard crash after the file was split but before the transaction was committed
 ===================================================================================
 
 Test offset computation to correctly factor in the index entries themselves.
 Also test that the new data size has the correct size if the transaction is aborted
 after the index has been replaced.
 
 Test repo has commits a, b, c, D, where D is large (grows the revlog enough that it
 transitions to non-inline storage). The clone initially has changes a, b
 and will transition to non-inline storage when adding c, D.
 
 If the transaction adding c, D is rolled back, then we don't undo the revlog split,
 but truncate the index and the data to remove both c and D.
 
 
   $ hg clone --quiet --rev 1 troffset-computation troffset-computation-copy
   $ cd troffset-computation-copy
 
 Reference size:
   $ f -s file
   file: size=1024
   $ f -s .hg/store/data/file*
   .hg/store/data/file.i: size=1174
 
   $ cat > .hg/hgrc <<EOF
   > [hooks]
   > pretxnchangegroup = python:$TESTTMP/killme.py:killme
   > EOF
 #if chg
   $ hg pull ../troffset-computation
   pulling from ../troffset-computation
   [255]
 #else
   $ hg pull ../troffset-computation
   pulling from ../troffset-computation
   Killed
   [137]
 #endif
 
 
 The revlog have been split on disk
 
   $ f -s .hg/store/data/file*
   .hg/store/data/file.d: size=132139
   .hg/store/data/file.i: size=256
 
   $ cat .hg/store/journal | tr -s '\000' ' ' | grep data/file | tail -1
   data/file.i 128
 
 The first file.i entry should match the "Reference size" above.
 The first file.d entry is the temporary record during the split,
 
 The second entry after the split happened. The sum of the second file.d
 and the second file.i entry should match the first file.i entry.
 
   $ cat .hg/store/journal | tr -s '\000' ' ' | grep data/file
   data/file.i 1174
   data/file.d 0
   data/file.d 1046
   data/file.i 128
   $ hg recover
   rolling back interrupted transaction
   (verify step skipped, run `hg verify` to check your repository content)
   $ f -s .hg/store/data/file*
   .hg/store/data/file.d: size=1046
   .hg/store/data/file.i: size=128
   $ hg tip
   changeset:   1:cfa8d6e60429
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     b
   
   $ hg verify -q
    warning: revlog 'data/file.d' not in fncache!
   1 warnings encountered!
   hint: run "hg debugrebuildfncache" to recover from corrupt fncache
   $ hg debugrebuildfncache --only-data
   adding data/file.d
   1 items added, 0 removed from fncache
   $ hg verify -q
   $ cd ..
 
 Test a hard crash right before the index is move into place
 ===========================================================
 
 Now retry the procedure but intercept the rename of the index and check that
 the journal does not contain the new index size. This demonstrates the edge case
 where the data file is left as garbage.
 
   $ hg clone --quiet --rev 1 troffset-computation troffset-computation-copy2
   $ cd troffset-computation-copy2
 
 Reference size:
   $ f -s file
   file: size=1024
   $ f -s .hg/store/data/file*
   .hg/store/data/file.i: size=1174
 
   $ cat > .hg/hgrc <<EOF
   > [extensions]
   > intercept_rename = $TESTTMP/intercept_before_rename.py
   > [hooks]
   > pretxnchangegroup = python:$TESTTMP/killme.py:killme
   > EOF
 #if chg
   $ hg pull ../troffset-computation
   pulling from ../troffset-computation
   [255]
 #else
   $ hg pull ../troffset-computation
   pulling from ../troffset-computation
   Killed
   [137]
 #endif
 
 The data file is created, but the revlog is still inline
 
   $ f -s .hg/store/data/file*
   .hg/store/data/file.d: size=132139
   .hg/store/data/file.i: size=132395
 
   $ cat .hg/store/journal | tr -s '\000' ' ' | grep data/file
   data/file.i 1174
   data/file.d 0
   data/file.d 1046
 
   $ hg recover
   rolling back interrupted transaction
   (verify step skipped, run `hg verify` to check your repository content)
   $ f -s .hg/store/data/file*
   .hg/store/data/file.d: size=1046
   .hg/store/data/file.i: size=1174
   $ hg tip
   changeset:   1:cfa8d6e60429
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     b
   
   $ hg verify -q
   $ cd ..
 
 Test a hard crash right after the index is move into place
 ===========================================================
 
 Now retry the procedure but intercept the rename of the index.
 
 Things get corrupted /o\
 
   $ hg clone --quiet --rev 1 troffset-computation troffset-computation-crash-after-rename
   $ cd troffset-computation-crash-after-rename
 
 Reference size:
   $ f -s file
   file: size=1024
   $ f -s .hg/store/data/file*
   .hg/store/data/file.i: size=1174
 
   $ cat > .hg/hgrc <<EOF
   > [extensions]
   > intercept_rename = $TESTTMP/intercept_after_rename.py
   > [hooks]
   > pretxnchangegroup = python:$TESTTMP/killme.py:killme
   > EOF
 #if chg
   $ hg pull ../troffset-computation
   pulling from ../troffset-computation
   [255]
 #else
   $ hg pull ../troffset-computation
   pulling from ../troffset-computation
   Killed
   [137]
 #endif
 
 the revlog has been split on disk
 
   $ f -s .hg/store/data/file*
   .hg/store/data/file.d: size=132139
   .hg/store/data/file.i: size=256
 
   $ cat .hg/store/journal | tr -s '\000' ' ' | grep data/file
   data/file.i 1174
   data/file.d 0
   data/file.d 1046
 
   $ hg recover
   rolling back interrupted transaction
   abort: attempted to truncate data/file.i to 1174 bytes, but it was already 256 bytes
   
   [255]
   $ f -s .hg/store/data/file*
   .hg/store/data/file.d: size=1046
   .hg/store/data/file.i: size=256
   $ hg tip
   changeset:   1:cfa8d6e60429
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     b
   
   $ hg verify -q
   abandoned transaction found - run hg recover
    warning: revlog 'data/file.d' not in fncache!
    file@0: data length off by -131093 bytes
    file@2: unpacking fa1120531cc1: partial read of revlog data/file.d; expected 21 bytes from offset 1046, got 0
    file@3: unpacking a631378adaa3: partial read of revlog data/file.d; expected 131072 bytes from offset 1067, got -21
    file@?: rev 2 points to nonexistent changeset 2
    (expected )
    file@?: fa1120531cc1 not in manifests
    file@?: rev 3 points to nonexistent changeset 3
    (expected )
    file@?: a631378adaa3 not in manifests
   not checking dirstate because of previous errors
   3 warnings encountered!
   hint: run "hg debugrebuildfncache" to recover from corrupt fncache
   7 integrity errors encountered!
   (first damaged changeset appears to be 0)
   [1]
   $ cd ..
 
 Have the transaction rollback itself without any hard crash
 ===========================================================
 
 
 Repeat the original test but let hg rollback the transaction.
 
   $ hg clone --quiet --rev 1 troffset-computation troffset-computation-copy-rb
   $ cd troffset-computation-copy-rb
   $ cat > .hg/hgrc <<EOF
   > [hooks]
   > pretxnchangegroup = false
   > EOF
   $ hg pull ../troffset-computation
   pulling from ../troffset-computation
   searching for changes
   adding changesets
   adding manifests
   adding file changes
   transaction abort!
   rollback completed
   abort: pretxnchangegroup hook exited with status 1
   [40]
 
 File are still split on disk, with the expected size.
 
   $ f -s .hg/store/data/file*
   .hg/store/data/file.d: size=1046
   .hg/store/data/file.i: size=128
 
   $ hg tip
   changeset:   1:cfa8d6e60429
   tag:         tip
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     b
   
   $ hg verify -q
    warning: revlog 'data/file.d' not in fncache!
   1 warnings encountered!
   hint: run "hg debugrebuildfncache" to recover from corrupt fncache
   $ cd ..
 
+Read race
+=========
+
+We check that a client that started reading a revlog (its index) after the
+split and end reading (the data) after the rollback should be fine
+
+  $ hg clone --quiet --rev 1 troffset-computation troffset-computation-race
+  $ cd troffset-computation-race
+  $ cat > .hg/hgrc <<EOF
+  > [hooks]
+  > pretxnchangegroup=$RUNTESTDIR/testlib/wait-on-file 5 $TESTTMP/reader-index-read $TESTTMP/writer-revlog-split
+  > pretxnclose = false
+  > EOF
+
+start a reader
+
+  $ hg cat --rev 0 file \
+  > --config "extensions.wait_read=$TESTTMP/reader_wait_split.py" \
+  > 2> $TESTTMP/reader.stderr \
+  > > $TESTTMP/reader.stdout &
+
+Do a failed pull in //
+
+  $ hg pull ../troffset-computation
+  pulling from ../troffset-computation
+  searching for changes
+  adding changesets
+  adding manifests
+  adding file changes
+  transaction abort!
+  rollback completed
+  abort: pretxnclose hook exited with status 1
+  [40]
+  $ touch $TESTTMP/writer-revlog-unsplit
+  $ wait
+
+The reader should be fine
+  $ cat $TESTTMP/reader.stderr
+  $ cat $TESTTMP/reader.stdout
+                     1 (no-eol)
+  $ cd ..