The search for reuse phase for *all* the objects scans *all*
the packfiles, looking for the best candidate to serve back to the
client.

This can lead to an expensive operation when the number of
packfiles and objects is high.

Add parameter "pack.searchForReuseTimeout" to limit the time spent
on this search.

Change-Id: I54f5cddb6796fdc93ad9585c2ab4b44854fa6c48

Update tests to record the number of events fired post-setup and only
assert for events fired during BatchRefUpdate.execute. For tests which
use writeLooseRef to setup refs, create new tests which assert the
number of RefsChangedEvent(s) rather than updating the existing ones
to call RefDirectory.exactRef as it changes the code path.

Change-Id: I0187811628d179d9c7e874c9bb8a7ddb44dd9df4
Signed-off-by: Kaushik Lingarkar <quic_kaushikl@quicinc.com>

Don't create the stream eagerly in lock(); that may cause JGit to
exceed OS or JVM limits on open file descriptors if many locks need
to be created, for instance when creating many refs. Instead create
the output stream only when one really needs to write something.

Bug: 573328
Change-Id: If9441ed40494d46f594a896d34a5c4f56f91ebf4
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

Don't create the stream eagerly in lock(); that may cause JGit to
exceed OS or JVM limits on open file descriptors if many locks need
to be created, for instance when creating many refs. Instead create
the output stream only when one really needs to write something.

Bug: 573328
Change-Id: If9441ed40494d46f594a896d34a5c4f56f91ebf4
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

Add new constructors to PackFile to improve a common use case where
callers know the directory, id, and extension, but previously needed to
construct a valid file name (with prefix, '.', etc) to create a
PackFile. Most callers can use the variant that has id as an ObjectId,
but provide an id as String variant too.

Change-Id: I39e4466abe8c9509f5916d5bfe675066570b8585
Signed-off-by: Nasser Grainawi <quic_nasserg@quicinc.com>

Provide a recovery path for objects being referenced during the pack
pruning race. Due to the pack pruning race, it is possible for objects
to become referenced after a pack has been deemed safe to prune, but
before it actually gets pruned. If this happened previously, the newly
referenced objects would be missing and potentially result in a
corrupted ref.

Add the ability to recover from this situation when an object is missing
but happens to still be available in a pack in the "preserved"
directory. This is likely only useful when used in conjunction with the
--preserve-old-packs GC option, which prunes packs by hard-linking to
the preserved directory. If an object is missing and found in a pack in
the preserved directory, immediately recover that pack and its
associated files (idx, bitmaps...) by moving them back to the original
pack directory, and then retry the operation that would have failed due
to the missing object. This retry can now succeed and the repository
may avoid corruption. This approach should drastically reduce the
chance of a corrupt repository during pack pruning at very little extra
cost. This extra cost should only be incurred when objects are missing
and a failure would normally occur.

Change-Id: I2a704e3276b88cc892159d9bfe2455c6eec64252
Signed-off-by: Martin Fick <quic_mfick@quicinc.com>
Signed-off-by: Nasser Grainawi <quic_nasserg@quicinc.com>

The only extension that was ever consulted from the bitmap was the
bitmap index. We can simplify the Pack code as well as the code of
all the callers if we focus on just that usage.

Change-Id: I799ddfdee93142af67ce5081d14a430d36aa4c15
Signed-off-by: Nasser Grainawi <quic_nasserg@quicinc.com>

The PackFile class is intended to be a central place to do all
common pack filename manipulation and parsing to help reduce repeated
code and bugs. Use the PackFile class in the Pack class and in many
tests to ensure it works well in a variety of situations. Later changes
will expand use of PackFiles to even more areas.

Change-Id: I921b30f865759162bae46ddd2c6d669de06add4a
Signed-off-by: Nasser Grainawi <quic_nasserg@quicinc.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Pack better represents the purpose of the object and paves the way to
add a PackFile object that extends File.

Change-Id: I39b4f697902d395e9b6df5e8ce53078ce72fcea3
Signed-off-by: Nasser Grainawi <quic_nasserg@quicinc.com>

We sometimes want to get all the refs except specific prefixes,
similarly to getRefsByPrefix that gets all the refs of a specific
prefix.

We now create a new method that gets all refs matching a prefix except a
set of specific prefixes.

One use-case is for Gerrit to be able to get all the refs except
refs/changes; in Gerrit we often have lots of refs/changes, but very
little other refs. Currently, to get all the refs except refs/changes we
need to get all the refs and then filter the refs/changes, which is very
inefficient. With this method, we can simply skip the unneeded prefix so
that we don't have to go over all the elements.

RefDirectory still uses the inefficient implementation, since there
isn't a simple way to use Refcursor to achieve the efficient
implementation (as done in ReftableDatabase).

Signed-off-by: Gal Paikin <paiking@google.com>
Change-Id: I8c5db581acdeb6698e3d3a2abde8da32f70c854c

Path#getFileName can return null. Fix the warning by asserting the file
name isn't null.

Change-Id: I7f2fe75b46113d8be1d14e3f18dd77da27df25ed
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

File#listFiles can return null. Use Files#list instead to fix the
problem.

Change-Id: I74e0b49aa6dae370219507c64aa43be4d8aa7b82
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

File#listFiles can return null, assert it is not null to fix the
warning.

Change-Id: I28fc668fee760d39965e6e039003ac9f85fd461b
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

If pack or index files are guarded by a pack lock (.keep file)
deleteOrphans() should not touch the respective files protected by the
lock file. Otherwise it may interfere with PackInserter concurrently
inserting a new pack file and its index.

The problem was caused by the following race.

All mentioned files are located in  "objects/pack/".
File endings relevant in "pack" dir:
  .pack
  .keep
  .idx
  .bitmap

When ReceivePack receives a pack file it executes the following steps:

ReceivePack.service():
  receivePackAndCheckConnectivity():
    receivePack():
      receive the pack
      parse the pack, returns packLock (.keep file)
      PackInserter.flush():
        write tmpPck file:  "insert_<random>.pack"
        write tmpIdx file:  "insert_<random>.idx"
        real pack name: "pack-<SHA1>.pack"
        real index name: "pack-<SHA1>.idx"
        atomic rename tmpPack to realPack
        atomic rename tmpIdx to tmpIdx
  execute commands
  unlock pack by removing .keep file
  trigger auto gc if enabled

When PackInserter.flush() renames the temporary pack to the final
"pack-xxx.pack" file  the temporary pack index file "insert_xxx.idx"
has no matching .pack file with the same base name for a short interval.
If deleteOrphans() ran during that interval it deduced the pack index
file was orphaned. Subsequently the missing pack index caused
MissingObjectExceptions since objects contained in the pack couldn't be
looked up anymore.

Bug: https://bugs.chromium.org/p/gerrit/issues/detail?id=13544
Change-Id: I559c81e4b1d7c487f92a751bd78b987d32c98719
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Fix IOException occurring when calling
GC on a repository with absent objects/pack folder.

Change-Id: I5be1333a0726f4d7491afd25ddac85451686c30a
Signed-off-by: Nail Samatov <sanail@yandex.ru>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Due to an integer overflow bug, the current "Index file is too large
for jgit" check did not work properly and subsequently a
NegativeArraySizeException was raised.

Change-Id: I2736efb28987c29e56bc946563b7fa781898a94a
Signed-off-by: Marc Strapetz <marc.strapetz@syntevo.com>

The change Ic0b974fa (c217d33, "Documentation/technical/reftable:
improve repo layout") defines a new repository layout, which was
agreed with the git-core mailing list.

It addresses the following problems:

* old git clients will not recognize reftable-based repositories, and
  look at encompassing directories.

* Poorly written tools might write directly into
  .git/refs/heads/BRANCH.

Since we consider JGit reftable as experimental (git-core doesn't
support it yet), we have no backward compatibility. If you created a
repository with reftable between mid-Nov 2019 and now, you can do the
following to convert:

  mv .git/refs .git/reftable/tables.list
  git config core.repositoryformatversion 1
  git config extensions.refStorage reftable

Change-Id: I80df35b9d22a8ab893dcbe9fbd051d924788d6a5
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

The Java Language Specification recommends listing modifiers in
the following order:

1. Annotations
2. public
3. protected
4. private
5. abstract
6. static
7. final
8. transient
9. volatile
10. synchronized
11. native
12. strictfp

Not following this convention has no technical impact, but will reduce
the code's readability because most developers are used to the standard
order.

This was detected using SonarLint.

Change-Id: I9cddecb4f4234dae1021b677e915be23d349a380
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

The merged table contains handles to open files. A full compaction
causes those files to be closed, and so further lookups would fail
with EBADF.

Change-Id: I7bb74f7228ecc7fec9535b00e56a617a9c18e00e
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Change-Id: I64b0c057dd0a12aef2f3d56fa0c8a10e3b23fffd
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Change-Id: Icebe8071eeefbc13d3bdbc231c568209cdc26195
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Java GC evicts all SoftReferences when the used heap size comes close to
the maximum heap size. This means peaks in heap memory consumption can
flush the complete WindowCache which was observed to have negative
impact on performance of upload-pack in Gerrit.

Hence add a boolean option core.packedGitUseStrongRefs to allow using
strong references to reference packfile pages cached in the WindowCache.

If this option is set to true Java gc can no longer flush the
WindowCache to free memory if the used heap comes close to the maximum
heap size. On the other hand this provides more predictable performance.

Bug: 553573
Change-Id: I9de406293087ab0fa61130c8e0829775762ece8d
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

This is the format given by the Eclipse legal doc generator [1].

[1] https://www.eclipse.org/projects/tools/documentation.php?id=technology.jgit

Bug: 548298
Change-Id: I8d8cabc998ba1b083e3f0906a8d558d391ffb6c4
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Add the following statistics
- cache hit count and hit ratio
- cache miss count and miss ratio
- count of successful and failed loads
- rate of failed loads
- load, eviction and request count
- average and total load time

Use LongAdder instead of AtomicLong to implement counters in order to
improve scalability.

Optionally expose these metrics via JMX, they are registered with the
platform MBean server if the config option jmx.WindowCacheStats = true
in the user or system level git config.

Bug: 553573
Change-Id: Ia2d5246ef69b9c2bd594a23934424bc5800774aa
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

The reftable format supports fast inverse (SHA1 => ref) queries.

If the ref database does not support fast inverse queries, it may be
advantageous to build a complete SHA1 to ref map in advance for
multiple uses. To let applications decide, this function indicates
whether the inverse map is available.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Change-Id: Idaf7e01075906972ec21332cade285289619c2b3

Reftable-enabled repositories don't have a file called HEAD. Check for
reftable/ instead.

This fixes repository creation on reftable in Gerrit.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Change-Id: I778c2be01d96aaf135affae4b457b5fe5b483bee

Change-Id: Iab7d3a08906e826e26572f534512a09d3a5876b0
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Reftable is a binary, block-based storage format for the ref-database.
It provides several advantages over the traditional packed + loose
storage format:

 * O(1) write performance, even for deletions and transactions.

 * atomic updates to the ref database.

 * O(log N) lookup and prefix scans

 * free from restrictions imposed by the file system: it is
   case-sensitive even on case-insensitive file systems, and has
   no inherent limitations for directory/file conflicts

 * prefix compression reduces space usage for repetitive ref names,
   such as gerrit's refs/changes/xx/xxxxx format.

FileReftableDatabase is based on FileReftableStack, which does
compactions inline. This is simple, and has good median performance,
but every so often it will rewrite the entire ref database.

For testing, a FileReftableTest (mirroring RefUpdateTest) is added to
check for Reftable specific behavior. This must be done separately, as
reflogs have different semantics.

Add a reftable flavor of BatchRefUpdateTest.

Add a FileReftableStackTest to exercise compaction.

Add FileRepository#convertToReftable so existing testdata can be
reused.

CQ: 21007
Change-Id: I1837f268e91c6b446cb0155061727dbaccb714b8
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Change-Id: I583491f621e54401c60150efb285fcc7243a9355
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>

This doesn't yet ensure that _all_ repositories are closed. It only
handles the obvious, local, and easy cases.

Change-Id: I0f9f8607791f0f03ed1f5ad71e9595e78b78892f
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

Since [1] the gerrit project includes jgit as a submodule, and has this
warning enabled, resulting in 100s of warnings in the console.

Also enable the warning here, and fix them.

At the same time, add missing braces around adjacent and nearby one-line
blocks.

[1] https://gerrit-review.googlesource.com/c/gerrit/+/227897

Change-Id: I81df3fc7ed6eedf6874ce1a3bedfa727a1897e4c
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

Change-Id: Id28804ace2572e8f659271660e78454a0d6ccc49
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

PackedBatchRefUpdate was creating a new packed-refs list that was
potentially unsorted. This would be papered over when the list was
read back from disk in parsePackedRef, which detects unsorted ref
lists on reading, and sorts them. However, the BatchRefUpdate also
installed the new (unsorted) list in-memory in
RefDirectory#packedRefs.

With the timestamp granularity code committed to stable-5.1, we can
more often accurately decide that the packed-refs file is clean, and
will return the erroneous unsorted data more often. Unluckily timed
delays also cause the file to be clean, hence this problem was
exacerbated under load.

The symptom is that refs added by a BatchRefUpdate would stop being
visible directly after they were added. In particular, the Gerrit
integration tests uses BatchRefUpdate in its setup for creating the
Admin group, and then tries to read it out directly afterward.

The tests recreates one failure case. A better approach would be to
revise RefList.Builder, so it detects out-of-order lists and
automatically sorts them.

Fixes https://bugs.eclipse.org/bugs/show_bug.cgi?id=548716 and
https://bugs.chromium.org/p/gerrit/issues/detail?id=11373.

Bug: 548716
Change-Id: I613c8059964513ce2370543620725b540b3cb6d1
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

If we use the default system reader FileStoreAttributes cannot persist
attributes in userConfig when tests run in Bazel due to sandboxing.
Hence we need to ensure that all tests use MockSystemReader (and
especially a mocked userConfig).

Change-Id: Ic1ad8e2ec5a150c5433434a5f6667d6c4674c87d
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Increase the safety factor to 2.5x for extra safety if max of measured
timestamp resolution and measured minimal racy threshold is < 100ms, use
1.25 otherwise since for large filesystem resolution values the
influence of finite resolution of the system clock should be negligible.

Before, not yet using the newly introduced minRacyThreshold measurement,
the threshold was 1.1x FS resolution, and we could issue the
following sequence of events,

  start
  create-file
  read-file (currentTime)
  end

which had the following timestamps:

  create-file 1564589081
  start 1564589082
  read 1564589082
  end 1564589082

In this case, the difference between create-file and read is 5ms,
which exceeded the 4ms FS resolution, even though the events together
took just 2ms of runtime.

Reproduce with:
  bazel test --runs_per_test=100 \
    //org.eclipse.jgit.test:org_eclipse_jgit_internal_storage_file_FileSnapshotTest

The file system timestamp resolution is 4ms in this case.

This code assumes that the kernel and the JVM use the same clock that
is synchronized with the file system clock. This seems plausible,
given the resolution of System.currentTimeMillis() and the latency for
a gettimeofday system call (typically ~1us), but it would be good to
justify this with specifications.

Also cover a source of flakiness: if the test runs under extreme load,
then we could have

  start
  create-file
  <long delay>
  read
  end

which would register as an unmodified file. Avoid this by skipping the
test if end-start is too big.

[msohn]:
- downported from master to stable-5.1
- skip test if resolution is below 10ms
- adjust safety factor to 1.25 for resolutions above 100ms

Change-Id: I87d2cf035e01c44b7ba8364c410a860aa8e312ef
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

To enable persisting the minimal racy threshold per FileStore add a
new config option to the user global git configuration:

- Config section is "filesystem"
- Config subsection is concatenation of
  - Java vendor (system property "java.vendor")
  - Java version (system property "java.version")
  - FileStore's name, on Windows we use the attribute volume:vsn instead
    since  the name is not necessarily unique.
  - separated by '|'
  e.g.
    "AdoptOpenJDK|1.8.0_212-b03|/dev/disk1s1"
  The same prefix is used as for filesystem timestamp resolution, so
  both values are stored in the same config section
- The config key for minmal racy threshold is "minRacyThreshold" as a
  time value, supported time units are those supported by
  DefaultTypedConfigGetter#getTimeUnit
- measure for 3 seconds to limit runtime which depends on hardware, OS
  and Java version being used

If the minimal racy threshold is configured for a given FileStore the
configured value is used instead of measuring it.

When the minimal racy threshold was measured it is persisted in the user
global git configuration.

Rename FileStoreAttributeCache to FileStoreAttributes since this class
is now declared public in order to enable exposing all attributes in one
object.

Example:

[filesystem "AdoptOpenJDK|11.0.3|/dev/disk1s1"]
	timestampResolution = 7000 nanoseconds
	minRacyThreshold = 3440 microseconds

Change-Id: I22195e488453aae8d011b0a8e3276fe3d99deaea
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
Also-By: Marc Strapetz <marc.strapetz@syntevo.com>

By running FileSnapshotTest#detectFileModified we found that the sum of
measured filesystem timestamp resolution and measured clock resolution
may yield a too small interval after a file has been modified which we
need to consider racily clean. In our tests we didn't find this behavior
on all systems we tested on, e.g. on MacOS using APFS and Java 8 and 11
this effect was not observed.

On Linux (SLES 15, kernel 4.12.14-150.22-default) we collected the
following test results using Java 8 and 11:

In 23-98% of 10000 test runs (depending on filesystem type and Java
version) the test failed, which means the effective interval which needs
to be considered racily clean after a file was modified is larger than
the measured file timestamp resolution.

"delta" is the observed interval after a file has been modified but
FileSnapshot did not yet detect the modification:

"resolution" is the measured sum of file timestamp resolution and clock
resolution seen in Java.

Java version    filesystem  failures resolution  min delta   max delta
1.8.0_212-b04   btrfs	    98.6%       1 ms        3.6 ms      6.6 ms
1.8.0_212-b04   ext4        82.6%       3 ms        1.1 ms      4.1 ms
1.8.0_212-b04   xfs         23.8%       4 ms        3.7 ms      3.9 ms
1.8.0_212-b04   zfs         23.1%       3 ms        4.8 ms      5.0 ms
11.0.3+7        btrfs       98.1%       3 us        0.7 ms      4.7 ms
11.0.3+7        ext4        98.1%       6 us        0.7 ms      4.7 ms
11.0.3+7        xfs         98.5%       7 us        0.1 ms      8.0 ms
11.0.3+7        zfs         98.4%       7 us        0.7 ms      5.2 ms

Mac OS
1.8.0_212       APFS        0%          1 s
11.0.3+7        APFS        0%          6 us

The observed delta is not distributed according to a normal gaussian
distribution but rather random in the observed range between "min delta"
and "max delta".

Run this test after measuring file timestamp resolution in
FS.FileAttributeCache to auto-configure JGit since it's unclear what
mechanism is causing this effect.

In FileSnapshot#isRacyClean use the maximum of the measured timestamp
resolution and the measured "delta" as explained above to decide if a
given FileSnapshot is to be considered racily clean. Add a 30% safety
margin to ensure we are on the safe side.

Change-Id: I1c8bb59f6486f174b7bbdc63072777ddbe06694d
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

These are useful to avoid typos, and also for tab completion.

Change-Id: I0f2d267e46b36bc40297c9657c447f3fd8b9f831
Signed-off-by: David Turner <dturner@twosigma.com>

Repeat the test 10000 times to get statistics if measured
fsTimestampResolution is working in practice to detect racy git
situations.

Add a class to compute statistics for this test. Log delta between
lastModified and time when FileSnapshot failed to detect modification.
This happens if the racy git limit determined by measuring filesystem
timestamp resolution and clock resolution is too small. If it would be
correct FileSnapshot would always detect modification or mark it
modified if time since modification is smaller than the racy git limit.

Change-Id: Iabe7af1a7211ca58480f8902d4fa4e366932fc77
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

This should help to detect if measured fsTimeResolution is too small.

Change-Id: Id1f54dbdedb52b17859904e47776fa3a5887b8be
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

When filesystem timestamp resolution is very high some tests don't work
since runtime of the test setup is too long to reach a racily clean
FileSnapshot. Hence skip these tests when timestamp resolution is higher
than 10 millisecond.

Change-Id: Ie47dd10eda22037b5c1ebff6b6becce0654ea807
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

This helps to avoid some time critical tests can't prepare the test
fixture intended since measuring timestamp resolution takes time.

Change-Id: Ib34023e682a106070ca97e98ef16789a4dfb97b4
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

- use Path instead of File
- create test directories, files and output stream using Files methods
- delete unused list "files"

Change-Id: I8c5c601eca9f613efb5618d33b262277df92a06a
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

This enables higher file timestamp resolution on filesystems like ext4,
Mac APFS (1ns) or NTFS (100ns) providing high timestamp resolution on
filesystem level.

Note:
- on some OSes Java 8,9 truncate milliseconds, see
https://bugs.openjdk.java.net/browse/JDK-8177809, fixed in Java 10
- UnixFileAttributes truncates timestamp resolution to microseconds when
converting the internal representation to FileTime exposed in the API,
see https://bugs.openjdk.java.net/browse/JDK-8181493
- WindowsFileAttributes also provides only microsecond resolution

Change-Id: I25ffff31a3c6f725fc345d4ddc2f26da3b88f6f2
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Add a unittest.

In commit I5485db55 ("Fix FileSnapshot's consideration of file size"),
the special casing of UNKNOWN_SIZE was forgotten.

This change, together with I493f3b57b ("Measure file timestamp
resolution used in FileSnapshot") introduced a regression that would
occasionally surface in Gerrit integration tests marked UseLocalDisk,
with the symptom that creating the Admin user in NoteDb failed with a
LOCK_FAILURE.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Change-Id: I7ffd972581f815c144f810481103c7985af5feb0

As reported by Error Prone:

An inner class should be static unless it references members of its
enclosing class. An inner class that is made non-static unnecessarily
uses more memory and does not make the intent of the class clear.

See https://errorprone.info/bugpattern/ClassCanBeStatic

Change-Id: Ib99d120532630dba63cf400cc1c61c318286fc41
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>
(cherry picked from commit ee40efcea4)

Change-Id: I0644690e93c19c224c1d896fe3593f8b38901cbc
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

The only remaining code where the return value is ignored is in tests.
Update them to store the value and perform a basic assertion.

Change-Id: I29ef5bd5dd0648aac3490f9e47ecc74544109652
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

Test that JGit detects that packfiles have changed even if they are
repacked multiple times in one tick of the filesystem timer.

Test that this detection works also when repacking doesn't change the
length or the filekey of the packfile. In this case where a modified
file can't be detected by looking at file metadata JGit should still
detect too fast modification by racy git checks and trigger rescanning
the pack list and consequently rereading of packfile content.

Change-Id: I67682cfb807c58afc6de9375224ff7489d6618fb
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

If the attributes of FileSnapshot don't detect modification of a
packfile read the packfile's checksum and compare it against the
checksum cached in the loaded packfile.

Since reading the checksum needs less IO than reloading the complete
packfile this may help to reduce the overhead to detect modficiation
when a gc completes while ObjectDirectory scans for packfiles in another
thread.

Bug: 546891
Change-Id: I9811b497eb11b8a85ae689081dc5d949ca8c4be5
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>