When Repository.close() decrements the useCount to 0 currently the cache
immediately evicts the repository from WindowCache and RepositoryCache.
This leads to I/O overhead on busy repositories because pack files and
references are inserted and deleted from the cache frequently.

This commit defers the eviction of a repository from the caches until
last use of the repository is older than time to live. The eviction is
handled by a background task running periodically.

Add two new configuration parameters:
* core.repositoryCacheExpireAfter: cache entries are evicted if the
cache entry wasn't accessed longer than this time in milliseconds
* core.repositoryCacheCleanupDelay: defines the interval in milliseconds
for running a background task evicting expired cache entries. If set to
-1 the delay is set to min(repositoryCacheExpireAfter, 10 minutes). If
set to 0 the time based eviction is switched off and no background task
is started. If time based eviction is switched off the JVM can still
evict cache entries if heap memory is running low.

Change-Id: I4a0214ad8b4a193985dda6a0ade63b70bdb948d7
Also-by: Matthias Sohn <matthias.sohn@sap.com>
Also-by: Hugo Arès <hugo.ares@ericsson.com>
Also-by: Sasa Zivkov <sasa.zivkov@sap.com>

RepositoryCache has 2 methods to remove a repository from the cache but
they are never called when a repository is closed. Users of the cache
were expected to call one of those 2 methods but how could they have
called them at proper time without having visibility of the repository
usage count.

Ideally, I would have reworked the RepositoryCache to wrap any
repository it opens in a class that would be responsible to unregister
them from the cache when it's really closed, i.e. when usage counter
reaches 0. The problem preventing the wrapping solution is the
RepositoryCache.register method that allows to register an already
opened repository in the cache. Such repositories cannot be wrapped
because callers are still holding a reference on the unwrapped
repository.

Document that RepositoryCache.close method is removing the repository
from the cache as well as closing it and rework
RepositoryCache.unregister method to only remove the repository from the
cache. Use the latter to unregister repository when Repository.doClose
is getting executed.

Change-Id: Ia364816e4da8d7b6cfa72f10758ca31aa8a1f9db
Signed-off-by: Hugo Arès <hugo.ares@ericsson.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Repository has a usage counter that is initialized to 1 at
instantiation and this counter is decremented when Repository.close
method is called. There is also a Repository.incrementOpen method that
RepositoryCache uses to increment the usage count when it's returning a
repository that is already opened.

The problem was that RepositoryCache was incrementing the usage count
for repositories that it just opened or registered. The usage count was
2 when it should have been 1.

Incrementing usage count is now only be done for repository that are
served from the cache.

This bug is causing slow memory increase of our Gerrit server until the
server become slow. Even if the RepositoryCache is using SoftReference,
it seems that the JVM is not garbage collecting the repositories because
it's not yet on the edge of being out of memory.

To test this change, I replicated all repositories(11k) from Gerrit
master to one slave. The Gerrit master used memory after this test was
10GB without this change and 3.5GB with.

Change-Id: I86c7b36174e384f106b51fe92f306018fd1dbdf0
Signed-off-by: Hugo Arès <hugo.ares@ericsson.com>

Add methods that allow to unregister repositories from the
RepositoryCache individually.

Bug: 470234
Change-Id: Ib918a634d829c9898072ae7bdeb22b099a32b1c9
Signed-off-by: Tobias Oberlies <tobias.oberlies@sap.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Change-Id: I63a74651689c10426d5f150ab2e027c6b63cab95
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

This breaks all existing callers once. Applications are not supposed
to build against the internal storage API unless they can accept API
churn and make necessary updates as versions change.

Change-Id: I2ab1327c202ef2003565e1b0770a583970e432e9

A few classes such as Constanrs are marked with @SuppressWarnings, as are
toString() methods with many liternal, but otherwise $NLS-n$ is used for
string containing text that should not be translated. A few literals may
fall into the gray zone, but mostly I've tried to only tag the obvious
ones.

Change-Id: I22e50a77e2bf9e0b842a66bdf674e8fa1692f590

This move isolates all of the local file specific implementation code
into a single package, where their package-private methods and support
classes are properly hidden away from the rest of the core library.

Because of the sheer number of files impacted, I have limited this
change to only the renames and the updated imports.

Change-Id: Icca4884e1a418f83f8b617d0c4c78b73d8a4bd17
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Some types of repositories might not be stored on local disk.  For
these, they will most likely return null for getDirectory() as the
java.io.File type cannot describe where their storage is, its not
in the host's filesystem.

Document that getDirectory() can return null now, and update all
current non-test callers in JGit that might run into problems on
such repositories.  For the most part, just act like its bare.

Change-Id: I061236a691372a267fd7d41f0550650e165d2066
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

To support other storage models other than just the local filesystem,
we split the Repository class into a nearly abstract interface and
then create a concrete subclass called FileRepository with the file
based IO implementation.

We are using an abstract class for Repository rather than the much
more generic interface, as implementers will want to inherit a large
array of utility functions, such as resolve(String).  Having these in
a base class makes it easy to inherit them.

This isn't the final home for lib.FileRepository.  Future changes
will rename it into storage.file.FileRepository, but to do that we
need to also move a number of other related class, which we aren't
quite ready to do.

Change-Id: I1bd54ea0500337799a8e792874c272eb14d555f7
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

On Windows, FS_Win32_Cygwin has been used if a Cygwin Git installation
is present in the PATH. Assuming that the user works with the Cygwin
Git installation may result in unnecessary overhead if he actually
does not.

Applications built on top of jgit may have more knowledge on the
actually used Git client (Cygwin or not) and hence should be able to
configure which FS to use accordingly.

Change-Id: Ifc4278078b298781d55cf5421e9647a21fa5db24

Change-Id: Icfe9205994c6810fcd880054a586e9eef29df9a1
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>

Not all occurrences of ".git" are replaced by this constant, only
those where it actually refers to the directory with that name, i.e
not the ".git" directory suffix.

Asserts and comment are also excluded from replacement.

Change-Id: I65a9da89aedd53817f2ea3eaab4f9c2bed35d7ee
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>

According the javadoc, and implied by the name of the class, NB
is about network byte order. The purpose of moving the IO only,
and non-byte order related functions to another class is to
make it easier for new contributors to understand that they
can use these functions in general and it's also makes it easier
to understand where to put new IO related utility functions

Change-Id: I4a9f6b39d5564bc8a694b366e7ff3cc758c5181b
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Per CQ 3448 this is the initial contribution of the JGit project
to eclipse.org.  It is derived from the historical JGit repository
at commit 3a2dd9921c.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>