org.eclipse.jgit.storage.dfs.DfsObjDatabase Maven / Gradle / Ivy
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* This program and the accompanying materials are made available
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package org.eclipse.jgit.storage.dfs;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.atomic.AtomicReference;
import org.eclipse.jgit.lib.ObjectDatabase;
import org.eclipse.jgit.lib.ObjectInserter;
import org.eclipse.jgit.lib.ObjectReader;
import org.eclipse.jgit.storage.pack.PackExt;
/** Manages objects stored in {@link DfsPackFile} on a storage system. */
public abstract class DfsObjDatabase extends ObjectDatabase {
private static final PackList NO_PACKS = new PackList(new DfsPackFile[0]);
/** Sources for a pack file. */
public static enum PackSource {
/** The pack is created by ObjectInserter due to local activity. */
INSERT,
/**
* The pack is created by PackParser due to a network event.
*
* A received pack can be from either a push into the repository, or a
* fetch into the repository, the direction doesn't matter. A received
* pack was built by the remote Git implementation and may not match the
* storage layout preferred by this version. Received packs are likely
* to be either compacted or garbage collected in the future.
*/
RECEIVE,
/**
* Pack was created by Git garbage collection by this implementation.
*
* This source is only used by the {@link DfsGarbageCollector} when it
* builds a pack file by traversing the object graph and copying all
* reachable objects into a new pack stream.
*
* @see DfsGarbageCollector
*/
GC,
/**
* The pack was created by compacting multiple packs together.
*
* Packs created by compacting multiple packs together aren't nearly as
* efficient as a fully garbage collected repository, but may save disk
* space by reducing redundant copies of base objects.
*
* @see DfsPackCompactor
*/
COMPACT,
/**
* Pack was created by Git garbage collection.
*
* This pack contains only unreachable garbage that was found during the
* last GC pass. It is retained in a new pack until it is safe to prune
* these objects from the repository.
*/
UNREACHABLE_GARBAGE;
}
private final AtomicReference packList;
private final DfsRepository repository;
private DfsReaderOptions readerOptions;
/**
* Initialize an object database for our repository.
*
* @param repository
* repository owning this object database.
*
* @param options
* how readers should access the object database.
*/
protected DfsObjDatabase(DfsRepository repository,
DfsReaderOptions options) {
this.repository = repository;
this.packList = new AtomicReference(NO_PACKS);
this.readerOptions = options;
}
/** @return configured reader options, such as read-ahead. */
public DfsReaderOptions getReaderOptions() {
return readerOptions;
}
@Override
public ObjectReader newReader() {
return new DfsReader(this);
}
@Override
public ObjectInserter newInserter() {
return new DfsInserter(this);
}
/**
* Scan and list all available pack files in the repository.
*
* @return list of available packs. The returned array is shared with the
* implementation and must not be modified by the caller.
* @throws IOException
* the pack list cannot be initialized.
*/
public DfsPackFile[] getPacks() throws IOException {
return scanPacks(NO_PACKS).packs;
}
/** @return repository owning this object database. */
protected DfsRepository getRepository() {
return repository;
}
/**
* List currently known pack files in the repository, without scanning.
*
* @return list of available packs. The returned array is shared with the
* implementation and must not be modified by the caller.
*/
public DfsPackFile[] getCurrentPacks() {
return packList.get().packs;
}
/**
* Generate a new unique name for a pack file.
*
* @param source
* where the pack stream is created.
* @return a unique name for the pack file. Must not collide with any other
* pack file name in the same DFS.
* @throws IOException
* a new unique pack description cannot be generated.
*/
protected abstract DfsPackDescription newPack(PackSource source)
throws IOException;
/**
* Commit a pack and index pair that was written to the DFS.
*
* Committing the pack/index pair makes them visible to readers. The JGit
* DFS code always writes the pack, then the index. This allows a simple
* commit process to do nothing if readers always look for both files to
* exist and the DFS performs atomic creation of the file (e.g. stream to a
* temporary file and rename to target on close).
*
* During pack compaction or GC the new pack file may be replacing other
* older files. Implementations should remove those older files (if any) as
* part of the commit of the new file.
*
* This method is a trivial wrapper around
* {@link #commitPackImpl(Collection, Collection)} that calls the
* implementation and fires events.
*
* @param desc
* description of the new packs.
* @param replaces
* if not null, list of packs to remove.
* @throws IOException
* the packs cannot be committed. On failure a rollback must
* also be attempted by the caller.
*/
protected void commitPack(Collection desc,
Collection replaces) throws IOException {
commitPackImpl(desc, replaces);
getRepository().fireEvent(new DfsPacksChangedEvent());
}
/**
* Implementation of pack commit.
*
* @see #commitPack(Collection, Collection)
*
* @param desc
* description of the new packs.
* @param replaces
* if not null, list of packs to remove.
* @throws IOException
* the packs cannot be committed.
*/
protected abstract void commitPackImpl(Collection desc,
Collection replaces) throws IOException;
/**
* Try to rollback a pack creation.
*
* JGit DFS always writes the pack first, then the index. If the pack does
* not yet exist, then neither does the index. A safe DFS implementation
* would try to remove both files to ensure they are really gone.
*
* A rollback does not support failures, as it only occurs when there is
* already a failure in progress. A DFS implementor may wish to log
* warnings/error messages when a rollback fails, but should not send new
* exceptions up the Java callstack.
*
* @param desc
* pack to delete.
*/
protected abstract void rollbackPack(Collection desc);
/**
* List the available pack files.
*
* The returned list must support random access and must be mutable by the
* caller. It is sorted in place using the natural sorting of the returned
* DfsPackDescription objects.
*
* @return available packs. May be empty if there are no packs.
* @throws IOException
* the packs cannot be listed and the object database is not
* functional to the caller.
*/
protected abstract List listPacks() throws IOException;
/**
* Open a pack, pack index, or other related file for reading.
*
* @param desc
* description of pack related to the data that will be read.
* This is an instance previously obtained from
* {@link #listPacks()}, but not necessarily from the same
* DfsObjDatabase instance.
* @param ext
* file extension that will be read i.e "pack" or "idx".
* @return channel to read the file.
* @throws FileNotFoundException
* the file does not exist.
* @throws IOException
* the file cannot be opened.
*/
protected abstract ReadableChannel openFile(
DfsPackDescription desc, PackExt ext)
throws FileNotFoundException, IOException;
/**
* Open a pack, pack index, or other related file for writing.
*
* @param desc
* description of pack related to the data that will be written.
* This is an instance previously obtained from
* {@link #newPack(PackSource)}.
* @param ext
* file extension that will be written i.e "pack" or "idx".
* @return channel to write the file.
* @throws IOException
* the file cannot be opened.
*/
protected abstract DfsOutputStream writeFile(
DfsPackDescription desc, PackExt ext) throws IOException;
void addPack(DfsPackFile newPack) throws IOException {
PackList o, n;
do {
o = packList.get();
if (o == NO_PACKS) {
// The repository may not have needed any existing objects to
// complete the current task of creating a pack (e.g. push of a
// pack with no external deltas). Because we don't scan for
// newly added packs on missed object lookups, scan now to
// make sure all older packs are available in the packList.
o = scanPacks(o);
// Its possible the scan identified the pack we were asked to
// add, as the pack was already committed via commitPack().
// If this is the case return without changing the list.
for (DfsPackFile p : o.packs) {
if (p == newPack)
return;
}
}
DfsPackFile[] packs = new DfsPackFile[1 + o.packs.length];
packs[0] = newPack;
System.arraycopy(o.packs, 0, packs, 1, o.packs.length);
n = new PackList(packs);
} while (!packList.compareAndSet(o, n));
}
private PackList scanPacks(final PackList original) throws IOException {
PackList o, n;
synchronized (packList) {
do {
o = packList.get();
if (o != original) {
// Another thread did the scan for us, while we
// were blocked on the monitor above.
//
return o;
}
n = scanPacksImpl(o);
if (n == o)
return n;
} while (!packList.compareAndSet(o, n));
}
getRepository().fireEvent(new DfsPacksChangedEvent());
return n;
}
private PackList scanPacksImpl(PackList old) throws IOException {
DfsBlockCache cache = DfsBlockCache.getInstance();
Map forReuse = reuseMap(old);
List scanned = listPacks();
Collections.sort(scanned);
List list = new ArrayList(scanned.size());
boolean foundNew = false;
for (DfsPackDescription dsc : scanned) {
DfsPackFile oldPack = forReuse.remove(dsc);
if (oldPack != null) {
list.add(oldPack);
} else {
list.add(cache.getOrCreate(dsc, null));
foundNew = true;
}
}
for (DfsPackFile p : forReuse.values())
p.close();
if (list.isEmpty())
return new PackList(NO_PACKS.packs);
if (!foundNew)
return old;
return new PackList(list.toArray(new DfsPackFile[list.size()]));
}
private static Map reuseMap(PackList old) {
Map forReuse
= new HashMap();
for (DfsPackFile p : old.packs) {
if (p.invalid()) {
// The pack instance is corrupted, and cannot be safely used
// again. Do not include it in our reuse map.
//
p.close();
continue;
}
DfsPackFile prior = forReuse.put(p.getPackDescription(), p);
if (prior != null) {
// This should never occur. It should be impossible for us
// to have two pack files with the same name, as all of them
// came out of the same directory. If it does, we promised to
// close any PackFiles we did not reuse, so close the second,
// readers are likely to be actively using the first.
//
forReuse.put(prior.getPackDescription(), prior);
p.close();
}
}
return forReuse;
}
/** Clears the cached list of packs, forcing them to be scanned again. */
protected void clearCache() {
packList.set(NO_PACKS);
}
@Override
public void close() {
// PackList packs = packList.get();
packList.set(NO_PACKS);
// TODO Close packs if they aren't cached.
// for (DfsPackFile p : packs.packs)
// p.close();
}
private static final class PackList {
/** All known packs, sorted. */
final DfsPackFile[] packs;
PackList(final DfsPackFile[] packs) {
this.packs = packs;
}
}
}