/*
* Copyright (C) 2010, Google Inc.
* and other copyright owners as documented in the project's IP log.
*
* This program and the accompanying materials are made available
* under the terms of the Eclipse Distribution License v1.0 which
* accompanies this distribution, is reproduced below, and is
* available at http://www.eclipse.org/org/documents/edl-v10.php
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* - Redistributions of source code must retain the above copyright
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package org.eclipse.jgit.storage.pack;
import java.io.EOFException;
import java.io.IOException;
import java.io.OutputStream;
import java.util.zip.Deflater;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.LargeObjectException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.lib.ObjectReader;
import org.eclipse.jgit.lib.ProgressMonitor;
import org.eclipse.jgit.util.TemporaryBuffer;
class DeltaWindow {
private static final int NEXT_RES = 0;
private static final int NEXT_SRC = 1;
private final PackConfig config;
private final DeltaCache deltaCache;
private final ObjectReader reader;
private final DeltaWindowEntry[] window;
/** Maximum number of bytes to admit to the window at once. */
private final long maxMemory;
/** Maximum depth we should create for any delta chain. */
private final int maxDepth;
/** Amount of memory we have loaded right now. */
private long loaded;
// The object we are currently considering needs a lot of state:
/** Position of {@link #res} within {@link #window} array. */
private int resSlot;
/**
* Maximum delta chain depth the current object can have.
* <p>
* This can be smaller than {@link #maxDepth}.
*/
private int resMaxDepth;
/** Window entry of the object we are currently considering. */
private DeltaWindowEntry res;
/** If we have a delta for {@link #res}, this is the shortest found yet. */
private TemporaryBuffer.Heap bestDelta;
/** If we have {@link #bestDelta}, the window position it was created by. */
private int bestSlot;
/** Used to compress cached deltas. */
private Deflater deflater;
DeltaWindow(PackConfig pc, DeltaCache dc, ObjectReader or) {
config = pc;
deltaCache = dc;
reader = or;
// C Git increases the window size supplied by the user by 1.
// We don't know why it does this, but if the user asks for
// window=10, it actually processes with window=11. Because
// the window size has the largest direct impact on the final
// pack file size, we match this odd behavior here to give us
// a better chance of producing a similar sized pack as C Git.
//
// We would prefer to directly honor the user's request since
// PackWriter has a minimum of 2 for the window size, but then
// users might complain that JGit is creating a bigger pack file.
//
window = new DeltaWindowEntry[config.getDeltaSearchWindowSize() + 1];
for (int i = 0; i < window.length; i++)
window[i] = new DeltaWindowEntry();
maxMemory = config.getDeltaSearchMemoryLimit();
maxDepth = config.getMaxDeltaDepth();
}
void search(ProgressMonitor monitor, ObjectToPack[] toSearch, int off,
int cnt) throws IOException {
try {
for (int end = off + cnt; off < end; off++) {
monitor.update(1);
res = window[resSlot];
if (0 < maxMemory) {
clear(res);
int tail = next(resSlot);
final long need = estimateSize(toSearch[off]);
while (maxMemory < loaded + need && tail != resSlot) {
clear(window[tail]);
tail = next(tail);
}
}
res.set(toSearch[off]);
if (res.object.isDoNotDelta()) {
// PackWriter marked edge objects with the
// do-not-delta flag. They are the only ones
// that appear in toSearch with it set, but
// we don't actually want to make a delta for
// them, just need to push them into the window
// so they can be read by other objects.
//
keepInWindow();
} else {
// Search for a delta for the current window slot.
//
search();
}
}
} finally {
if (deflater != null)
deflater.end();
}
}
private static long estimateSize(ObjectToPack ent) {
return DeltaIndex.estimateIndexSize(ent.getWeight());
}
private void clear(DeltaWindowEntry ent) {
if (ent.index != null)
loaded -= ent.index.getIndexSize();
else if (res.buffer != null)
loaded -= ent.buffer.length;
ent.set(null);
}
private void search() throws IOException {
// TODO(spearce) If the object is used as a base for other
// objects in this pack we should limit the depth we create
// for ourselves to be the remainder of our longest dependent
// chain and the configured maximum depth. This can happen
// when the dependents are being reused out a pack, but we
// cannot be because we are near the edge of a thin pack.
//
resMaxDepth = maxDepth;
// Loop through the window backwards, considering every entry.
// This lets us look at the bigger objects that came before.
//
for (int srcSlot = prior(resSlot); srcSlot != resSlot; srcSlot = prior(srcSlot)) {
DeltaWindowEntry src = window[srcSlot];
if (src.empty())
break;
if (delta(src, srcSlot) == NEXT_RES) {
bestDelta = null;
return;
}
}
// We couldn't find a suitable delta for this object, but it may
// still be able to act as a base for another one.
//
if (bestDelta == null) {
keepInWindow();
return;
}
// Select this best matching delta as the base for the object.
//
ObjectToPack srcObj = window[bestSlot].object;
ObjectToPack resObj = res.object;
if (srcObj.isDoNotDelta()) {
// The source (the delta base) is an edge object outside of the
// pack. Its part of the common base set that the peer already
// has on hand, so we don't want to send it. We have to store
// an ObjectId and *NOT* an ObjectToPack for the base to ensure
// the base isn't included in the outgoing pack file.
//
resObj.setDeltaBase(srcObj.copy());
} else {
// The base is part of the pack we are sending, so it should be
// a direct pointer to the base.
//
resObj.setDeltaBase(srcObj);
}
resObj.setDeltaDepth(srcObj.getDeltaDepth() + 1);
resObj.clearReuseAsIs();
cacheDelta(srcObj, resObj);
// Discard the cached best result, otherwise it leaks.
//
bestDelta = null;
// If this should be the end of a chain, don't keep
// it in the window. Just move on to the next object.
//
if (resObj.getDeltaDepth() == maxDepth)
return;
shuffleBaseUpInPriority();
keepInWindow();
}
private int delta(final DeltaWindowEntry src, final int srcSlot)
throws IOException {
// Objects must use only the same type as their delta base.
// If we are looking at something where that isn't true we
// have exhausted everything of the correct type and should
// move on to the next thing to examine.
//
if (src.type() != res.type()) {
keepInWindow();
return NEXT_RES;
}
// Only consider a source with a short enough delta chain.
if (src.depth() > resMaxDepth)
return NEXT_SRC;
// Estimate a reasonable upper limit on delta size.
int msz = deltaSizeLimit(res, resMaxDepth, src);
if (msz <= 8)
return NEXT_SRC;
// If we have to insert a lot to make this work, find another.
if (res.size() - src.size() > msz)
return NEXT_SRC;
// If the sizes are radically different, this is a bad pairing.
if (res.size() < src.size() / 16)
return NEXT_SRC;
DeltaIndex srcIndex;
try {
srcIndex = index(src);
} catch (LargeObjectException tooBig) {
// If the source is too big to work on, skip it.
dropFromWindow(srcSlot);
return NEXT_SRC;
} catch (IOException notAvailable) {
if (src.object.isDoNotDelta()) {
// This is an edge that is suddenly not available.
dropFromWindow(srcSlot);
return NEXT_SRC;
} else {
throw notAvailable;
}
}
byte[] resBuf;
try {
resBuf = buffer(res);
} catch (LargeObjectException tooBig) {
// If its too big, move on to another item.
return NEXT_RES;
}
// If we already have a delta for the current object, abort
// encoding early if this new pairing produces a larger delta.
if (bestDelta != null && bestDelta.length() < msz)
msz = (int) bestDelta.length();
TemporaryBuffer.Heap delta = new TemporaryBuffer.Heap(msz);
try {
if (!srcIndex.encode(delta, resBuf, msz))
return NEXT_SRC;
} catch (IOException deltaTooBig) {
// This only happens when the heap overflows our limit.
return NEXT_SRC;
}
if (isBetterDelta(src, delta)) {
bestDelta = delta;
bestSlot = srcSlot;
}
return NEXT_SRC;
}
private void cacheDelta(ObjectToPack srcObj, ObjectToPack resObj) {
if (Integer.MAX_VALUE < bestDelta.length())
return;
int rawsz = (int) bestDelta.length();
if (deltaCache.canCache(rawsz, srcObj, resObj)) {
try {
byte[] zbuf = new byte[deflateBound(rawsz)];
ZipStream zs = new ZipStream(deflater(), zbuf);
bestDelta.writeTo(zs, null);
bestDelta = null;
int len = zs.finish();
resObj.setCachedDelta(deltaCache.cache(zbuf, len, rawsz));
resObj.setCachedSize(rawsz);
} catch (IOException err) {
deltaCache.credit(rawsz);
} catch (OutOfMemoryError err) {
deltaCache.credit(rawsz);
}
}
}
private static int deflateBound(int insz) {
return insz + ((insz + 7) >> 3) + ((insz + 63) >> 6) + 11;
}
private void shuffleBaseUpInPriority() {
// Shuffle the entire window so that the best match we just used
// is at our current index, and our current object is at the index
// before it. Slide any entries in between to make space.
//
window[resSlot] = window[bestSlot];
DeltaWindowEntry next = res;
int slot = prior(resSlot);
for (; slot != bestSlot; slot = prior(slot)) {
DeltaWindowEntry e = window[slot];
window[slot] = next;
next = e;
}
window[slot] = next;
}
private void keepInWindow() {
resSlot = next(resSlot);
}
private int next(int slot) {
if (++slot == window.length)
return 0;
return slot;
}
private int prior(int slot) {
if (slot == 0)
return window.length - 1;
return slot - 1;
}
private void dropFromWindow(@SuppressWarnings("unused") int srcSlot) {
// We should drop the current source entry from the window,
// it is somehow invalid for us to work with.
}
private boolean isBetterDelta(DeltaWindowEntry src,
TemporaryBuffer.Heap resDelta) {
if (bestDelta == null)
return true;
// If both delta sequences are the same length, use the one
// that has a shorter delta chain since it would be faster
// to access during reads.
//
if (resDelta.length() == bestDelta.length())
return src.depth() < window[bestSlot].depth();
return resDelta.length() < bestDelta.length();
}
private static int deltaSizeLimit(DeltaWindowEntry res, int maxDepth,
DeltaWindowEntry src) {
// Ideally the delta is at least 50% of the original size,
// but we also want to account for delta header overhead in
// the pack file (to point to the delta base) so subtract off
// some of those header bytes from the limit.
//
final int limit = res.size() / 2 - 20;
// Distribute the delta limit over the entire chain length.
// This is weighted such that deeper items in the chain must
// be even smaller than if they were earlier in the chain, as
// they cost significantly more to unpack due to the increased
// number of recursive unpack calls.
//
final int remainingDepth = maxDepth - src.depth();
return (limit * remainingDepth) / maxDepth;
}
private DeltaIndex index(DeltaWindowEntry ent)
throws MissingObjectException, IncorrectObjectTypeException,
IOException, LargeObjectException {
DeltaIndex idx = ent.index;
if (idx == null) {
try {
idx = new DeltaIndex(buffer(ent));
} catch (OutOfMemoryError noMemory) {
LargeObjectException e = new LargeObjectException(ent.object);
e.initCause(noMemory);
throw e;
}
if (0 < maxMemory)
loaded += idx.getIndexSize() - idx.getSourceSize();
ent.index = idx;
}
return idx;
}
private byte[] buffer(DeltaWindowEntry ent) throws MissingObjectException,
IncorrectObjectTypeException, IOException, LargeObjectException {
byte[] buf = ent.buffer;
if (buf == null) {
buf = PackWriter.buffer(config, reader, ent.object);
if (0 < maxMemory)
loaded += buf.length;
ent.buffer = buf;
}
return buf;
}
private Deflater deflater() {
if (deflater == null)
deflater = new Deflater(config.getCompressionLevel());
else
deflater.reset();
return deflater;
}
static final class ZipStream extends OutputStream {
private final Deflater deflater;
private final byte[] zbuf;
private int outPtr;
ZipStream(Deflater deflater, byte[] zbuf) {
this.deflater = deflater;
this.zbuf = zbuf;
}
int finish() throws IOException {
deflater.finish();
for (;;) {
if (outPtr == zbuf.length)
throw new EOFException();
int n = deflater.deflate(zbuf, outPtr, zbuf.length - outPtr);
if (n == 0) {
if (deflater.finished())
return outPtr;
throw new IOException();
}
outPtr += n;
}
}
@Override
public void write(byte[] b, int off, int len) throws IOException {
deflater.setInput(b, off, len);
for (;;) {
if (outPtr == zbuf.length)
throw new EOFException();
int n = deflater.deflate(zbuf, outPtr, zbuf.length - outPtr);
if (n == 0) {
if (deflater.needsInput())
break;
throw new IOException();
}
outPtr += n;
}
}
@Override
public void write(int b) throws IOException {
throw new UnsupportedOperationException();
}
}
}