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IndexPack: Use stack-based recursion for delta resolution 

Replace 'method' with 'heap'-based recursion for resolving deltas.

Git packfile delta-chain depth can exceed 50 levels in certain files
(the packfile of the JGit project itself has >800 objects with
chain-length >50). Using method-based recursion on such packfiles will
quickly throw a StackOverflowError on VMs with constrained stack.

Benefits:

* packfile delta-resolution no longer limited by the maximum number
  of stack frames permitted on the current thread.

* slight performance improvement
  (3% speed increase on the packfile of the JGit project)

Change-Id: I1d9b3a8ba3c6d874d83cb93ebf171c6ab193e6cc
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
stable-0.11
roberto 14 years ago committed by Shawn O. Pearce
parent
4170913b1b
commit
b5f0a7d7ff
1 changed files with 131 additions and 52 deletions
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  1. 155
      org.eclipse.jgit/src/org/eclipse/jgit/transport/IndexPack.java

155
org.eclipse.jgit/src/org/eclipse/jgit/transport/IndexPack.java
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@ -490,15 +490,15 @@ public class IndexPack {
}
private void resolveDeltas(final PackedObjectInfo oe) throws IOException {
final int oldCRC = oe.getCRC();
if (baseById.get(oe) != null || baseByPos.containsKey(oe.getOffset()))
resolveDeltas(oe.getOffset(), oldCRC, Constants.OBJ_BAD, null, oe);
}
UnresolvedDelta children = firstChildOf(oe);
if (children == null)
return;
DeltaVisit visit = new DeltaVisit();
visit.nextChild = children;
private void resolveDeltas(final long pos, final int oldCRC, int type,
byte[] data, PackedObjectInfo oe) throws IOException {
crc.reset();
position(pos);
position(oe.getOffset());
int c = readFrom(Source.FILE);
final int typeCode = (c >> 4) & 7;
long sz = c & 15;
@ -514,20 +514,50 @@ public class IndexPack {
case Constants.OBJ_TREE:
case Constants.OBJ_BLOB:
case Constants.OBJ_TAG:
type = typeCode;
data = inflateAndReturn(Source.FILE, sz);
visit.data = inflateAndReturn(Source.FILE, sz);
break;
default:
throw new IOException(MessageFormat.format(
JGitText.get().unknownObjectType, typeCode));
}
if (oe.getCRC() != (int) crc.getValue()) {
throw new IOException(MessageFormat.format(
JGitText.get().corruptionDetectedReReadingAt,
oe.getOffset()));
}
resolveDeltas(visit.next(), typeCode);
}
private void resolveDeltas(DeltaVisit visit, final int type)
throws IOException {
do {
final long pos = visit.delta.position;
crc.reset();
position(pos);
int c = readFrom(Source.FILE);
final int typeCode = (c >> 4) & 7;
long sz = c & 15;
int shift = 4;
while ((c & 0x80) != 0) {
c = readFrom(Source.FILE);
sz += (c & 0x7f) << shift;
shift += 7;
}
switch (typeCode) {
case Constants.OBJ_OFS_DELTA: {
c = readFrom(Source.FILE) & 0xff;
while ((c & 128) != 0)
c = readFrom(Source.FILE) & 0xff;
data = BinaryDelta.apply(data, inflateAndReturn(Source.FILE, sz));
visit.data = BinaryDelta.apply(visit.parent.data, inflateAndReturn(Source.FILE, sz));
break;
}
case Constants.OBJ_REF_DELTA: {
crc.update(buf, fill(Source.FILE, 20), 20);
use(20);
data = BinaryDelta.apply(data, inflateAndReturn(Source.FILE, sz));
visit.data = BinaryDelta.apply(visit.parent.data, inflateAndReturn(Source.FILE, sz));
break;
}
default:
@ -535,22 +565,25 @@ public class IndexPack {
}
final int crc32 = (int) crc.getValue();
if (oldCRC != crc32)
if (visit.delta.crc != crc32)
throw new IOException(MessageFormat.format(JGitText.get().corruptionDetectedReReadingAt, pos));
if (oe == null) {
objectDigest.update(Constants.encodedTypeString(type));
objectDigest.update((byte) ' ');
objectDigest.update(Constants.encodeASCII(data.length));
objectDigest.update(Constants.encodeASCII(visit.data.length));
objectDigest.update((byte) 0);
objectDigest.update(data);
objectDigest.update(visit.data);
tempObjectId.fromRaw(objectDigest.digest(), 0);
verifySafeObject(tempObjectId, type, data);
verifySafeObject(tempObjectId, type, visit.data);
PackedObjectInfo oe;
oe = new PackedObjectInfo(pos, crc32, tempObjectId);
addObjectAndTrack(oe);
}
resolveChildDeltas(pos, type, data, oe);
visit.nextChild = firstChildOf(oe);
visit = visit.next();
} while (visit != null);
}
private UnresolvedDelta removeBaseById(final AnyObjectId id){
@ -569,29 +602,34 @@ public class IndexPack {
return tail;
}
private void resolveChildDeltas(final long pos, int type, byte[] data,
PackedObjectInfo oe) throws IOException {
private UnresolvedDelta firstChildOf(PackedObjectInfo oe) {
UnresolvedDelta a = reverse(removeBaseById(oe));
UnresolvedDelta b = reverse(baseByPos.remove(pos));
while (a != null && b != null) {
if (a.position < b.position) {
resolveDeltas(a.position, a.crc, type, data, null);
UnresolvedDelta b = reverse(baseByPos.remove(oe.getOffset()));
if (a == null)
return b;
if (b == null)
return a;
UnresolvedDelta first = null;
UnresolvedDelta last = null;
while (a != null || b != null) {
UnresolvedDelta curr;
if (b == null || (a != null && a.position < b.position)) {
curr = a;
a = a.next;
} else {
resolveDeltas(b.position, b.crc, type, data, null);
curr = b;
b = b.next;
}
if (last != null)
last.next = curr;
else
first = curr;
last = curr;
curr.next = null;
}
resolveChildDeltaChain(type, data, a);
resolveChildDeltaChain(type, data, b);
}
private void resolveChildDeltaChain(final int type, final byte[] data,
UnresolvedDelta a) throws IOException {
while (a != null) {
resolveDeltas(a.position, a.crc, type, data, null);
a = a.next;
}
return first;
}
private void fixThinPack(final ProgressMonitor progress) throws IOException {
@ -617,18 +655,22 @@ public class IndexPack {
missing.add(baseId);
continue;
}
final byte[] data = ldr.getCachedBytes(Integer.MAX_VALUE);
final DeltaVisit visit = new DeltaVisit();
visit.data = ldr.getCachedBytes(Integer.MAX_VALUE);
final int typeCode = ldr.getType();
final PackedObjectInfo oe;
crc.reset();
packOut.seek(end);
writeWhole(def, typeCode, data);
writeWhole(def, typeCode, visit.data);
oe = new PackedObjectInfo(end, (int) crc.getValue(), baseId);
entries[entryCount++] = oe;
end = packOut.getFilePointer();
resolveChildDeltas(oe.getOffset(), typeCode, data, oe);
visit.nextChild = firstChildOf(oe);
resolveDeltas(visit.next(), typeCode);
if (progress.isCancelled())
throw new IOException(JGitText.get().downloadCancelledDuringIndexing);
}
@ -1076,6 +1118,43 @@ public class IndexPack {
}
}
private static class DeltaVisit {
final UnresolvedDelta delta;
byte[] data;
DeltaVisit parent;
UnresolvedDelta nextChild;
DeltaVisit() {
this.delta = null; // At the root of the stack we have a base.
}
DeltaVisit(DeltaVisit parent) {
this.parent = parent;
this.delta = parent.nextChild;
parent.nextChild = delta.next;
}
DeltaVisit next() {
// If our parent has no more children, discard it.
if (parent != null && parent.nextChild == null) {
parent.data = null;
parent = parent.parent;
}
if (nextChild != null)
return new DeltaVisit(this);
// If we have no child ourselves, our parent must (if it exists),
// due to the discard rule above. With no parent, we are done.
if (parent != null)
return new DeltaVisit(parent);
return null;
}
}
/**
* Rename the pack to it's final name and location and open it.
* <p>

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