HistogramDiff: Convert stack recursion to heap managed queue
Each time the longest common substring is found the diff algorithm recurses to reprocess the regions before and after the common string. Large files with many edits can trigger StackOverflowError as the algorithm attempts to process a deeply split tree of regions. This is especially prone to happen in servers where the Java stack size may have been limited to 1M or even 256K. To keep edits produced in order a queue is used to process edits in a depth-first strategy. Change-Id: Iae7260c6934efdffac7c7bee4d3633a8208924f7
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@ -43,6 +43,9 @@
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package org.eclipse.jgit.diff;
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import java.util.ArrayList;
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import java.util.List;
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/**
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* An extended form of Bram Cohen's patience diff algorithm.
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* <p>
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@ -130,15 +133,14 @@ public void setMaxChainLength(int maxLen) {
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public <S extends Sequence> void diffNonCommon(EditList edits,
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HashedSequenceComparator<S> cmp, HashedSequence<S> a,
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HashedSequence<S> b, Edit region) {
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new State<S>(edits, cmp, a, b).diffReplace(region);
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new State<S>(edits, cmp, a, b).diffRegion(region);
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}
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private class State<S extends Sequence> {
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private final HashedSequenceComparator<S> cmp;
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private final HashedSequence<S> a;
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private final HashedSequence<S> b;
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private final List<Edit> queue = new ArrayList<Edit>();
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/** Result edits we have determined that must be made to convert a to b. */
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final EditList edits;
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@ -151,7 +153,13 @@ private class State<S extends Sequence> {
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this.edits = edits;
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}
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void diffReplace(Edit r) {
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void diffRegion(Edit r) {
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diffReplace(r);
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while (!queue.isEmpty())
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diff(queue.remove(queue.size() - 1));
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}
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private void diffReplace(Edit r) {
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Edit lcs = new HistogramDiffIndex<S>(maxChainLength, cmp, a, b, r)
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.findLongestCommonSequence();
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if (lcs != null) {
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@ -163,8 +171,8 @@ void diffReplace(Edit r) {
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//
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edits.add(r);
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} else {
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diff(r.before(lcs));
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diff(r.after(lcs));
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queue.add(r.after(lcs));
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queue.add(r.before(lcs));
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}
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} else if (fallback instanceof LowLevelDiffAlgorithm) {
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