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Improve performance in CharOperation #3386

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Dec 11, 2024
Merged

Improve performance in CharOperation #3386

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2 changes: 1 addition & 1 deletion org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/core/compiler/CharOperation.java
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Original file line number Diff line number Diff line change
Expand Up @@ -3750,7 +3750,7 @@ public static final char[] replace(
next : for (int i = 0; i < max;) {
int index = indexOf(toBeReplaced, array, true, i);
if (index == -1) {
i++;
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The actual bug is here: If index == -1, there is not hit. No need to scan again from the next offset.

What I like about this impl here: it's garbage-free whereas the proposed solution needs to encode the char arrays as ISO or UTF-8.

Do you have time to measure the pressure on the GC if your version of replace is used in tight loops?

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agree, that sounds like a better fix. One should compare the measurement for both solutions.

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If you guys are happier with a smaller change, then I'm fine with it. I'll just abort the loop at that point and be done with it.

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Yes, please

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using "break" instead of "continue" and removing the "next" label would be prettier, but i am OK with this fix

i = max; // end
continue next;
}
if (occurrenceCount == starts.length) {
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22 changes: 22 additions & 0 deletions ....tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/CharOperationTest.java
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Expand Up @@ -170,4 +170,26 @@ public void test012() {
4,
true));
}

public void testReplacePerformance001() {
// This is the test that takes an excessively long time
// The improvement here is drastic, 99% reduction in time
testReplaceImpl("This is one line with no matches\n", 9, 0.01);
}

private void testReplaceImpl(String oneLine, int power, double multiplier) {
String total = oneLine;
for( int i = 0; i < power; i++ ) {
total = total + total; // Double the length
}
total = oneLine + total;

// Now replace
long start = System.currentTimeMillis();
char[] found = CharOperation.replace(total.toCharArray(), new char[]{'/'}, new char[] {'z'});
assertNotNull(found);
long end = System.currentTimeMillis();
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long spent = end - start;
assertTrue(spent < 10);
}
}
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