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8261859: gc/g1/TestStringDeduplicationTableRehash.java failed with "R…
…untimeException: 'Rehash Count: 0' found in stdout"

Reviewed-by: ayang, sjohanss, tschatzl
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Kim Barrett committed Mar 2, 2021
1 parent f18c019 commit f304b74e0aeeeaa8aa7c552e04aec43040995300
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Showing 2 changed files with 39 additions and 26 deletions.
@@ -395,32 +395,33 @@ bool StringDedupTable::is_rehashing() {
StringDedupTable* StringDedupTable::prepare_resize() {
size_t size = _table->_size;

// Check if the hashtable needs to be resized
// Decide whether to resize, and compute desired new size if so.
if (_table->_entries > _table->_grow_threshold) {
// Grow table, double the size
size *= 2;
if (size > _max_size) {
// Too big, don't resize
return NULL;
// Compute new size.
size_t needed = _table->_entries / _grow_load_factor;
if (needed < _max_size) {
size = round_up_power_of_2(needed);
} else {
size = _max_size;
}
} else if (_table->_entries < _table->_shrink_threshold) {
// Shrink table, half the size
size /= 2;
if (size < _min_size) {
// Too small, don't resize
return NULL;
}
} else if (StringDeduplicationResizeALot) {
// Force grow
size *= 2;
if (size > _max_size) {
// Too big, force shrink instead
size /= 4;
// Compute new size. We can't shrink by more than a factor of 2,
// because the partitioning for parallelization doesn't support more.
if (size > _min_size) size /= 2;
}
// If no change in size needed (and not forcing resize) then done.
if (size == _table->_size) {
if (!StringDeduplicationResizeALot) {
return NULL; // Don't resize.
} else if (size < _max_size) {
size *= 2; // Force grow, but not past _max_size.
} else {
size /= 2; // Can't force grow, so force shrink instead.
}
} else {
// Resize not needed
return NULL;
}
assert(size <= _max_size, "invariant: %zu", size);
assert(size >= _min_size, "invariant: %zu", size);
assert(is_power_of_2(size), "invariant: %zu", size);

// Update statistics
_resize_count++;
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2014, 2019, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2014, 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@@ -43,6 +43,9 @@ class TestStringDeduplicationTools {
private static final int MB = 1024 * 1024;
private static final int StringLength = 50;

private static final int LargeNumberOfStrings = 10000;
private static final int SmallNumberOfStrings = 10;

private static Field valueField;
private static Unsafe unsafe;
private static byte[] dummy;
@@ -69,7 +72,11 @@ private static Object getValue(String string) {
}

private static void doFullGc(int numberOfTimes) {
List<List<String>> newStrings = new ArrayList<List<String>>();
for (int i = 0; i < numberOfTimes; i++) {
// Create some more strings for every collection, to ensure
// there will be deduplication work that will be reported.
newStrings.add(createStrings(SmallNumberOfStrings, SmallNumberOfStrings));
System.out.println("Begin: Full GC " + (i + 1) + "/" + numberOfTimes);
System.gc();
System.out.println("End: Full GC " + (i + 1) + "/" + numberOfTimes);
@@ -80,7 +87,11 @@ private static void doYoungGc(int numberOfTimes) {
// Provoke at least numberOfTimes young GCs
final int objectSize = 128;
final int maxObjectInYoung = (Xmn * MB) / objectSize;
List<List<String>> newStrings = new ArrayList<List<String>>();
for (int i = 0; i < numberOfTimes; i++) {
// Create some more strings for every collection, to ensure
// there will be deduplication work that will be reported.
newStrings.add(createStrings(SmallNumberOfStrings, SmallNumberOfStrings));
System.out.println("Begin: Young GC " + (i + 1) + "/" + numberOfTimes);
for (int j = 0; j < maxObjectInYoung + 1; j++) {
dummy = new byte[objectSize];
@@ -318,9 +329,6 @@ public static OutputAnalyzer run() throws Exception {
* Tests
*/

private static final int LargeNumberOfStrings = 10000;
private static final int SmallNumberOfStrings = 10;

private static final int MaxAgeThreshold = 15;
private static final int DefaultAgeThreshold = 3;
private static final int MinAgeThreshold = 1;
@@ -376,7 +384,11 @@ public static void testTableRehash() throws Exception {
"-XX:+StringDeduplicationRehashALot");
output.shouldContain("Concurrent String Deduplication");
output.shouldContain("Deduplicated:");
output.shouldNotContain("Rehash Count: 0");
// Ensure there have been some rehashes. Can't check for never
// being zero, because the first collection might trigger a resize,
// which suppresses rehash. But as written, some collections should
// not lead to a resize, and those will do a rehash.
output.shouldMatch(".* Rehash Count: [1-9].*");
output.shouldNotContain("Hash Seed: 0x0");
output.shouldHaveExitValue(0);
}

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