1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
|
/*
* Copyright (C) 2019 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.collect;
import com.google.caliper.BeforeExperiment;
import com.google.caliper.Benchmark;
import com.google.caliper.Param;
import com.google.common.math.IntMath;
import java.math.RoundingMode;
/** Benchmark of implementations of {@link ImmutableSet#hashFloodingDetected(Object[])}. */
public class ImmutableSetHashFloodingDetectionBenchmark {
private static final int TEST_CASES = 0x100;
@Param({"10", "100", "1000", "10000"})
int size;
@Param Impl impl;
private static final Object[][] tables = new Object[TEST_CASES][];
@BeforeExperiment
public void setUp() {
int tableSize = ImmutableSet.chooseTableSize(size);
int mask = tableSize - 1;
for (int i = 0; i < TEST_CASES; i++) {
tables[i] = new Object[tableSize];
for (int j = 0; j < size; j++) {
Object o = new Object();
for (int k = o.hashCode(); ; k++) {
int index = k & mask;
if (tables[i][index] == null) {
tables[i][index] = o;
break;
}
}
}
}
}
enum Impl {
EXHAUSTIVE {
int maxRunBeforeFallback(int tableSize) {
return 12 * IntMath.log2(tableSize, RoundingMode.UNNECESSARY);
}
@Override
boolean hashFloodingDetected(Object[] hashTable) {
int maxRunBeforeFallback = maxRunBeforeFallback(hashTable.length);
// Test for a run wrapping around the end of the table, then check for runs in the middle.
int endOfStartRun;
for (endOfStartRun = 0; endOfStartRun < hashTable.length; ) {
if (hashTable[endOfStartRun] == null) {
break;
}
endOfStartRun++;
if (endOfStartRun > maxRunBeforeFallback) {
return true;
}
}
int startOfEndRun;
for (startOfEndRun = hashTable.length - 1; startOfEndRun > endOfStartRun; startOfEndRun--) {
if (hashTable[startOfEndRun] == null) {
break;
}
if (endOfStartRun + (hashTable.length - 1 - startOfEndRun) > maxRunBeforeFallback) {
return true;
}
}
for (int i = endOfStartRun + 1; i < startOfEndRun; i++) {
for (int runLength = 0; i < startOfEndRun && hashTable[i] != null; i++) {
runLength++;
if (runLength > maxRunBeforeFallback) {
return true;
}
}
}
return false;
}
},
SEPARATE_RANGES {
int maxRunBeforeFallback(int tableSize) {
return 13 * IntMath.log2(tableSize, RoundingMode.UNNECESSARY);
}
@Override
boolean hashFloodingDetected(Object[] hashTable) {
int maxRunBeforeFallback = maxRunBeforeFallback(hashTable.length);
// Test for a run wrapping around the end of the table, then check for runs in the middle.
int endOfStartRun;
for (endOfStartRun = 0; endOfStartRun < hashTable.length; ) {
if (hashTable[endOfStartRun] == null) {
break;
}
endOfStartRun++;
if (endOfStartRun > maxRunBeforeFallback) {
return true;
}
}
int startOfEndRun;
for (startOfEndRun = hashTable.length - 1; startOfEndRun > endOfStartRun; startOfEndRun--) {
if (hashTable[startOfEndRun] == null) {
break;
}
if (endOfStartRun + (hashTable.length - 1 - startOfEndRun) > maxRunBeforeFallback) {
return true;
}
}
// If this part returns true, there is definitely a run of size maxRunBeforeFallback/2.
// If this part returns false, there are definitely no runs of size >= maxRunBeforeFallback.
int testBlockSize = maxRunBeforeFallback / 2;
for (int i = endOfStartRun + 1; i + testBlockSize <= startOfEndRun; i += testBlockSize) {
boolean runGood = false;
for (int j = 0; j < testBlockSize; j++) {
if (hashTable[i + j] == null) {
runGood = true;
break;
}
}
if (!runGood) {
return true;
}
}
return false;
}
};
abstract boolean hashFloodingDetected(Object[] array);
}
@Benchmark
public int detect(int reps) {
int count = 0;
for (int i = 0; i < reps; i++) {
if (impl.hashFloodingDetected(tables[i & 0xFF])) {
count++;
}
}
return count;
}
}
|
