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
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
|
/*
* Copyright 2023 The original 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 dev.morling.onebrc;
import java.io.File;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.StandardOpenOption;
import java.util.*;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class CalculateAverage_breejesh {
private static final String FILE = "./measurements.txt";
private static final int TWO_BYTE_TO_INT = 480 + 48; // 48 is the ASCII code for '0'
private static final int THREE_BYTE_TO_INT = 4800 + 480 + 48;
private static final class Measurement {
private int min;
private int max;
private int total;
private int count;
public Measurement(int value) {
this.min = value;
this.max = value;
this.total = value;
this.count = 1;
}
@Override
public String toString() {
StringBuilder result = new StringBuilder();
result.append(min / 10.0);
result.append("/");
result.append(Math.round(((double) total) / count) / 10.0);
result.append("/");
result.append(max / 10.0);
return result.toString();
}
private void append(int min, int max, int total, int count) {
if (min < this.min)
this.min = min;
if (max > this.max)
this.max = max;
this.total += total;
this.count += count;
}
public void append(int value) {
append(value, value, value, 1);
}
public void merge(Measurement other) {
append(other.min, other.max, other.total, other.count);
}
}
public static void main(String[] args) throws Exception {
// long start = System.currentTimeMillis();
// Find system details to determine cores and
var file = new File(args.length > 0 ? args[0] : FILE);
long fileSize = file.length();
var numberOfCores = fileSize > 1_000_000 ? Runtime.getRuntime().availableProcessors() : 1;
var splitSectionSize = (int) Math.min(Integer.MAX_VALUE, fileSize / numberOfCores); // bytebuffer position is an int, so can be max Integer.MAX_VALUE
var segmentCount = (int) (fileSize / splitSectionSize);
// Divide file into segments
ExecutorService executor = Executors.newFixedThreadPool(segmentCount);
List<CompletableFuture<Map<String, Measurement>>> futures = new ArrayList<>();
for (int i = 0; i < segmentCount; i++) {
long sectionStart = i * (long) splitSectionSize;
long sectionEnd = Math.min(fileSize, sectionStart + splitSectionSize + 100);
var fileChannel = (FileChannel) Files.newByteChannel(file.toPath(), StandardOpenOption.READ);
CompletableFuture<Map<String, Measurement>> future = CompletableFuture.supplyAsync(() -> {
MappedByteBuffer currentBuffer = null;
try {
currentBuffer = fileChannel.map(FileChannel.MapMode.READ_ONLY, sectionStart, sectionEnd - sectionStart);
}
catch (IOException e) {
throw new RuntimeException(e);
}
// Skip till new line for unequal segments, not to be done for first section
if (sectionStart > 0) {
while (currentBuffer.get() != '\n')
;
}
Map<String, Measurement> map = new HashMap<>();
while (currentBuffer.position() < splitSectionSize) {
// Read station
String str = getStationFromBuffer(currentBuffer);
// Read number
int value = getValueFromBuffer(currentBuffer);
if (map.containsKey(str)) {
map.get(str).append(value);
}
else {
map.put(str, new Measurement(value));
}
}
return map;
}, executor);
futures.add(future);
}
CompletableFuture.allOf(futures.toArray(new CompletableFuture[0])).join();
Map<String, Measurement> finalMap = new TreeMap<>();
for (CompletableFuture<Map<String, Measurement>> future : futures) {
Map<String, Measurement> map = future.get();
map.keySet().stream().forEach(
key -> {
if (finalMap.containsKey(key)) {
finalMap.get(key).merge(map.get(key));
}
else {
finalMap.put(key, map.get(key));
}
});
}
System.out.println(finalMap);
// System.out.printf("Time %s", System.currentTimeMillis() - start);
System.exit(0);
}
private static String getStationFromBuffer(MappedByteBuffer currentBuffer) {
byte currentByte;
var byteCounter = 0;
var buffer = new byte[100];
while ((currentByte = currentBuffer.get()) != ';') {
buffer[byteCounter++] = currentByte;
}
return new String(buffer, 0, byteCounter, StandardCharsets.UTF_8);
}
private static int getValueFromBuffer(MappedByteBuffer currentBuffer) {
int value;
byte[] nums = new byte[4];
currentBuffer.get(nums);
if (nums[1] == '.') {
// case of n.n
value = (nums[0] * 10 + nums[2] - TWO_BYTE_TO_INT);
}
else {
if (nums[3] == '.') {
// case of -nn.n
value = -(nums[1] * 100 + nums[2] * 10 + currentBuffer.get() - THREE_BYTE_TO_INT);
}
else if (nums[0] == '-') {
// case of -n.n
value = -(nums[1] * 10 + nums[3] - TWO_BYTE_TO_INT);
}
else {
// case of nn.n
value = (nums[0] * 100 + nums[1] * 10 + nums[3] - THREE_BYTE_TO_INT);
}
currentBuffer.get(); // new line
}
return value;
}
}
|
