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
|
/*
* 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.*;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.StandardCharsets;
import java.util.*;
import java.util.concurrent.*;
public class CalculateAverage_fatroom {
private static final String FILE = "./measurements.txt";
private static class MeasurementAggregator {
private double min;
private double max;
private double sum;
private long count;
public MeasurementAggregator() {
this.min = 1000;
this.max = -1000;
this.sum = 0;
this.count = 0;
}
public void consume(double value) {
this.min = value > this.min ? this.min : value;
this.max = this.max > value ? this.max : value;
this.sum += value;
this.count++;
}
public MeasurementAggregator combineWith(MeasurementAggregator that) {
this.min = that.min > this.min ? this.min : that.min;
this.max = this.max > that.max ? this.max : that.max;
this.sum += that.sum;
this.count += that.count;
return this;
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append(min / 10.0).append("/").append(Math.round(sum / count) / 10.0).append("/").append(max / 10.0);
return sb.toString();
}
}
public static void main(String[] args) throws IOException, InterruptedException, ExecutionException {
int SEGMENT_LENGTH = 256_000_000; // 256 MB
RandomAccessFile file = new RandomAccessFile(FILE, "r");
long fileSize = file.length();
long position = 0;
List<Callable<Map<String, MeasurementAggregator>>> tasks = new ArrayList<>();
while (position < fileSize) {
long end = Math.min(position + SEGMENT_LENGTH, fileSize);
int length = (int) (end - position);
MappedByteBuffer buffer = file.getChannel().map(FileChannel.MapMode.READ_ONLY, position, length);
while (buffer.get(length - 1) != '\n') {
length--;
}
final int finalLength = length;
tasks.add(() -> processBuffer(buffer, finalLength));
position += length;
}
var executor = Executors.newFixedThreadPool(tasks.size());
Map<String, MeasurementAggregator> aggregates = new TreeMap<>();
for (var future : executor.invokeAll(tasks)) {
var segmentAggregates = future.get();
for (var entry : segmentAggregates.entrySet()) {
aggregates.merge(entry.getKey(), entry.getValue(), MeasurementAggregator::combineWith);
}
}
executor.shutdown();
executor.awaitTermination(Long.MAX_VALUE, TimeUnit.SECONDS);
System.out.println(aggregates);
}
private static Map<String, MeasurementAggregator> processBuffer(MappedByteBuffer source, int length) {
Map<String, MeasurementAggregator> aggregates = new HashMap<>(500);
String station;
byte[] buffer = new byte[64];
int measurementLength;
int idx = 0;
for (int i = 0; i < length; ++i) {
byte b = source.get(i);
buffer[idx++] = b;
if (b == ';') {
station = new String(buffer, 0, idx - 1, StandardCharsets.UTF_8);
measurementLength = 3;
source.position(i + 1);
buffer[0] = source.get(++i);
buffer[1] = source.get(++i);
buffer[2] = source.get(++i);
buffer[3] = source.get(++i);
if (buffer[3] != '\n') {
measurementLength++;
buffer[4] = source.get(++i);
if (buffer[4] != '\n') {
i++;
measurementLength++;
}
}
aggregates.computeIfAbsent(station, s -> new MeasurementAggregator()).consume(parseMeasurement(buffer, measurementLength));
idx = 0;
}
}
return aggregates;
}
static double parseMeasurement(byte[] source, int size) {
int isNegativeSignPresent = ~(source[0] >> 4) & 1;
int firstDigit = source[isNegativeSignPresent] - '0';
int secondDigit = source[size - 3] - '0';
int thirdDigit = source[size - 1] - '0';
int has4 = (size - isNegativeSignPresent) >> 2;
int value = has4 * firstDigit * 100 + secondDigit * 10 + thirdDigit;
return -isNegativeSignPresent ^ value - isNegativeSignPresent;
}
}
|
