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Demonstrating classic thread safety issue with object reference being reused and passed to another thread
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Thread-0 Person{name='Init', age=0} | |
Thread-0 Person{name='Init', age=0} | |
Thread-0 Person{name='Init', age=0} | |
main Person{name='Foo', age=-1356876606} | |
Thread-0 Person{name='Foo', age=-1356876606} | |
Thread-0 Person{name='Foo', age=-1356876606} | |
Thread-0 Person{name='Foo', age=-1356876606} | |
main Person{name='Bar', age=1050348248} | |
Thread-0 Person{name='Bar', age=1050348248} | |
Thread-0 Person{name='Bar', age=1050348248} | |
Thread-0 Person{name='Bar', age=1050348248} | |
main Person{name='Baz', age=-803476628} | |
Thread-0 Person{name='Baz', age=-803476628} | |
Thread-0 Person{name='Baz', age=-803476628} | |
Thread-0 Person{name='Baz', age=-803476628} | |
main Person{name='Foo', age=-293422591} | |
Thread-0 Person{name='Foo', age=-293422591} | |
Thread-0 Person{name='Foo', age=-293422591} |
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package com.github.stantonk.java_sandbox; | |
import java.util.Random; | |
public class ThreadSafetyViolationObjectReference { | |
public static class Person { | |
public String name; | |
public Integer age; | |
public Person(String name, int age) { | |
this.name = name; | |
this.age = age; | |
} | |
@Override | |
public String toString() { | |
final StringBuilder sb = new StringBuilder("Person{"); | |
sb.append("name='").append(name).append('\''); | |
sb.append(", age=").append(age); | |
sb.append('}'); | |
return sb.toString(); | |
} | |
} | |
public static void main(String[] args) { | |
Person p = new Person("Init", 0); | |
// This thread demonstrates | |
Thread thread = new Thread(() -> { | |
while (true) { | |
// notice, p is now shared across threads! mutations in the | |
// main thread will be visible in this thread as well | |
System.out.println(String.format("%s %s", Thread.currentThread().getName(), p)); | |
sleep(1000); | |
} | |
}); | |
thread.setDaemon(true); | |
thread.start(); | |
String[] names = {"Foo", "Bar", "Baz"}; | |
int i = 0; | |
while (true) { | |
sleep(3000); | |
p.name = names[i]; | |
p.age = new Random().nextInt(); | |
System.out.println(String.format("%s %s", Thread.currentThread().getName(), p)); | |
i = (i % 2 == 0 && i != 0) ? 0 : i + 1; | |
} | |
} | |
private static void sleep(long millis) { | |
try { | |
Thread.sleep(millis); | |
} catch (InterruptedException e) { | |
e.printStackTrace(); | |
} | |
} | |
} |
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