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How to simulate constructor race conditions?
How to demonstrate race conditions around values that aren't published properly?
I got the following code from 《java concurrency in practice》:
public class Holder{
private int n;
public Holder(int n){this.n = n;}
public void assertSanity(){
if(n != n) throw new AssertionError("This statement is false.");
}
}
I am just wondering the condition n != n, is this could be true under a certain circumstance？
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Within a process or program, we can run multiple threads concurrently to improve the performance. Threads, unlike heavyweight process, are lightweight and run inside a single process – they share the same address space, the resources allocated and the environment of that process.
Java is a multi-threaded programming language which means we can develop multi-threaded program using Java.
lang. Thread class provides the join() method which allows one thread to wait until another thread completes its execution.
Explanation: When you want to sleep a thread, condition variable can be used. In C under Linux, there is a function pthread_cond_wait() to wait or sleep. On the other hand, there is a function pthread_cond_signal() to wake up sleeping or waiting thread. Threads can wait on a condition variable.
My guess is that you are asking something similar to these questions:
I'm guessing the book is talking about the possibility of sharing a reference to an object before it is completely constructed, an act referred to is improper publishing.
Suppose that n != n is broken down into the following steps:
Access n on the right side of the operand
Access n on the left side of the operand
Compare values
Then it follows that it is not hard to imagine a case in which the value of n is changed between the first two steps. Now I know what you are thinking, "but n is never changed". Actually, it is, because two threads could share access to an instance of Holder before the constructor for that instance has completely run.
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