Re: static initialization and thread safety (Bobrowski, Maciej)

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Re: static initialization and thread safety (Bobrowski, Maciej)

Valentin Kovalenko
The short answer is yes.

This is described in JLS 12.4.2. Detailed Initialization Procedure (https://docs.oracle.com/javase/specs/jls/se8/html/jls-12.html#jls-12.4.2), and expressed via the initialization lock LC. There is also the following note regarding possible optimizations of initialization procedure: "An implementation may optimize this procedure by eliding the lock acquisition in step 1 (and release in step 4/5) when it can determine that the initialization of the class has already completed, provided that, in terms of the memory model, all happens-before orderings that would exist if the lock were acquired, still exist when the optimization is performed."
 
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Date: Tue, 4 Apr 2017 14:49:34 +0000
From: "Bobrowski, Maciej" <[hidden email]>
To: "[hidden email]"
        <[hidden email]>
Subject: [concurrency-interest] static initialization and thread
        safety
Message-ID:
        <[hidden email]>
Content-Type: text/plain; charset="utf-8"

I was wondering what guarantees there are about non-final fields initialized as part of class initialization. Let's consider


Class Point{

    int x, y;

    public Point(int x, int y) {
         this.x = x;
         this.y = y;
    }
}

Class Init{
    public static Point p = new Point(1,2)
    public static Point p2;

    static {
        p2 = new Point(3 , 4)
        p2.x = 10
    }

}

If I have multiple threads trying to read p and p2, would ALL threads wait until those objects are fully constructed and assigned to corresponding fields (like in final fields case) due to initial;ization semantics, or is that not the case?

Thanks!
Maciej


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