Double checked locking technique for Java_127926469

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Gumtree : Double-checked locking technique for Java

Created by Tony Lam, last modified on Aug 17, 2009

This technique is used to avoid unnecessary object creation in the multi-threading environment when lazy instantiation is used.

// Works with acquire/release semantics for volatile
// Broken under Java 1.4 and earlier semantics for volatile
class Foo {
    private volatile Helper helper = null;
    public Helper getHelper() {
        if (helper == null) {
            synchronized(this) {
                if (null == helper)
                    helper = new Helper();
            }
        }
        return helper;
    }
}

References:

• The "Double-Checked Locking is Broken" Declaration - Must read
• Double-checked locking - Wikipedia entry on this technique

Document generated by Confluence on Apr 01, 2015 00:11

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