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How to implement thread-safe HashMap lazy initialization when getting value in Java?


By : Mister_Piccolo
Date : July 30 2020, 04:00 AM
will be helpful for those in need stringEnumMap should be a ConcurrentHashMap>, and use computeIfAbsent to do the lazy initialization.
code :


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Is this lazy initialization pattern for objects in a hashmap thread-safe?


By : user3507352
Date : March 29 2020, 07:55 AM
I wish this help you No, this construct is not thread-safe.
Assume that thread writer is putting something into the map, and the map, being too small, must be resized. This is done inside the synchronized block, so you may think you are fine.

Thread safe lazy initialization on iOS


By : user3676055
Date : March 29 2020, 07:55 AM
I hope this helps you . This solution works
Note that this solution only works if myController is accessed on a background thread the first time. It will deadlock if called on the main thread.
code :
- (UIViewController *)myController
    if (_myController == nil) {
        dispatch_sync(dispatch_get_main_queue(), ^ { if (_myController == nil) _myController = [[MyViewController alloc] init]; });
    }
    return _myController;
}

How to implement thread-safe lazy initialization?


By : user3822148
Date : March 29 2020, 07:55 AM
I wish this helpful for you For singletons there is an elegant solution by delegating the task to the JVM code for static initialization.
code :
public class Something {
    private Something() {
    }

    private static class LazyHolder {
            public static final Something INSTANCE = new Something();
    }

    public static Something getInstance() {
            return LazyHolder.INSTANCE;
    }
}

Thread-safe lazy initialization


By : pramod_pams
Date : March 29 2020, 07:55 AM
like below fixes the issue As @JB Nizet pointed out, the main problem is that you could have a non-empty array whose hash happens to be 0. You need to be able to distinguish "Hash is really 0" from "Hash is unknown". You could use a nullable Integer for this:
code :
private final AtomicReference<Integer> hashcode = new AtomicReference<>();

@Override
public int hashCode() {
    Integer h = hashcode.get();
    if (h != null) return h;
    int computedHash = Arrays.hashCode(array);
    hashcode.compareAndSet(null, computedHash);
    return computedHash;
}

Is Spring's @Lazy initialization thread-safe?


By : 신형섭
Date : March 29 2020, 07:55 AM
I hope this helps . I dont know anywhere Spring claims for safe publication of the beans managed by IoC container.
However, quick glance through the bean factory/application context code detects that there are a lot of crucial places guarded by synchronization (e.g. registering/unregistering bean definition, post-processing phase etc). See many of the methods in DefaultSingletonBeanRegistry has synchronized blocks.
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