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Made LazyValue virtual thread friendly #34479

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Jul 26, 2023
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Made LazyValue virtual thread friendly #34479

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16 changes: 12 additions & 4 deletions independent-projects/arc/runtime/src/main/java/io/quarkus/arc/impl/LazyValue.java
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Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
package io.quarkus.arc.impl;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.Supplier;

/**
Expand All @@ -10,6 +12,8 @@ public class LazyValue<T> {

private final Supplier<T> supplier;

private final Lock lock = new ReentrantLock();

private transient volatile T value;

public LazyValue(Supplier<T> supplier) {
Expand All @@ -21,11 +25,15 @@ public T get() {
if (valueCopy != null) {
return valueCopy;
}
synchronized (this) {

lock.lock();
try {
if (value == null) {
value = supplier.get();
}
return value;
} finally {
lock.unlock();
}
}

Expand All @@ -34,9 +42,9 @@ public T getIfPresent() {
}

public void clear() {
synchronized (this) {
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you can check outside of this critical zone if it has already happened and save entering into it.
@mkouba do we expect to be able to init it again, after a clear?

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Yes that can happen - first thing coming to my mind is dynamic resolution and caching of its result which can then be cleared and subsequently cached again - the cache is a LazyValue.
See https://github.com/quarkusio/quarkus/blob/main/independent-projects/arc/runtime/src/main/java/io/quarkus/arc/impl/InstanceImpl.java#L304

value = null;
}
lock.lock();
value = null;
lock.unlock();
}

public boolean isSet() {
Expand Down