Hide CodecContextSupplier

[mdsal.git] / binding / mdsal-binding-dom-codec / src / main / java / org / opendaylight / mdsal / binding / dom / codec / impl / LazyCodecContextSupplier.java

diff --git a/binding/mdsal-binding-dom-codec/src/main/java/org/opendaylight/mdsal/binding/dom/codec/impl/LazyCodecContextSupplier.java b/binding/mdsal-binding-dom-codec/src/main/java/org/opendaylight/mdsal/binding/dom/codec/impl/LazyCodecContextSupplier.java
new file mode 100644 (file)
index 0000000..051bd3e
--- /dev/null
+++ b/binding/mdsal-binding-dom-codec/src/main/java/org/opendaylight/mdsal/binding/dom/codec/impl/LazyCodecContextSupplier.java
@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2024 PANTHEON.tech, s.r.o. and others.  All rights reserved.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v1.0 which accompanies this distribution,
+ * and is available at http://www.eclipse.org/legal/epl-v10.html
+ */
+package org.opendaylight.mdsal.binding.dom.codec.impl;
+
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
+import org.eclipse.jdt.annotation.NonNull;
+
+/**
+ * Abstract base class for lazily-instantiated {@link CodecContextSupplier} instances.
+ *
+ * @param <C> {@link CodecContext} type
+ */
+public abstract sealed class LazyCodecContextSupplier<C extends CodecContext> implements CodecContextSupplier
+        permits CommonDataObjectCodecPrototype {
+    private static final VarHandle INSTANCE;
+
+    static {
+        try {
+            INSTANCE = MethodHandles.lookup().findVarHandle(LazyCodecContextSupplier.class, "instance",
+                CodecContext.class);
+        } catch (NoSuchFieldException | IllegalAccessException e) {
+            throw new ExceptionInInitializerError(e);
+        }
+    }
+
+    // Accessed via INSTANCE
+    @SuppressWarnings("unused")
+    @SuppressFBWarnings(value = "UUF_UNUSED_FIELD", justification = "https://github.com/spotbugs/spotbugs/issues/2749")
+    private volatile C instance;
+
+    @Override
+    public final C getCodecContext() {
+        final var existing = (C) INSTANCE.getAcquire(this);
+        return existing != null ? existing : loadInstance();
+    }
+
+    private @NonNull C loadInstance() {
+        final var tmp = createInstance();
+        final var witness = (C) INSTANCE.compareAndExchangeRelease(this, null, tmp);
+        return witness == null ? tmp : witness;
+    }
+
+    // This method must allow concurrent loading, i.e. nothing in it may have effects outside of the loaded object
+    abstract @NonNull C createInstance();
+}