org.eclipse.milo.opcua.sdk.server.AbstractLifecycle Maven / Gradle / Ivy
/*
* Copyright (c) 2019 the Eclipse Milo Authors
*
* This program and the accompanying materials are made
* available under the terms of the Eclipse Public License 2.0
* which is available at https://www.eclipse.org/legal/epl-2.0/
*
* SPDX-License-Identifier: EPL-2.0
*/
package org.eclipse.milo.opcua.sdk.server;
import java.util.concurrent.atomic.AtomicReference;
public abstract class AbstractLifecycle implements Lifecycle {
private final AtomicReference state = new AtomicReference<>(LifecycleState.NEW);
/**
* {@inheritDoc}
*
* Subsequent invocations throw {@link IllegalStateException}.
*
* @throws IllegalStateException on subsequent invocations.
*/
@Override
public final void startup() throws IllegalStateException {
LifecycleState previous =
state.getAndUpdate(prev -> prev == LifecycleState.NEW ? LifecycleState.RUNNING : prev);
if (previous == LifecycleState.NEW) {
this.onStartup();
} else {
throw new IllegalStateException("cannot call startup when state=" + previous);
}
}
/**
* {@inheritDoc}
*
* If {@link #startup()} hasn't been called yet {@link IllegalStateException} is thrown.
*
* Subsequent invocations have no effect.
*
* @throws IllegalStateException if not started yet.
*/
@Override
public final void shutdown() throws IllegalStateException {
LifecycleState previous =
state.getAndUpdate(prev -> prev == LifecycleState.RUNNING ? LifecycleState.STOPPED : prev);
if (previous == LifecycleState.RUNNING) {
this.onShutdown();
} else if (previous == LifecycleState.NEW) {
throw new IllegalStateException("Cannot call shutdown, never started.");
}
}
/**
* @return {@code true} after {@link #startup()} is called and before {@link #shutdown()} is called.
*/
public final boolean isRunning() {
return this.state.get() == LifecycleState.RUNNING;
}
/**
* Execute startup logic, if there is any.
*/
protected abstract void onStartup();
/**
* Execute shutdown logic, if there is any.
*/
protected abstract void onShutdown();
private enum LifecycleState {
NEW, RUNNING, STOPPED
}
}