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Diffstat (limited to 'controlloop/common/controller-tdjam/src/main/java/org/onap/policy/controlloop/tdjam/SerialWorkQueue.java')
-rw-r--r-- | controlloop/common/controller-tdjam/src/main/java/org/onap/policy/controlloop/tdjam/SerialWorkQueue.java | 123 |
1 files changed, 123 insertions, 0 deletions
diff --git a/controlloop/common/controller-tdjam/src/main/java/org/onap/policy/controlloop/tdjam/SerialWorkQueue.java b/controlloop/common/controller-tdjam/src/main/java/org/onap/policy/controlloop/tdjam/SerialWorkQueue.java new file mode 100644 index 000000000..7d83765a3 --- /dev/null +++ b/controlloop/common/controller-tdjam/src/main/java/org/onap/policy/controlloop/tdjam/SerialWorkQueue.java @@ -0,0 +1,123 @@ +/*- + * ============LICENSE_START======================================================= + * ONAP + * ================================================================================ + * Copyright (C) 2020 AT&T Intellectual Property. All rights reserved. + * ================================================================================ + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + * ============LICENSE_END========================================================= + */ + +package org.onap.policy.controlloop.tdjam; + +import java.util.LinkedList; +import lombok.Getter; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +/** + * This class provides a way to handle synchronization, with minimal blocking. Requests + * are queued until {@link #start()} is invoked. + */ +public class SerialWorkQueue { + private static Logger logger = LoggerFactory.getLogger(SerialWorkQueue.class); + + // current work list + private LinkedList<Runnable> workQueue; + + @Getter + private boolean running = false; + + /** + * Constructor - no initial Runnable. + */ + public SerialWorkQueue() { + workQueue = new LinkedList<>(); + } + + /** + * Constructor - initial 'Runnable' is specified. + * + * @param runnable an initial 'Runnnable' to run + */ + public SerialWorkQueue(Runnable runnable) { + workQueue = new LinkedList<>(); + workQueue.add(runnable); + } + + /** + * Starts the queue. If the current thread is the first to start it, then the current + * thread will process any requests in the queue before returning. + */ + public void start() { + Runnable item; + + synchronized (this) { + if (running) { + // already running + return; + } + + running = true; + item = workQueue.peekFirst(); + } + + if (item != null) { + processQueue(item); + } + } + + /** + * Called to add a 'Runnable' to the work queue. If the queue was empty, the current + * thread is used to process the queue. + * + * @param work the Runnable to be queued, and eventually run + */ + public void queueAndRun(Runnable work) { + synchronized (this) { + workQueue.add(work); + if (!running || workQueue.size() > 1) { + // there was already work in the queue, so presumably there is + // already an associated thread running + return; + } + // if we reach this point, the queue was empty when this method was + // called, so this thread will process the queue + } + + processQueue(work); + } + + /** + * Internal method to process the work queue until it is empty. Note that entries + * could be added by this thread or another one while we are working. + * + * @param firstItem the first item in the queue + */ + private void processQueue(Runnable firstItem) { + Runnable next = firstItem; + while (next != null) { + try { + next.run(); + } catch (Exception e) { + logger.error("SerialWorkQueue.processQueue exception", e); + } + + synchronized (this) { + // remove the job we just ran + workQueue.removeFirst(); + next = workQueue.peekFirst(); + } + } + } +} |