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java/org/apache/tomcat/util/threads/TaskQueue.java

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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.
+ */
+package org.apache.tomcat.util.threads;
+
+import java.util.Collection;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.RejectedExecutionException;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * As task queue specifically designed to run with a thread pool executor. The
+ * task queue is optimised to properly utilize threads within a thread pool
+ * executor. If you use a normal queue, the executor will spawn threads when
+ * there are idle threads and you wont be able to force items onto the queue
+ * itself.
+ */
+public class TaskQueue extends LinkedBlockingQueue<Runnable> {
+
+    private static final long serialVersionUID = 1L;
+
+    private transient volatile ThreadPoolExecutor parent = null;
+
+    // No need to be volatile. This is written and read in a single thread
+    // (when stopping a context and firing the  listeners)
+    private Integer forcedRemainingCapacity = null;
+
+    public TaskQueue() {
+        super();
+    }
+
+    public TaskQueue(int capacity) {
+        super(capacity);
+    }
+
+    public TaskQueue(Collection<? extends Runnable> c) {
+        super(c);
+    }
+
+    public void setParent(ThreadPoolExecutor tp) {
+        parent = tp;
+    }
+
+    public boolean force(Runnable o) {
+        if (parent == null || parent.isShutdown()) throw new RejectedExecutionException("Executor not running, can't force a command into the queue");
+        return super.offer(o); //forces the item onto the queue, to be used if the task is rejected
+    }
+
+    public boolean force(Runnable o, long timeout, TimeUnit unit) throws InterruptedException {
+        if (parent == null || parent.isShutdown()) throw new RejectedExecutionException("Executor not running, can't force a command into the queue");
+        return super.offer(o,timeout,unit); //forces the item onto the queue, to be used if the task is rejected
+    }
+
+    @Override
+    public boolean offer(Runnable o) {
+      //we can't do any checks
+        if (parent==null) return super.offer(o);
+        //we are maxed out on threads, simply queue the object
+        if (parent.getPoolSize() == parent.getMaximumPoolSize()) return super.offer(o);
+        //we have idle threads, just add it to the queue
+        if (parent.getSubmittedCount()<=(parent.getPoolSize())) return super.offer(o);
+        //if we have less threads than maximum force creation of a new thread
+        if (parent.getPoolSize()<parent.getMaximumPoolSize()) return false;
+        //if we reached here, we need to add it to the queue
+        return super.offer(o);
+    }
+
+
+    @Override
+    public Runnable poll(long timeout, TimeUnit unit)
+            throws InterruptedException {
+        Runnable runnable = super.poll(timeout, unit);
+        if (runnable == null && parent != null) {
+            // the poll timed out, it gives an opportunity to stop the current
+            // thread if needed to avoid memory leaks.
+            parent.stopCurrentThreadIfNeeded();
+        }
+        return runnable;
+    }
+
+    @Override
+    public Runnable take() throws InterruptedException {
+        if (parent != null && parent.currentThreadShouldBeStopped()) {
+            return poll(parent.getKeepAliveTime(TimeUnit.MILLISECONDS),
+                    TimeUnit.MILLISECONDS);
+            // yes, this may return null (in case of timeout) which normally
+            // does not occur with take()
+            // but the ThreadPoolExecutor implementation allows this
+        }
+        return super.take();
+    }
+
+    @Override
+    public int remainingCapacity() {
+        if (forcedRemainingCapacity != null) {
+            // ThreadPoolExecutor.setCorePoolSize checks that
+            // remainingCapacity==0 to allow to interrupt idle threads
+            // I don't see why, but this hack allows to conform to this
+            // "requirement"
+            return forcedRemainingCapacity.intValue();
+        }
+        return super.remainingCapacity();
+    }
+
+    public void setForcedRemainingCapacity(Integer forcedRemainingCapacity) {
+        this.forcedRemainingCapacity = forcedRemainingCapacity;
+    }
+
+}