keith-turner commented on a change in pull request #402: ACCUMULO-4615: Updated 
get status for thread safety and with a per-task timeout
URL: https://github.com/apache/accumulo/pull/402#discussion_r180182724
 
 

 ##########
 File path: 
server/master/src/main/java/org/apache/accumulo/master/TimeoutTaskExecutor.java
 ##########
 @@ -0,0 +1,249 @@
+/*
+ * 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.accumulo.master;
+
+import com.google.common.base.Preconditions;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import javax.annotation.concurrent.NotThreadSafe;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+/**
+ * Runs one or more tasks with a timeout per task (instead of a timeout for 
the entire pool). Uses callbacks to invoke functions on successful, timed out, 
or
+ * tasks that error.
+ *
+ * This class uses an underlying fixed thread pool to schedule the submitted 
tasks. Once a task is submitted, the desired end time for the task is recorded 
and
+ * used to determine the timeout for the task's associated {@link Future}.
+ *
+ * The timeout will not be exact as the start time is recorded prior to 
submitting the {@link Callable}. This may result in an effective timeout that is
+ * slightly smaller than expected. The timeout used during initialization 
should be adjusted accordingly.
+ *
+ * The {@link TimeoutTaskExecutor} itself is not a thread-safe class. Only a 
single thread should submit tasks and complete them.
+ *
+ * @param <T> The return type for the corresponding Callable.
+ * @param <C> The type of Callable submitted to this executor.
+ */
+@NotThreadSafe
+public class TimeoutTaskExecutor<T, C extends Callable<T>> implements 
AutoCloseable {
+
+  private final static Logger log = 
LoggerFactory.getLogger(TimeoutTaskExecutor.class);
+
+  private final long timeoutInNanos;
+  private final ExecutorService executorService;
+  private final BlockingQueue<WrappedTask> startedTasks;
+  private final List<WrappedTask> wrappedTasks;
+
+  private SuccessCallback<T,C> successCallback;
+  private ExceptionCallback<C> exceptionCallback;
+  private TimeoutCallback<C> timeoutCallback;
+
+  /**
+   * Constructs a new TimeoutTaskExecutor that will use the given number of 
worker threads and timeout. Takes an expected number of Callables to initialize 
the
+   * underlying data structures appropriately.
+   * <p>
+   * If the expectedNumCallables is sized too small, this executor will block 
on calls to submit() once the internal queue is full.
+   *
+   * @param numThreads           The number of threads to use.
+   * @param timeoutInMillis      The timeout for each task in milliseconds.
+   * @param expectedNumCallables The expected number of callables you will 
schedule. Note this is used for an underlying BlockingQueue. If sized too small 
this will cause blocking
+   *                             when calling submit().
+   * @throws IllegalArgumentException If numThreads is less than 1 or 
expectedNumCallables is negative.
+   */
+  public TimeoutTaskExecutor(int numThreads, long timeoutInMillis, int 
expectedNumCallables) {
+    Preconditions.checkArgument(numThreads >= 1, "Number of threads must be at 
least 1.");
+    Preconditions.checkArgument(expectedNumCallables >= 0, "The expected 
number of callables must be non-negative.");
+
+    this.executorService = Executors.newFixedThreadPool(numThreads);
+    this.startedTasks = new ArrayBlockingQueue<>(expectedNumCallables);
+    this.timeoutInNanos = TimeUnit.MILLISECONDS.toNanos(timeoutInMillis);
+    this.wrappedTasks = new ArrayList<>(expectedNumCallables);
+  }
+
+  /**
+   * Submits a new task to the executor.
+   *
+   * @param callable Task to run
+   */
+  public void submit(C callable) {
 
 Review comment:
   It would be nice to add a sanity check that makes this fail if complete() 
was called

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