MAPREDUCE-7315. LocatedFileStatusFetcher to collect/publish IOStatistics. (#2579)

Part of the HADOOP-16830 IOStatistics API feature.

If the source FileSystem's listing RemoteIterators
implement IOStatisticsSource, these are collected and served through
the IOStatisticsSource API. If they are not: getIOStatistics() returns
null. 

Only the listing statistics are collected; FileSystem.globStatus() doesn't
provide any, so IO use there is not included in the aggregate results.

Contributed by Steve Loughran.

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/LocatedFileStatusFetcher.java

@@ -21,6 +21,7 @@
 import java.io.IOException;
 import java.util.LinkedList;
 import java.util.List;
+import java.util.StringJoiner;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutorService;
@@ -37,6 +38,9 @@
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.fs.PathFilter;
 import org.apache.hadoop.fs.RemoteIterator;
+import org.apache.hadoop.fs.statistics.IOStatistics;
+import org.apache.hadoop.fs.statistics.IOStatisticsSnapshot;
+import org.apache.hadoop.fs.statistics.IOStatisticsSource;
 import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
 
 import org.apache.hadoop.thirdparty.com.google.common.annotations.VisibleForTesting;
@@ -52,6 +56,9 @@
 
 import org.apache.hadoop.util.concurrent.HadoopExecutors;
 
+import static org.apache.hadoop.fs.statistics.IOStatisticsSupport.retrieveIOStatistics;
+import static org.apache.hadoop.fs.statistics.IOStatisticsSupport.snapshotIOStatistics;
+
 /**
  * Utility class to fetch block locations for specified Input paths using a
  * configured number of threads.
@@ -60,7 +67,7 @@
  * configuration.
  */
 @Private
-public class LocatedFileStatusFetcher {
+public class LocatedFileStatusFetcher implements IOStatisticsSource {
 
   public static final Logger LOG =
       LoggerFactory.getLogger(LocatedFileStatusFetcher.class.getName());
@@ -87,6 +94,12 @@ public class LocatedFileStatusFetcher {
 
   private volatile Throwable unknownError;
 
+  /**
+   * Demand created IO Statistics: only if the filesystem
+   * returns statistics does this fetch collect them.
+   */
+  private IOStatisticsSnapshot iostats;
+
   /**
    * Instantiate.
    * The newApi switch is only used to configure what exception is raised
@@ -227,6 +240,45 @@ private void decrementRunningAndCheckCompletion() {
     }
   }
 
+  /**
+   * Return any IOStatistics collected during listing.
+   * @return IO stats accrued.
+   */
+  @Override
+  public synchronized IOStatistics getIOStatistics() {
+    return iostats;
+  }
+
+  /**
+   * Add the statistics of an individual thread's scan.
+   * @param stats possibly null statistics.
+   */
+  private void addResultStatistics(IOStatistics stats) {
+    if (stats != null) {
+      // demand creation of IO statistics.
+      synchronized (this) {
+        LOG.debug("Adding IOStatistics: {}", stats);
+        if (iostats == null) {
+          // demand create the statistics
+          iostats = snapshotIOStatistics(stats);
+        } else {
+          iostats.aggregate(stats);
+        }
+      }
+    }
+  }
+
+  @Override
+  public String toString() {
+    final IOStatistics ioStatistics = getIOStatistics();
+    StringJoiner stringJoiner = new StringJoiner(", ",
+        LocatedFileStatusFetcher.class.getSimpleName() + "[", "]");
+    if (ioStatistics != null) {
+      stringJoiner.add("IOStatistics=" + ioStatistics);
+    }
+    return stringJoiner.toString();
+  }
+
   /**
    * Retrieves block locations for the given @link {@link FileStatus}, and adds
    * additional paths to the process queue if required.
@@ -266,6 +318,8 @@ public Result call() throws Exception {
             }
           }
         }
+        // aggregate any stats
+        result.stats = retrieveIOStatistics(iter);
       } else {
         result.locatedFileStatuses.add(fileStatus);
       }
@@ -276,6 +330,7 @@ private static class Result {
       private List<FileStatus> locatedFileStatuses = new LinkedList<>();
       private List<FileStatus> dirsNeedingRecursiveCalls = new LinkedList<>();
       private FileSystem fs;
+      private IOStatistics stats;
     }
   }
 
@@ -290,6 +345,7 @@ private class ProcessInputDirCallback implements
     @Override
     public void onSuccess(ProcessInputDirCallable.Result result) {
       try {
+        addResultStatistics(result.stats);
         if (!result.locatedFileStatuses.isEmpty()) {
           resultQueue.add(result.locatedFileStatuses);
         }