From db4a6205ebf045a866bfad4c4751a3372c34af24 Mon Sep 17 00:00:00 2001
From: Andy Seaborne <andy@apache.org>
Date: Mon, 29 Jan 2018 21:37:10 +0000
Subject: [PATCH] Fix to releasing old tasks

---
 .../apache/jena/fuseki/async/AsyncPool.java   | 25 +++++++++++++------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/jena-fuseki2/jena-fuseki-core/src/main/java/org/apache/jena/fuseki/async/AsyncPool.java b/jena-fuseki2/jena-fuseki-core/src/main/java/org/apache/jena/fuseki/async/AsyncPool.java
index 92c810b6be1..2cca42ec1cf 100644
--- a/jena-fuseki2/jena-fuseki-core/src/main/java/org/apache/jena/fuseki/async/AsyncPool.java
+++ b/jena-fuseki2/jena-fuseki-core/src/main/java/org/apache/jena/fuseki/async/AsyncPool.java
@@ -26,10 +26,12 @@
 import org.apache.jena.fuseki.Fuseki ;
 import org.apache.jena.fuseki.server.DataService ;
 
-/** The set of currently active async tasks */
+/** The set of currently active and recently completed tasks. */
 public class AsyncPool
 {
+    // Max concurrent tasks.
     private static int nMaxThreads = 4 ;
+    // Number of finished tasks kept.
     private static int MAX_FINISHED = 20 ;
     
     // See Executors.newCachedThreadPool and Executors.newFixedThreadPool 
@@ -38,12 +40,14 @@ public class AsyncPool
                                                               new LinkedBlockingQueue<Runnable>()) ;
     private final Object mutex = new Object() ; 
     private long counter = 0 ;
-    private Map<String, AsyncTask> runningTasks = new LinkedHashMap<>() ; 
+    private Map<String, AsyncTask> runningTasks = new LinkedHashMap<>() ;
     private Map<String, AsyncTask> finishedTasks = new LinkedHashMap<>() ;
+    // Finite FIFO of finished tasks. 
+    private LinkedList<AsyncTask> finishedTasksList = new LinkedList<>();
     
     private static AsyncPool instance = new AsyncPool() ;
-    public static AsyncPool get() 
-    { return instance ; }
+
+    public static AsyncPool get() { return instance ; }
 
     private AsyncPool() { }
     
@@ -78,9 +82,13 @@ public void finished(AsyncTask task) {
         synchronized(mutex) {
             String id = task.getTaskId() ;
             runningTasks.remove(id) ;
-            while ( finishedTasks.size() >= MAX_FINISHED )
-                finishedTasks.remove(task.getTaskId()) ;
+            // Reduce old tasks list
+            while ( finishedTasksList.size() >= MAX_FINISHED ) {
+                AsyncTask oldTask = finishedTasksList.removeFirst();
+                finishedTasks.remove(oldTask.getTaskId());
+            }
             finishedTasks.put(id, task) ;
+            finishedTasksList.add(task);
         }
     }
 
@@ -90,7 +98,10 @@ public AsyncTask getRunningTask(String taskId) {
         }
     }
 
-    /** Get for any state */
+    /**
+     * Get a task - whether running or finished. Return null for no such task and also
+     * retired tasks. Only a limited number of old, finished tasks are remembered.
+     */
     public AsyncTask getTask(String taskId) {
         synchronized(mutex) {
             AsyncTask task = runningTasks.get(taskId) ;