From 886afcba049a96533b70f77695858b01b595c6d0 Mon Sep 17 00:00:00 2001
From: pgweiss <pgweiss@71c3de6d-444a-0410-be80-ed276b4c234a>
Date: Tue, 25 May 2010 16:21:10 +0000
Subject: [PATCH] Avoid race condition that can lead to a job being executed
 concurrently on two different executors by accident.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@31362 71c3de6d-444a-0410-be80-ed276b4c234a
---
 core/src/main/java/hudson/model/Executor.java |  2 +
 core/src/main/java/hudson/model/Queue.java    | 43 ++++++++++++++++++-
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/core/src/main/java/hudson/model/Executor.java b/core/src/main/java/hudson/model/Executor.java
index c74027849b..2f0c51ccef 100644
--- a/core/src/main/java/hudson/model/Executor.java
+++ b/core/src/main/java/hudson/model/Executor.java
@@ -113,6 +113,8 @@ public class Executor extends Thread implements ModelObject {
                     try {
                         startTime = System.currentTimeMillis();
                         executable = task.createExecutable();
+                        queue.completePop(queueItem);
+                        
                         if (executable instanceof Actionable) {
                         	for (Action action: queueItem.getActions()) {
                         		((Actionable) executable).addAction(action);
diff --git a/core/src/main/java/hudson/model/Queue.java b/core/src/main/java/hudson/model/Queue.java
index b601acaf9b..ffb5f05c1b 100644
--- a/core/src/main/java/hudson/model/Queue.java
+++ b/core/src/main/java/hudson/model/Queue.java
@@ -132,6 +132,20 @@ public class Queue extends ResourceController implements Saveable {
      */
     private final ItemList<BlockedItem> blockedProjects = new ItemList<BlockedItem>();
 
+    /**
+     * Popped items are the keys, the value is when the item was placed in the Map.
+     * When an item is popped it is placed here.  The Executor that popped it should
+     * remove it via {@link #completePop()} once it creates the {@link Executable}.
+     */
+    private final Map<Item,Long> popped = new HashMap<Item,Long> ();
+    
+    /**
+     * How long we wait for an {@link Executor} to call {@link #completePop()} before
+     * we assume that something has gone wrong and remove an {@link Item} from
+     * {@link #popped}.
+     */
+    private final long poppedWaitTime = 1000*60*1; // One minute
+    
     /**
      * {@link Task}s that can be built immediately
      * that are waiting for available {@link Executor}.
@@ -743,6 +757,7 @@ public class Queue extends ResourceController implements Saveable {
                         // if so, just build it
                         LOGGER.fine("Pop returning " + offer.item + " for " + exec.getName());
                         offer.item.future.startExecuting(exec);
+                        popped.put(offer.item, System.currentTimeMillis());
                         return offer.item;
                     }
                     // otherwise run a queue maintenance
@@ -866,9 +881,35 @@ public class Queue extends ResourceController implements Saveable {
         } catch (AbstractMethodError e) {
             // earlier versions don't have the "isConcurrentBuild" method, so fall back gracefully
         }
-        return !buildables.containsKey(t);
+        return !(buildables.containsKey(t) || taskIsPopped(t));
     }
 
+    /**
+     * Check if an {@link Item} of a given {@link Task} has been recently popped and
+     * the {@Executor} has not yet created an {@link Executable} for it. 
+     */
+    private boolean taskIsPopped (Task t) {
+    	long cutoff = System.currentTimeMillis() - poppedWaitTime;
+    	for (Map.Entry<Item,Long> e : popped.entrySet()) {
+    		if (e.getValue() < cutoff) {
+    			popped.remove(e.getKey());
+    		} else if (e.getKey().task == t) {
+    			return true;
+    		}
+    	}
+    	return false;
+    }
+    
+    /**
+     * Queue maintenance.
+     * <p>
+     * Tell the Queue that a popped item has been started, so we don't have to track
+     * it in the Queue anymore.
+     */
+    public synchronized void completePop (Item i) {
+    	popped.remove(i);
+    }
+        
     /**
      * Queue maintenance.
      * <p>
-- 
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