From 1cde431ec7e0f5f29ec329c1949c7f5c76366ce5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kjetil=20=C3=98rbekk?= <kjetil.orbekk@gmail.com>
Date: Wed, 25 Apr 2012 14:27:33 +0200
Subject: Fix thread starvation bug in Client.

---
 same/src/main/java/com/orbekk/same/Client.java | 98 +++++++++++++++-----------
 1 file changed, 58 insertions(+), 40 deletions(-)

(limited to 'same/src/main/java/com/orbekk/same/Client.java')

diff --git a/same/src/main/java/com/orbekk/same/Client.java b/same/src/main/java/com/orbekk/same/Client.java
index 5a7918c..bef096b 100644
--- a/same/src/main/java/com/orbekk/same/Client.java
+++ b/same/src/main/java/com/orbekk/same/Client.java
@@ -4,6 +4,7 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.CancellationException;
 import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Future;
 
 import org.slf4j.Logger;
@@ -31,6 +32,7 @@ public class Client {
     private volatile Future<Integer> currentMasterProposal = null;
     private volatile MasterState masterInfo;
     private final RpcFactory rpcf;
+    private final ExecutorService executor;
     
     private List<StateChangedListener> stateListeners =
             new ArrayList<StateChangedListener>();
@@ -155,18 +157,71 @@ public class Client {
                 return;
             }
             connectionState = ConnectionState.UNSTABLE;
+            executor.execute(new MasterStarter(request));
             done.run(Empty.getDefaultInstance());
-            tryBecomeMaster(request);
         }
     };
     
+    private class MasterStarter implements Runnable {
+        private final MasterState failedMaster;
+        
+        public MasterStarter(MasterState failedMaster) {
+            this.failedMaster = failedMaster;
+        }
+        
+        @Override public void run() {
+            logger.info("Trying to become master. Failed master: {}.",
+                    failedMaster);
+            List<String> paxosUrls = state.getList(State.PARTICIPANTS);
+            paxosUrls.remove(failedMaster.getMasterLocation());
+            MasterProposer proposer = new MasterProposer(getClientState(), paxosUrls,
+                    connections, rpcf);
+            if (masterController == null) {
+                logger.warn("Could not become master: No master controller.");
+                return;
+            }
+            Runnable sleeperTask = new Runnable() {
+                @Override public synchronized void run() {
+                    try {
+                        wait(MASTER_TAKEOVER_TIMEOUT);
+                    } catch (InterruptedException e) {
+                    }
+                }
+            };
+            synchronized (this) {
+                if (failedMaster.getMasterId() < masterInfo.getMasterId()) {
+                    logger.info("Master election aborted. Master already chosen.");
+                    return;
+                }
+                currentMasterProposal = proposer.startProposalTask(
+                        masterInfo.getMasterId() + 1, sleeperTask);
+            }
+            Integer result = null;
+            try {
+                result = currentMasterProposal.get();
+            } catch (InterruptedException e) {
+            } catch (ExecutionException e) {
+                logger.error("Error electing master: ", e);
+            } catch (CancellationException e) {
+            }
+            if (!currentMasterProposal.isCancelled() && result != null &&
+                    masterInfo.getMasterId() <= failedMaster.getMasterId()) {
+                masterController.enableMaster(new State(state), result);
+            } else {
+                logger.info("Master election aborted. Master already chosen.");
+            }
+        }
+    }
+    
     public Client(State state, ConnectionManager connections,
-            String myUrl, String myLocation, RpcFactory rpcf) {
+            String myUrl, String myLocation, RpcFactory rpcf,
+            ExecutorService executor) {
         this.state = state;
         this.connections = connections;
         this.myUrl = myUrl;
         this.myLocation = myLocation;
         this.rpcf = rpcf;
+        this.executor = executor;
     }
 
     public void start() {
@@ -174,6 +229,7 @@ public class Client {
 
     public void interrupt() {
         connectionState = ConnectionState.DISCONNECTED;
+        executor.shutdown();
     }
 
     void performWork() {
@@ -242,44 +298,6 @@ public class Client {
         return newServiceImpl;
     }
     
-    private void tryBecomeMaster(MasterState failedMaster) {
-        List<String> paxosUrls = state.getList(State.PARTICIPANTS);
-        paxosUrls.remove(failedMaster.getMasterLocation());
-        MasterProposer proposer = new MasterProposer(getClientState(), paxosUrls,
-                connections, rpcf);
-        if (masterController == null) {
-            logger.warn("Could not become master: No master controller.");
-            return;
-        }
-        Runnable sleeperTask = new Runnable() {
-            @Override public synchronized void run() {
-                try {
-                    wait(MASTER_TAKEOVER_TIMEOUT);
-                } catch (InterruptedException e) {
-                }
-            }
-        };
-        synchronized (this) {
-            if (failedMaster.getMasterId() < masterInfo.getMasterId()) {
-                logger.info("Master election aborted. Master already chosen.");
-                return;
-            }
-            currentMasterProposal = proposer.startProposalTask(
-                    masterInfo.getMasterId() + 1, sleeperTask);
-        }
-        Integer result = null;
-        try {
-            result = currentMasterProposal.get();
-        } catch (InterruptedException e) {
-        } catch (ExecutionException e) {
-            logger.error("Error electing master: ", e);
-        } catch (CancellationException e) {
-        }
-        if (!currentMasterProposal.isCancelled() && result != null) {
-            masterController.enableMaster(new State(state), result);
-        }
-    }
-    
     private synchronized void abortMasterElection() {
         if (currentMasterProposal != null && !currentMasterProposal.isDone()) {
             boolean status = currentMasterProposal.cancel(true);
-- 
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