From 5f36d81e47fd142ee7b7c172012917b11411db8d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kjetil=20=C3=98rbekk?= <kjetil.orbekk@gmail.com>
Date: Tue, 24 Jan 2012 11:27:57 +0100
Subject: Refactor Paxos: Return proposal values.

---
 .../main/java/com/orbekk/paxos/MasterProposer.java | 37 ++++++++++++++--------
 .../main/java/com/orbekk/paxos/PaxosService.java   | 10 ++++--
 .../java/com/orbekk/paxos/PaxosServiceImpl.java    | 14 ++++----
 3 files changed, 39 insertions(+), 22 deletions(-)

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

diff --git a/same/src/main/java/com/orbekk/paxos/MasterProposer.java b/same/src/main/java/com/orbekk/paxos/MasterProposer.java
index 912de7e..7bc4350 100644
--- a/same/src/main/java/com/orbekk/paxos/MasterProposer.java
+++ b/same/src/main/java/com/orbekk/paxos/MasterProposer.java
@@ -17,37 +17,48 @@ public class MasterProposer {
         this.connections = connections;
     }
     
-    private boolean internalPropose(int proposalNumber) {
+    private int internalPropose(int proposalNumber) {
+        int bestPromise = proposalNumber;
         int promises = 0;
         for (String url : paxosUrls) {
             PaxosService paxos = connections.getPaxos(url);
-            boolean success = paxos.propose(myUrl, proposalNumber);
-            if (success) {
+            int result = paxos.propose(myUrl, proposalNumber);
+            if (result == proposalNumber) {
                 promises += 1;
             }
+            bestPromise = Math.min(bestPromise, result);
+        }
+        if (promises > paxosUrls.size() / 2) {
+            return proposalNumber;
+        } else {
+            return bestPromise;
         }
-        return promises > paxosUrls.size() / 2;
     }
     
-    private boolean internalAcceptRequest(int proposalNumber) {
+    private int internalAcceptRequest(int proposalNumber) {
+        int bestAccepted = proposalNumber;
         int accepts = 0;
         for (String url : paxosUrls) {
             PaxosService paxos = connections.getPaxos(url);
-            boolean success = paxos.acceptRequest(myUrl, proposalNumber);
-            if (success) {
+            int result = paxos.acceptRequest(myUrl, proposalNumber);
+            if (result == proposalNumber) {
                 accepts += 1;
             }
+            bestAccepted = Math.min(bestAccepted, result);
+        }
+        if (accepts > paxosUrls.size() / 2) {
+            return proposalNumber;
+        } else {
+            return bestAccepted;
         }
-        return accepts > paxosUrls.size() / 2;        
     }
 
     public boolean propose(int proposalNumber) {
-        boolean success = false;
-        success = internalPropose(proposalNumber);
-        if (success) {
-            success = internalAcceptRequest(proposalNumber);
+        int result = internalPropose(proposalNumber);
+        if (result == proposalNumber) {
+            result = internalAcceptRequest(proposalNumber);
         }
-        if (success) {
+        if (result == proposalNumber) {
             return true;
         } else {
             return false;
diff --git a/same/src/main/java/com/orbekk/paxos/PaxosService.java b/same/src/main/java/com/orbekk/paxos/PaxosService.java
index b515fa9..a92a794 100644
--- a/same/src/main/java/com/orbekk/paxos/PaxosService.java
+++ b/same/src/main/java/com/orbekk/paxos/PaxosService.java
@@ -1,6 +1,12 @@
 package com.orbekk.paxos;
 
 public interface PaxosService {
-    boolean propose(String clientUrl, int proposalNumber);
-    boolean acceptRequest(String clientUrl, int proposalNumber); 
+    
+    /**
+     * @return N == proposalNumber if a promise is made.
+     *      -M if another promise already was made, where M is the promise
+     *      highest proposal number.
+     */
+    int propose(String clientUrl, int proposalNumber);
+    int acceptRequest(String clientUrl, int proposalNumber); 
 }
diff --git a/same/src/main/java/com/orbekk/paxos/PaxosServiceImpl.java b/same/src/main/java/com/orbekk/paxos/PaxosServiceImpl.java
index 1e8387e..3ecf523 100644
--- a/same/src/main/java/com/orbekk/paxos/PaxosServiceImpl.java
+++ b/same/src/main/java/com/orbekk/paxos/PaxosServiceImpl.java
@@ -17,36 +17,36 @@ public class PaxosServiceImpl implements PaxosService {
     }
 
     @Override
-    public synchronized boolean propose(String clientUrl,
+    public synchronized int propose(String clientUrl,
             int proposalNumber) {
         if (proposalNumber > highestPromise) {
-            highestPromise = proposalNumber;
             logger.info(tag + "propose({}, {}) = accepted",
                     new Object[]{clientUrl, proposalNumber});
-            return true;
+            highestPromise = proposalNumber;
+            return highestPromise;
         } else {
             logger.info(tag + "propose({}, {}) = rejected " +
                     "(promised: {})",
                     new Object[]{clientUrl, proposalNumber,
                             highestPromise});
-            return false;
+            return -highestPromise;
         }
     }
 
     @Override
-    public synchronized boolean acceptRequest(String clientUrl,
+    public synchronized int acceptRequest(String clientUrl,
             int proposalNumber) {
         if (proposalNumber == highestPromise) {
             logger.info(tag + "acceptRequest({}, {}) = accepted",
                     new Object[]{clientUrl, proposalNumber});
             highestAcceptedValue = proposalNumber;
-            return true;
+            return highestAcceptedValue;
         } else {
             logger.info(tag + "acceptRequest({}, {}) = rejected " +
                     "(promise={})",
                     new Object[]{clientUrl, proposalNumber,
                             highestPromise});
-            return false;
+            return -highestPromise;
         }
     }
 }
-- 
cgit v1.2.3