From 6e269323f8e459b3dcd40aaca54f7cf7fe9d3d9b Mon Sep 17 00:00:00 2001
From: leventov <leventov@ya.ru>
Date: Thu, 23 Jul 2015 00:45:25 +0300
Subject: [PATCH] Make nested contexts acquisition ordered

---
 README.md                                          | 14 ++++++++++++++
 .../openhft/chronicle/map/NestedContextsTest.java  | 13 +++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/README.md b/README.md
index 588d3802d..2b3a3430c 100644
--- a/README.md
+++ b/README.md
@@ -1927,6 +1927,13 @@ Using nested contexts:
         if (source == target)
             throw new IllegalArgumentException("loops are forbidden");
 
+        // order for consistent lock acquisition => avoid dead lock
+        if (target < source) {
+            int t = source;
+            source = target;
+            target = t;
+        }
+
         try (ExternalMapQueryContext<Integer, Set<Integer>, ?> sc = graph.queryContext(source)) {
             sc.updateLock().lock();
             try (ExternalMapQueryContext<Integer, Set<Integer>, ?> tc =
@@ -2000,6 +2007,13 @@ Using nested contexts:
 
     public static boolean removeEdge(
             ChronicleMap<Integer, Set<Integer>> graph, int source, int target) {
+        // order for consistent lock acquisition => avoid dead lock
+        if (target < source) {
+            int t = source;
+            source = target;
+            target = t;
+        }
+        
         try (ExternalMapQueryContext<Integer, Set<Integer>, ?> sc = graph.queryContext(source)) {
             sc.updateLock().lock();
             MapEntry<Integer, Set<Integer>> sEntry = sc.entry();
diff --git a/src/test/java/net/openhft/chronicle/map/NestedContextsTest.java b/src/test/java/net/openhft/chronicle/map/NestedContextsTest.java
index dc52d5420..88c3f574d 100644
--- a/src/test/java/net/openhft/chronicle/map/NestedContextsTest.java
+++ b/src/test/java/net/openhft/chronicle/map/NestedContextsTest.java
@@ -81,6 +81,12 @@ public class NestedContextsTest {
             ChronicleMap<Integer, Set<Integer>> graph, int source, int target) {
         if (source == target)
             throw new IllegalArgumentException("loops are forbidden");
+        // order for consistent lock acquisition => avoid dead lock
+        if (target < source) {
+            int t = source;
+            source = target;
+            target = t;
+        }
 
         try (ExternalMapQueryContext<Integer, Set<Integer>, ?> sc = graph.queryContext(source)) {
             sc.updateLock().lock();
@@ -155,6 +161,13 @@ public class NestedContextsTest {
 
     public static boolean removeEdge(
             ChronicleMap<Integer, Set<Integer>> graph, int source, int target) {
+        // order for consistent lock acquisition => avoid dead lock
+        if (target < source) {
+            int t = source;
+            source = target;
+            target = t;
+        }
+
         try (ExternalMapQueryContext<Integer, Set<Integer>, ?> sc = graph.queryContext(source)) {
             sc.updateLock().lock();
             MapEntry<Integer, Set<Integer>> sEntry = sc.entry();