From f9a5d666e40d462cfd13fb31e590b0aa25db3133 Mon Sep 17 00:00:00 2001
From: Spencer T Brody <spencer@mongodb.com>
Date: Wed, 16 Jul 2014 17:42:56 -0400
Subject: SERVER-14587 Add hash function to OID so it can be stored in an
 unordered_map

---
 src/mongo/bson/oid.cpp                    |  6 ++++++
 src/mongo/bson/oid.h                      | 10 ++++++++++
 src/mongo/db/repl/repl_coordinator_impl.h |  5 ++---
 3 files changed, 18 insertions(+), 3 deletions(-)

(limited to 'src')

diff --git a/src/mongo/bson/oid.cpp b/src/mongo/bson/oid.cpp
index 92664fd753c..b073c8efa49 100644
--- a/src/mongo/bson/oid.cpp
+++ b/src/mongo/bson/oid.cpp
@@ -50,6 +50,12 @@ namespace mongo {
         boost::hash_combine(seed, z);
     }
 
+    size_t OID::Hasher::operator() (const OID& oid) const {
+        size_t seed = 0;
+        oid.hash_combine(seed);
+        return seed;
+    }
+
     // machine # before folding in the process id
     OID::MachineAndPid OID::ourMachine;
 
diff --git a/src/mongo/bson/oid.h b/src/mongo/bson/oid.h
index b98e070eeac..d5063dc5f1b 100644
--- a/src/mongo/bson/oid.h
+++ b/src/mongo/bson/oid.h
@@ -53,6 +53,16 @@ namespace mongo {
     */
     class OID {
     public:
+
+        /**
+         * Functor compatible with std::hash for std::unordered_{map,set}
+         * Warning: The hash function is subject to change. Do not use in cases where hashes need
+         *          to be consistent across versions.
+         */
+        struct Hasher {
+            size_t operator() (const OID& oid) const;
+        };
+
         OID() : a(0), b(0) { }
 
         enum {
diff --git a/src/mongo/db/repl/repl_coordinator_impl.h b/src/mongo/db/repl/repl_coordinator_impl.h
index 62e043f9d0c..97260d0fae7 100644
--- a/src/mongo/db/repl/repl_coordinator_impl.h
+++ b/src/mongo/db/repl/repl_coordinator_impl.h
@@ -31,7 +31,6 @@
 #include <boost/scoped_ptr.hpp>
 #include <boost/thread/mutex.hpp>
 #include <boost/thread/condition_variable.hpp>
-#include <map>
 #include <vector>
 
 #include "mongo/base/status.h"
@@ -40,6 +39,7 @@
 #include "mongo/db/repl/repl_coordinator.h"
 #include "mongo/db/repl/replication_executor.h"
 #include "mongo/db/repl/topology_coordinator_impl.h"
+#include "mongo/platform/unordered_map.h"
 #include "mongo/util/net/hostandport.h"
 
 namespace mongo {
@@ -189,8 +189,7 @@ namespace repl {
         boost::scoped_ptr<boost::thread> _topCoordDriverThread;
 
         // Maps nodes in this replication group to the last oplog operation they have committed
-        // TODO(spencer): change to unordered_map
-        typedef std::map<OID, OpTime> SlaveOpTimeMap;
+        typedef unordered_map<OID, OpTime, OID::Hasher> SlaveOpTimeMap;
         SlaveOpTimeMap _slaveOpTimeMap;
 
         // Current ReplicaSet state
-- 
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