From fdced7082a9aa49c09de41e7f63b51fc3bf073ef Mon Sep 17 00:00:00 2001
From: Eliot Horowitz <eliot@10gen.com>
Date: Thu, 1 Jul 2010 01:06:13 -0400
Subject: [PATCH] mostly done with a real distributed lock

---
 client/distlock.h | 124 ++++++++++++++++++++++++++++++++++++++++++++++
 s/chunk.cpp       |   1 +
 2 files changed, 125 insertions(+)
 create mode 100644 client/distlock.h

diff --git a/client/distlock.h b/client/distlock.h
new file mode 100644
index 00000000000..d14c1c9cc0f
--- /dev/null
+++ b/client/distlock.h
@@ -0,0 +1,124 @@
+// distlock.h
+
+/*    Copyright 2009 10gen Inc.
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+
+
+/**
+ * distribuetd locking mechanism
+ */
+
+#include "../pch.h"
+#include "dbclient.h"
+#include "redef_macros.h"
+
+namespace mongo {
+
+    extern string ourHostname;
+
+    class DistributedLock {
+    public:
+        DistributedLock( const ConnectionString& conn , const string& ns , const BSONObj& key , const string& field )
+            : _conn(conn), _ns(ns), _key(key.getOwned()), _field(field){
+        }
+
+        int getState(){
+            return _state.get();
+        }
+
+        bool isLocked(){
+            return _state.get() != 0;
+        }
+        
+        bool lock_try(){
+            // recursive
+            if ( getState() > 0 )
+                return true;
+
+            ScopedDbConnection conn( _conn );
+            
+            { // make sure its there so we can use simple update logic below
+                BSONObj o = conn->findOne( _ns , _key );
+                if ( o.isEmpty() ){
+                    conn->update( _ns , _key , BSON( "$set" << BSON( _field << BSON( "state" << 0 ) ) ) , 1 );
+                }
+            }
+
+
+            BSONObjBuilder b;
+            b.appendElements( _key );
+            b.append( _field + ".state" , 0 );
+            
+
+            conn->update( _ns , b.obj() , BSON( "$set" << BSON( _field + ".state" << 1 << "who" << myid() ) ) );
+            assert(0);
+            conn.done();
+        }
+
+        void unlock(){
+            ScopedDbConnection conn( _conn );
+            conn->update( _ns , _key, BSON( "$set" << BSON( _field + ".state" << 0 ) ) );
+            conn.done();
+
+            _state.set( 0 );
+        }
+
+        string myid(){
+            string s = _myid.get();
+            if ( s.empty() ){
+                stringstream ss;
+                ss << ourHostname << ":" << time(0) << ":" << rand();
+                s = ss.str();
+                _myid.set( s );
+            }
+
+            return s;
+        }
+
+    private:
+        ConnectionString _conn;
+        string _ns;
+        BSONObj _key;
+        string _field;
+        ThreadLocalValue<int> _state;
+        ThreadLocalValue<string> _myid;
+    };
+    
+    class dist_lock_try {
+    public:
+
+        dist_lock_try( DistributedLock * lock )
+            : _lock(lock){
+            _got = _lock->lock_try();
+        }
+
+        ~dist_lock_try(){
+            if ( _got ){
+                _lock->unlock();
+            }
+        }
+
+        bool got() const {
+            return _got;
+        }
+
+    private:
+        DistributedLock * _lock;
+        bool _got;
+        
+    };
+
+}
+
diff --git a/s/chunk.cpp b/s/chunk.cpp
index bb262d4d09b..9702c5382f8 100644
--- a/s/chunk.cpp
+++ b/s/chunk.cpp
@@ -21,6 +21,7 @@
 #include "config.h"
 #include "../util/unittest.h"
 #include "../client/connpool.h"
+#include "../client/distlock.h"
 #include "../db/queryutil.h"
 #include "cursors.h"
 #include "strategy.h"