Use intrusive_ptr rather than shared_ptr for BSONObj

Advantages:
* Owned BSONObj now uses 1 heap allocation rather than 3
* sizeof(BSONObj) is now 16 rather than 24 (on 64 bit)
* perftest bson shows it to be much faster

Change in BSONObj constructor API for owned case to make sure old code gets
updated to allocate room for the ref count. Anyone using BSONObjBuilder doesn't
need to worry about this change.

1 files changed, 1 insertions, 2 deletions

diff --git a/db/jsobj.cpp b/db/jsobj.cpp
index c761b947ed3..da4c44d00c7 100644
--- a/db/jsobj.cpp
+++ b/db/jsobj.cpp
@@ -897,8 +897,7 @@ namespace mongo {
         }
 
         if ( n ) {
-            int len;
-            init( b.decouple(len), true );
+            *this = b.obj();
         }
 
         return n;