SERVER-13237: benchRun should use a thread-safe random number generator

2 files changed, 18 insertions, 6 deletions

diff --git a/src/mongo/shell/bench.cpp b/src/mongo/shell/bench.cpp
index ae4fe3e0e59..9f016a5b65f 100644
--- a/src/mongo/shell/bench.cpp
+++ b/src/mongo/shell/bench.cpp
@@ -155,6 +155,7 @@ namespace mongo {
 
         throwGLE = false;
         breakOnTrap = true;
+        randomSeed = 1314159265358979323;
     }
 
     BenchRunConfig *BenchRunConfig::createFromBson( const BSONObj &args ) {
@@ -177,6 +178,8 @@ namespace mongo {
 
         if ( args["parallel"].isNumber() )
             this->parallel = args["parallel"].numberInt();
+        if ( args["randomSeed"].isNumber() )
+            this->randomSeed = args["randomSeed"].numberInt();
         if ( args["seconds"].isNumber() )
             this->seconds = args["seconds"].number();
         if ( ! args["hideResults"].eoo() )
@@ -320,8 +323,9 @@ namespace mongo {
         return b.obj();
     }
 
-    BenchRunWorker::BenchRunWorker(size_t id, const BenchRunConfig *config, BenchRunState *brState)
-        : _id(id), _config(config), _brState(brState) {
+    BenchRunWorker::BenchRunWorker(size_t id, const BenchRunConfig *config, BenchRunState *brState,
+                                   int64_t randomSeed)
+        : _id(id), _config(config), _brState(brState), _randomSeed(randomSeed) {
     }
 
     BenchRunWorker::~BenchRunWorker() {}
@@ -341,7 +345,7 @@ namespace mongo {
         long long count = 0;
         mongo::Timer timer;
 
-        BsonTemplateEvaluator bsonTemplateEvaluator;
+        BsonTemplateEvaluator bsonTemplateEvaluator(_randomSeed);
         invariant(bsonTemplateEvaluator.setId(_id) == BsonTemplateEvaluator::StatusSuccess);
 
         if (_config->username != "") {
@@ -785,8 +789,11 @@ namespace mongo {
              }
 
              // Start threads
-             for ( unsigned i = 0; i < _config->parallel; i++ ) {
-                 BenchRunWorker *worker = new BenchRunWorker(i, _config.get(), &_brState);
+             for ( int64_t i = 0; i < _config->parallel; i++ ) {
+                 // Make a unique random seed for the worker. 
+                 int64_t seed = _config->randomSeed +  i;
+                 BenchRunWorker *worker = new BenchRunWorker(i, _config.get(),
+                                                             &_brState, seed);
                  worker->start();
                  _workers.push_back(worker);
              }
diff --git a/src/mongo/shell/bench.h b/src/mongo/shell/bench.h
index f7a58799465..280d7c1399d 100644
--- a/src/mongo/shell/bench.h
+++ b/src/mongo/shell/bench.h
@@ -102,6 +102,9 @@ namespace mongo {
          */
         double seconds;
 
+        /// Base random seed for threads
+        int64_t randomSeed;
+
         bool hideResults;
         bool handleErrors;
         bool hideErrors;
@@ -325,7 +328,8 @@ namespace mongo {
          *
          * "id" is a positive integer which should uniquely identify the worker.
          */
-        BenchRunWorker(size_t id, const BenchRunConfig *config, BenchRunState *brState);
+        BenchRunWorker(size_t id, const BenchRunConfig *config,
+                       BenchRunState *brState, int64_t randomSeed);
         ~BenchRunWorker();
 
         /**
@@ -355,6 +359,7 @@ namespace mongo {
         const BenchRunConfig *_config;
         BenchRunState *_brState;
         BenchRunStats _stats;
+        int64_t _randomSeed;
     };
 
     /**