From 009e2e4e0a1c1bbcfcc1acb4b18f035dee7b31fb Mon Sep 17 00:00:00 2001
From: Eliot Horowitz <eliot@10gen.com>
Date: Tue, 6 Apr 2010 13:49:51 -0400
Subject: [PATCH] adaptive sleep for ClientCusror::yield SERVER-975

---
 db/client.cpp       | 17 +++++++++++++++++
 db/client.h         |  2 ++
 db/clientcursor.cpp |  1 +
 util/goodies.h      |  4 ++++
 4 files changed, 24 insertions(+)

diff --git a/db/client.cpp b/db/client.cpp
index d8114c2c291..dbfcbd02aae 100644
--- a/db/client.cpp
+++ b/db/client.cpp
@@ -275,4 +275,21 @@ namespace mongo {
 
     } handshakeCmd;
 
+
+    int Client::recommendedYieldMicros(){
+        int num = 0;
+        {
+            scoped_lock bl(clientsMutex);
+            num = clients.size();
+        }
+        
+        if ( --num <= 0 ) // -- is for myself
+            return 0;
+        
+        if ( num > 50 )
+            num = 50;
+
+        num *= 100;
+        return num;
+    }
 }
diff --git a/db/client.h b/db/client.h
index 022c530fd12..96dbdc085c6 100644
--- a/db/client.h
+++ b/db/client.h
@@ -45,6 +45,8 @@ namespace mongo {
         static mongo::mutex clientsMutex;
         static set<Client*> clients; // always be in clientsMutex when manipulating this
 
+        static int recommendedYieldMicros();
+
         class GodScope {
             bool _prev;
         public:
diff --git a/db/clientcursor.cpp b/db/clientcursor.cpp
index 3a1c7391640..5b40cf29a14 100644
--- a/db/clientcursor.cpp
+++ b/db/clientcursor.cpp
@@ -233,6 +233,7 @@ namespace mongo {
             
         {
             dbtempreleasecond unlock;
+            sleepmicros( Client::recommendedYieldMicros() );
         }
 
         if ( ClientCursor::find( id , false ) == 0 ){
diff --git a/util/goodies.h b/util/goodies.h
index f6a1f4c55d2..5b6c834480d 100644
--- a/util/goodies.h
+++ b/util/goodies.h
@@ -191,6 +191,8 @@ namespace mongo {
         boost::thread::sleep(xt);
     }
     inline void sleepmicros(int s) {
+        if ( s <= 0 )
+            return;
         boost::xtime xt;
         boost::xtime_get(&xt, boost::TIME_UTC);
         xt.sec += ( s / 1000000 );
@@ -211,6 +213,8 @@ namespace mongo {
         }
     }
     inline void sleepmicros(int s) {
+        if ( s <= 0 )
+            return;
         struct timespec t;
         t.tv_sec = (int)(s / 1000000);
         t.tv_nsec = 1000 * ( s % 1000000 );