Attempt to detect impact of disabling dns prefetching on transaction latency

This is also meant to exercise the field trial infrastructure.

r=mbelshe
Review URL: http://codereview.chromium.org/50084

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@12271 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 22 insertions, 8 deletions

diff --git a/base/field_trial.cc b/base/field_trial.cc
index 901ba16..d0085e6 100644
--- a/base/field_trial.cc
+++ b/base/field_trial.cc
@@ -63,6 +63,7 @@ FieldTrialList::FieldTrialList()
 }
 
 FieldTrialList::~FieldTrialList() {
+  AutoLock auto_lock(lock_);
   while (!registered_.empty()) {
     RegistrationList::iterator it = registered_.begin();
     it->second->Release();
@@ -74,8 +75,8 @@ FieldTrialList::~FieldTrialList() {
 
 // static
 void FieldTrialList::Register(FieldTrial* trial) {
-  DCHECK(global_->CalledOnValidThread());
-  DCHECK(!Find(trial->name()));
+  AutoLock auto_lock(global_->lock_);
+  DCHECK(!global_->PreLockedFind(trial->name()));
   trial->AddRef();
   global_->registered_[trial->name()] = trial;
 }
@@ -96,11 +97,17 @@ std::string FieldTrialList::FindFullName(const std::string& name) {
   return "";
 }
 
-  // static
+// static
 FieldTrial* FieldTrialList::Find(const std::string& name) {
-  DCHECK(global_->CalledOnValidThread());
-  RegistrationList::iterator it = global_->registered_.find(name);
-  if (global_->registered_.end() == it)
+  if (!global_)
+    return NULL;
+  AutoLock auto_lock(global_->lock_);
+  return global_->PreLockedFind(name);
+}
+
+FieldTrial* FieldTrialList::PreLockedFind(const std::string& name) {
+  RegistrationList::iterator it = registered_.find(name);
+  if (registered_.end() == it)
     return NULL;
   return it->second;
 }
diff --git a/base/field_trial.h b/base/field_trial.h
index bde6717..3d922d1 100644
--- a/base/field_trial.h
+++ b/base/field_trial.h
@@ -47,7 +47,7 @@
 // happened (randomly) to be assigned to:
 
 // HISTOGRAM_COUNTS(FieldTrial::MakeName("Memory.RendererTotal",
-//                                       "MemoryExperiment"), count);
+//                                       "MemoryExperiment").data(), count);
 
 // The above code will create 3 distinct histograms, with each run of the
 // application being assigned to of of teh three groups, and for each group, the
@@ -65,6 +65,7 @@
 #include <map>
 #include <string>
 
+#include "base/lock.h"
 #include "base/non_thread_safe.h"
 #include "base/ref_counted.h"
 #include "base/time.h"
@@ -140,7 +141,7 @@ class FieldTrial : public base::RefCounted<FieldTrial> {
 // Class with a list of all active field trials.  A trial is active if it has
 // been registered, which includes evaluating its state based on its probaility.
 // Only one instance of this class exists.
-class FieldTrialList : NonThreadSafe {
+class FieldTrialList {
  public:
   // This singleton holds the global list of registered FieldTrials.
   FieldTrialList();
@@ -172,11 +173,17 @@ class FieldTrialList : NonThreadSafe {
   }
 
  private:
+  // Helper function should be called only while holding lock_.
+  FieldTrial* PreLockedFind(const std::string& name);
+
   typedef std::map<std::string, FieldTrial*> RegistrationList;
 
   static FieldTrialList* global_;  // The singleton of this class.
 
   base::Time application_start_time_;
+
+  // Lock for access to registered_.
+  Lock lock_;
   RegistrationList registered_;
 
   DISALLOW_COPY_AND_ASSIGN(FieldTrialList);