Feature to disable field trials in old versions of Chromium. Field trials...

base/metrics/field_trial.cc

Index: base/metrics/field_trial.cc
===================================================================
--- base/metrics/field_trial.cc	(revision 71562)
+++ base/metrics/field_trial.cc	(working copy)
@@ -7,14 +7,18 @@
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "base/stringprintf.h"
+#include "base/utf_string_conversions.h"
 
+using base::Time;
+using base::TimeDelta;

[jar (doing other things), 2011/01/18 19:39:44]

Given that all the code is in a "namespace base" group, do we need these using
statements?

[rtenneti, 2011/01/19 01:45:28]

Done.

+
 namespace base {
 
 // static
-const int FieldTrial::kNotParticipating = -1;
+const int FieldTrial::kNotFinalized = -1;
 
 // static
-const int FieldTrial::kAllRemainingProbability = -2;
+const int FieldTrial::kDefaultGroupNumber = 0;
 
 // static
 bool FieldTrial::enable_benchmarking_ = false;
@@ -28,30 +32,56 @@
 // FieldTrial methods and members.
 
 FieldTrial::FieldTrial(const std::string& name,
-                       const Probability total_probability)
+                       const Probability total_probability,
+                       const std::string& default_group_name,
+                       const int year,
+                       const int month,
+                       const int day_of_month)
   : name_(name),
     divisor_(total_probability),
+    default_group_name_(default_group_name),
     random_(static_cast<Probability>(divisor_ * base::RandDouble())),
     accumulated_group_probability_(0),
-    next_group_number_(0),
-    group_(kNotParticipating) {
+    next_group_number_(kDefaultGroupNumber+1),
+    group_(kNotFinalized),
+    expiration_year_(year),

[jar (doing other things), 2011/01/18 19:39:44]

If these are only used in the constructor, and then discarded, could we avoid
having member slots to hold this data?

[rtenneti, 2011/01/19 01:45:28]

Done.

+    expiration_month_(month),
+    expiration_day_of_month_(day_of_month) {
+  DCHECK(!default_group_name_.empty());
   FieldTrialList::Register(this);
+
+  DCHECK_GT(expiration_year_, 1970);
+  DCHECK_GT(expiration_month_, 0);
+  DCHECK_LT(expiration_month_, 13);
+  DCHECK_GT(expiration_day_of_month_, 0);
+  DCHECK_LT(expiration_day_of_month_, 32);
+
+  base::Time::Exploded exploded;
+  exploded.year = expiration_year_;
+  exploded.month = expiration_month_;
+  exploded.day_of_week = 0;  // Should be unusued.
+  exploded.day_of_month = expiration_day_of_month_;
+  exploded.hour = 0;
+  exploded.minute = 0;
+  exploded.second = 0;
+  exploded.millisecond = 0;
+
+  base::Time expiration_time = Time::FromLocalExploded(exploded);

[jar (doing other things), 2011/01/18 19:39:44]

If we were to save anything (rather than expiration_month_, etc.), we could save
this expiration time.  I don't think we need it beyond line 70.

[rtenneti, 2011/01/19 01:45:28]

Done.

+  disable_field_trial_ = (GetBuildTime() > expiration_time) ? true : false;
 }
 
 int FieldTrial::AppendGroup(const std::string& name,
                             Probability group_probability) {
   DCHECK(group_probability <= divisor_);
-  DCHECK(group_probability >=0 ||
-         group_probability == kAllRemainingProbability);
-  if (group_probability == kAllRemainingProbability) {
-    accumulated_group_probability_ = divisor_;
-  } else {
-    if (enable_benchmarking_)
-      group_probability = 0;
-    accumulated_group_probability_ += group_probability;
-  }
+  DCHECK_GE(group_probability, 0);
+
+  if (enable_benchmarking_ || disable_field_trial_)
+    group_probability = 0;
+
+  accumulated_group_probability_ += group_probability;
+
   DCHECK(accumulated_group_probability_ <= divisor_);
-  if (group_ == kNotParticipating && accumulated_group_probability_ > random_) {
+  if (group_ == kNotFinalized && accumulated_group_probability_ > random_) {
     // This is the group that crossed the random line, so we do the assignment.
     group_ = next_group_number_;
     if (name.empty())
@@ -62,6 +92,20 @@
   return next_group_number_++;
 }
 
+int FieldTrial::group() {
+  if (group_ == kNotFinalized) {
+    accumulated_group_probability_ = divisor_;
+    group_ = kDefaultGroupNumber;
+    group_name_ = default_group_name_;
+  }
+  return group_;
+}
+
+std::string FieldTrial::group_name() {
+  group();  // call group() to make group assignment was done.
+  return group_name_;
+}
+
 // static
 std::string FieldTrial::MakeName(const std::string& name_prefix,
                                  const std::string& trial_name) {
@@ -76,6 +120,16 @@
   enable_benchmarking_ = true;
 }
 
+// static
+Time FieldTrial::GetBuildTime() {
+  Time integral_build_time;
+  const char* kDateTime = __DATE__ " " __TIME__;
+  bool result = Time::FromString(ASCIIToWide(kDateTime).c_str(),
+                                 &integral_build_time);
+  DCHECK(result);
+  return integral_build_time;
+}
+
 FieldTrial::~FieldTrial() {}
 
 //------------------------------------------------------------------------------
@@ -129,7 +183,7 @@
   FieldTrial* field_trial = Find(name);
   if (field_trial)
     return field_trial->group();
-  return FieldTrial::kNotParticipating;
+  return FieldTrial::kNotFinalized;
 }
 
 // static
@@ -149,7 +203,7 @@
   for (RegistrationList::iterator it = global_->registered_.begin();
        it != global_->registered_.end(); ++it) {
     const std::string name = it->first;
-    const std::string group_name = it->second->group_name();
+    const std::string group_name = it->second->group_name_internal();
     if (group_name.empty())
       continue;  // No definitive winner in this trial.

[jar (doing other things), 2011/01/18 19:39:44]

This method is used to serialize fieldTrial settings for use in a renderer
processes.
Perhaps we should use the default_name when he have not finalized the group, and
yet avoid setting the browser side group to anything.  (i.e., we should not
finalize).  I'd be fearful that a process might race to spawn while a FieldTrial
is being constructed, and wouldn't want it to finalize it by accident, but the
default_group is supposed to be "safe" as a fallback.

The only risk is that an early spawn might hear about a different fieldTrial
setting than a later spawned process... but we already have the problem that
early spawns might not even know that there was a fieldTrial defined later!

WDYT?

[rtenneti, 2011/01/19 01:45:28]

Done.

     DCHECK_EQ(name.find(kPersistentStringSeparator), std::string::npos);
@@ -184,12 +238,13 @@
     FieldTrial *field_trial(FieldTrialList::Find(name));
     if (field_trial) {
       // In single process mode, we may have already created the field trial.
-      if (field_trial->group_name() != group_name)
+      if (field_trial->group_name_internal() != group_name)
         return false;
       continue;
     }
     const int kTotalProbability = 100;
-    field_trial = new FieldTrial(name, kTotalProbability);
+    field_trial =
+        new FieldTrial(name, kTotalProbability, group_name, 2011, 6, 30);

[jar (doing other things), 2011/01/18 19:39:44]

That code won't define field trials in the renderer process starting later this
year.

We need to use some calculated constants such as:
kTWO_YEARS_FROM_NOW, 1, 1)

so that it is always in the future,

[rtenneti, 2011/01/19 01:45:28]

Done.

     field_trial->AppendGroup(group_name, kTotalProbability);
   }
   return true;