Added a Unique ID for a Field Trial containing it's hashed name and the selected group ID.

base/metrics/field_trial.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/metrics/field_trial.h"
 
 #include "base/build_time.h"
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "base/sha1.h"
 #include "base/stringprintf.h"
 #include "base/string_util.h"
 #include "base/utf_string_conversions.h"
 
 namespace base {
 
-// static
+static const char kHistogramFieldTrialSeparator('_');
+
+// statics
 const int FieldTrial::kNotFinalized = -1;
-
-// static
 const int FieldTrial::kDefaultGroupNumber = 0;
-
-// static
+const uint32 FieldTrial::kReservedHashValue = 0;
 bool FieldTrial::enable_benchmarking_ = false;
 
-// static
 const char FieldTrialList::kPersistentStringSeparator('/');
-
-static const char kHistogramFieldTrialSeparator('_');
-
-// static
 int FieldTrialList::kExpirationYearInFuture = 0;
 
-
 //------------------------------------------------------------------------------
 // FieldTrial methods and members.
 
 FieldTrial::FieldTrial(const std::string& name,
                        const Probability total_probability,
                        const std::string& default_group_name,
                        const int year,
                        const int month,
                        const int day_of_month)
   : name_(name),
+    name_hash_(HashName(name)),
     divisor_(total_probability),
     default_group_name_(default_group_name),
     random_(static_cast<Probability>(divisor_ * RandDouble())),
     accumulated_group_probability_(0),
     next_group_number_(kDefaultGroupNumber + 1),
     group_(kNotFinalized),
+    group_name_hash_(kReservedHashValue),
     enable_field_trial_(true) {
   DCHECK_GT(total_probability, 0);
   DCHECK(!name_.empty());
   DCHECK(!default_group_name_.empty());
   FieldTrialList::Register(this);
 
   DCHECK_GT(year, 1970);
   DCHECK_GT(month, 0);
   DCHECK_LT(month, 13);
   DCHECK_GT(day_of_month, 0);
@@ skipping 28 matching lines @@
 }
 
 void FieldTrial::Disable() {
   enable_field_trial_ = false;
 
   // In case we are disabled after initialization, we need to switch
   // the trial to the default group.
   if (group_ != kNotFinalized) {
     group_ = kDefaultGroupNumber;
     group_name_ = default_group_name_;
+    group_name_hash_ = HashName(group_name_);
   }
 }
 
 int FieldTrial::AppendGroup(const std::string& name,
                             Probability group_probability) {
   DCHECK_LE(group_probability, divisor_);
   DCHECK_GE(group_probability, 0);
 
   if (enable_benchmarking_ || !enable_field_trial_)
     group_probability = 0;
 
   accumulated_group_probability_ += group_probability;
 
   DCHECK_LE(accumulated_group_probability_, divisor_);
   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())
       StringAppendF(&group_name_, "%d", group_);
     else
       group_name_ = name;
+    group_name_hash_ = HashName(group_name_);
     FieldTrialList::NotifyFieldTrialGroupSelection(name_, group_name_);
   }
   return next_group_number_++;
 }
 
 int FieldTrial::group() {
   if (group_ == kNotFinalized) {
     accumulated_group_probability_ = divisor_;
     group_ = kDefaultGroupNumber;
     group_name_ = default_group_name_;
+    group_name_hash_ = HashName(group_name_);
     FieldTrialList::NotifyFieldTrialGroupSelection(name_, group_name_);
   }
   return group_;
 }
 
 std::string FieldTrial::group_name() {
   group();  // call group() to make sure group assignment was done.
   DCHECK(!group_name_.empty());
   return group_name_;
 }
 
+bool FieldTrial::GetNameGroupId(NameGroupId* name_group_id) {
+  if (group_name_hash_ == kReservedHashValue)
+    return false;
+  name_group_id->name = name_hash_;
+  name_group_id->group = group_name_hash_;
+  return true;
+}
+
 // static
 std::string FieldTrial::MakeName(const std::string& name_prefix,
                                  const std::string& trial_name) {
   std::string big_string(name_prefix);
   big_string.append(1, kHistogramFieldTrialSeparator);
   return big_string.append(FieldTrialList::FindFullName(trial_name));
 }
 
 // static
 void FieldTrial::EnableBenchmarking() {
@@ skipping 15 matching lines @@
   SHA1HashBytes(reinterpret_cast<const unsigned char*>(input.c_str()),
                 input.size(),
                 sha1_hash);
 
   COMPILE_ASSERT(sizeof(uint64) < sizeof(sha1_hash), need_more_data);
   uint64* bits = reinterpret_cast<uint64*>(&sha1_hash[0]);
 
   return BitsToOpenEndedUnitInterval(*bits);
 }
 
+// static
+uint32 FieldTrial::HashName(const std::string& name) {
+  // SHA-1 is designed to produce a uniformly random spread in its output space,
+  // even for nearly-identical inputs.
+  unsigned char sha1_hash[kSHA1Length];
+  SHA1HashBytes(reinterpret_cast<const unsigned char*>(name.c_str()),
+                name.size(),
+                sha1_hash);
+
+  COMPILE_ASSERT(sizeof(uint32) < sizeof(sha1_hash), need_more_data);
+  uint32* bits = reinterpret_cast<uint32*>(&sha1_hash[0]);
+
+  // We only DCHECK, since this should not happen because the registration
+  // of the experiment on the server should have already warn the developer.
+  // If this ever happen, we'll ignore this experiment/group when reporting.
+  DCHECK(*bits != kReservedHashValue);
+  return *bits;
+}
+
 //------------------------------------------------------------------------------
 // FieldTrialList methods and members.
 
 // static
 FieldTrialList* FieldTrialList::global_ = NULL;
 
 // static
 bool FieldTrialList::used_without_global_ = false;
 
 FieldTrialList::FieldTrialList(const std::string& client_id)
@@ skipping 58 matching lines @@
   return "";
 }
 
 // static
 bool FieldTrialList::TrialExists(const std::string& name) {
   return Find(name) != NULL;
 }
 
 // static
 void FieldTrialList::StatesToString(std::string* output) {
+  DCHECK(output->empty());
   if (!global_)
     return;
-  DCHECK(output->empty());
   AutoLock auto_lock(global_->lock_);
 
   for (RegistrationList::iterator it = global_->registered_.begin();
        it != global_->registered_.end(); ++it) {
     const std::string name = it->first;
     std::string group_name = it->second->group_name_internal();
     if (group_name.empty())
       continue;  // Should not include uninitialized trials.
     DCHECK_EQ(name.find(kPersistentStringSeparator), std::string::npos);
     DCHECK_EQ(group_name.find(kPersistentStringSeparator), std::string::npos);
     output->append(name);
     output->append(1, kPersistentStringSeparator);
     output->append(group_name);
     output->append(1, kPersistentStringSeparator);
   }
 }
 
 // static
+void FieldTrialList::GetFieldTrialNameGroupIds(
+    std::vector<FieldTrial::NameGroupId>* name_group_ids) {
+  DCHECK(name_group_ids->empty());
+  if (!global_)
+    return;
+  AutoLock auto_lock(global_->lock_);
+
+  for (RegistrationList::iterator it = global_->registered_.begin();
+       it != global_->registered_.end(); ++it) {
+    FieldTrial::NameGroupId name_group_id;
+    if (it->second->GetNameGroupId(&name_group_id))
+      name_group_ids->push_back(name_group_id);
+  }
+}
+
+// static
 bool FieldTrialList::CreateTrialsInChildProcess(
     const std::string& parent_trials) {
   DCHECK(global_);
   if (parent_trials.empty() || !global_)
     return true;
 
   size_t next_item = 0;
   while (next_item < parent_trials.length()) {
     size_t name_end = parent_trials.find(kPersistentStringSeparator, next_item);
     if (name_end == parent_trials.npos || next_item == name_end)
@@ skipping 93 matching lines @@
 }
 
 FieldTrial* FieldTrialList::PreLockedFind(const std::string& name) {
   RegistrationList::iterator it = registered_.find(name);
   if (registered_.end() == it)
     return NULL;
   return it->second;
 }
 
 }  // namespace base