components/metrics/persistent_system_profile.cc - cobalt - Git at Google

 // Copyright 2017 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 "components/metrics/persistent_system_profile.h"

 #include <set>

 #include "base/atomicops.h"
 #include "base/bits.h"
 #include "base/memory/singleton.h"
 #include "base/metrics/persistent_memory_allocator.h"
 #include "base/pickle.h"
 #include "base/stl_util.h"
 #include "components/variations/active_field_trials.h"

 namespace metrics {

 namespace {

 // To provide atomic addition of records so that there is no confusion between
 // writers and readers, all of the metadata about a record is contained in a
 // structure that can be stored as a single atomic 32-bit word.
 union RecordHeader {
   struct {
     unsigned continued : 1;  // Flag indicating if there is more after this.
     unsigned type : 7;       // The type of this record.
     unsigned amount : 24;    // The amount of data to follow.
   } as_parts;
   base::subtle::Atomic32 as_atomic;
 };

 constexpr uint32_t kTypeIdSystemProfile = 0x330A7150;  // SHA1(SystemProfile)
 constexpr size_t kSystemProfileAllocSize = 4 << 10;    // 4 KiB
 constexpr size_t kMaxRecordSize = (1 << 24) - sizeof(RecordHeader);

 static_assert(sizeof(RecordHeader) == sizeof(base::subtle::Atomic32),
               "bad RecordHeader size");

 // Calculate the size of a record based on the amount of data. This adds room
 // for the record header and rounds up to the next multiple of the record-header
 // size.
 size_t CalculateRecordSize(size_t data_amount) {
   return base::bits::Align(data_amount + sizeof(RecordHeader),
                            sizeof(RecordHeader));
 }

 }  // namespace

 PersistentSystemProfile::RecordAllocator::RecordAllocator(
     base::PersistentMemoryAllocator* memory_allocator,
     size_t min_size)
     : allocator_(memory_allocator),
       has_complete_profile_(false),
       alloc_reference_(0),
       alloc_size_(0),
       end_offset_(0) {
   AddSegment(min_size);
 }

 PersistentSystemProfile::RecordAllocator::RecordAllocator(
     const base::PersistentMemoryAllocator* memory_allocator)
     : allocator_(
           const_cast<base::PersistentMemoryAllocator*>(memory_allocator)),
       alloc_reference_(0),
       alloc_size_(0),
       end_offset_(0) {}

 void PersistentSystemProfile::RecordAllocator::Reset() {
   // Clear the first word of all blocks so they're known to be "empty".
   alloc_reference_ = 0;
   while (NextSegment()) {
     // Get the block as a char* and cast it. It can't be fetched directly as
     // an array of RecordHeader because that's not a fundamental type and only
     // arrays of fundamental types are allowed.
     RecordHeader* header =
         reinterpret_cast<RecordHeader*>(allocator_->GetAsArray<char>(
             alloc_reference_, kTypeIdSystemProfile, sizeof(RecordHeader)));
     DCHECK(header);
     base::subtle::NoBarrier_Store(&header->as_atomic, 0);
   }

   // Reset member variables.
   has_complete_profile_ = false;
   alloc_reference_ = 0;
   alloc_size_ = 0;
   end_offset_ = 0;
 }

 bool PersistentSystemProfile::RecordAllocator::Write(RecordType type,
                                                      base::StringPiece record) {
   const char* data = record.data();
   size_t remaining_size = record.size();

   // Allocate space and write records until everything has been stored.
   do {
     if (end_offset_ == alloc_size_) {
       if (!AddSegment(remaining_size))
         return false;
     }
     // Write out as much of the data as possible. |data| and |remaining_size|
     // are updated in place.
     if (!WriteData(type, &data, &remaining_size))
       return false;
   } while (remaining_size > 0);

   return true;
 }

 bool PersistentSystemProfile::RecordAllocator::HasMoreData() const {
   if (alloc_reference_ == 0 && !NextSegment())
     return false;

   char* block =
       allocator_->GetAsArray<char>(alloc_reference_, kTypeIdSystemProfile,
                                    base::PersistentMemoryAllocator::kSizeAny);
   if (!block)
     return false;

   RecordHeader header;
   header.as_atomic = base::subtle::Acquire_Load(
       reinterpret_cast<base::subtle::Atomic32*>(block + end_offset_));
   return header.as_parts.type != kUnusedSpace;
 }

 bool PersistentSystemProfile::RecordAllocator::Read(RecordType* type,
                                                     std::string* record) const {
   *type = kUnusedSpace;
   record->clear();

   // Access data and read records until everything has been loaded.
   while (true) {
     if (end_offset_ == alloc_size_) {
       if (!NextSegment())
         return false;
     }
     if (ReadData(type, record))
       return *type != kUnusedSpace;
   }
 }

 bool PersistentSystemProfile::RecordAllocator::NextSegment() const {
   base::PersistentMemoryAllocator::Iterator iter(allocator_, alloc_reference_);
   alloc_reference_ = iter.GetNextOfType(kTypeIdSystemProfile);
   alloc_size_ = allocator_->GetAllocSize(alloc_reference_);
   end_offset_ = 0;
   return alloc_reference_ != 0;
 }

 bool PersistentSystemProfile::RecordAllocator::AddSegment(size_t min_size) {
   if (NextSegment()) {
     // The first record-header should have been zeroed as part of the allocation
     // or by the "reset" procedure.
     DCHECK_EQ(0, base::subtle::NoBarrier_Load(
                      allocator_->GetAsArray<base::subtle::Atomic32>(
                          alloc_reference_, kTypeIdSystemProfile, 1)));
     return true;
   }

   DCHECK_EQ(0U, alloc_reference_);
   DCHECK_EQ(0U, end_offset_);

   size_t size =
       std::max(CalculateRecordSize(min_size), kSystemProfileAllocSize);

   uint32_t ref = allocator_->Allocate(size, kTypeIdSystemProfile);
   if (!ref)
     return false;  // Allocator must be full.
   allocator_->MakeIterable(ref);

   alloc_reference_ = ref;
   alloc_size_ = allocator_->GetAllocSize(ref);
   return true;
 }

 bool PersistentSystemProfile::RecordAllocator::WriteData(RecordType type,
                                                          const char** data,
                                                          size_t* data_size) {
   char* block =
       allocator_->GetAsArray<char>(alloc_reference_, kTypeIdSystemProfile,
                                    base::PersistentMemoryAllocator::kSizeAny);
   if (!block)
     return false;  // It's bad if there is no accessible block.

   const size_t max_write_size = std::min(
       kMaxRecordSize, alloc_size_ - end_offset_ - sizeof(RecordHeader));
   const size_t write_size = std::min(*data_size, max_write_size);
   const size_t record_size = CalculateRecordSize(write_size);
   DCHECK_LT(write_size, record_size);

   // Write the data and the record header.
   RecordHeader header;
   header.as_atomic = 0;
   header.as_parts.type = type;
   header.as_parts.amount = write_size;
   header.as_parts.continued = (write_size < *data_size);
   size_t offset = end_offset_;
   end_offset_ += record_size;
   DCHECK_GE(alloc_size_, end_offset_);
   if (end_offset_ < alloc_size_) {
     // An empty record header has to be next before this one gets written.
     base::subtle::NoBarrier_Store(
         reinterpret_cast<base::subtle::Atomic32*>(block + end_offset_), 0);
   }
   memcpy(block + offset + sizeof(header), *data, write_size);
   base::subtle::Release_Store(
       reinterpret_cast<base::subtle::Atomic32*>(block + offset),
       header.as_atomic);

   // Account for what was stored and prepare for follow-on records with any
   // remaining data.
   *data += write_size;
   *data_size -= write_size;

   return true;
 }

 bool PersistentSystemProfile::RecordAllocator::ReadData(
     RecordType* type,
     std::string* record) const {
   DCHECK_GT(alloc_size_, end_offset_);

   char* block =
       allocator_->GetAsArray<char>(alloc_reference_, kTypeIdSystemProfile,
                                    base::PersistentMemoryAllocator::kSizeAny);
   if (!block) {
     *type = kUnusedSpace;
     return true;  // No more data.
   }

   // Get and validate the record header.
   RecordHeader header;
   header.as_atomic = base::subtle::Acquire_Load(
       reinterpret_cast<base::subtle::Atomic32*>(block + end_offset_));
   bool continued = !!header.as_parts.continued;
   if (header.as_parts.type == kUnusedSpace) {
     *type = kUnusedSpace;
     return true;  // End of all records.
   } else if (*type == kUnusedSpace) {
     *type = static_cast<RecordType>(header.as_parts.type);
   } else if (*type != header.as_parts.type) {
     NOTREACHED();  // Continuation didn't match start of record.
     *type = kUnusedSpace;
     record->clear();
     return false;
   }
   size_t read_size = header.as_parts.amount;
   if (end_offset_ + sizeof(header) + read_size > alloc_size_) {
     NOTREACHED();  // Invalid header amount.
     *type = kUnusedSpace;
     return true;  // Don't try again.
   }

   // Append the record data to the output string.
   record->append(block + end_offset_ + sizeof(header), read_size);
   end_offset_ += CalculateRecordSize(read_size);
   DCHECK_GE(alloc_size_, end_offset_);

   return !continued;
 }

 PersistentSystemProfile::PersistentSystemProfile() {}

 PersistentSystemProfile::~PersistentSystemProfile() {}

 void PersistentSystemProfile::RegisterPersistentAllocator(
     base::PersistentMemoryAllocator* memory_allocator) {
   DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

   // Create and store the allocator. A |min_size| of "1" ensures that a memory
   // block is reserved now.
   RecordAllocator allocator(memory_allocator, 1);
   allocators_.push_back(std::move(allocator));
   all_have_complete_profile_ = false;
 }

 void PersistentSystemProfile::DeregisterPersistentAllocator(
     base::PersistentMemoryAllocator* memory_allocator) {
   DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

   // This would be more efficient with a std::map but it's not expected that
   // allocators will get deregistered with any frequency, if at all.
   base::EraseIf(allocators_, [=](RecordAllocator& records) {
     return records.allocator() == memory_allocator;
   });
 }

 void PersistentSystemProfile::SetSystemProfile(
     const std::string& serialized_profile,
     bool complete) {
   DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

   if (allocators_.empty() || serialized_profile.empty())
     return;

   for (auto& allocator : allocators_) {
     // Don't overwrite a complete profile with an incomplete one.
     if (!complete && allocator.has_complete_profile())
       continue;
     // A full system profile always starts fresh. Incomplete keeps existing
     // records for merging.
     if (complete)
       allocator.Reset();
     // Write out the serialized profile.
     allocator.Write(kSystemProfileProto, serialized_profile);
     // Indicate if this is a complete profile.
     if (complete)
       allocator.set_complete_profile();
   }

   if (complete)
     all_have_complete_profile_ = true;
 }

 void PersistentSystemProfile::SetSystemProfile(
     const SystemProfileProto& profile,
     bool complete) {
   // Avoid serialization if passed profile is not complete and all allocators
   // already have complete ones.
   if (!complete && all_have_complete_profile_)
     return;

   std::string serialized_profile;
   if (!profile.SerializeToString(&serialized_profile))
     return;
   SetSystemProfile(serialized_profile, complete);
 }

 void PersistentSystemProfile::AddFieldTrial(base::StringPiece trial,
                                             base::StringPiece group) {
   DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
   DCHECK(!trial.empty());
   DCHECK(!group.empty());

   base::Pickle pickler;
   pickler.WriteString(trial);
   pickler.WriteString(group);

   WriteToAll(kFieldTrialInfo,
              base::StringPiece(static_cast<const char*>(pickler.data()),
                                pickler.size()));
 }

 // static
 bool PersistentSystemProfile::HasSystemProfile(
     const base::PersistentMemoryAllocator& memory_allocator) {
   const RecordAllocator records(&memory_allocator);
   return records.HasMoreData();
 }

 // static
 bool PersistentSystemProfile::GetSystemProfile(
     const base::PersistentMemoryAllocator& memory_allocator,
     SystemProfileProto* system_profile) {
   const RecordAllocator records(&memory_allocator);

   RecordType type;
   std::string record;
   do {
     if (!records.Read(&type, &record))
       return false;
   } while (type != kSystemProfileProto);

   if (!system_profile)
     return true;

   if (!system_profile->ParseFromString(record))
     return false;

   MergeUpdateRecords(memory_allocator, system_profile);
   return true;
 }

 // static
 void PersistentSystemProfile::MergeUpdateRecords(
     const base::PersistentMemoryAllocator& memory_allocator,
     SystemProfileProto* system_profile) {
   const RecordAllocator records(&memory_allocator);

   RecordType type;
   std::string record;
   std::set<uint32_t> known_field_trial_ids;

   // This is done separate from the code that gets the profile because it
   // compartmentalizes the code and makes it possible to reuse this section
   // should it be needed to merge "update" records into a new "complete"
   // system profile that somehow didn't get all the updates.
   while (records.Read(&type, &record)) {
     switch (type) {
       case kUnusedSpace:
         // These should never be returned.
         NOTREACHED();
         break;

       case kSystemProfileProto:
         // Profile was passed in; ignore this one.
         break;

       case kFieldTrialInfo: {
         // Get the set of known trial IDs so duplicates don't get added.
         if (known_field_trial_ids.empty()) {
           for (int i = 0; i < system_profile->field_trial_size(); ++i) {
             known_field_trial_ids.insert(
                 system_profile->field_trial(i).name_id());
           }
         }

         base::Pickle pickler(record.data(), record.size());
         base::PickleIterator iter(pickler);
         base::StringPiece trial;
         base::StringPiece group;
         if (iter.ReadStringPiece(&trial) && iter.ReadStringPiece(&group)) {
           variations::ActiveGroupId field_ids =
               variations::MakeActiveGroupId(trial, group);
           if (!base::ContainsKey(known_field_trial_ids, field_ids.name)) {
             SystemProfileProto::FieldTrial* field_trial =
                 system_profile->add_field_trial();
             field_trial->set_name_id(field_ids.name);
             field_trial->set_group_id(field_ids.group);
             known_field_trial_ids.insert(field_ids.name);
           }
         }
       } break;
     }
   }
 }

 void PersistentSystemProfile::WriteToAll(RecordType type,
                                          base::StringPiece record) {
   for (auto& allocator : allocators_)
     allocator.Write(type, record);
 }

 GlobalPersistentSystemProfile* GlobalPersistentSystemProfile::GetInstance() {
   return base::Singleton<
       GlobalPersistentSystemProfile,
       base::LeakySingletonTraits<GlobalPersistentSystemProfile>>::get();
 }

 }  // namespace metrics
	// Copyright 2017 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 "components/metrics/persistent_system_profile.h"

	#include <set>

	#include "base/atomicops.h"
	#include "base/bits.h"
	#include "base/memory/singleton.h"
	#include "base/metrics/persistent_memory_allocator.h"
	#include "base/pickle.h"
	#include "base/stl_util.h"
	#include "components/variations/active_field_trials.h"

	namespace metrics {

	namespace {

	// To provide atomic addition of records so that there is no confusion between
	// writers and readers, all of the metadata about a record is contained in a
	// structure that can be stored as a single atomic 32-bit word.
	union RecordHeader {
	struct {
	unsigned continued : 1; // Flag indicating if there is more after this.
	unsigned type : 7; // The type of this record.
	unsigned amount : 24; // The amount of data to follow.
	} as_parts;
	base::subtle::Atomic32 as_atomic;
	};

	constexpr uint32_t kTypeIdSystemProfile = 0x330A7150; // SHA1(SystemProfile)
	constexpr size_t kSystemProfileAllocSize = 4 << 10; // 4 KiB
	constexpr size_t kMaxRecordSize = (1 << 24) - sizeof(RecordHeader);

	static_assert(sizeof(RecordHeader) == sizeof(base::subtle::Atomic32),
	"bad RecordHeader size");

	// Calculate the size of a record based on the amount of data. This adds room
	// for the record header and rounds up to the next multiple of the record-header
	// size.
	size_t CalculateRecordSize(size_t data_amount) {
	return base::bits::Align(data_amount + sizeof(RecordHeader),
	sizeof(RecordHeader));
	}

	} // namespace

	PersistentSystemProfile::RecordAllocator::RecordAllocator(
	base::PersistentMemoryAllocator* memory_allocator,
	size_t min_size)
	: allocator_(memory_allocator),
	has_complete_profile_(false),
	alloc_reference_(0),
	alloc_size_(0),
	end_offset_(0) {
	AddSegment(min_size);
	}

	PersistentSystemProfile::RecordAllocator::RecordAllocator(
	const base::PersistentMemoryAllocator* memory_allocator)
	: allocator_(
	const_cast<base::PersistentMemoryAllocator*>(memory_allocator)),
	alloc_reference_(0),
	alloc_size_(0),
	end_offset_(0) {}

	void PersistentSystemProfile::RecordAllocator::Reset() {
	// Clear the first word of all blocks so they're known to be "empty".
	alloc_reference_ = 0;
	while (NextSegment()) {
	// Get the block as a char* and cast it. It can't be fetched directly as
	// an array of RecordHeader because that's not a fundamental type and only
	// arrays of fundamental types are allowed.
	RecordHeader* header =
	reinterpret_cast<RecordHeader*>(allocator_->GetAsArray<char>(
	alloc_reference_, kTypeIdSystemProfile, sizeof(RecordHeader)));
	DCHECK(header);
	base::subtle::NoBarrier_Store(&header->as_atomic, 0);
	}

	// Reset member variables.
	has_complete_profile_ = false;
	alloc_reference_ = 0;
	alloc_size_ = 0;
	end_offset_ = 0;
	}

	bool PersistentSystemProfile::RecordAllocator::Write(RecordType type,
	base::StringPiece record) {
	const char* data = record.data();
	size_t remaining_size = record.size();

	// Allocate space and write records until everything has been stored.
	do {
	if (end_offset_ == alloc_size_) {
	if (!AddSegment(remaining_size))
	return false;
	}
	// Write out as much of the data as possible. \|data\| and \|remaining_size\|
	// are updated in place.
	if (!WriteData(type, &data, &remaining_size))
	return false;
	} while (remaining_size > 0);

	return true;
	}

	bool PersistentSystemProfile::RecordAllocator::HasMoreData() const {
	if (alloc_reference_ == 0 && !NextSegment())
	return false;

	char* block =
	allocator_->GetAsArray<char>(alloc_reference_, kTypeIdSystemProfile,
	base::PersistentMemoryAllocator::kSizeAny);
	if (!block)
	return false;

	RecordHeader header;
	header.as_atomic = base::subtle::Acquire_Load(
	reinterpret_cast<base::subtle::Atomic32*>(block + end_offset_));
	return header.as_parts.type != kUnusedSpace;
	}

	bool PersistentSystemProfile::RecordAllocator::Read(RecordType* type,
	std::string* record) const {
	*type = kUnusedSpace;
	record->clear();

	// Access data and read records until everything has been loaded.
	while (true) {
	if (end_offset_ == alloc_size_) {
	if (!NextSegment())
	return false;
	}
	if (ReadData(type, record))
	return *type != kUnusedSpace;
	}
	}

	bool PersistentSystemProfile::RecordAllocator::NextSegment() const {
	base::PersistentMemoryAllocator::Iterator iter(allocator_, alloc_reference_);
	alloc_reference_ = iter.GetNextOfType(kTypeIdSystemProfile);
	alloc_size_ = allocator_->GetAllocSize(alloc_reference_);
	end_offset_ = 0;
	return alloc_reference_ != 0;
	}

	bool PersistentSystemProfile::RecordAllocator::AddSegment(size_t min_size) {
	if (NextSegment()) {
	// The first record-header should have been zeroed as part of the allocation
	// or by the "reset" procedure.
	DCHECK_EQ(0, base::subtle::NoBarrier_Load(
	allocator_->GetAsArray<base::subtle::Atomic32>(
	alloc_reference_, kTypeIdSystemProfile, 1)));
	return true;
	}

	DCHECK_EQ(0U, alloc_reference_);
	DCHECK_EQ(0U, end_offset_);

	size_t size =
	std::max(CalculateRecordSize(min_size), kSystemProfileAllocSize);

	uint32_t ref = allocator_->Allocate(size, kTypeIdSystemProfile);
	if (!ref)
	return false; // Allocator must be full.
	allocator_->MakeIterable(ref);

	alloc_reference_ = ref;
	alloc_size_ = allocator_->GetAllocSize(ref);
	return true;
	}

	bool PersistentSystemProfile::RecordAllocator::WriteData(RecordType type,
	const char** data,
	size_t* data_size) {
	char* block =
	allocator_->GetAsArray<char>(alloc_reference_, kTypeIdSystemProfile,
	base::PersistentMemoryAllocator::kSizeAny);
	if (!block)
	return false; // It's bad if there is no accessible block.

	const size_t max_write_size = std::min(
	kMaxRecordSize, alloc_size_ - end_offset_ - sizeof(RecordHeader));
	const size_t write_size = std::min(*data_size, max_write_size);
	const size_t record_size = CalculateRecordSize(write_size);
	DCHECK_LT(write_size, record_size);

	// Write the data and the record header.
	RecordHeader header;
	header.as_atomic = 0;
	header.as_parts.type = type;
	header.as_parts.amount = write_size;
	header.as_parts.continued = (write_size < *data_size);
	size_t offset = end_offset_;
	end_offset_ += record_size;
	DCHECK_GE(alloc_size_, end_offset_);
	if (end_offset_ < alloc_size_) {
	// An empty record header has to be next before this one gets written.
	base::subtle::NoBarrier_Store(
	reinterpret_cast<base::subtle::Atomic32*>(block + end_offset_), 0);
	}
	memcpy(block + offset + sizeof(header), *data, write_size);
	base::subtle::Release_Store(
	reinterpret_cast<base::subtle::Atomic32*>(block + offset),
	header.as_atomic);

	// Account for what was stored and prepare for follow-on records with any
	// remaining data.
	*data += write_size;
	*data_size -= write_size;

	return true;
	}

	bool PersistentSystemProfile::RecordAllocator::ReadData(
	RecordType* type,
	std::string* record) const {
	DCHECK_GT(alloc_size_, end_offset_);

	char* block =
	allocator_->GetAsArray<char>(alloc_reference_, kTypeIdSystemProfile,
	base::PersistentMemoryAllocator::kSizeAny);
	if (!block) {
	*type = kUnusedSpace;
	return true; // No more data.
	}

	// Get and validate the record header.
	RecordHeader header;
	header.as_atomic = base::subtle::Acquire_Load(
	reinterpret_cast<base::subtle::Atomic32*>(block + end_offset_));
	bool continued = !!header.as_parts.continued;
	if (header.as_parts.type == kUnusedSpace) {
	*type = kUnusedSpace;
	return true; // End of all records.
	} else if (*type == kUnusedSpace) {
	*type = static_cast<RecordType>(header.as_parts.type);
	} else if (*type != header.as_parts.type) {
	NOTREACHED(); // Continuation didn't match start of record.
	*type = kUnusedSpace;
	record->clear();
	return false;
	}
	size_t read_size = header.as_parts.amount;
	if (end_offset_ + sizeof(header) + read_size > alloc_size_) {
	NOTREACHED(); // Invalid header amount.
	*type = kUnusedSpace;
	return true; // Don't try again.
	}

	// Append the record data to the output string.
	record->append(block + end_offset_ + sizeof(header), read_size);
	end_offset_ += CalculateRecordSize(read_size);
	DCHECK_GE(alloc_size_, end_offset_);

	return !continued;
	}

	PersistentSystemProfile::PersistentSystemProfile() {}

	PersistentSystemProfile::~PersistentSystemProfile() {}

	void PersistentSystemProfile::RegisterPersistentAllocator(
	base::PersistentMemoryAllocator* memory_allocator) {
	DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

	// Create and store the allocator. A \|min_size\| of "1" ensures that a memory
	// block is reserved now.
	RecordAllocator allocator(memory_allocator, 1);
	allocators_.push_back(std::move(allocator));
	all_have_complete_profile_ = false;
	}

	void PersistentSystemProfile::DeregisterPersistentAllocator(
	base::PersistentMemoryAllocator* memory_allocator) {
	DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

	// This would be more efficient with a std::map but it's not expected that
	// allocators will get deregistered with any frequency, if at all.
	base::EraseIf(allocators_, [=](RecordAllocator& records) {
	return records.allocator() == memory_allocator;
	});
	}

	void PersistentSystemProfile::SetSystemProfile(
	const std::string& serialized_profile,
	bool complete) {
	DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

	if (allocators_.empty() \|\| serialized_profile.empty())
	return;

	for (auto& allocator : allocators_) {
	// Don't overwrite a complete profile with an incomplete one.
	if (!complete && allocator.has_complete_profile())
	continue;
	// A full system profile always starts fresh. Incomplete keeps existing
	// records for merging.
	if (complete)
	allocator.Reset();
	// Write out the serialized profile.
	allocator.Write(kSystemProfileProto, serialized_profile);
	// Indicate if this is a complete profile.
	if (complete)
	allocator.set_complete_profile();
	}

	if (complete)
	all_have_complete_profile_ = true;
	}

	void PersistentSystemProfile::SetSystemProfile(
	const SystemProfileProto& profile,
	bool complete) {
	// Avoid serialization if passed profile is not complete and all allocators
	// already have complete ones.
	if (!complete && all_have_complete_profile_)
	return;

	std::string serialized_profile;
	if (!profile.SerializeToString(&serialized_profile))
	return;
	SetSystemProfile(serialized_profile, complete);
	}

	void PersistentSystemProfile::AddFieldTrial(base::StringPiece trial,
	base::StringPiece group) {
	DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
	DCHECK(!trial.empty());
	DCHECK(!group.empty());

	base::Pickle pickler;
	pickler.WriteString(trial);
	pickler.WriteString(group);

	WriteToAll(kFieldTrialInfo,
	base::StringPiece(static_cast<const char*>(pickler.data()),
	pickler.size()));
	}

	// static
	bool PersistentSystemProfile::HasSystemProfile(
	const base::PersistentMemoryAllocator& memory_allocator) {
	const RecordAllocator records(&memory_allocator);
	return records.HasMoreData();
	}

	// static
	bool PersistentSystemProfile::GetSystemProfile(
	const base::PersistentMemoryAllocator& memory_allocator,
	SystemProfileProto* system_profile) {
	const RecordAllocator records(&memory_allocator);

	RecordType type;
	std::string record;
	do {
	if (!records.Read(&type, &record))
	return false;
	} while (type != kSystemProfileProto);

	if (!system_profile)
	return true;

	if (!system_profile->ParseFromString(record))
	return false;

	MergeUpdateRecords(memory_allocator, system_profile);
	return true;
	}

	// static
	void PersistentSystemProfile::MergeUpdateRecords(
	const base::PersistentMemoryAllocator& memory_allocator,
	SystemProfileProto* system_profile) {
	const RecordAllocator records(&memory_allocator);

	RecordType type;
	std::string record;
	std::set<uint32_t> known_field_trial_ids;

	// This is done separate from the code that gets the profile because it
	// compartmentalizes the code and makes it possible to reuse this section
	// should it be needed to merge "update" records into a new "complete"
	// system profile that somehow didn't get all the updates.
	while (records.Read(&type, &record)) {
	switch (type) {
	case kUnusedSpace:
	// These should never be returned.
	NOTREACHED();
	break;

	case kSystemProfileProto:
	// Profile was passed in; ignore this one.
	break;

	case kFieldTrialInfo: {
	// Get the set of known trial IDs so duplicates don't get added.
	if (known_field_trial_ids.empty()) {
	for (int i = 0; i < system_profile->field_trial_size(); ++i) {
	known_field_trial_ids.insert(
	system_profile->field_trial(i).name_id());
	}
	}

	base::Pickle pickler(record.data(), record.size());
	base::PickleIterator iter(pickler);
	base::StringPiece trial;
	base::StringPiece group;
	if (iter.ReadStringPiece(&trial) && iter.ReadStringPiece(&group)) {
	variations::ActiveGroupId field_ids =
	variations::MakeActiveGroupId(trial, group);
	if (!base::ContainsKey(known_field_trial_ids, field_ids.name)) {
	SystemProfileProto::FieldTrial* field_trial =
	system_profile->add_field_trial();
	field_trial->set_name_id(field_ids.name);
	field_trial->set_group_id(field_ids.group);
	known_field_trial_ids.insert(field_ids.name);
	}
	}
	} break;
	}
	}
	}

	void PersistentSystemProfile::WriteToAll(RecordType type,
	base::StringPiece record) {
	for (auto& allocator : allocators_)
	allocator.Write(type, record);
	}

	GlobalPersistentSystemProfile* GlobalPersistentSystemProfile::GetInstance() {
	return base::Singleton<
	GlobalPersistentSystemProfile,
	base::LeakySingletonTraits<GlobalPersistentSystemProfile>>::get();
	}

	} // namespace metrics