blob: cb01c410f5d65e15d89dbcee2b39f3f9a17e2fe2 [file] [log] [blame]
// Copyright 2016 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/persistent_histogram_allocator.h"
#include <memory>
#include "base/atomicops.h"
#include "base/files/file_path.h"
#include "base/files/file_util.h"
#include "base/files/important_file_writer.h"
#include "base/files/memory_mapped_file.h"
#include "base/lazy_instance.h"
#include "base/logging.h"
#include "base/memory/ptr_util.h"
#include "base/metrics/histogram.h"
#include "base/metrics/histogram_base.h"
#include "base/metrics/histogram_samples.h"
#include "base/metrics/metrics_hashes.h"
#include "base/metrics/persistent_sample_map.h"
#include "base/metrics/sparse_histogram.h"
#include "base/metrics/statistics_recorder.h"
#include "base/numerics/safe_conversions.h"
#include "base/pickle.h"
#include "base/process/process_handle.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_split.h"
#include "base/strings/stringprintf.h"
#include "base/synchronization/lock.h"
namespace base {
namespace {
// Type identifiers used when storing in persistent memory so they can be
// identified during extraction; the first 4 bytes of the SHA1 of the name
// is used as a unique integer. A "version number" is added to the base
// so that, if the structure of that object changes, stored older versions
// will be safely ignored.
enum : uint32_t {
kTypeIdRangesArray = 0xBCEA225A + 1, // SHA1(RangesArray) v1
kTypeIdCountsArray = 0x53215530 + 1, // SHA1(CountsArray) v1
// The current globally-active persistent allocator for all new histograms.
// The object held here will obviously not be destructed at process exit
// but that's best since PersistentMemoryAllocator objects (that underlie
// GlobalHistogramAllocator objects) are explicitly forbidden from doing
// anything essential at exit anyway due to the fact that they depend on data
// managed elsewhere and which could be destructed first. An AtomicWord is
// used instead of std::atomic because the latter can create global ctors
// and dtors.
subtle::AtomicWord g_histogram_allocator = 0;
// Take an array of range boundaries and create a proper BucketRanges object
// which is returned to the caller. A return of nullptr indicates that the
// passed boundaries are invalid.
std::unique_ptr<BucketRanges> CreateRangesFromData(
HistogramBase::Sample* ranges_data,
uint32_t ranges_checksum,
size_t count) {
// To avoid racy destruction at shutdown, the following may be leaked.
std::unique_ptr<BucketRanges> ranges(new BucketRanges(count));
DCHECK_EQ(count, ranges->size());
for (size_t i = 0; i < count; ++i) {
if (i > 0 && ranges_data[i] <= ranges_data[i - 1])
return nullptr;
ranges->set_range(i, ranges_data[i]);
if (ranges->checksum() != ranges_checksum)
return nullptr;
return ranges;
// Calculate the number of bytes required to store all of a histogram's
// "counts". This will return zero (0) if |bucket_count| is not valid.
size_t CalculateRequiredCountsBytes(size_t bucket_count) {
// 2 because each "sample count" also requires a backup "logged count"
// used for calculating the delta during snapshot operations.
const size_t kBytesPerBucket = 2 * sizeof(HistogramBase::AtomicCount);
// If the |bucket_count| is such that it would overflow the return type,
// perhaps as the result of a malicious actor, then return zero to
// indicate the problem to the caller.
if (bucket_count > std::numeric_limits<size_t>::max() / kBytesPerBucket)
return 0;
return bucket_count * kBytesPerBucket;
} // namespace
const Feature kPersistentHistogramsFeature{
PersistentMemoryAllocator* allocator)
: allocator_(allocator), record_iterator_(allocator) {}
PersistentSparseHistogramDataManager::~PersistentSparseHistogramDataManager() =
PersistentSparseHistogramDataManager::UseSampleMapRecords(uint64_t id,
const void* user) {
base::AutoLock auto_lock(lock_);
return GetSampleMapRecordsWhileLocked(id)->Acquire(user);
uint64_t id) {
auto found = sample_records_.find(id);
if (found != sample_records_.end())
return found->second.get();
std::unique_ptr<PersistentSampleMapRecords>& samples = sample_records_[id];
samples = std::make_unique<PersistentSampleMapRecords>(this, id);
return samples.get();
bool PersistentSparseHistogramDataManager::LoadRecords(
PersistentSampleMapRecords* sample_map_records) {
// DataManager must be locked in order to access the found_ field of any
// PersistentSampleMapRecords object.
base::AutoLock auto_lock(lock_);
bool found = false;
// If there are already "found" entries for the passed object, move them.
if (!sample_map_records->found_.empty()) {
sample_map_records->records_.reserve(sample_map_records->records_.size() +
found = true;
// Acquiring a lock is a semi-expensive operation so load some records with
// each call. More than this number may be loaded if it takes longer to
// find at least one matching record for the passed object.
const int kMinimumNumberToLoad = 10;
const uint64_t match_id = sample_map_records->sample_map_id_;
// Loop while no enty is found OR we haven't yet loaded the minimum number.
// This will continue reading even after a match is found.
for (int count = 0; !found || count < kMinimumNumberToLoad; ++count) {
// Get the next sample-record. The iterator will always resume from where
// it left off even if it previously had nothing further to return.
uint64_t found_id;
PersistentMemoryAllocator::Reference ref =
// Stop immediately if there are none.
if (!ref)
// The sample-record could be for any sparse histogram. Add the reference
// to the appropriate collection for later use.
if (found_id == match_id) {
found = true;
} else {
PersistentSampleMapRecords* samples =
return found;
PersistentSparseHistogramDataManager* data_manager,
uint64_t sample_map_id)
: data_manager_(data_manager), sample_map_id_(sample_map_id) {}
PersistentSampleMapRecords::~PersistentSampleMapRecords() = default;
PersistentSampleMapRecords* PersistentSampleMapRecords::Acquire(
const void* user) {
user_ = user;
seen_ = 0;
return this;
void PersistentSampleMapRecords::Release(const void* user) {
DCHECK_EQ(user_, user);
user_ = nullptr;
PersistentMemoryAllocator::Reference PersistentSampleMapRecords::GetNext() {
// If there are no unseen records, lock and swap in all the found ones.
if (records_.size() == seen_) {
if (!data_manager_->LoadRecords(this))
return false;
// Return the next record. Records *must* be returned in the same order
// they are found in the persistent memory in order to ensure that all
// objects using this data always have the same state. Race conditions
// can cause duplicate records so using the "first found" is the only
// guarantee that all objects always access the same one.
DCHECK_LT(seen_, records_.size());
return records_[seen_++];
PersistentMemoryAllocator::Reference PersistentSampleMapRecords::CreateNew(
HistogramBase::Sample value) {
return PersistentSampleMap::CreatePersistentRecord(data_manager_->allocator_,
sample_map_id_, value);
// This data will be held in persistent memory in order for processes to
// locate and use histograms created elsewhere.
struct PersistentHistogramAllocator::PersistentHistogramData {
// SHA1(Histogram): Increment this if structure changes!
static constexpr uint32_t kPersistentTypeId = 0xF1645910 + 3;
// Expected size for 32/64-bit check.
static constexpr size_t kExpectedInstanceSize =
40 + 2 * HistogramSamples::Metadata::kExpectedInstanceSize;
int32_t histogram_type;
int32_t flags;
int32_t minimum;
int32_t maximum;
uint32_t bucket_count;
PersistentMemoryAllocator::Reference ranges_ref;
uint32_t ranges_checksum;
subtle::Atomic32 counts_ref; // PersistentMemoryAllocator::Reference
HistogramSamples::Metadata samples_metadata;
HistogramSamples::Metadata logged_metadata;
// Space for the histogram name will be added during the actual allocation
// request. This must be the last field of the structure. A zero-size array
// or a "flexible" array would be preferred but is not (yet) valid C++.
char name[sizeof(uint64_t)]; // Force 64-bit alignment on 32-bit builds.
PersistentHistogramAllocator* allocator)
: allocator_(allocator), memory_iter_(allocator->memory_allocator()) {}
PersistentHistogramAllocator::Iterator::GetNextWithIgnore(Reference ignore) {
PersistentMemoryAllocator::Reference ref;
while ((ref = memory_iter_.GetNextOfType<PersistentHistogramData>()) != 0) {
if (ref != ignore)
return allocator_->GetHistogram(ref);
return nullptr;
std::unique_ptr<PersistentMemoryAllocator> memory)
: memory_allocator_(std::move(memory)),
sparse_histogram_data_manager_(memory_allocator_.get()) {}
PersistentHistogramAllocator::~PersistentHistogramAllocator() = default;
std::unique_ptr<HistogramBase> PersistentHistogramAllocator::GetHistogram(
Reference ref) {
// Unfortunately, the histogram "pickle" methods cannot be used as part of
// the persistance because the deserialization methods always create local
// count data (while these must reference the persistent counts) and always
// add it to the local list of known histograms (while these may be simple
// references to histograms in other processes).
PersistentHistogramData* data =
const size_t length = memory_allocator_->GetAllocSize(ref);
// Check that metadata is reasonable: name is null-terminated and non-empty,
// ID fields have been loaded with a hash of the name (0 is considered
// unset/invalid).
if (!data || data->name[0] == '\0' ||
reinterpret_cast<char*>(data)[length - 1] != '\0' ||
data-> == 0 || data-> == 0 ||
// Note: Sparse histograms use |id + 1| in |logged_metadata|.
(data-> != data-> &&
data-> != data-> + 1) ||
// Most non-matching values happen due to truncated names. Ideally, we
// could just verify the name length based on the overall alloc length,
// but that doesn't work because the allocated block may have been
// aligned to the next boundary value.
HashMetricName(data->name) != data-> {
return nullptr;
return CreateHistogram(data);
std::unique_ptr<HistogramBase> PersistentHistogramAllocator::AllocateHistogram(
HistogramType histogram_type,
const std::string& name,
int minimum,
int maximum,
const BucketRanges* bucket_ranges,
int32_t flags,
Reference* ref_ptr) {
// If the allocator is corrupt, don't waste time trying anything else.
// This also allows differentiating on the dashboard between allocations
// failed due to a corrupt allocator and the number of process instances
// with one, the latter being idicated by "newly corrupt", below.
if (memory_allocator_->IsCorrupt())
return nullptr;
// Create the metadata necessary for a persistent sparse histogram. This
// is done first because it is a small subset of what is required for
// other histograms. The type is "under construction" so that a crash
// during the datafill doesn't leave a bad record around that could cause
// confusion by another process trying to read it. It will be corrected
// once histogram construction is complete.
PersistentHistogramData* histogram_data =
offsetof(PersistentHistogramData, name) + name.length() + 1);
if (histogram_data) {
memcpy(histogram_data->name, name.c_str(), name.size() + 1);
histogram_data->histogram_type = histogram_type;
histogram_data->flags = flags | HistogramBase::kIsPersistent;
// Create the remaining metadata necessary for regular histograms.
if (histogram_type != SPARSE_HISTOGRAM) {
size_t bucket_count = bucket_ranges->bucket_count();
size_t counts_bytes = CalculateRequiredCountsBytes(bucket_count);
if (counts_bytes == 0) {
// |bucket_count| was out-of-range.
return nullptr;
// Since the StasticsRecorder keeps a global collection of BucketRanges
// objects for re-use, it would be dangerous for one to hold a reference
// from a persistent allocator that is not the global one (which is
// permanent once set). If this stops being the case, this check can
// become an "if" condition beside "!ranges_ref" below and before
// set_persistent_reference() farther down.
DCHECK_EQ(this, GlobalHistogramAllocator::Get());
// Re-use an existing BucketRanges persistent allocation if one is known;
// otherwise, create one.
PersistentMemoryAllocator::Reference ranges_ref =
if (!ranges_ref) {
size_t ranges_count = bucket_count + 1;
size_t ranges_bytes = ranges_count * sizeof(HistogramBase::Sample);
ranges_ref =
memory_allocator_->Allocate(ranges_bytes, kTypeIdRangesArray);
if (ranges_ref) {
HistogramBase::Sample* ranges_data =
ranges_ref, kTypeIdRangesArray, ranges_count);
if (ranges_data) {
for (size_t i = 0; i < bucket_ranges->size(); ++i)
ranges_data[i] = bucket_ranges->range(i);
} else {
// This should never happen but be tolerant if it does.
ranges_ref = PersistentMemoryAllocator::kReferenceNull;
} else {
DCHECK_EQ(kTypeIdRangesArray, memory_allocator_->GetType(ranges_ref));
// Only continue here if all allocations were successful. If they weren't,
// there is no way to free the space but that's not really a problem since
// the allocations only fail because the space is full or corrupt and so
// any future attempts will also fail.
if (ranges_ref && histogram_data) {
histogram_data->minimum = minimum;
histogram_data->maximum = maximum;
// |bucket_count| must fit within 32-bits or the allocation of the counts
// array would have failed for being too large; the allocator supports
// less than 4GB total size.
histogram_data->bucket_count = static_cast<uint32_t>(bucket_count);
histogram_data->ranges_ref = ranges_ref;
histogram_data->ranges_checksum = bucket_ranges->checksum();
} else {
histogram_data = nullptr; // Clear this for proper handling below.
if (histogram_data) {
// Create the histogram using resources in persistent memory. This ends up
// resolving the "ref" values stored in histogram_data instad of just
// using what is already known above but avoids duplicating the switch
// statement here and serves as a double-check that everything is
// correct before commiting the new histogram to persistent space.
std::unique_ptr<HistogramBase> histogram = CreateHistogram(histogram_data);
DCHECK_NE(0U, histogram_data->;
DCHECK_NE(0U, histogram_data->;
PersistentMemoryAllocator::Reference histogram_ref =
if (ref_ptr != nullptr)
*ref_ptr = histogram_ref;
// By storing the reference within the allocator to this histogram, the
// next import (which will happen before the next histogram creation)
// will know to skip it.
// See also the comment in ImportHistogramsToStatisticsRecorder().
subtle::NoBarrier_Store(&last_created_, histogram_ref);
return histogram;
return nullptr;
void PersistentHistogramAllocator::FinalizeHistogram(Reference ref,
bool registered) {
if (registered) {
// If the created persistent histogram was registered then it needs to
// be marked as "iterable" in order to be found by other processes. This
// happens only after the histogram is fully formed so it's impossible for
// code iterating through the allocator to read a partially created record.
} else {
// If it wasn't registered then a race condition must have caused two to
// be created. The allocator does not support releasing the acquired memory
// so just change the type to be empty.
memory_allocator_->ChangeType(ref, 0,
void PersistentHistogramAllocator::MergeHistogramDeltaToStatisticsRecorder(
HistogramBase* histogram) {
HistogramBase* existing = GetOrCreateStatisticsRecorderHistogram(histogram);
if (!existing) {
// The above should never fail but if it does, no real harm is done.
// The data won't be merged but it also won't be recorded as merged
// so a future try, if successful, will get what was missed. If it
// continues to fail, some metric data will be lost but that is better
// than crashing.
// Merge the delta from the passed object to the one in the SR.
void PersistentHistogramAllocator::MergeHistogramFinalDeltaToStatisticsRecorder(
const HistogramBase* histogram) {
HistogramBase* existing = GetOrCreateStatisticsRecorderHistogram(histogram);
if (!existing) {
// The above should never fail but if it does, no real harm is done.
// Some metric data will be lost but that is better than crashing.
// Merge the delta from the passed object to the one in the SR.
PersistentSampleMapRecords* PersistentHistogramAllocator::UseSampleMapRecords(
uint64_t id,
const void* user) {
return sparse_histogram_data_manager_.UseSampleMapRecords(id, user);
void PersistentHistogramAllocator::CreateTrackingHistograms(StringPiece name) {
void PersistentHistogramAllocator::UpdateTrackingHistograms() {
void PersistentHistogramAllocator::ClearLastCreatedReferenceForTesting() {
subtle::NoBarrier_Store(&last_created_, 0);
std::unique_ptr<HistogramBase> PersistentHistogramAllocator::CreateHistogram(
PersistentHistogramData* histogram_data_ptr) {
if (!histogram_data_ptr)
return nullptr;
// Sparse histograms are quite different so handle them as a special case.
if (histogram_data_ptr->histogram_type == SPARSE_HISTOGRAM) {
std::unique_ptr<HistogramBase> histogram =
SparseHistogram::PersistentCreate(this, histogram_data_ptr->name,
return histogram;
// Copy the configuration fields from histogram_data_ptr to local storage
// because anything in persistent memory cannot be trusted as it could be
// changed at any moment by a malicious actor that shares access. The local
// values are validated below and then used to create the histogram, knowing
// they haven't changed between validation and use.
int32_t histogram_type = histogram_data_ptr->histogram_type;
int32_t histogram_flags = histogram_data_ptr->flags;
int32_t histogram_minimum = histogram_data_ptr->minimum;
int32_t histogram_maximum = histogram_data_ptr->maximum;
uint32_t histogram_bucket_count = histogram_data_ptr->bucket_count;
uint32_t histogram_ranges_ref = histogram_data_ptr->ranges_ref;
uint32_t histogram_ranges_checksum = histogram_data_ptr->ranges_checksum;
HistogramBase::Sample* ranges_data =
histogram_ranges_ref, kTypeIdRangesArray,
const uint32_t max_buckets =
std::numeric_limits<uint32_t>::max() / sizeof(HistogramBase::Sample);
size_t required_bytes =
(histogram_bucket_count + 1) * sizeof(HistogramBase::Sample);
size_t allocated_bytes =
if (!ranges_data || histogram_bucket_count < 2 ||
histogram_bucket_count >= max_buckets ||
allocated_bytes < required_bytes) {
return nullptr;
std::unique_ptr<const BucketRanges> created_ranges = CreateRangesFromData(
ranges_data, histogram_ranges_checksum, histogram_bucket_count + 1);
if (!created_ranges)
return nullptr;
const BucketRanges* ranges =
size_t counts_bytes = CalculateRequiredCountsBytes(histogram_bucket_count);
PersistentMemoryAllocator::Reference counts_ref =
if (counts_bytes == 0 ||
(counts_ref != 0 &&
memory_allocator_->GetAllocSize(counts_ref) < counts_bytes)) {
return nullptr;
// The "counts" data (including both samples and logged samples) is a delayed
// persistent allocation meaning that though its size and storage for a
// reference is defined, no space is reserved until actually needed. When
// it is needed, memory will be allocated from the persistent segment and
// a reference to it stored at the passed address. Other threads can then
// notice the valid reference and access the same data.
DelayedPersistentAllocation counts_data(memory_allocator_.get(),
kTypeIdCountsArray, counts_bytes, 0);
// A second delayed allocations is defined using the same reference storage
// location as the first so the allocation of one will automatically be found
// by the other. Within the block, the first half of the space is for "counts"
// and the second half is for "logged counts".
DelayedPersistentAllocation logged_data(
memory_allocator_.get(), &histogram_data_ptr->counts_ref,
kTypeIdCountsArray, counts_bytes, counts_bytes / 2,
// Create the right type of histogram.
const char* name = histogram_data_ptr->name;
std::unique_ptr<HistogramBase> histogram;
switch (histogram_type) {
histogram = Histogram::PersistentCreate(
name, histogram_minimum, histogram_maximum, ranges, counts_data,
logged_data, &histogram_data_ptr->samples_metadata,
histogram = LinearHistogram::PersistentCreate(
name, histogram_minimum, histogram_maximum, ranges, counts_data,
logged_data, &histogram_data_ptr->samples_metadata,
histogram = BooleanHistogram::PersistentCreate(
name, ranges, counts_data, logged_data,
histogram = CustomHistogram::PersistentCreate(
name, ranges, counts_data, logged_data,
return nullptr;
if (histogram) {
DCHECK_EQ(histogram_type, histogram->GetHistogramType());
return histogram;
const HistogramBase* histogram) {
// This should never be called on the global histogram allocator as objects
// created there are already within the global statistics recorder.
DCHECK_NE(GlobalHistogramAllocator::Get(), this);
HistogramBase* existing =
if (existing)
return existing;
// Adding the passed histogram to the SR would cause a problem if the
// allocator that holds it eventually goes away. Instead, create a new
// one from a serialized version. Deserialization calls the appropriate
// FactoryGet() which will create the histogram in the global persistent-
// histogram allocator if such is set.
base::Pickle pickle;
PickleIterator iter(pickle);
existing = DeserializeHistogramInfo(&iter);
if (!existing)
return nullptr;
// Make sure there is no "serialization" flag set.
DCHECK_EQ(0, existing->flags() & HistogramBase::kIPCSerializationSourceFlag);
// Record the newly created histogram in the SR.
return StatisticsRecorder::RegisterOrDeleteDuplicate(existing);
GlobalHistogramAllocator::~GlobalHistogramAllocator() = default;
// static
void GlobalHistogramAllocator::CreateWithPersistentMemory(
void* base,
size_t size,
size_t page_size,
uint64_t id,
StringPiece name) {
new GlobalHistogramAllocator(std::make_unique<PersistentMemoryAllocator>(
base, size, page_size, id, name, false))));
// static
void GlobalHistogramAllocator::CreateWithLocalMemory(
size_t size,
uint64_t id,
StringPiece name) {
Set(WrapUnique(new GlobalHistogramAllocator(
std::make_unique<LocalPersistentMemoryAllocator>(size, id, name))));
#if !defined(OS_NACL)
// static
bool GlobalHistogramAllocator::CreateWithFile(
const FilePath& file_path,
size_t size,
uint64_t id,
StringPiece name) {
bool exists = PathExists(file_path);
File file(
std::unique_ptr<MemoryMappedFile> mmfile(new MemoryMappedFile());
if (exists) {
size = saturated_cast<size_t>(file.GetLength());
mmfile->Initialize(std::move(file), MemoryMappedFile::READ_WRITE);
} else {
mmfile->Initialize(std::move(file), {0, size},
if (!mmfile->IsValid() ||
!FilePersistentMemoryAllocator::IsFileAcceptable(*mmfile, true)) {
return false;
Set(WrapUnique(new GlobalHistogramAllocator(
std::make_unique<FilePersistentMemoryAllocator>(std::move(mmfile), size,
id, name, false))));
return true;
// static
bool GlobalHistogramAllocator::CreateWithActiveFile(const FilePath& base_path,
const FilePath& active_path,
const FilePath& spare_path,
size_t size,
uint64_t id,
StringPiece name) {
// Old "active" becomes "base".
if (!base::ReplaceFile(active_path, base_path, nullptr))
base::DeleteFile(base_path, /*recursive=*/false);
// Move any "spare" into "active". Okay to continue if file doesn't exist.
if (!spare_path.empty()) {
base::ReplaceFile(spare_path, active_path, nullptr);
return base::GlobalHistogramAllocator::CreateWithFile(active_path, size, id,
// static
bool GlobalHistogramAllocator::CreateWithActiveFileInDir(const FilePath& dir,
size_t size,
uint64_t id,
StringPiece name) {
FilePath base_path, active_path, spare_path;
ConstructFilePaths(dir, name, &base_path, &active_path, &spare_path);
return CreateWithActiveFile(base_path, active_path, spare_path, size, id,
// static
FilePath GlobalHistogramAllocator::ConstructFilePath(const FilePath& dir,
StringPiece name) {
return dir.AppendASCII(name).AddExtension(
// static
FilePath GlobalHistogramAllocator::ConstructFilePathForUploadDir(
const FilePath& dir,
StringPiece name,
base::Time stamp,
ProcessId pid) {
return ConstructFilePath(
StringPrintf("%.*s-%lX-%lX", static_cast<int>(name.length()),,
static_cast<long>(stamp.ToTimeT()), static_cast<long>(pid)));
// static
bool GlobalHistogramAllocator::ParseFilePath(const FilePath& path,
std::string* out_name,
Time* out_stamp,
ProcessId* out_pid) {
std::string filename = path.BaseName().AsUTF8Unsafe();
std::vector<base::StringPiece> parts = base::SplitStringPiece(
filename, "-.", base::KEEP_WHITESPACE, base::SPLIT_WANT_ALL);
if (parts.size() != 4)
return false;
if (out_name)
*out_name = parts[0].as_string();
if (out_stamp) {
int64_t stamp;
if (!HexStringToInt64(parts[1], &stamp))
return false;
*out_stamp = Time::FromTimeT(static_cast<time_t>(stamp));
if (out_pid) {
int64_t pid;
if (!HexStringToInt64(parts[2], &pid))
return false;
*out_pid = static_cast<ProcessId>(pid);
return true;
// static
void GlobalHistogramAllocator::ConstructFilePaths(const FilePath& dir,
StringPiece name,
FilePath* out_base_path,
FilePath* out_active_path,
FilePath* out_spare_path) {
if (out_base_path)
*out_base_path = ConstructFilePath(dir, name);
if (out_active_path) {
*out_active_path =
ConstructFilePath(dir, name.as_string().append("-active"));
if (out_spare_path) {
*out_spare_path = ConstructFilePath(dir, name.as_string().append("-spare"));
// static
void GlobalHistogramAllocator::ConstructFilePathsForUploadDir(
const FilePath& active_dir,
const FilePath& upload_dir,
const std::string& name,
FilePath* out_upload_path,
FilePath* out_active_path,
FilePath* out_spare_path) {
if (out_upload_path) {
*out_upload_path = ConstructFilePathForUploadDir(
upload_dir, name, Time::Now(), GetCurrentProcId());
if (out_active_path) {
*out_active_path =
ConstructFilePath(active_dir, name + std::string("-active"));
if (out_spare_path) {
*out_spare_path =
ConstructFilePath(active_dir, name + std::string("-spare"));
// static
bool GlobalHistogramAllocator::CreateSpareFile(const FilePath& spare_path,
size_t size) {
FilePath temp_spare_path = spare_path.AddExtension(FILE_PATH_LITERAL(".tmp"));
bool success = true;
File spare_file(temp_spare_path, File::FLAG_CREATE_ALWAYS |
if (!spare_file.IsValid())
return false;
MemoryMappedFile mmfile;
mmfile.Initialize(std::move(spare_file), {0, size},
success = mmfile.IsValid();
if (success)
success = ReplaceFile(temp_spare_path, spare_path, nullptr);
if (!success)
DeleteFile(temp_spare_path, /*recursive=*/false);
return success;
// static
bool GlobalHistogramAllocator::CreateSpareFileInDir(const FilePath& dir,
size_t size,
StringPiece name) {
FilePath spare_path;
ConstructFilePaths(dir, name, nullptr, nullptr, &spare_path);
return CreateSpareFile(spare_path, size);
#endif // !defined(OS_NACL)
// static
void GlobalHistogramAllocator::CreateWithSharedMemoryHandle(
const SharedMemoryHandle& handle,
size_t size) {
std::unique_ptr<SharedMemory> shm(
new SharedMemory(handle, /*readonly=*/false));
if (!shm->Map(size) ||
!SharedPersistentMemoryAllocator::IsSharedMemoryAcceptable(*shm)) {
Set(WrapUnique(new GlobalHistogramAllocator(
std::move(shm), 0, StringPiece(), /*readonly=*/false))));
// static
void GlobalHistogramAllocator::Set(
std::unique_ptr<GlobalHistogramAllocator> allocator) {
// Releasing or changing an allocator is extremely dangerous because it
// likely has histograms stored within it. If the backing memory is also
// also released, future accesses to those histograms will seg-fault.
size_t existing = StatisticsRecorder::GetHistogramCount();
DVLOG_IF(1, existing)
<< existing << " histograms were created before persistence was enabled.";
// static
GlobalHistogramAllocator* GlobalHistogramAllocator::Get() {
return reinterpret_cast<GlobalHistogramAllocator*>(
// static
GlobalHistogramAllocator::ReleaseForTesting() {
GlobalHistogramAllocator* histogram_allocator = Get();
if (!histogram_allocator)
return nullptr;
PersistentMemoryAllocator* memory_allocator =
// Before releasing the memory, it's necessary to have the Statistics-
// Recorder forget about the histograms contained therein; otherwise,
// some operations will try to access them and the released memory.
PersistentMemoryAllocator::Iterator iter(memory_allocator);
const PersistentHistogramData* data;
while ((data = iter.GetNextOfObject<PersistentHistogramData>()) != nullptr) {
subtle::Release_Store(&g_histogram_allocator, 0);
return WrapUnique(histogram_allocator);
void GlobalHistogramAllocator::SetPersistentLocation(const FilePath& location) {
persistent_location_ = location;
const FilePath& GlobalHistogramAllocator::GetPersistentLocation() const {
return persistent_location_;
bool GlobalHistogramAllocator::WriteToPersistentLocation() {
#if defined(OS_NACL)
// NACL doesn't support file operations, including ImportantFileWriter.
return false;
// Stop if no destination is set.
if (persistent_location_.empty()) {
NOTREACHED() << "Could not write \"" << Name() << "\" persistent histograms"
<< " to file because no location was set.";
return false;
StringPiece contents(static_cast<const char*>(data()), used());
if (!ImportantFileWriter::WriteFileAtomically(persistent_location_,
contents)) {
LOG(ERROR) << "Could not write \"" << Name() << "\" persistent histograms"
<< " to file: " << persistent_location_.value();
return false;
return true;
void GlobalHistogramAllocator::DeletePersistentLocation() {
#if defined(OS_NACL)
if (persistent_location_.empty())
// Open (with delete) and then immediately close the file by going out of
// scope. This is the only cross-platform safe way to delete a file that may
// be open elsewhere. Open handles will continue to operate normally but
// new opens will not be possible.
File file(persistent_location_,
std::unique_ptr<PersistentMemoryAllocator> memory)
: PersistentHistogramAllocator(std::move(memory)),
import_iterator_(this) {
void GlobalHistogramAllocator::ImportHistogramsToStatisticsRecorder() {
// Skip the import if it's the histogram that was last created. Should a
// race condition cause the "last created" to be overwritten before it
// is recognized here then the histogram will be created and be ignored
// when it is detected as a duplicate by the statistics-recorder. This
// simple check reduces the time of creating persistent histograms by
// about 40%.
Reference record_to_ignore = last_created();
// There is no lock on this because the iterator is lock-free while still
// guaranteed to only return each entry only once. The StatisticsRecorder
// has its own lock so the Register operation is safe.
while (true) {
std::unique_ptr<HistogramBase> histogram =
if (!histogram)
} // namespace base