| // 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_sample_map.h" |
| |
| #include "base/logging.h" |
| #include "base/stl_util.h" |
| |
| namespace base { |
| |
| typedef HistogramBase::Count Count; |
| typedef HistogramBase::Sample Sample; |
| |
| namespace { |
| |
| // An iterator for going through a PersistentSampleMap. The logic here is |
| // identical to that of SampleMapIterator but with different data structures. |
| // Changes here likely need to be duplicated there. |
| class PersistentSampleMapIterator : public SampleCountIterator { |
| public: |
| typedef std::map<HistogramBase::Sample, HistogramBase::Count*> |
| SampleToCountMap; |
| |
| explicit PersistentSampleMapIterator(const SampleToCountMap& sample_counts); |
| ~PersistentSampleMapIterator() override; |
| |
| // SampleCountIterator: |
| bool Done() const override; |
| void Next() override; |
| void Get(HistogramBase::Sample* min, |
| HistogramBase::Sample* max, |
| HistogramBase::Count* count) const override; |
| |
| private: |
| void SkipEmptyBuckets(); |
| |
| SampleToCountMap::const_iterator iter_; |
| const SampleToCountMap::const_iterator end_; |
| }; |
| |
| PersistentSampleMapIterator::PersistentSampleMapIterator( |
| const SampleToCountMap& sample_counts) |
| : iter_(sample_counts.begin()), |
| end_(sample_counts.end()) { |
| SkipEmptyBuckets(); |
| } |
| |
| PersistentSampleMapIterator::~PersistentSampleMapIterator() {} |
| |
| bool PersistentSampleMapIterator::Done() const { |
| return iter_ == end_; |
| } |
| |
| void PersistentSampleMapIterator::Next() { |
| DCHECK(!Done()); |
| ++iter_; |
| SkipEmptyBuckets(); |
| } |
| |
| void PersistentSampleMapIterator::Get(Sample* min, |
| Sample* max, |
| Count* count) const { |
| DCHECK(!Done()); |
| if (min) |
| *min = iter_->first; |
| if (max) |
| *max = iter_->first + 1; |
| if (count) |
| *count = *iter_->second; |
| } |
| |
| void PersistentSampleMapIterator::SkipEmptyBuckets() { |
| while (!Done() && *iter_->second == 0) { |
| ++iter_; |
| } |
| } |
| |
| // This structure holds an entry for a PersistentSampleMap within a persistent |
| // memory allocator. The "id" must be unique across all maps held by an |
| // allocator or they will get attached to the wrong sample map. |
| struct SampleRecord { |
| uint64_t id; // Unique identifier of owner. |
| Sample value; // The value for which this record holds a count. |
| Count count; // The count associated with the above value. |
| }; |
| |
| // The type-id used to identify sample records inside an allocator. |
| const uint32_t kTypeIdSampleRecord = 0x8FE6A69F + 1; // SHA1(SampleRecord) v1 |
| |
| } // namespace |
| |
| PersistentSampleMap::PersistentSampleMap( |
| uint64_t id, |
| PersistentMemoryAllocator* allocator, |
| Metadata* meta) |
| : HistogramSamples(id, meta), |
| allocator_(allocator) { |
| // This is created once but will continue to return new iterables even when |
| // it has previously reached the end. |
| allocator->CreateIterator(&sample_iter_); |
| |
| // Load all existing samples during construction. It's no worse to do it |
| // here than at some point in the future and could be better if construction |
| // takes place on some background thread. New samples could be created at |
| // any time by parallel threads; if so, they'll get loaded when needed. |
| ImportSamples(kAllSamples); |
| } |
| |
| PersistentSampleMap::~PersistentSampleMap() {} |
| |
| void PersistentSampleMap::Accumulate(Sample value, Count count) { |
| *GetOrCreateSampleCountStorage(value) += count; |
| IncreaseSum(static_cast<int64_t>(count) * value); |
| IncreaseRedundantCount(count); |
| } |
| |
| Count PersistentSampleMap::GetCount(Sample value) const { |
| // Have to override "const" to make sure all samples have been loaded before |
| // being able to know what value to return. |
| Count* count_pointer = |
| const_cast<PersistentSampleMap*>(this)->GetSampleCountStorage(value); |
| return count_pointer ? *count_pointer : 0; |
| } |
| |
| Count PersistentSampleMap::TotalCount() const { |
| // Have to override "const" in order to make sure all samples have been |
| // loaded before trying to iterate over the map. |
| const_cast<PersistentSampleMap*>(this)->ImportSamples(kAllSamples); |
| |
| Count count = 0; |
| for (const auto& entry : sample_counts_) { |
| count += *entry.second; |
| } |
| return count; |
| } |
| |
| scoped_ptr<SampleCountIterator> PersistentSampleMap::Iterator() const { |
| // Have to override "const" in order to make sure all samples have been |
| // loaded before trying to iterate over the map. |
| const_cast<PersistentSampleMap*>(this)->ImportSamples(kAllSamples); |
| return make_scoped_ptr(new PersistentSampleMapIterator(sample_counts_)); |
| } |
| |
| bool PersistentSampleMap::AddSubtractImpl(SampleCountIterator* iter, |
| Operator op) { |
| Sample min; |
| Sample max; |
| Count count; |
| for (; !iter->Done(); iter->Next()) { |
| iter->Get(&min, &max, &count); |
| if (min + 1 != max) |
| return false; // SparseHistogram only supports bucket with size 1. |
| |
| *GetOrCreateSampleCountStorage(min) += |
| (op == HistogramSamples::ADD) ? count : -count; |
| } |
| return true; |
| } |
| |
| Count* PersistentSampleMap::GetSampleCountStorage(Sample value) { |
| DCHECK_LE(0, value); |
| |
| // If |value| is already in the map, just return that. |
| auto it = sample_counts_.find(value); |
| if (it != sample_counts_.end()) |
| return it->second; |
| |
| // Import any new samples from persistent memory looking for the value. |
| return ImportSamples(value); |
| } |
| |
| Count* PersistentSampleMap::GetOrCreateSampleCountStorage(Sample value) { |
| // Get any existing count storage. |
| Count* count_pointer = GetSampleCountStorage(value); |
| if (count_pointer) |
| return count_pointer; |
| |
| // Create a new record in persistent memory for the value. |
| PersistentMemoryAllocator::Reference ref = |
| allocator_->Allocate(sizeof(SampleRecord), kTypeIdSampleRecord); |
| SampleRecord* record = |
| allocator_->GetAsObject<SampleRecord>(ref, kTypeIdSampleRecord); |
| if (!record) { |
| // If the allocator was unable to create a record then it is full or |
| // corrupt. Instead, allocate the counter from the heap. This sample will |
| // not be persistent, will not be shared, and will leak but it's better |
| // than crashing. |
| NOTREACHED() << "full=" << allocator_->IsFull() |
| << ", corrupt=" << allocator_->IsCorrupt(); |
| count_pointer = new Count(0); |
| sample_counts_[value] = count_pointer; |
| return count_pointer; |
| } |
| record->id = id(); |
| record->value = value; |
| record->count = 0; // Should already be zero but don't trust other processes. |
| allocator_->MakeIterable(ref); |
| |
| // A race condition between two independent processes (i.e. two independent |
| // histogram objects sharing the same sample data) could cause two of the |
| // above records to be created. The allocator, however, forces a strict |
| // ordering on iterable objects so use the import method to actually add the |
| // just-created record. This ensures that all PersistentSampleMap objects |
| // will always use the same record, whichever was first made iterable. |
| // Thread-safety within a process where multiple threads use the same |
| // histogram object is delegated to the controlling histogram object which, |
| // for sparse histograms, is a lock object. |
| count_pointer = ImportSamples(value); |
| DCHECK(count_pointer); |
| return count_pointer; |
| } |
| |
| Count* PersistentSampleMap::ImportSamples(Sample until_value) { |
| // TODO(bcwhite): This import operates in O(V+N) total time per sparse |
| // histogram where V is the number of values for this object and N is |
| // the number of other iterable objects in the allocator. This becomes |
| // O(S*(SV+N)) or O(S^2*V + SN) overall where S is the number of sparse |
| // histograms. |
| // |
| // This is actually okay when histograms are expected to exist for the |
| // lifetime of the program, spreading the cost out, and S and V are |
| // relatively small, as is the current case. |
| // |
| // However, it is not so good for objects that are created, detroyed, and |
| // recreated on a periodic basis, such as when making a snapshot of |
| // sparse histograms owned by another, ongoing process. In that case, the |
| // entire cost is compressed into a single sequential operation... on the |
| // UI thread no less. |
| // |
| // This will be addressed in a future CL. |
| |
| uint32_t type_id; |
| PersistentMemoryAllocator::Reference ref; |
| while ((ref = allocator_->GetNextIterable(&sample_iter_, &type_id)) != 0) { |
| if (type_id == kTypeIdSampleRecord) { |
| SampleRecord* record = |
| allocator_->GetAsObject<SampleRecord>(ref, kTypeIdSampleRecord); |
| if (!record) |
| continue; |
| |
| // A sample record has been found but may not be for this histogram. |
| if (record->id != id()) |
| continue; |
| |
| // Check if the record's value is already known. |
| if (!ContainsKey(sample_counts_, record->value)) { |
| // No: Add it to map of known values if the value is valid. |
| if (record->value >= 0) |
| sample_counts_[record->value] = &record->count; |
| } else { |
| // Yes: Ignore it; it's a duplicate caused by a race condition -- see |
| // code & comment in GetOrCreateSampleCountStorage() for details. |
| // Check that nothing ever operated on the duplicate record. |
| DCHECK_EQ(0, record->count); |
| } |
| |
| // Stop if it's the value being searched for. |
| if (record->value == until_value) |
| return &record->count; |
| } |
| } |
| |
| return nullptr; |
| } |
| |
| } // namespace base |