base/metrics/histogram_samples.cc - chromium/src.git - Git at Google

 // Copyright (c) 2012 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/histogram_samples.h"

 #include <limits>

 #include "base/compiler_specific.h"
 #include "base/metrics/histogram_functions.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/numerics/safe_conversions.h"
 #include "base/numerics/safe_math.h"
 #include "base/pickle.h"

 namespace base {

 namespace {

 // A shorthand constant for the max value of size_t.
 constexpr size_t kSizeMax = std::numeric_limits<size_t>::max();

 // A constant stored in an AtomicSingleSample (as_atomic) to indicate that the
 // sample is "disabled" and no further accumulation should be done with it. The
 // value is chosen such that it will be MAX_UINT16 for both |bucket| & |count|,
 // and thus less likely to conflict with real use. Conflicts are explicitly
 // handled in the code but it's worth making them as unlikely as possible.
 constexpr int32_t kDisabledSingleSample = -1;

 class SampleCountPickleIterator : public SampleCountIterator {
  public:
   explicit SampleCountPickleIterator(PickleIterator* iter);

   bool Done() const override;
   void Next() override;
   void Get(HistogramBase::Sample* min,
            int64_t* max,
            HistogramBase::Count* count) const override;

  private:
   PickleIterator* const iter_;

   HistogramBase::Sample min_;
   int64_t max_;
   HistogramBase::Count count_;
   bool is_done_;
 };

 SampleCountPickleIterator::SampleCountPickleIterator(PickleIterator* iter)
     : iter_(iter),
       is_done_(false) {
   Next();
 }

 bool SampleCountPickleIterator::Done() const {
   return is_done_;
 }

 void SampleCountPickleIterator::Next() {
   DCHECK(!Done());
   if (!iter_->ReadInt(&min_) || !iter_->ReadInt64(&max_) ||
       !iter_->ReadInt(&count_)) {
     is_done_ = true;
   }
 }

 void SampleCountPickleIterator::Get(HistogramBase::Sample* min,
                                     int64_t* max,
                                     HistogramBase::Count* count) const {
   DCHECK(!Done());
   *min = min_;
   *max = max_;
   *count = count_;
 }

 }  // namespace

 static_assert(sizeof(HistogramSamples::AtomicSingleSample) ==
                   sizeof(subtle::Atomic32),
               "AtomicSingleSample isn't 32 bits");

 HistogramSamples::SingleSample HistogramSamples::AtomicSingleSample::Load()
     const {
   AtomicSingleSample single_sample = subtle::Acquire_Load(&as_atomic);

   // If the sample was extracted/disabled, it's still zero to the outside.
   if (single_sample.as_atomic == kDisabledSingleSample)
     single_sample.as_atomic = 0;

   return single_sample.as_parts;
 }

 HistogramSamples::SingleSample HistogramSamples::AtomicSingleSample::Extract(
     bool disable) {
   AtomicSingleSample single_sample = subtle::NoBarrier_AtomicExchange(
       &as_atomic, disable ? kDisabledSingleSample : 0);
   if (single_sample.as_atomic == kDisabledSingleSample)
     single_sample.as_atomic = 0;
   return single_sample.as_parts;
 }

 bool HistogramSamples::AtomicSingleSample::Accumulate(
     size_t bucket,
     HistogramBase::Count count) {
   if (count == 0)
     return true;

   // Convert the parameters to 16-bit variables because it's all 16-bit below.
   // To support decrements/subtractions, divide the |count| into sign/value and
   // do the proper operation below. The alternative is to change the single-
   // sample's count to be a signed integer (int16_t) and just add an int16_t
   // |count16| but that is somewhat wasteful given that the single-sample is
   // never expected to have a count less than zero.
   if (count < -std::numeric_limits<uint16_t>::max() ||
       count > std::numeric_limits<uint16_t>::max() ||
       bucket > std::numeric_limits<uint16_t>::max()) {
     return false;
   }
   bool count_is_negative = count < 0;
   uint16_t count16 = static_cast<uint16_t>(count_is_negative ? -count : count);
   uint16_t bucket16 = static_cast<uint16_t>(bucket);

   // A local, unshared copy of the single-sample is necessary so the parts
   // can be manipulated without worrying about atomicity.
   AtomicSingleSample single_sample;

   bool sample_updated;
   do {
     subtle::Atomic32 original = subtle::Acquire_Load(&as_atomic);
     if (original == kDisabledSingleSample)
       return false;
     single_sample.as_atomic = original;
     if (single_sample.as_atomic != 0) {
       // Only the same bucket (parameter and stored) can be counted multiple
       // times.
       if (single_sample.as_parts.bucket != bucket16)
         return false;
     } else {
       // The |single_ sample| was zero so becomes the |bucket| parameter, the
       // contents of which were checked above to fit in 16 bits.
       single_sample.as_parts.bucket = bucket16;
     }

     // Update count, making sure that it doesn't overflow.
     CheckedNumeric<uint16_t> new_count(single_sample.as_parts.count);
     if (count_is_negative)
       new_count -= count16;
     else
       new_count += count16;
     if (!new_count.AssignIfValid(&single_sample.as_parts.count))
       return false;

     // Don't let this become equivalent to the "disabled" value.
     if (single_sample.as_atomic == kDisabledSingleSample)
       return false;

     // Store the updated single-sample back into memory. |existing| is what
     // was in that memory location at the time of the call; if it doesn't
     // match |original| then the swap didn't happen so loop again.
     subtle::Atomic32 existing = subtle::Release_CompareAndSwap(
         &as_atomic, original, single_sample.as_atomic);
     sample_updated = (existing == original);
   } while (!sample_updated);

   return true;
 }

 bool HistogramSamples::AtomicSingleSample::IsDisabled() const {
   return subtle::Acquire_Load(&as_atomic) == kDisabledSingleSample;
 }

 HistogramSamples::LocalMetadata::LocalMetadata() {
   // This is the same way it's done for persistent metadata since no ctor
   // is called for the data members in that case.
   memset(this, 0, sizeof(*this));
 }

 HistogramSamples::HistogramSamples(uint64_t id, Metadata* meta)
     : meta_(meta) {
   DCHECK(meta_->id == 0 || meta_->id == id);

   // It's possible that |meta| is contained in initialized, read-only memory
   // so it's essential that no write be done in that case.
   if (!meta_->id)
     meta_->id = id;
 }

 // This mustn't do anything with |meta_|. It was passed to the ctor and may
 // be invalid by the time this dtor gets called.
 HistogramSamples::~HistogramSamples() = default;

 void HistogramSamples::Add(const HistogramSamples& other) {
   IncreaseSumAndCount(other.sum(), other.redundant_count());
   std::unique_ptr<SampleCountIterator> it = other.Iterator();
   bool success = AddSubtractImpl(it.get(), ADD);
   DCHECK(success);
 }

 bool HistogramSamples::AddFromPickle(PickleIterator* iter) {
   int64_t sum;
   HistogramBase::Count redundant_count;

   if (!iter->ReadInt64(&sum) || !iter->ReadInt(&redundant_count))
     return false;

   IncreaseSumAndCount(sum, redundant_count);

   SampleCountPickleIterator pickle_iter(iter);
   return AddSubtractImpl(&pickle_iter, ADD);
 }

 void HistogramSamples::Subtract(const HistogramSamples& other) {
   IncreaseSumAndCount(-other.sum(), -other.redundant_count());
   std::unique_ptr<SampleCountIterator> it = other.Iterator();
   bool success = AddSubtractImpl(it.get(), SUBTRACT);
   DCHECK(success);
 }

 void HistogramSamples::Serialize(Pickle* pickle) const {
   pickle->WriteInt64(sum());
   pickle->WriteInt(redundant_count());

   HistogramBase::Sample min;
   int64_t max;
   HistogramBase::Count count;
   for (std::unique_ptr<SampleCountIterator> it = Iterator(); !it->Done();
        it->Next()) {
     it->Get(&min, &max, &count);
     pickle->WriteInt(min);
     pickle->WriteInt64(max);
     pickle->WriteInt(count);
   }
 }

 bool HistogramSamples::AccumulateSingleSample(HistogramBase::Sample value,
                                               HistogramBase::Count count,
                                               size_t bucket) {
   if (single_sample().Accumulate(bucket, count)) {
     // Success. Update the (separate) sum and redundant-count.
     IncreaseSumAndCount(strict_cast<int64_t>(value) * count, count);
     return true;
   }
   return false;
 }

 void HistogramSamples::IncreaseSumAndCount(int64_t sum,
                                            HistogramBase::Count count) {
 #ifdef ARCH_CPU_64_BITS
   subtle::NoBarrier_AtomicIncrement(&meta_->sum, sum);
 #else
   meta_->sum += sum;
 #endif
   subtle::NoBarrier_AtomicIncrement(&meta_->redundant_count, count);
 }

 void HistogramSamples::RecordNegativeSample(NegativeSampleReason reason,
                                             HistogramBase::Count increment) {
   UMA_HISTOGRAM_ENUMERATION("UMA.NegativeSamples.Reason", reason,
                             MAX_NEGATIVE_SAMPLE_REASONS);
   UMA_HISTOGRAM_CUSTOM_COUNTS("UMA.NegativeSamples.Increment", increment, 1,
                               1 << 30, 100);
   UmaHistogramSparse("UMA.NegativeSamples.Histogram",
                      static_cast<int32_t>(id()));
 }

 SampleCountIterator::~SampleCountIterator() = default;

 bool SampleCountIterator::GetBucketIndex(size_t* index) const {
   DCHECK(!Done());
   return false;
 }

 SingleSampleIterator::SingleSampleIterator(HistogramBase::Sample min,
                                            int64_t max,
                                            HistogramBase::Count count)
     : SingleSampleIterator(min, max, count, kSizeMax) {}

 SingleSampleIterator::SingleSampleIterator(HistogramBase::Sample min,
                                            int64_t max,
                                            HistogramBase::Count count,
                                            size_t bucket_index)
     : min_(min), max_(max), bucket_index_(bucket_index), count_(count) {}

 SingleSampleIterator::~SingleSampleIterator() = default;

 bool SingleSampleIterator::Done() const {
   return count_ == 0;
 }

 void SingleSampleIterator::Next() {
   DCHECK(!Done());
   count_ = 0;
 }

 void SingleSampleIterator::Get(HistogramBase::Sample* min,
                                int64_t* max,
                                HistogramBase::Count* count) const {
   DCHECK(!Done());
   if (min != nullptr)
     *min = min_;
   if (max != nullptr)
     *max = max_;
   if (count != nullptr)
     *count = count_;
 }

 bool SingleSampleIterator::GetBucketIndex(size_t* index) const {
   DCHECK(!Done());
   if (bucket_index_ == kSizeMax)
     return false;
   *index = bucket_index_;
   return true;
 }

 }  // namespace base
	// Copyright (c) 2012 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/histogram_samples.h"

	#include <limits>

	#include "base/compiler_specific.h"
	#include "base/metrics/histogram_functions.h"
	#include "base/metrics/histogram_macros.h"
	#include "base/numerics/safe_conversions.h"
	#include "base/numerics/safe_math.h"
	#include "base/pickle.h"

	namespace base {

	namespace {

	// A shorthand constant for the max value of size_t.
	constexpr size_t kSizeMax = std::numeric_limits<size_t>::max();

	// A constant stored in an AtomicSingleSample (as_atomic) to indicate that the
	// sample is "disabled" and no further accumulation should be done with it. The
	// value is chosen such that it will be MAX_UINT16 for both \|bucket\| & \|count\|,
	// and thus less likely to conflict with real use. Conflicts are explicitly
	// handled in the code but it's worth making them as unlikely as possible.
	constexpr int32_t kDisabledSingleSample = -1;

	class SampleCountPickleIterator : public SampleCountIterator {
	public:
	explicit SampleCountPickleIterator(PickleIterator* iter);

	bool Done() const override;
	void Next() override;
	void Get(HistogramBase::Sample* min,
	int64_t* max,
	HistogramBase::Count* count) const override;

	private:
	PickleIterator* const iter_;

	HistogramBase::Sample min_;
	int64_t max_;
	HistogramBase::Count count_;
	bool is_done_;
	};

	SampleCountPickleIterator::SampleCountPickleIterator(PickleIterator* iter)
	: iter_(iter),
	is_done_(false) {
	Next();
	}

	bool SampleCountPickleIterator::Done() const {
	return is_done_;
	}

	void SampleCountPickleIterator::Next() {
	DCHECK(!Done());
	if (!iter_->ReadInt(&min_) \|\| !iter_->ReadInt64(&max_) \|\|
	!iter_->ReadInt(&count_)) {
	is_done_ = true;
	}
	}

	void SampleCountPickleIterator::Get(HistogramBase::Sample* min,
	int64_t* max,
	HistogramBase::Count* count) const {
	DCHECK(!Done());
	*min = min_;
	*max = max_;
	*count = count_;
	}

	} // namespace

	static_assert(sizeof(HistogramSamples::AtomicSingleSample) ==
	sizeof(subtle::Atomic32),
	"AtomicSingleSample isn't 32 bits");

	HistogramSamples::SingleSample HistogramSamples::AtomicSingleSample::Load()
	const {
	AtomicSingleSample single_sample = subtle::Acquire_Load(&as_atomic);

	// If the sample was extracted/disabled, it's still zero to the outside.
	if (single_sample.as_atomic == kDisabledSingleSample)
	single_sample.as_atomic = 0;

	return single_sample.as_parts;
	}

	HistogramSamples::SingleSample HistogramSamples::AtomicSingleSample::Extract(
	bool disable) {
	AtomicSingleSample single_sample = subtle::NoBarrier_AtomicExchange(
	&as_atomic, disable ? kDisabledSingleSample : 0);
	if (single_sample.as_atomic == kDisabledSingleSample)
	single_sample.as_atomic = 0;
	return single_sample.as_parts;
	}

	bool HistogramSamples::AtomicSingleSample::Accumulate(
	size_t bucket,
	HistogramBase::Count count) {
	if (count == 0)
	return true;

	// Convert the parameters to 16-bit variables because it's all 16-bit below.
	// To support decrements/subtractions, divide the \|count\| into sign/value and
	// do the proper operation below. The alternative is to change the single-
	// sample's count to be a signed integer (int16_t) and just add an int16_t
	// \|count16\| but that is somewhat wasteful given that the single-sample is
	// never expected to have a count less than zero.
	if (count < -std::numeric_limits<uint16_t>::max() \|\|
	count > std::numeric_limits<uint16_t>::max() \|\|
	bucket > std::numeric_limits<uint16_t>::max()) {
	return false;
	}
	bool count_is_negative = count < 0;
	uint16_t count16 = static_cast<uint16_t>(count_is_negative ? -count : count);
	uint16_t bucket16 = static_cast<uint16_t>(bucket);

	// A local, unshared copy of the single-sample is necessary so the parts
	// can be manipulated without worrying about atomicity.
	AtomicSingleSample single_sample;

	bool sample_updated;
	do {
	subtle::Atomic32 original = subtle::Acquire_Load(&as_atomic);
	if (original == kDisabledSingleSample)
	return false;
	single_sample.as_atomic = original;
	if (single_sample.as_atomic != 0) {
	// Only the same bucket (parameter and stored) can be counted multiple
	// times.
	if (single_sample.as_parts.bucket != bucket16)
	return false;
	} else {
	// The \|single_ sample\| was zero so becomes the \|bucket\| parameter, the
	// contents of which were checked above to fit in 16 bits.
	single_sample.as_parts.bucket = bucket16;
	}

	// Update count, making sure that it doesn't overflow.
	CheckedNumeric<uint16_t> new_count(single_sample.as_parts.count);
	if (count_is_negative)
	new_count -= count16;
	else
	new_count += count16;
	if (!new_count.AssignIfValid(&single_sample.as_parts.count))
	return false;

	// Don't let this become equivalent to the "disabled" value.
	if (single_sample.as_atomic == kDisabledSingleSample)
	return false;

	// Store the updated single-sample back into memory. \|existing\| is what
	// was in that memory location at the time of the call; if it doesn't
	// match \|original\| then the swap didn't happen so loop again.
	subtle::Atomic32 existing = subtle::Release_CompareAndSwap(
	&as_atomic, original, single_sample.as_atomic);
	sample_updated = (existing == original);
	} while (!sample_updated);

	return true;
	}

	bool HistogramSamples::AtomicSingleSample::IsDisabled() const {
	return subtle::Acquire_Load(&as_atomic) == kDisabledSingleSample;
	}

	HistogramSamples::LocalMetadata::LocalMetadata() {
	// This is the same way it's done for persistent metadata since no ctor
	// is called for the data members in that case.
	memset(this, 0, sizeof(*this));
	}

	HistogramSamples::HistogramSamples(uint64_t id, Metadata* meta)
	: meta_(meta) {
	DCHECK(meta_->id == 0 \|\| meta_->id == id);

	// It's possible that \|meta\| is contained in initialized, read-only memory
	// so it's essential that no write be done in that case.
	if (!meta_->id)
	meta_->id = id;
	}

	// This mustn't do anything with \|meta_\|. It was passed to the ctor and may
	// be invalid by the time this dtor gets called.
	HistogramSamples::~HistogramSamples() = default;

	void HistogramSamples::Add(const HistogramSamples& other) {
	IncreaseSumAndCount(other.sum(), other.redundant_count());
	std::unique_ptr<SampleCountIterator> it = other.Iterator();
	bool success = AddSubtractImpl(it.get(), ADD);
	DCHECK(success);
	}

	bool HistogramSamples::AddFromPickle(PickleIterator* iter) {
	int64_t sum;
	HistogramBase::Count redundant_count;

	if (!iter->ReadInt64(&sum) \|\| !iter->ReadInt(&redundant_count))
	return false;

	IncreaseSumAndCount(sum, redundant_count);

	SampleCountPickleIterator pickle_iter(iter);
	return AddSubtractImpl(&pickle_iter, ADD);
	}

	void HistogramSamples::Subtract(const HistogramSamples& other) {
	IncreaseSumAndCount(-other.sum(), -other.redundant_count());
	std::unique_ptr<SampleCountIterator> it = other.Iterator();
	bool success = AddSubtractImpl(it.get(), SUBTRACT);
	DCHECK(success);
	}

	void HistogramSamples::Serialize(Pickle* pickle) const {
	pickle->WriteInt64(sum());
	pickle->WriteInt(redundant_count());

	HistogramBase::Sample min;
	int64_t max;
	HistogramBase::Count count;
	for (std::unique_ptr<SampleCountIterator> it = Iterator(); !it->Done();
	it->Next()) {
	it->Get(&min, &max, &count);
	pickle->WriteInt(min);
	pickle->WriteInt64(max);
	pickle->WriteInt(count);
	}
	}

	bool HistogramSamples::AccumulateSingleSample(HistogramBase::Sample value,
	HistogramBase::Count count,
	size_t bucket) {
	if (single_sample().Accumulate(bucket, count)) {
	// Success. Update the (separate) sum and redundant-count.
	IncreaseSumAndCount(strict_cast<int64_t>(value) * count, count);
	return true;
	}
	return false;
	}

	void HistogramSamples::IncreaseSumAndCount(int64_t sum,
	HistogramBase::Count count) {
	#ifdef ARCH_CPU_64_BITS
	subtle::NoBarrier_AtomicIncrement(&meta_->sum, sum);
	#else
	meta_->sum += sum;
	#endif
	subtle::NoBarrier_AtomicIncrement(&meta_->redundant_count, count);
	}

	void HistogramSamples::RecordNegativeSample(NegativeSampleReason reason,
	HistogramBase::Count increment) {
	UMA_HISTOGRAM_ENUMERATION("UMA.NegativeSamples.Reason", reason,
	MAX_NEGATIVE_SAMPLE_REASONS);
	UMA_HISTOGRAM_CUSTOM_COUNTS("UMA.NegativeSamples.Increment", increment, 1,
	1 << 30, 100);
	UmaHistogramSparse("UMA.NegativeSamples.Histogram",
	static_cast<int32_t>(id()));
	}

	SampleCountIterator::~SampleCountIterator() = default;

	bool SampleCountIterator::GetBucketIndex(size_t* index) const {
	DCHECK(!Done());
	return false;
	}

	SingleSampleIterator::SingleSampleIterator(HistogramBase::Sample min,
	int64_t max,
	HistogramBase::Count count)
	: SingleSampleIterator(min, max, count, kSizeMax) {}

	SingleSampleIterator::SingleSampleIterator(HistogramBase::Sample min,
	int64_t max,
	HistogramBase::Count count,
	size_t bucket_index)
	: min_(min), max_(max), bucket_index_(bucket_index), count_(count) {}

	SingleSampleIterator::~SingleSampleIterator() = default;

	bool SingleSampleIterator::Done() const {
	return count_ == 0;
	}

	void SingleSampleIterator::Next() {
	DCHECK(!Done());
	count_ = 0;
	}

	void SingleSampleIterator::Get(HistogramBase::Sample* min,
	int64_t* max,
	HistogramBase::Count* count) const {
	DCHECK(!Done());
	if (min != nullptr)
	*min = min_;
	if (max != nullptr)
	*max = max_;
	if (count != nullptr)
	*count = count_;
	}

	bool SingleSampleIterator::GetBucketIndex(size_t* index) const {
	DCHECK(!Done());
	if (bucket_index_ == kSizeMax)
	return false;
	*index = bucket_index_;
	return true;
	}

	} // namespace base