Refactor histogram_persistence to be a class.

base/metrics/histogram_persistence.cc

Index: base/metrics/histogram_persistence.cc
diff --git a/base/metrics/histogram_persistence.cc b/base/metrics/histogram_persistence.cc
deleted file mode 100644
index f18d17528354329cd4995615d2451f6a52c59302..0000000000000000000000000000000000000000
--- a/base/metrics/histogram_persistence.cc
+++ /dev/null
@@ -1,516 +0,0 @@
-// Copyright (c) 2015 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_persistence.h"
-
-#include "base/lazy_instance.h"
-#include "base/logging.h"
-#include "base/memory/scoped_ptr.h"
-#include "base/metrics/histogram.h"
-#include "base/metrics/histogram_base.h"
-#include "base/metrics/histogram_samples.h"
-#include "base/metrics/statistics_recorder.h"
-#include "base/synchronization/lock.h"
-
-namespace base {
-
-namespace {
-
-// Enumerate possible creation results for reporting.
-enum CreateHistogramResultType {
-  // Everything was fine.
-  CREATE_HISTOGRAM_SUCCESS = 0,
-
-  // Pointer to metadata was not valid.
-  CREATE_HISTOGRAM_INVALID_METADATA_POINTER,
-
-  // Histogram metadata was not valid.
-  CREATE_HISTOGRAM_INVALID_METADATA,
-
-  // Ranges information was not valid.
-  CREATE_HISTOGRAM_INVALID_RANGES_ARRAY,
-
-  // Counts information was not valid.
-  CREATE_HISTOGRAM_INVALID_COUNTS_ARRAY,
-
-  // Could not allocate histogram memory due to corruption.
-  CREATE_HISTOGRAM_ALLOCATOR_CORRUPT,
-
-  // Could not allocate histogram memory due to lack of space.
-  CREATE_HISTOGRAM_ALLOCATOR_FULL,
-
-  // Could not allocate histogram memory due to unknown error.
-  CREATE_HISTOGRAM_ALLOCATOR_ERROR,
-
-  // Histogram was of unknown type.
-  CREATE_HISTOGRAM_UNKNOWN_TYPE,
-
-  // Instance has detected a corrupt allocator (recorded only once).
-  CREATE_HISTOGRAM_ALLOCATOR_NEWLY_CORRUPT,
-
-  // Always keep this at the end.
-  CREATE_HISTOGRAM_MAX
-};
-
-// Name of histogram for storing results of local operations.
-const char kResultHistogram[] = "UMA.CreatePersistentHistogram.Result";
-
-// 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 {
-  kTypeIdHistogram   = 0xF1645910 + 2,  // SHA1(Histogram) v2
-  kTypeIdRangesArray = 0xBCEA225A + 1,  // SHA1(RangesArray) v1
-  kTypeIdCountsArray = 0x53215530 + 1,  // SHA1(CountsArray) v1
-};
-
-// This data must be held in persistent memory in order for processes to
-// locate and use histograms created elsewhere. All elements must be of a
-// fixed width to ensure 32/64-bit interoperability.
-struct PersistentHistogramData {
-  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;
-  PersistentMemoryAllocator::Reference counts_ref;
-  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[1];
-};
-
-// The object held here will obviously not be destructed at process exit
-// but that's okay since PersistentMemoryAllocator 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.
-PersistentMemoryAllocator* g_allocator = nullptr;
-
-// 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.
-BucketRanges* CreateRangesFromData(HistogramBase::Sample* ranges_data,
-                                   uint32_t ranges_checksum,
-                                   size_t count) {
-  scoped_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]);
-  }
-
-  ranges->ResetChecksum();
-  if (ranges->checksum() != ranges_checksum)
-    return nullptr;
-
-  return ranges.release();
-}
-
-// 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 unsigned 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<uint32_t>::max() / kBytesPerBucket)
-    return 0;
-
-  return bucket_count * kBytesPerBucket;
-}
-
-}  // namespace
-
-const Feature kPersistentHistogramsFeature{
-  "PersistentHistograms", FEATURE_DISABLED_BY_DEFAULT
-};
-
-// Get the histogram in which create results are stored. This is copied almost
-// exactly from the STATIC_HISTOGRAM_POINTER_BLOCK macro but with added code
-// to prevent recursion (a likely occurance because the creation of a new
-// histogram can end up calling this.)
-HistogramBase* GetCreateHistogramResultHistogram() {
-  static base::subtle::AtomicWord atomic_histogram_pointer = 0;
-  HistogramBase* histogram_pointer(
-      reinterpret_cast<HistogramBase*>(
-          base::subtle::Acquire_Load(&atomic_histogram_pointer)));
-  if (!histogram_pointer) {
-    // It's possible for multiple threads to make it here in parallel but
-    // they'll always return the same result as there is a mutex in the Get.
-    // The purpose of the "initialized" variable is just to ensure that
-    // the same thread doesn't recurse which is also why it doesn't have
-    // to be atomic.
-    static bool initialized = false;
-    if (!initialized) {
-      initialized = true;
-      if (g_allocator) {
-        DLOG(WARNING) << "Creating the results-histogram inside persistent"
-                      << " memory can cause future allocations to crash if"
-                      << " that memory is ever released (for testing).";
-      }
-
-      histogram_pointer = LinearHistogram::FactoryGet(
-          kResultHistogram, 1, CREATE_HISTOGRAM_MAX, CREATE_HISTOGRAM_MAX + 1,
-          HistogramBase::kUmaTargetedHistogramFlag);
-      base::subtle::Release_Store(
-          &atomic_histogram_pointer,
-          reinterpret_cast<base::subtle::AtomicWord>(histogram_pointer));
-    }
-  }
-  return histogram_pointer;
-}
-
-// Record the result of a histogram creation.
-void RecordCreateHistogramResult(CreateHistogramResultType result) {
-  HistogramBase* result_histogram = GetCreateHistogramResultHistogram();
-  if (result_histogram)
-    result_histogram->Add(result);
-}
-
-void SetPersistentHistogramMemoryAllocator(
-    PersistentMemoryAllocator* 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.
-  CHECK(!g_allocator);
-  g_allocator = allocator;
-}
-
-PersistentMemoryAllocator* GetPersistentHistogramMemoryAllocator() {
-  return g_allocator;
-}
-
-PersistentMemoryAllocator*
-ReleasePersistentHistogramMemoryAllocatorForTesting() {
-  PersistentMemoryAllocator* allocator = g_allocator;
-  if (!allocator)
-    return nullptr;
-
-  // 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;
-  PersistentMemoryAllocator::Reference ref;
-  uint32_t type_id;
-  allocator->CreateIterator(&iter);
-  while ((ref = allocator->GetNextIterable(&iter, &type_id)) != 0) {
-    if (type_id == kTypeIdHistogram) {
-      PersistentHistogramData* histogram_data =
-          allocator->GetAsObject<PersistentHistogramData>(
-              ref, kTypeIdHistogram);
-      DCHECK(histogram_data);
-      StatisticsRecorder::ForgetHistogramForTesting(histogram_data->name);
-
-      // If a test breaks here then a memory region containing a histogram
-      // actively used by this code is being released back to the test.
-      // If that memory segment were to be deleted, future calls to create
-      // persistent histograms would crash. To avoid this, have the test call
-      // the method GetCreateHistogramResultHistogram() *before* setting the
-      // (temporary) memory allocator via SetPersistentMemoryAllocator() so
-      // that the histogram is instead allocated from the process heap.
-      DCHECK_NE(kResultHistogram, histogram_data->name);
-    }
-  }
-
-  g_allocator = nullptr;
-  return allocator;
-};
-
-HistogramBase* CreatePersistentHistogram(
-    PersistentMemoryAllocator* allocator,
-    PersistentHistogramData* histogram_data_ptr) {
-  if (!histogram_data_ptr) {
-    RecordCreateHistogramResult(CREATE_HISTOGRAM_INVALID_METADATA_POINTER);
-    NOTREACHED();
-    return nullptr;
-  }
-
-  // Copy the histogram_data 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 contents of histogram_data are
-  // validated below; the local copy is to ensure that the contents cannot
-  // be externally changed between validation and use.
-  PersistentHistogramData histogram_data = *histogram_data_ptr;
-
-  HistogramBase::Sample* ranges_data =
-      allocator->GetAsObject<HistogramBase::Sample>(histogram_data.ranges_ref,
-                                                    kTypeIdRangesArray);
-  if (!ranges_data || histogram_data.bucket_count < 2 ||
-      histogram_data.bucket_count + 1 >
-          std::numeric_limits<uint32_t>::max() /
-              sizeof(HistogramBase::Sample) ||
-      allocator->GetAllocSize(histogram_data.ranges_ref) <
-          (histogram_data.bucket_count + 1) * sizeof(HistogramBase::Sample)) {
-    RecordCreateHistogramResult(CREATE_HISTOGRAM_INVALID_RANGES_ARRAY);
-    NOTREACHED();
-    return nullptr;
-  }
-  // To avoid racy destruction at shutdown, the following will be leaked.
-  const BucketRanges* ranges = CreateRangesFromData(
-      ranges_data,
-      histogram_data.ranges_checksum,
-      histogram_data.bucket_count + 1);
-  if (!ranges) {
-    RecordCreateHistogramResult(CREATE_HISTOGRAM_INVALID_RANGES_ARRAY);
-    NOTREACHED();
-    return nullptr;
-  }
-  ranges = StatisticsRecorder::RegisterOrDeleteDuplicateRanges(ranges);
-
-  HistogramBase::AtomicCount* counts_data =
-      allocator->GetAsObject<HistogramBase::AtomicCount>(
-          histogram_data.counts_ref, kTypeIdCountsArray);
-  size_t counts_bytes =
-      CalculateRequiredCountsBytes(histogram_data.bucket_count);
-  if (!counts_data || !counts_bytes ||
-      allocator->GetAllocSize(histogram_data.counts_ref) < counts_bytes) {
-    RecordCreateHistogramResult(CREATE_HISTOGRAM_INVALID_COUNTS_ARRAY);
-    NOTREACHED();
-    return nullptr;
-  }
-
-  // After the main "counts" array is a second array using for storing what
-  // was previously logged. This is used to calculate the "delta" during
-  // snapshot operations.
-  HistogramBase::AtomicCount* logged_data =
-      counts_data + histogram_data.bucket_count;
-
-  std::string name(histogram_data_ptr->name);
-  HistogramBase* histogram = nullptr;
-  switch (histogram_data.histogram_type) {
-    case HISTOGRAM:
-      histogram = Histogram::PersistentGet(
-          name,
-          histogram_data.minimum,
-          histogram_data.maximum,
-          ranges,
-          counts_data,
-          logged_data,
-          histogram_data.bucket_count,
-          &histogram_data_ptr->samples_metadata,
-          &histogram_data_ptr->logged_metadata);
-      DCHECK(histogram);
-      break;
-    case LINEAR_HISTOGRAM:
-      histogram = LinearHistogram::PersistentGet(
-          name,
-          histogram_data.minimum,
-          histogram_data.maximum,
-          ranges,
-          counts_data,
-          logged_data,
-          histogram_data.bucket_count,
-          &histogram_data_ptr->samples_metadata,
-          &histogram_data_ptr->logged_metadata);
-      DCHECK(histogram);
-      break;
-    case BOOLEAN_HISTOGRAM:
-      histogram = BooleanHistogram::PersistentGet(
-          name,
-          ranges,
-          counts_data,
-          logged_data,
-          &histogram_data_ptr->samples_metadata,
-          &histogram_data_ptr->logged_metadata);
-      DCHECK(histogram);
-      break;
-    case CUSTOM_HISTOGRAM:
-      histogram = CustomHistogram::PersistentGet(
-          name,
-          ranges,
-          counts_data,
-          logged_data,
-          histogram_data.bucket_count,
-          &histogram_data_ptr->samples_metadata,
-          &histogram_data_ptr->logged_metadata);
-      DCHECK(histogram);
-      break;
-    default:
-      NOTREACHED();
-  }
-
-  if (histogram) {
-    DCHECK_EQ(histogram_data.histogram_type, histogram->GetHistogramType());
-    histogram->SetFlags(histogram_data.flags);
-    RecordCreateHistogramResult(CREATE_HISTOGRAM_SUCCESS);
-  } else {
-    RecordCreateHistogramResult(CREATE_HISTOGRAM_UNKNOWN_TYPE);
-  }
-
-  return histogram;
-}
-
-HistogramBase* GetPersistentHistogram(
-    PersistentMemoryAllocator* allocator,
-    int32_t ref) {
-  // Unfortunately, the above "pickle" methods cannot be used as part of the
-  // persistance because the deserialization methods always create local
-  // count data (these must referenced the persistent counts) and always add
-  // it to the local list of known histograms (these may be simple references
-  // to histograms in other processes).
-  PersistentHistogramData* histogram_data =
-      allocator->GetAsObject<PersistentHistogramData>(ref, kTypeIdHistogram);
-  size_t length = allocator->GetAllocSize(ref);
-  if (!histogram_data ||
-      reinterpret_cast<char*>(histogram_data)[length - 1] != '\0') {
-    RecordCreateHistogramResult(CREATE_HISTOGRAM_INVALID_METADATA);
-    NOTREACHED();
-    return nullptr;
-  }
-  return CreatePersistentHistogram(allocator, histogram_data);
-}
-
-HistogramBase* GetNextPersistentHistogram(
-    PersistentMemoryAllocator* allocator,
-    PersistentMemoryAllocator::Iterator* iter) {
-  PersistentMemoryAllocator::Reference ref;
-  uint32_t type_id;
-  while ((ref = allocator->GetNextIterable(iter, &type_id)) != 0) {
-    if (type_id == kTypeIdHistogram)
-      return GetPersistentHistogram(allocator, ref);
-  }
-  return nullptr;
-}
-
-void FinalizePersistentHistogram(PersistentMemoryAllocator::Reference ref,
-                                 bool registered) {
-  // If the created persistent histogram was registered then it needs to
-  // be marked as "iterable" in order to be found by other processes.
-  if (registered)
-    GetPersistentHistogramMemoryAllocator()->MakeIterable(ref);
-  // 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.
-  else
-    GetPersistentHistogramMemoryAllocator()->SetType(ref, 0);
-}
-
-HistogramBase* AllocatePersistentHistogram(
-    PersistentMemoryAllocator* allocator,
-    HistogramType histogram_type,
-    const std::string& name,
-    int minimum,
-    int maximum,
-    const BucketRanges* bucket_ranges,
-    int32_t flags,
-    PersistentMemoryAllocator::Reference* ref_ptr) {
-  if (!allocator)
-    return nullptr;
-
-  // 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 (allocator->IsCorrupt()) {
-    RecordCreateHistogramResult(CREATE_HISTOGRAM_ALLOCATOR_CORRUPT);
-    return nullptr;
-  }
-
-  // If CalculateRequiredCountsBytes() returns zero then the bucket_count
-  // was not valid.
-  size_t bucket_count = bucket_ranges->bucket_count();
-  size_t counts_bytes = CalculateRequiredCountsBytes(bucket_count);
-  if (!counts_bytes) {
-    NOTREACHED();
-    return nullptr;
-  }
-
-  size_t ranges_bytes = (bucket_count + 1) * sizeof(HistogramBase::Sample);
-  PersistentMemoryAllocator::Reference ranges_ref =
-      allocator->Allocate(ranges_bytes, kTypeIdRangesArray);
-  PersistentMemoryAllocator::Reference counts_ref =
-      allocator->Allocate(counts_bytes, kTypeIdCountsArray);
-  PersistentMemoryAllocator::Reference histogram_ref =
-      allocator->Allocate(offsetof(PersistentHistogramData, name) +
-                          name.length() + 1, kTypeIdHistogram);
-  HistogramBase::Sample* ranges_data =
-      allocator->GetAsObject<HistogramBase::Sample>(ranges_ref,
-                                                    kTypeIdRangesArray);
-  PersistentHistogramData* histogram_data =
-      allocator->GetAsObject<PersistentHistogramData>(histogram_ref,
-                                                      kTypeIdHistogram);
-
-  // 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 and so any future
-  // attempts will also fail.
-  if (counts_ref && ranges_data && histogram_data) {
-    strcpy(histogram_data->name, name.c_str());
-    for (size_t i = 0; i < bucket_ranges->size(); ++i)
-      ranges_data[i] = bucket_ranges->range(i);
-
-    histogram_data->histogram_type = histogram_type;
-    histogram_data->flags = flags;
-    histogram_data->minimum = minimum;
-    histogram_data->maximum = maximum;
-    histogram_data->bucket_count = static_cast<uint32_t>(bucket_count);
-    histogram_data->ranges_ref = ranges_ref;
-    histogram_data->ranges_checksum = bucket_ranges->checksum();
-    histogram_data->counts_ref = counts_ref;
-
-    // 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.
-    HistogramBase* histogram =
-        CreatePersistentHistogram(allocator, histogram_data);
-    DCHECK(histogram);
-    if (ref_ptr != nullptr)
-      *ref_ptr = histogram_ref;
-    return histogram;
-  }
-
-  CreateHistogramResultType result;
-  if (allocator->IsCorrupt()) {
-    RecordCreateHistogramResult(CREATE_HISTOGRAM_ALLOCATOR_NEWLY_CORRUPT);
-    result = CREATE_HISTOGRAM_ALLOCATOR_CORRUPT;
-  } else if (allocator->IsFull()) {
-    result = CREATE_HISTOGRAM_ALLOCATOR_FULL;
-  } else {
-    result = CREATE_HISTOGRAM_ALLOCATOR_ERROR;
-  }
-  RecordCreateHistogramResult(result);
-  NOTREACHED() << "error=" << result;
-
-  return nullptr;
-}
-
-void ImportPersistentHistograms() {
-  // The lock protects against concurrent access to the iterator and is created
-  // in a thread-safe manner when needed.
-  static base::LazyInstance<base::Lock>::Leaky lock = LAZY_INSTANCE_INITIALIZER;
-
-  if (g_allocator) {
-    base::AutoLock auto_lock(lock.Get());
-
-    // Each call resumes from where it last left off so need persistant
-    // iterator. This class has a constructor so even the definition has
-    // to be protected by the lock in order to be thread-safe.
-    static PersistentMemoryAllocator::Iterator iter;
-    if (iter.is_clear())
-      g_allocator->CreateIterator(&iter);
-
-    while (true) {
-      HistogramBase* histogram = GetNextPersistentHistogram(g_allocator, &iter);
-      if (!histogram)
-        break;
-      StatisticsRecorder::RegisterOrDeleteDuplicate(histogram);
-    }
-  }
-}
-
-}  // namespace base