[tracing] Switch to new heap dump format.

base/trace_event/heap_profiler_heap_dump_writer.cc

-// Copyright 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/trace_event/heap_profiler_heap_dump_writer.h"
-
-#include <stdint.h>
-
-#include <algorithm>
-#include <iterator>
-#include <tuple>
-#include <utility>
-#include <vector>
-
-#include "base/format_macros.h"
-#include "base/logging.h"
-#include "base/macros.h"
-#include "base/strings/stringprintf.h"
-#include "base/trace_event/heap_profiler_serialization_state.h"
-#include "base/trace_event/heap_profiler_stack_frame_deduplicator.h"
-#include "base/trace_event/heap_profiler_type_name_deduplicator.h"
-#include "base/trace_event/trace_config.h"
-#include "base/trace_event/trace_event_argument.h"
-#include "base/trace_event/trace_log.h"
-
-// Most of what the |HeapDumpWriter| does is aggregating detailed information
-// about the heap and deciding what to dump. The Input to this process is a list
-// of |AllocationContext|s and size pairs.
-//
-// The pairs are grouped into |Bucket|s. A bucket is a group of (context, size)
-// pairs where the properties of the contexts share a prefix. (Type name is
-// considered a list of length one here.) First all pairs are put into one
-// bucket that represents the entire heap. Then this bucket is recursively
-// broken down into smaller buckets. Each bucket keeps track of whether further
-// breakdown is possible.
-
-namespace base {
-namespace trace_event {
-namespace internal {
-namespace {
-
-// Denotes a property of |AllocationContext| to break down by.
-enum class BreakDownMode { kByBacktrace, kByTypeName };
-
-// A group of bytes for which the context shares a prefix.
-struct Bucket {
-  Bucket()
-      : size(0),
-        count(0),
-        backtrace_cursor(0),
-        is_broken_down_by_type_name(false) {}
-
-  std::vector<std::pair<const AllocationContext*, AllocationMetrics>>
-      metrics_by_context;
-
-  // The sum of the sizes of |metrics_by_context|.
-  size_t size;
-
-  // The sum of number of allocations of |metrics_by_context|.
-  size_t count;
-
-  // The index of the stack frame that has not yet been broken down by. For all
-  // elements in this bucket, the stack frames 0 up to (but not including) the
-  // cursor, must be equal.
-  size_t backtrace_cursor;
-
-  // When true, the type name for all elements in this bucket must be equal.
-  bool is_broken_down_by_type_name;
-};
-
-// Comparison operator to order buckets by their size.
-bool operator<(const Bucket& lhs, const Bucket& rhs) {
-  return lhs.size < rhs.size;
-}
-
-// Groups the allocations in the bucket by |break_by|. The buckets in the
-// returned list will have |backtrace_cursor| advanced or
-// |is_broken_down_by_type_name| set depending on the property to group by.
-std::vector<Bucket> GetSubbuckets(const Bucket& bucket,
-                                  BreakDownMode break_by) {
-  std::unordered_map<const void*, Bucket> breakdown;
-
-  if (break_by == BreakDownMode::kByBacktrace) {
-    for (const auto& context_and_metrics : bucket.metrics_by_context) {
-      const Backtrace& backtrace = context_and_metrics.first->backtrace;
-      const StackFrame* begin = std::begin(backtrace.frames);
-      const StackFrame* end = begin + backtrace.frame_count;
-      const StackFrame* cursor = begin + bucket.backtrace_cursor;
-
-      DCHECK_LE(cursor, end);
-
-      if (cursor != end) {
-        Bucket& subbucket = breakdown[cursor->value];
-        subbucket.size += context_and_metrics.second.size;
-        subbucket.count += context_and_metrics.second.count;
-        subbucket.metrics_by_context.push_back(context_and_metrics);
-        subbucket.backtrace_cursor = bucket.backtrace_cursor + 1;
-        subbucket.is_broken_down_by_type_name =
-            bucket.is_broken_down_by_type_name;
-        DCHECK_GT(subbucket.size, 0u);
-        DCHECK_GT(subbucket.count, 0u);
-      }
-    }
-  } else if (break_by == BreakDownMode::kByTypeName) {
-    if (!bucket.is_broken_down_by_type_name) {
-      for (const auto& context_and_metrics : bucket.metrics_by_context) {
-        const AllocationContext* context = context_and_metrics.first;
-        Bucket& subbucket = breakdown[context->type_name];
-        subbucket.size += context_and_metrics.second.size;
-        subbucket.count += context_and_metrics.second.count;
-        subbucket.metrics_by_context.push_back(context_and_metrics);
-        subbucket.backtrace_cursor = bucket.backtrace_cursor;
-        subbucket.is_broken_down_by_type_name = true;
-        DCHECK_GT(subbucket.size, 0u);
-        DCHECK_GT(subbucket.count, 0u);
-      }
-    }
-  }
-
-  std::vector<Bucket> buckets;
-  buckets.reserve(breakdown.size());
-  for (auto key_bucket : breakdown)
-    buckets.push_back(key_bucket.second);
-
-  return buckets;
-}
-
-// Breaks down the bucket by |break_by|. Returns only buckets that contribute
-// more than |min_size_bytes| to the total size. The long tail is omitted.
-std::vector<Bucket> BreakDownBy(const Bucket& bucket,
-                                BreakDownMode break_by,
-                                size_t min_size_bytes) {
-  std::vector<Bucket> buckets = GetSubbuckets(bucket, break_by);
-
-  // Ensure that |buckets| is a max-heap (the data structure, not memory heap),
-  // so its front contains the largest bucket. Buckets should be iterated
-  // ordered by size, but sorting the vector is overkill because the long tail
-  // of small buckets will be discarded. By using a max-heap, the optimal case
-  // where all but the first bucket are discarded is O(n). The worst case where
-  // no bucket is discarded is doing a heap sort, which is O(n log n).
-  std::make_heap(buckets.begin(), buckets.end());
-
-  // Keep including buckets until adding one would increase the number of
-  // bytes accounted for by |min_size_bytes|. The large buckets end up in
-  // [it, end()), [begin(), it) is the part that contains the max-heap
-  // of small buckets.
-  std::vector<Bucket>::iterator it;
-  for (it = buckets.end(); it != buckets.begin(); --it) {
-    if (buckets.front().size < min_size_bytes)
-      break;
-
-    // Put the largest bucket in [begin, it) at |it - 1| and max-heapify
-    // [begin, it - 1). This puts the next largest bucket at |buckets.front()|.
-    std::pop_heap(buckets.begin(), it);
-  }
-
-  // At this point, |buckets| looks like this (numbers are bucket sizes):
-  //
-  // <-- max-heap of small buckets --->
-  //                                  <-- large buckets by ascending size -->
-  // [ 19 | 11 | 13 | 7 | 2 | 5 | ... | 83 | 89 | 97 ]
-  //   ^                                ^              ^
-  //   |                                |              |
-  //   begin()                          it             end()
-
-  // Discard the long tail of buckets that contribute less than a percent.
-  buckets.erase(buckets.begin(), it);
-
-  return buckets;
-}
-
-}  // namespace
-
-bool operator<(Entry lhs, Entry rhs) {
-  // There is no need to compare |size|. If the backtrace and type name are
-  // equal then the sizes must be equal as well.
-  return std::tie(lhs.stack_frame_id, lhs.type_id) <
-         std::tie(rhs.stack_frame_id, rhs.type_id);
-}
-
-HeapDumpWriter::HeapDumpWriter(StackFrameDeduplicator* stack_frame_deduplicator,
-                               TypeNameDeduplicator* type_name_deduplicator,
-                               uint32_t breakdown_threshold_bytes)
-    : stack_frame_deduplicator_(stack_frame_deduplicator),
-      type_name_deduplicator_(type_name_deduplicator),
-      breakdown_threshold_bytes_(breakdown_threshold_bytes) {
-}
-
-HeapDumpWriter::~HeapDumpWriter() {}
-
-bool HeapDumpWriter::AddEntryForBucket(const Bucket& bucket) {
-  // The contexts in the bucket are all different, but the [begin, cursor) range
-  // is equal for all contexts in the bucket, and the type names are the same if
-  // |is_broken_down_by_type_name| is set.
-  DCHECK(!bucket.metrics_by_context.empty());
-
-  const AllocationContext* context = bucket.metrics_by_context.front().first;
-
-  const StackFrame* backtrace_begin = std::begin(context->backtrace.frames);
-  const StackFrame* backtrace_end = backtrace_begin + bucket.backtrace_cursor;
-  DCHECK_LE(bucket.backtrace_cursor, arraysize(context->backtrace.frames));
-
-  Entry entry;
-  entry.stack_frame_id = stack_frame_deduplicator_->Insert(
-      backtrace_begin, backtrace_end);
-
-  // Deduplicate the type name, or use ID -1 if type name is not set.
-  entry.type_id = bucket.is_broken_down_by_type_name
-                      ? type_name_deduplicator_->Insert(context->type_name)
-                      : -1;
-
-  entry.size = bucket.size;
-  entry.count = bucket.count;
-
-  auto position_and_inserted = entries_.insert(entry);
-  return position_and_inserted.second;
-}
-
-void HeapDumpWriter::BreakDown(const Bucket& bucket) {
-  auto by_backtrace = BreakDownBy(bucket,
-                                  BreakDownMode::kByBacktrace,
-                                  breakdown_threshold_bytes_);
-  auto by_type_name = BreakDownBy(bucket,
-                                  BreakDownMode::kByTypeName,
-                                  breakdown_threshold_bytes_);
-
-  // Insert entries for the buckets. If a bucket was not present before, it has
-  // not been broken down before, so recursively continue breaking down in that
-  // case. There might be multiple routes to the same entry (first break down
-  // by type name, then by backtrace, or first by backtrace and then by type),
-  // so a set is used to avoid dumping and breaking down entries more than once.
-
-  for (const Bucket& subbucket : by_backtrace)
-    if (AddEntryForBucket(subbucket))
-      BreakDown(subbucket);
-
-  for (const Bucket& subbucket : by_type_name)
-    if (AddEntryForBucket(subbucket))
-      BreakDown(subbucket);
-}
-
-const std::set<Entry>& HeapDumpWriter::Summarize(
-    const std::unordered_map<AllocationContext, AllocationMetrics>&
-        metrics_by_context) {
-  // Start with one bucket that represents the entire heap. Iterate by
-  // reference, because the allocation contexts are going to point to allocation
-  // contexts stored in |metrics_by_context|.
-  Bucket root_bucket;
-  for (const auto& context_and_metrics : metrics_by_context) {
-    DCHECK_GT(context_and_metrics.second.size, 0u);
-    DCHECK_GT(context_and_metrics.second.count, 0u);
-    const AllocationContext* context = &context_and_metrics.first;
-    root_bucket.metrics_by_context.push_back(
-        std::make_pair(context, context_and_metrics.second));
-    root_bucket.size += context_and_metrics.second.size;
-    root_bucket.count += context_and_metrics.second.count;
-  }
-
-  AddEntryForBucket(root_bucket);
-
-  // Recursively break down the heap and fill |entries_| with entries to dump.
-  BreakDown(root_bucket);
-
-  return entries_;
-}
-
-std::unique_ptr<TracedValue> Serialize(const std::set<Entry>& entries) {
-  std::string buffer;
-  std::unique_ptr<TracedValue> traced_value(new TracedValue);
-
-  traced_value->BeginArray("entries");
-
-  for (const Entry& entry : entries) {
-    traced_value->BeginDictionary();
-
-    // Format size as hexadecimal string into |buffer|.
-    SStringPrintf(&buffer, "%" PRIx64, static_cast<uint64_t>(entry.size));
-    traced_value->SetString("size", buffer);
-
-    SStringPrintf(&buffer, "%" PRIx64, static_cast<uint64_t>(entry.count));
-    traced_value->SetString("count", buffer);
-
-    if (entry.stack_frame_id == -1) {
-      // An empty backtrace (which will have ID -1) is represented by the empty
-      // string, because there is no leaf frame to reference in |stackFrames|.
-      traced_value->SetString("bt", "");
-    } else {
-      // Format index of the leaf frame as a string, because |stackFrames| is a
-      // dictionary, not an array.
-      SStringPrintf(&buffer, "%i", entry.stack_frame_id);
-      traced_value->SetString("bt", buffer);
-    }
-
-    // Type ID -1 (cumulative size for all types) is represented by the absence
-    // of the "type" key in the dictionary.
-    if (entry.type_id != -1) {
-      // Format the type ID as a string.
-      SStringPrintf(&buffer, "%i", entry.type_id);
-      traced_value->SetString("type", buffer);
-    }
-
-    traced_value->EndDictionary();
-  }
-
-  traced_value->EndArray();  // "entries"
-  return traced_value;
-}
-
-}  // namespace internal
-
-std::unique_ptr<TracedValue> ExportHeapDump(
-    const std::unordered_map<AllocationContext, AllocationMetrics>&
-        metrics_by_context,
-    const HeapProfilerSerializationState& heap_profiler_serialization_state) {
-  internal::HeapDumpWriter writer(
-      heap_profiler_serialization_state.stack_frame_deduplicator(),
-      heap_profiler_serialization_state.type_name_deduplicator(),
-      heap_profiler_serialization_state
-          .heap_profiler_breakdown_threshold_bytes());
-  return Serialize(writer.Summarize(metrics_by_context));
-}
-
-}  // namespace trace_event
-}  // namespace base