Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1811 insertions, 0 deletions

diff --git a/js/src/gc/Statistics.cpp b/js/src/gc/Statistics.cpp
new file mode 100644
index 0000000000..66b1c40673
--- /dev/null
+++ b/js/src/gc/Statistics.cpp
@@ -0,0 +1,1811 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "gc/Statistics.h"
+
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Sprintf.h"
+#include "mozilla/TimeStamp.h"
+
+#include <algorithm>
+#include <stdarg.h>
+#include <stdio.h>
+#include <type_traits>
+
+#include "gc/GC.h"
+#include "gc/GCInternals.h"
+#include "gc/Memory.h"
+#include "js/Printer.h"
+#include "util/GetPidProvider.h"
+#include "util/Text.h"
+#include "vm/JSONPrinter.h"
+#include "vm/Runtime.h"
+#include "vm/Time.h"
+
+#include "gc/PrivateIterators-inl.h"
+
+using namespace js;
+using namespace js::gc;
+using namespace js::gcstats;
+
+using mozilla::DebugOnly;
+using mozilla::EnumeratedArray;
+using mozilla::Maybe;
+using mozilla::TimeDuration;
+using mozilla::TimeStamp;
+
+static const size_t BYTES_PER_MB = 1024 * 1024;
+
+/*
+ * If this fails, then you can either delete this assertion and allow all
+ * larger-numbered reasons to pile up in the last telemetry bucket, or switch
+ * to GC_REASON_3 and bump the max value.
+ */
+static_assert(JS::GCReason::NUM_TELEMETRY_REASONS >= JS::GCReason::NUM_REASONS);
+
+static inline auto AllPhaseKinds() {
+  return mozilla::MakeEnumeratedRange(PhaseKind::FIRST, PhaseKind::LIMIT);
+}
+
+static inline auto MajorGCPhaseKinds() {
+  return mozilla::MakeEnumeratedRange(PhaseKind::GC_BEGIN,
+                                      PhaseKind(size_t(PhaseKind::GC_END) + 1));
+}
+
+static const char* ExplainGCOptions(JS::GCOptions options) {
+  switch (options) {
+    case JS::GCOptions::Normal:
+      return "Normal";
+    case JS::GCOptions::Shrink:
+      return "Shrink";
+    case JS::GCOptions::Shutdown:
+      return "Shutdown";
+  }
+
+  MOZ_CRASH("Unexpected GCOptions value");
+}
+
+JS_PUBLIC_API const char* JS::ExplainGCReason(JS::GCReason reason) {
+  switch (reason) {
+#define SWITCH_REASON(name, _) \
+  case JS::GCReason::name:     \
+    return #name;
+    GCREASONS(SWITCH_REASON)
+#undef SWITCH_REASON
+
+    case JS::GCReason::NO_REASON:
+      return "NO_REASON";
+
+    default:
+      MOZ_CRASH("bad GC reason");
+  }
+}
+
+JS_PUBLIC_API bool JS::InternalGCReason(JS::GCReason reason) {
+  return reason < JS::GCReason::FIRST_FIREFOX_REASON;
+}
+
+const char* js::gcstats::ExplainAbortReason(GCAbortReason reason) {
+  switch (reason) {
+#define SWITCH_REASON(name, _) \
+  case GCAbortReason::name:    \
+    return #name;
+    GC_ABORT_REASONS(SWITCH_REASON)
+
+    default:
+      MOZ_CRASH("bad GC abort reason");
+#undef SWITCH_REASON
+  }
+}
+
+static FILE* MaybeOpenFileFromEnv(const char* env,
+                                  FILE* defaultFile = nullptr) {
+  const char* value = getenv(env);
+  if (!value) {
+    return defaultFile;
+  }
+
+  FILE* file;
+  if (strcmp(value, "none") == 0) {
+    file = nullptr;
+  } else if (strcmp(value, "stdout") == 0) {
+    file = stdout;
+  } else if (strcmp(value, "stderr") == 0) {
+    file = stderr;
+  } else {
+    char path[300];
+    if (value[0] != '/') {
+      const char* dir = getenv("MOZ_UPLOAD_DIR");
+      if (dir) {
+        SprintfLiteral(path, "%s/%s", dir, value);
+        value = path;
+      }
+    }
+
+    file = fopen(value, "a");
+    if (!file || setvbuf(file, nullptr, _IOLBF, 256) != 0) {
+      perror("Error opening log file");
+      MOZ_CRASH("Failed to open log file.");
+    }
+  }
+
+  return file;
+}
+
+struct PhaseKindInfo {
+  Phase firstPhase;
+  uint8_t telemetryBucket;
+  const char* name;
+};
+
+// PhaseInfo objects form a tree.
+struct PhaseInfo {
+  Phase parent;
+  Phase firstChild;
+  Phase nextSibling;
+  Phase nextWithPhaseKind;
+  PhaseKind phaseKind;
+  uint8_t depth;
+  const char* name;
+  const char* path;
+};
+
+// A table of PhaseInfo indexed by Phase.
+using PhaseTable = EnumeratedArray<Phase, Phase::LIMIT, PhaseInfo>;
+
+// A table of PhaseKindInfo indexed by PhaseKind.
+using PhaseKindTable =
+    EnumeratedArray<PhaseKind, PhaseKind::LIMIT, PhaseKindInfo>;
+
+#include "gc/StatsPhasesGenerated.inc"
+
+// Iterate the phases in a phase kind.
+class PhaseIter {
+  Phase phase;
+
+ public:
+  explicit PhaseIter(PhaseKind kind) : phase(phaseKinds[kind].firstPhase) {}
+  bool done() const { return phase == Phase::NONE; }
+  void next() { phase = phases[phase].nextWithPhaseKind; }
+  Phase get() const { return phase; }
+  operator Phase() const { return phase; }
+};
+
+static double t(TimeDuration duration) { return duration.ToMilliseconds(); }
+
+inline JSContext* Statistics::context() {
+  return gc->rt->mainContextFromOwnThread();
+}
+
+inline Phase Statistics::currentPhase() const {
+  return phaseStack.empty() ? Phase::NONE : phaseStack.back();
+}
+
+PhaseKind Statistics::currentPhaseKind() const {
+  // Public API to get the current phase kind, suppressing the synthetic
+  // PhaseKind::MUTATOR phase.
+
+  Phase phase = currentPhase();
+  MOZ_ASSERT_IF(phase == Phase::MUTATOR, phaseStack.length() == 1);
+  if (phase == Phase::NONE || phase == Phase::MUTATOR) {
+    return PhaseKind::NONE;
+  }
+
+  return phases[phase].phaseKind;
+}
+
+static Phase LookupPhaseWithParent(PhaseKind phaseKind, Phase parentPhase) {
+  for (PhaseIter phase(phaseKind); !phase.done(); phase.next()) {
+    if (phases[phase].parent == parentPhase) {
+      return phase;
+    }
+  }
+
+  return Phase::NONE;
+}
+
+static const char* PhaseKindName(PhaseKind kind) {
+  if (kind == PhaseKind::NONE) {
+    return "NONE";
+  }
+
+  return phaseKinds[kind].name;
+}
+
+Phase Statistics::lookupChildPhase(PhaseKind phaseKind) const {
+  if (phaseKind == PhaseKind::IMPLICIT_SUSPENSION) {
+    return Phase::IMPLICIT_SUSPENSION;
+  }
+  if (phaseKind == PhaseKind::EXPLICIT_SUSPENSION) {
+    return Phase::EXPLICIT_SUSPENSION;
+  }
+
+  MOZ_ASSERT(phaseKind < PhaseKind::LIMIT);
+
+  // Search all expanded phases that correspond to the required
+  // phase to find the one whose parent is the current expanded phase.
+  Phase phase = LookupPhaseWithParent(phaseKind, currentPhase());
+
+  if (phase == Phase::NONE) {
+    MOZ_CRASH_UNSAFE_PRINTF(
+        "Child phase kind %s not found under current phase kind %s",
+        PhaseKindName(phaseKind), PhaseKindName(currentPhaseKind()));
+  }
+
+  return phase;
+}
+
+inline auto AllPhases() {
+  return mozilla::MakeEnumeratedRange(Phase::FIRST, Phase::LIMIT);
+}
+
+void Statistics::gcDuration(TimeDuration* total, TimeDuration* maxPause) const {
+  *total = *maxPause = 0;
+  for (auto& slice : slices_) {
+    *total += slice.duration();
+    if (slice.duration() > *maxPause) {
+      *maxPause = slice.duration();
+    }
+  }
+  if (*maxPause > maxPauseInInterval) {
+    maxPauseInInterval = *maxPause;
+  }
+}
+
+void Statistics::sccDurations(TimeDuration* total,
+                              TimeDuration* maxPause) const {
+  *total = *maxPause = 0;
+  for (size_t i = 0; i < sccTimes.length(); i++) {
+    *total += sccTimes[i];
+    *maxPause = std::max(*maxPause, sccTimes[i]);
+  }
+}
+
+typedef Vector<UniqueChars, 8, SystemAllocPolicy> FragmentVector;
+
+static UniqueChars Join(const FragmentVector& fragments,
+                        const char* separator = "") {
+  const size_t separatorLength = strlen(separator);
+  size_t length = 0;
+  for (size_t i = 0; i < fragments.length(); ++i) {
+    length += fragments[i] ? strlen(fragments[i].get()) : 0;
+    if (i < (fragments.length() - 1)) {
+      length += separatorLength;
+    }
+  }
+
+  char* joined = js_pod_malloc<char>(length + 1);
+  if (!joined) {
+    return UniqueChars();
+  }
+
+  joined[length] = '\0';
+  char* cursor = joined;
+  for (size_t i = 0; i < fragments.length(); ++i) {
+    if (fragments[i]) {
+      strcpy(cursor, fragments[i].get());
+    }
+    cursor += fragments[i] ? strlen(fragments[i].get()) : 0;
+    if (i < (fragments.length() - 1)) {
+      if (separatorLength) {
+        strcpy(cursor, separator);
+      }
+      cursor += separatorLength;
+    }
+  }
+
+  return UniqueChars(joined);
+}
+
+static TimeDuration SumChildTimes(Phase phase,
+                                  const Statistics::PhaseTimes& phaseTimes) {
+  TimeDuration total = 0;
+  for (phase = phases[phase].firstChild; phase != Phase::NONE;
+       phase = phases[phase].nextSibling) {
+    total += phaseTimes[phase];
+  }
+  return total;
+}
+
+UniqueChars Statistics::formatCompactSliceMessage() const {
+  // Skip if we OOM'ed.
+  if (slices_.length() == 0) {
+    return UniqueChars(nullptr);
+  }
+
+  const size_t index = slices_.length() - 1;
+  const SliceData& slice = slices_.back();
+
+  char budgetDescription[200];
+  slice.budget.describe(budgetDescription, sizeof(budgetDescription) - 1);
+
+  const char* format =
+      "GC Slice %u - Pause: %.3fms of %s budget (@ %.3fms); Reason: %s; Reset: "
+      "%s%s; Times: ";
+  char buffer[1024];
+  SprintfLiteral(buffer, format, index, t(slice.duration()), budgetDescription,
+                 t(slice.start - slices_[0].start),
+                 ExplainGCReason(slice.reason),
+                 slice.wasReset() ? "yes - " : "no",
+                 slice.wasReset() ? ExplainAbortReason(slice.resetReason) : "");
+
+  FragmentVector fragments;
+  if (!fragments.append(DuplicateString(buffer)) ||
+      !fragments.append(
+          formatCompactSlicePhaseTimes(slices_[index].phaseTimes))) {
+    return UniqueChars(nullptr);
+  }
+  return Join(fragments);
+}
+
+UniqueChars Statistics::formatCompactSummaryMessage() const {
+  FragmentVector fragments;
+  if (!fragments.append(DuplicateString("Summary - "))) {
+    return UniqueChars(nullptr);
+  }
+
+  TimeDuration total, longest;
+  gcDuration(&total, &longest);
+
+  const double mmu20 = computeMMU(TimeDuration::FromMilliseconds(20));
+  const double mmu50 = computeMMU(TimeDuration::FromMilliseconds(50));
+
+  char buffer[1024];
+  if (!nonincremental()) {
+    SprintfLiteral(buffer,
+                   "Max Pause: %.3fms; MMU 20ms: %.1f%%; MMU 50ms: %.1f%%; "
+                   "Total: %.3fms; ",
+                   t(longest), mmu20 * 100., mmu50 * 100., t(total));
+  } else {
+    SprintfLiteral(buffer, "Non-Incremental: %.3fms (%s); ", t(total),
+                   ExplainAbortReason(nonincrementalReason_));
+  }
+  if (!fragments.append(DuplicateString(buffer))) {
+    return UniqueChars(nullptr);
+  }
+
+  SprintfLiteral(buffer,
+                 "Zones: %d of %d (-%d); Compartments: %d of %d (-%d); "
+                 "HeapSize: %.3f MiB; "
+                 "HeapChange (abs): %+d (%u); ",
+                 zoneStats.collectedZoneCount, zoneStats.zoneCount,
+                 zoneStats.sweptZoneCount, zoneStats.collectedCompartmentCount,
+                 zoneStats.compartmentCount, zoneStats.sweptCompartmentCount,
+                 double(preTotalHeapBytes) / BYTES_PER_MB,
+                 int32_t(counts[COUNT_NEW_CHUNK] - counts[COUNT_DESTROY_CHUNK]),
+                 counts[COUNT_NEW_CHUNK] + counts[COUNT_DESTROY_CHUNK]);
+  if (!fragments.append(DuplicateString(buffer))) {
+    return UniqueChars(nullptr);
+  }
+
+  MOZ_ASSERT_IF(counts[COUNT_ARENA_RELOCATED],
+                gcOptions == JS::GCOptions::Shrink);
+  if (gcOptions == JS::GCOptions::Shrink) {
+    SprintfLiteral(
+        buffer, "Kind: %s; Relocated: %.3f MiB; ", ExplainGCOptions(gcOptions),
+        double(ArenaSize * counts[COUNT_ARENA_RELOCATED]) / BYTES_PER_MB);
+    if (!fragments.append(DuplicateString(buffer))) {
+      return UniqueChars(nullptr);
+    }
+  }
+
+  return Join(fragments);
+}
+
+UniqueChars Statistics::formatCompactSlicePhaseTimes(
+    const PhaseTimes& phaseTimes) const {
+  static const TimeDuration MaxUnaccountedTime =
+      TimeDuration::FromMicroseconds(100);
+
+  FragmentVector fragments;
+  char buffer[128];
+  for (auto phase : AllPhases()) {
+    DebugOnly<uint8_t> level = phases[phase].depth;
+    MOZ_ASSERT(level < 4);
+
+    TimeDuration ownTime = phaseTimes[phase];
+    TimeDuration childTime = SumChildTimes(phase, phaseTimes);
+    if (ownTime > MaxUnaccountedTime) {
+      SprintfLiteral(buffer, "%s: %.3fms", phases[phase].name, t(ownTime));
+      if (!fragments.append(DuplicateString(buffer))) {
+        return UniqueChars(nullptr);
+      }
+
+      if (childTime && (ownTime - childTime) > MaxUnaccountedTime) {
+        MOZ_ASSERT(level < 3);
+        SprintfLiteral(buffer, "%s: %.3fms", "Other", t(ownTime - childTime));
+        if (!fragments.append(DuplicateString(buffer))) {
+          return UniqueChars(nullptr);
+        }
+      }
+    }
+  }
+  return Join(fragments, ", ");
+}
+
+UniqueChars Statistics::formatDetailedMessage() const {
+  FragmentVector fragments;
+
+  if (!fragments.append(formatDetailedDescription())) {
+    return UniqueChars(nullptr);
+  }
+
+  if (!slices_.empty()) {
+    for (unsigned i = 0; i < slices_.length(); i++) {
+      if (!fragments.append(formatDetailedSliceDescription(i, slices_[i]))) {
+        return UniqueChars(nullptr);
+      }
+      if (!fragments.append(formatDetailedPhaseTimes(slices_[i].phaseTimes))) {
+        return UniqueChars(nullptr);
+      }
+    }
+  }
+  if (!fragments.append(formatDetailedTotals())) {
+    return UniqueChars(nullptr);
+  }
+  if (!fragments.append(formatDetailedPhaseTimes(phaseTimes))) {
+    return UniqueChars(nullptr);
+  }
+
+  return Join(fragments);
+}
+
+UniqueChars Statistics::formatDetailedDescription() const {
+  TimeDuration sccTotal, sccLongest;
+  sccDurations(&sccTotal, &sccLongest);
+
+  const double mmu20 = computeMMU(TimeDuration::FromMilliseconds(20));
+  const double mmu50 = computeMMU(TimeDuration::FromMilliseconds(50));
+
+  const char* format =
+      "=================================================================\n\
+  Invocation Kind: %s\n\
+  Reason: %s\n\
+  Incremental: %s%s\n\
+  Zones Collected: %d of %d (-%d)\n\
+  Compartments Collected: %d of %d (-%d)\n\
+  MinorGCs since last GC: %d\n\
+  Store Buffer Overflows: %d\n\
+  MMU 20ms:%.1f%%; 50ms:%.1f%%\n\
+  SCC Sweep Total (MaxPause): %.3fms (%.3fms)\n\
+  HeapSize: %.3f MiB\n\
+  Chunk Delta (magnitude): %+d  (%d)\n\
+  Arenas Relocated: %.3f MiB\n\
+";
+
+  char buffer[1024];
+  SprintfLiteral(
+      buffer, format, ExplainGCOptions(gcOptions),
+      ExplainGCReason(slices_[0].reason), nonincremental() ? "no - " : "yes",
+      nonincremental() ? ExplainAbortReason(nonincrementalReason_) : "",
+      zoneStats.collectedZoneCount, zoneStats.zoneCount,
+      zoneStats.sweptZoneCount, zoneStats.collectedCompartmentCount,
+      zoneStats.compartmentCount, zoneStats.sweptCompartmentCount,
+      getCount(COUNT_MINOR_GC), getCount(COUNT_STOREBUFFER_OVERFLOW),
+      mmu20 * 100., mmu50 * 100., t(sccTotal), t(sccLongest),
+      double(preTotalHeapBytes) / BYTES_PER_MB,
+      getCount(COUNT_NEW_CHUNK) - getCount(COUNT_DESTROY_CHUNK),
+      getCount(COUNT_NEW_CHUNK) + getCount(COUNT_DESTROY_CHUNK),
+      double(ArenaSize * getCount(COUNT_ARENA_RELOCATED)) / BYTES_PER_MB);
+
+  return DuplicateString(buffer);
+}
+
+UniqueChars Statistics::formatDetailedSliceDescription(
+    unsigned i, const SliceData& slice) const {
+  char budgetDescription[200];
+  slice.budget.describe(budgetDescription, sizeof(budgetDescription) - 1);
+
+  const char* format =
+      "\
+  ---- Slice %u ----\n\
+    Reason: %s\n\
+    Trigger: %s\n\
+    Reset: %s%s\n\
+    State: %s -> %s\n\
+    Page Faults: %" PRIu64
+      "\n\
+    Pause: %.3fms of %s budget (@ %.3fms)\n\
+";
+
+  char triggerBuffer[100] = "n/a";
+  if (slice.trigger) {
+    Trigger trigger = slice.trigger.value();
+    SprintfLiteral(triggerBuffer, "%.3f MiB of %.3f MiB threshold\n",
+                   double(trigger.amount) / BYTES_PER_MB,
+                   double(trigger.threshold) / BYTES_PER_MB);
+  }
+
+  char buffer[1024];
+  SprintfLiteral(
+      buffer, format, i, ExplainGCReason(slice.reason), triggerBuffer,
+      slice.wasReset() ? "yes - " : "no",
+      slice.wasReset() ? ExplainAbortReason(slice.resetReason) : "",
+      gc::StateName(slice.initialState), gc::StateName(slice.finalState),
+      uint64_t(slice.endFaults - slice.startFaults), t(slice.duration()),
+      budgetDescription, t(slice.start - slices_[0].start));
+  return DuplicateString(buffer);
+}
+
+static bool IncludePhase(TimeDuration duration) {
+  // Don't include durations that will print as "0.000ms".
+  return duration.ToMilliseconds() >= 0.001;
+}
+
+UniqueChars Statistics::formatDetailedPhaseTimes(
+    const PhaseTimes& phaseTimes) const {
+  static const TimeDuration MaxUnaccountedChildTime =
+      TimeDuration::FromMicroseconds(50);
+
+  FragmentVector fragments;
+  char buffer[128];
+  for (auto phase : AllPhases()) {
+    uint8_t level = phases[phase].depth;
+    TimeDuration ownTime = phaseTimes[phase];
+    TimeDuration childTime = SumChildTimes(phase, phaseTimes);
+    if (IncludePhase(ownTime)) {
+      SprintfLiteral(buffer, "      %*s%s: %.3fms\n", level * 2, "",
+                     phases[phase].name, t(ownTime));
+      if (!fragments.append(DuplicateString(buffer))) {
+        return UniqueChars(nullptr);
+      }
+
+      if (childTime && (ownTime - childTime) > MaxUnaccountedChildTime) {
+        SprintfLiteral(buffer, "      %*s%s: %.3fms\n", (level + 1) * 2, "",
+                       "Other", t(ownTime - childTime));
+        if (!fragments.append(DuplicateString(buffer))) {
+          return UniqueChars(nullptr);
+        }
+      }
+    }
+  }
+  return Join(fragments);
+}
+
+UniqueChars Statistics::formatDetailedTotals() const {
+  TimeDuration total, longest;
+  gcDuration(&total, &longest);
+
+  const char* format =
+      "\
+  ---- Totals ----\n\
+    Total Time: %.3fms\n\
+    Max Pause: %.3fms\n\
+";
+  char buffer[1024];
+  SprintfLiteral(buffer, format, t(total), t(longest));
+  return DuplicateString(buffer);
+}
+
+void Statistics::formatJsonSlice(size_t sliceNum, JSONPrinter& json) const {
+  /*
+   * We number each of the slice properties to keep the code in
+   * GCTelemetry.jsm in sync.  See MAX_SLICE_KEYS.
+   */
+  json.beginObject();
+  formatJsonSliceDescription(sliceNum, slices_[sliceNum], json);  // # 1-11
+
+  json.beginObjectProperty("times");  // # 12
+  formatJsonPhaseTimes(slices_[sliceNum].phaseTimes, json);
+  json.endObject();
+
+  json.endObject();
+}
+
+UniqueChars Statistics::renderJsonSlice(size_t sliceNum) const {
+  Sprinter printer(nullptr, false);
+  if (!printer.init()) {
+    return UniqueChars(nullptr);
+  }
+  JSONPrinter json(printer, false);
+
+  formatJsonSlice(sliceNum, json);
+  return printer.release();
+}
+
+UniqueChars Statistics::renderNurseryJson() const {
+  Sprinter printer(nullptr, false);
+  if (!printer.init()) {
+    return UniqueChars(nullptr);
+  }
+  JSONPrinter json(printer, false);
+  gc->nursery().renderProfileJSON(json);
+  return printer.release();
+}
+
+#ifdef DEBUG
+void Statistics::log(const char* fmt, ...) {
+  va_list args;
+  va_start(args, fmt);
+  if (gcDebugFile) {
+    TimeDuration sinceStart = TimeStamp::Now() - TimeStamp::FirstTimeStamp();
+    fprintf(gcDebugFile, "%12.3f: ", sinceStart.ToMicroseconds());
+    vfprintf(gcDebugFile, fmt, args);
+    fprintf(gcDebugFile, "\n");
+    fflush(gcDebugFile);
+  }
+  va_end(args);
+}
+#endif
+
+UniqueChars Statistics::renderJsonMessage() const {
+  /*
+   * The format of the JSON message is specified by the GCMajorMarkerPayload
+   * type in profiler.firefox.com
+   * https://github.com/firefox-devtools/profiler/blob/master/src/types/markers.js#L62
+   *
+   * All the properties listed here are created within the timings property
+   * of the GCMajor marker.
+   */
+  if (aborted) {
+    return DuplicateString("{status:\"aborted\"}");  // May return nullptr
+  }
+
+  Sprinter printer(nullptr, false);
+  if (!printer.init()) {
+    return UniqueChars(nullptr);
+  }
+  JSONPrinter json(printer, false);
+
+  json.beginObject();
+  json.property("status", "completed");
+  formatJsonDescription(json);
+
+  json.beginObjectProperty("totals");
+  formatJsonPhaseTimes(phaseTimes, json);
+  json.endObject();
+
+  json.endObject();
+
+  return printer.release();
+}
+
+void Statistics::formatJsonDescription(JSONPrinter& json) const {
+  // If you change JSON properties here, please update:
+  // Firefox Profiler:
+  //   https://github.com/firefox-devtools/profiler
+
+  TimeDuration total, longest;
+  gcDuration(&total, &longest);
+  json.property("max_pause", longest, JSONPrinter::MILLISECONDS);
+  json.property("total_time", total, JSONPrinter::MILLISECONDS);
+  // We might be able to omit reason if profiler.firefox.com was able to retrive
+  // it from the first slice.  But it doesn't do this yet.
+  json.property("reason", ExplainGCReason(slices_[0].reason));
+  json.property("zones_collected", zoneStats.collectedZoneCount);
+  json.property("total_zones", zoneStats.zoneCount);
+  json.property("total_compartments", zoneStats.compartmentCount);
+  json.property("minor_gcs", getCount(COUNT_MINOR_GC));
+  json.property("minor_gc_number", gc->minorGCCount());
+  json.property("major_gc_number", gc->majorGCCount());
+  uint32_t storebufferOverflows = getCount(COUNT_STOREBUFFER_OVERFLOW);
+  if (storebufferOverflows) {
+    json.property("store_buffer_overflows", storebufferOverflows);
+  }
+  json.property("slices", slices_.length());
+
+  const double mmu20 = computeMMU(TimeDuration::FromMilliseconds(20));
+  const double mmu50 = computeMMU(TimeDuration::FromMilliseconds(50));
+  json.property("mmu_20ms", int(mmu20 * 100));
+  json.property("mmu_50ms", int(mmu50 * 100));
+
+  TimeDuration sccTotal, sccLongest;
+  sccDurations(&sccTotal, &sccLongest);
+  json.property("scc_sweep_total", sccTotal, JSONPrinter::MILLISECONDS);
+  json.property("scc_sweep_max_pause", sccLongest, JSONPrinter::MILLISECONDS);
+
+  if (nonincrementalReason_ != GCAbortReason::None) {
+    json.property("nonincremental_reason",
+                  ExplainAbortReason(nonincrementalReason_));
+  }
+  json.property("allocated_bytes", preTotalHeapBytes);
+  json.property("post_heap_size", postTotalHeapBytes);
+
+  uint32_t addedChunks = getCount(COUNT_NEW_CHUNK);
+  if (addedChunks) {
+    json.property("added_chunks", addedChunks);
+  }
+  uint32_t removedChunks = getCount(COUNT_DESTROY_CHUNK);
+  if (removedChunks) {
+    json.property("removed_chunks", removedChunks);
+  }
+  json.property("major_gc_number", startingMajorGCNumber);
+  json.property("minor_gc_number", startingMinorGCNumber);
+  json.property("slice_number", startingSliceNumber);
+}
+
+void Statistics::formatJsonSliceDescription(unsigned i, const SliceData& slice,
+                                            JSONPrinter& json) const {
+  // If you change JSON properties here, please update:
+  // Firefox Profiler:
+  //   https://github.com/firefox-devtools/profiler
+  //
+  char budgetDescription[200];
+  slice.budget.describe(budgetDescription, sizeof(budgetDescription) - 1);
+  TimeStamp originTime = TimeStamp::ProcessCreation();
+
+  json.property("slice", i);
+  json.property("pause", slice.duration(), JSONPrinter::MILLISECONDS);
+  json.property("reason", ExplainGCReason(slice.reason));
+  json.property("initial_state", gc::StateName(slice.initialState));
+  json.property("final_state", gc::StateName(slice.finalState));
+  json.property("budget", budgetDescription);
+  json.property("major_gc_number", startingMajorGCNumber);
+  if (slice.trigger) {
+    Trigger trigger = slice.trigger.value();
+    json.property("trigger_amount", trigger.amount);
+    json.property("trigger_threshold", trigger.threshold);
+  }
+  int64_t numFaults = slice.endFaults - slice.startFaults;
+  if (numFaults != 0) {
+    json.property("page_faults", numFaults);
+  }
+  json.property("start_timestamp", slice.start - originTime,
+                JSONPrinter::SECONDS);
+}
+
+void Statistics::formatJsonPhaseTimes(const PhaseTimes& phaseTimes,
+                                      JSONPrinter& json) const {
+  for (auto phase : AllPhases()) {
+    TimeDuration ownTime = phaseTimes[phase];
+    if (!ownTime.IsZero()) {
+      json.property(phases[phase].path, ownTime, JSONPrinter::MILLISECONDS);
+    }
+  }
+}
+
+Statistics::Statistics(GCRuntime* gc)
+    : gc(gc),
+      gcTimerFile(nullptr),
+      gcDebugFile(nullptr),
+      nonincrementalReason_(GCAbortReason::None),
+      creationTime_(TimeStamp::Now()),
+      tenuredAllocsSinceMinorGC(0),
+      preTotalHeapBytes(0),
+      postTotalHeapBytes(0),
+      preCollectedHeapBytes(0),
+      startingMinorGCNumber(0),
+      startingMajorGCNumber(0),
+      startingSliceNumber(0),
+      maxPauseInInterval(0),
+      sliceCallback(nullptr),
+      nurseryCollectionCallback(nullptr),
+      aborted(false),
+      enableProfiling_(false),
+      sliceCount_(0) {
+  for (auto& count : counts) {
+    count = 0;
+  }
+
+  for (auto& stat : stats) {
+    stat = 0;
+  }
+
+#ifdef DEBUG
+  for (const auto& duration : totalTimes_) {
+    using ElementType = std::remove_reference_t<decltype(duration)>;
+    static_assert(!std::is_trivially_constructible_v<ElementType>,
+                  "Statistics::Statistics will only initialize "
+                  "totalTimes_'s elements if their default constructor is "
+                  "non-trivial");
+    MOZ_ASSERT(duration.IsZero(),
+               "totalTimes_ default-initialization should have "
+               "default-initialized every element of totalTimes_ to zero");
+  }
+#endif
+
+  MOZ_ALWAYS_TRUE(phaseStack.reserve(MAX_PHASE_NESTING));
+  MOZ_ALWAYS_TRUE(suspendedPhases.reserve(MAX_SUSPENDED_PHASES));
+
+  gcTimerFile = MaybeOpenFileFromEnv("MOZ_GCTIMER");
+  gcDebugFile = MaybeOpenFileFromEnv("JS_GC_DEBUG");
+  gcProfileFile = MaybeOpenFileFromEnv("JS_GC_PROFILE_FILE", stderr);
+
+  gc::ReadProfileEnv("JS_GC_PROFILE",
+                     "Report major GCs taking more than N milliseconds for "
+                     "all or just the main runtime\n",
+                     &enableProfiling_, &profileWorkers_, &profileThreshold_);
+}
+
+Statistics::~Statistics() {
+  if (gcTimerFile && gcTimerFile != stdout && gcTimerFile != stderr) {
+    fclose(gcTimerFile);
+  }
+  if (gcDebugFile && gcDebugFile != stdout && gcDebugFile != stderr) {
+    fclose(gcDebugFile);
+  }
+}
+
+/* static */
+bool Statistics::initialize() {
+#ifdef DEBUG
+  // Sanity check generated tables.
+  for (auto i : AllPhases()) {
+    auto parent = phases[i].parent;
+    if (parent != Phase::NONE) {
+      MOZ_ASSERT(phases[i].depth == phases[parent].depth + 1);
+    }
+    auto firstChild = phases[i].firstChild;
+    if (firstChild != Phase::NONE) {
+      MOZ_ASSERT(i == phases[firstChild].parent);
+      MOZ_ASSERT(phases[i].depth == phases[firstChild].depth - 1);
+    }
+    auto nextSibling = phases[i].nextSibling;
+    if (nextSibling != Phase::NONE) {
+      MOZ_ASSERT(parent == phases[nextSibling].parent);
+      MOZ_ASSERT(phases[i].depth == phases[nextSibling].depth);
+    }
+    auto nextWithPhaseKind = phases[i].nextWithPhaseKind;
+    if (nextWithPhaseKind != Phase::NONE) {
+      MOZ_ASSERT(phases[i].phaseKind == phases[nextWithPhaseKind].phaseKind);
+      MOZ_ASSERT(parent != phases[nextWithPhaseKind].parent);
+    }
+  }
+  for (auto i : AllPhaseKinds()) {
+    MOZ_ASSERT(phases[phaseKinds[i].firstPhase].phaseKind == i);
+    for (auto j : AllPhaseKinds()) {
+      MOZ_ASSERT_IF(i != j, phaseKinds[i].telemetryBucket !=
+                                phaseKinds[j].telemetryBucket);
+    }
+  }
+#endif
+
+  return true;
+}
+
+JS::GCSliceCallback Statistics::setSliceCallback(
+    JS::GCSliceCallback newCallback) {
+  JS::GCSliceCallback oldCallback = sliceCallback;
+  sliceCallback = newCallback;
+  return oldCallback;
+}
+
+JS::GCNurseryCollectionCallback Statistics::setNurseryCollectionCallback(
+    JS::GCNurseryCollectionCallback newCallback) {
+  auto oldCallback = nurseryCollectionCallback;
+  nurseryCollectionCallback = newCallback;
+  return oldCallback;
+}
+
+TimeDuration Statistics::clearMaxGCPauseAccumulator() {
+  TimeDuration prior = maxPauseInInterval;
+  maxPauseInInterval = 0;
+  return prior;
+}
+
+TimeDuration Statistics::getMaxGCPauseSinceClear() {
+  return maxPauseInInterval;
+}
+
+// Sum up the time for a phase, including instances of the phase with different
+// parents.
+static TimeDuration SumPhase(PhaseKind phaseKind,
+                             const Statistics::PhaseTimes& times) {
+  TimeDuration sum;
+  for (PhaseIter phase(phaseKind); !phase.done(); phase.next()) {
+    sum += times[phase];
+  }
+  return sum;
+}
+
+static bool CheckSelfTime(Phase parent, Phase child,
+                          const Statistics::PhaseTimes& times,
+                          const Statistics::PhaseTimes& selfTimes,
+                          TimeDuration childTime) {
+  if (selfTimes[parent] < childTime) {
+    fprintf(
+        stderr,
+        "Parent %s time = %.3fms with %.3fms remaining, child %s time %.3fms\n",
+        phases[parent].name, times[parent].ToMilliseconds(),
+        selfTimes[parent].ToMilliseconds(), phases[child].name,
+        childTime.ToMilliseconds());
+    fflush(stderr);
+    return false;
+  }
+
+  return true;
+}
+
+static PhaseKind FindLongestPhaseKind(const Statistics::PhaseKindTimes& times) {
+  TimeDuration longestTime;
+  PhaseKind phaseKind = PhaseKind::NONE;
+  for (auto i : MajorGCPhaseKinds()) {
+    if (times[i] > longestTime) {
+      longestTime = times[i];
+      phaseKind = i;
+    }
+  }
+
+  return phaseKind;
+}
+
+static PhaseKind LongestPhaseSelfTimeInMajorGC(
+    const Statistics::PhaseTimes& times) {
+  // Start with total times per expanded phase, including children's times.
+  Statistics::PhaseTimes selfTimes(times);
+
+  // We have the total time spent in each phase, including descendant times.
+  // Loop over the children and subtract their times from their parent's self
+  // time.
+  for (auto i : AllPhases()) {
+    Phase parent = phases[i].parent;
+    if (parent != Phase::NONE) {
+      bool ok = CheckSelfTime(parent, i, times, selfTimes, times[i]);
+
+      // This happens very occasionally in release builds and frequently
+      // in Windows debug builds. Skip collecting longest phase telemetry
+      // if it does.
+#ifndef XP_WIN
+      MOZ_ASSERT(ok, "Inconsistent time data; see bug 1400153");
+#endif
+      if (!ok) {
+        return PhaseKind::NONE;
+      }
+
+      selfTimes[parent] -= times[i];
+    }
+  }
+
+  // Sum expanded phases corresponding to the same phase.
+  Statistics::PhaseKindTimes phaseKindTimes;
+  for (auto i : AllPhaseKinds()) {
+    phaseKindTimes[i] = SumPhase(i, selfTimes);
+  }
+
+  return FindLongestPhaseKind(phaseKindTimes);
+}
+
+void Statistics::printStats() {
+  if (aborted) {
+    fprintf(gcTimerFile,
+            "OOM during GC statistics collection. The report is unavailable "
+            "for this GC.\n");
+  } else {
+    UniqueChars msg = formatDetailedMessage();
+    if (msg) {
+      double secSinceStart =
+          (slices_[0].start - TimeStamp::ProcessCreation()).ToSeconds();
+      fprintf(gcTimerFile, "GC(T+%.3fs) %s\n", secSinceStart, msg.get());
+    }
+  }
+  fflush(gcTimerFile);
+}
+
+void Statistics::beginGC(JS::GCOptions options, const TimeStamp& currentTime) {
+  slices_.clearAndFree();
+  sccTimes.clearAndFree();
+  gcOptions = options;
+  nonincrementalReason_ = GCAbortReason::None;
+
+  preTotalHeapBytes = gc->heapSize.bytes();
+
+  preCollectedHeapBytes = 0;
+
+  startingMajorGCNumber = gc->majorGCCount();
+  startingSliceNumber = gc->gcNumber();
+
+  if (gc->lastGCEndTime()) {
+    timeSinceLastGC = currentTime - gc->lastGCEndTime();
+  }
+
+  totalGCTime_ = TimeDuration();
+}
+
+void Statistics::measureInitialHeapSize() {
+  MOZ_ASSERT(preCollectedHeapBytes == 0);
+  for (GCZonesIter zone(gc); !zone.done(); zone.next()) {
+    preCollectedHeapBytes += zone->gcHeapSize.bytes();
+  }
+}
+
+void Statistics::endGC() {
+  postTotalHeapBytes = gc->heapSize.bytes();
+
+  sendGCTelemetry();
+}
+
+TimeDuration Statistics::sumTotalParallelTime(PhaseKind phaseKind) const {
+  TimeDuration total;
+  for (const SliceData& slice : slices_) {
+    total += slice.totalParallelTimes[phaseKind];
+  }
+  return total;
+}
+
+void Statistics::sendGCTelemetry() {
+  JSRuntime* runtime = gc->rt;
+  // NOTE: "Compartmental" is term that was deprecated with the
+  // introduction of zone-based GC, but the old telemetry probe
+  // continues to be used.
+  runtime->metrics().GC_IS_COMPARTMENTAL(!gc->fullGCRequested);
+  runtime->metrics().GC_ZONE_COUNT(zoneStats.zoneCount);
+  runtime->metrics().GC_ZONES_COLLECTED(zoneStats.collectedZoneCount);
+
+  TimeDuration prepareTotal = phaseTimes[Phase::PREPARE];
+  TimeDuration markTotal = SumPhase(PhaseKind::MARK, phaseTimes);
+  TimeDuration markRootsTotal = SumPhase(PhaseKind::MARK_ROOTS, phaseTimes);
+
+  // Gray and weak marking time is counted under MARK_WEAK and not MARK_GRAY.
+  TimeDuration markWeakTotal = SumPhase(PhaseKind::MARK_WEAK, phaseTimes);
+  TimeDuration markGrayNotWeak =
+      SumPhase(PhaseKind::MARK_GRAY, phaseTimes) +
+      SumPhase(PhaseKind::MARK_INCOMING_GRAY, phaseTimes);
+  TimeDuration markGrayWeak = SumPhase(PhaseKind::MARK_GRAY_WEAK, phaseTimes);
+  TimeDuration markGrayTotal = markGrayNotWeak + markGrayWeak;
+  TimeDuration markNotGrayOrWeak = markTotal - markGrayNotWeak - markWeakTotal;
+  if (markNotGrayOrWeak < TimeDuration::FromMilliseconds(0)) {
+    markNotGrayOrWeak = TimeDuration();
+  }
+
+  size_t markCount = getCount(COUNT_CELLS_MARKED);
+
+  runtime->metrics().GC_PREPARE_MS(prepareTotal);
+  runtime->metrics().GC_MARK_MS(markNotGrayOrWeak);
+  if (markTotal >= TimeDuration::FromMicroseconds(1)) {
+    double markRate = double(markCount) / t(markTotal);
+    runtime->metrics().GC_MARK_RATE_2(uint32_t(markRate));
+  }
+  runtime->metrics().GC_SWEEP_MS(phaseTimes[Phase::SWEEP]);
+  if (gc->didCompactZones()) {
+    runtime->metrics().GC_COMPACT_MS(phaseTimes[Phase::COMPACT]);
+  }
+  runtime->metrics().GC_MARK_ROOTS_US(markRootsTotal);
+  runtime->metrics().GC_MARK_GRAY_MS_2(markGrayTotal);
+  runtime->metrics().GC_MARK_WEAK_MS(markWeakTotal);
+  runtime->metrics().GC_NON_INCREMENTAL(nonincremental());
+  if (nonincremental()) {
+    runtime->metrics().GC_NON_INCREMENTAL_REASON(
+        uint32_t(nonincrementalReason_));
+  }
+
+#ifdef DEBUG
+  // Reset happens non-incrementally, so only the last slice can be reset.
+  for (size_t i = 0; i < slices_.length() - 1; i++) {
+    MOZ_ASSERT(!slices_[i].wasReset());
+  }
+#endif
+  const auto& lastSlice = slices_.back();
+  runtime->metrics().GC_RESET(lastSlice.wasReset());
+  if (lastSlice.wasReset()) {
+    runtime->metrics().GC_RESET_REASON(uint32_t(lastSlice.resetReason));
+  }
+
+  TimeDuration total, longest;
+  gcDuration(&total, &longest);
+
+  runtime->metrics().GC_MS(total);
+  runtime->metrics().GC_MAX_PAUSE_MS_2(longest);
+
+  const double mmu50 = computeMMU(TimeDuration::FromMilliseconds(50));
+  runtime->metrics().GC_MMU_50(mmu50 * 100);
+
+  // Record scheduling telemetry for the main runtime but not for workers, which
+  // are scheduled differently.
+  if (!runtime->parentRuntime && timeSinceLastGC) {
+    runtime->metrics().GC_TIME_BETWEEN_S(timeSinceLastGC);
+    if (!nonincremental()) {
+      runtime->metrics().GC_SLICE_COUNT(slices_.length());
+    }
+  }
+
+  if (!lastSlice.wasReset() && preCollectedHeapBytes != 0) {
+    size_t bytesSurvived = 0;
+    for (ZonesIter zone(runtime, WithAtoms); !zone.done(); zone.next()) {
+      if (zone->wasCollected()) {
+        bytesSurvived += zone->gcHeapSize.retainedBytes();
+      }
+    }
+
+    MOZ_ASSERT(preCollectedHeapBytes >= bytesSurvived);
+    double survivalRate =
+        100.0 * double(bytesSurvived) / double(preCollectedHeapBytes);
+    runtime->metrics().GC_TENURED_SURVIVAL_RATE(uint32_t(survivalRate));
+
+    // Calculate 'effectiveness' in MB / second, on main thread only for now.
+    if (!runtime->parentRuntime) {
+      size_t bytesFreed = preCollectedHeapBytes - bytesSurvived;
+      TimeDuration clampedTotal =
+          TimeDuration::Max(total, TimeDuration::FromMilliseconds(1));
+      double effectiveness =
+          (double(bytesFreed) / BYTES_PER_MB) / clampedTotal.ToSeconds();
+      runtime->metrics().GC_EFFECTIVENESS(uint32_t(effectiveness));
+    }
+  }
+
+  // Parallel marking stats.
+  if (gc->isParallelMarkingEnabled()) {
+    TimeDuration wallTime = SumPhase(PhaseKind::PARALLEL_MARK, phaseTimes);
+    TimeDuration parallelRunTime =
+        sumTotalParallelTime(PhaseKind::PARALLEL_MARK) -
+        sumTotalParallelTime(PhaseKind::PARALLEL_MARK_WAIT);
+    TimeDuration parallelMarkTime =
+        sumTotalParallelTime(PhaseKind::PARALLEL_MARK_MARK);
+    if (wallTime && parallelMarkTime) {
+      uint32_t threadCount = gc->markers.length();
+      double speedup = parallelMarkTime / wallTime;
+      double utilization = parallelRunTime / (wallTime * threadCount);
+      runtime->metrics().GC_PARALLEL_MARK_SPEEDUP(uint32_t(speedup * 100.0));
+      runtime->metrics().GC_PARALLEL_MARK_UTILIZATION(
+          std::clamp<uint32_t>(utilization * 100.0, 0, 100));
+      runtime->metrics().GC_PARALLEL_MARK_INTERRUPTIONS(
+          getCount(COUNT_PARALLEL_MARK_INTERRUPTIONS));
+    }
+  }
+}
+
+void Statistics::beginNurseryCollection(JS::GCReason reason) {
+  count(COUNT_MINOR_GC);
+  startingMinorGCNumber = gc->minorGCCount();
+  if (nurseryCollectionCallback) {
+    (*nurseryCollectionCallback)(
+        context(), JS::GCNurseryProgress::GC_NURSERY_COLLECTION_START, reason);
+  }
+}
+
+void Statistics::endNurseryCollection(JS::GCReason reason) {
+  if (nurseryCollectionCallback) {
+    (*nurseryCollectionCallback)(
+        context(), JS::GCNurseryProgress::GC_NURSERY_COLLECTION_END, reason);
+  }
+
+  tenuredAllocsSinceMinorGC = 0;
+}
+
+Statistics::SliceData::SliceData(const SliceBudget& budget,
+                                 Maybe<Trigger> trigger, JS::GCReason reason,
+                                 TimeStamp start, size_t startFaults,
+                                 gc::State initialState)
+    : budget(budget),
+      reason(reason),
+      trigger(trigger),
+      initialState(initialState),
+      start(start),
+      startFaults(startFaults) {}
+
+void Statistics::beginSlice(const ZoneGCStats& zoneStats, JS::GCOptions options,
+                            const SliceBudget& budget, JS::GCReason reason,
+                            bool budgetWasIncreased) {
+  MOZ_ASSERT(phaseStack.empty() ||
+             (phaseStack.length() == 1 && phaseStack[0] == Phase::MUTATOR));
+
+  this->zoneStats = zoneStats;
+
+  TimeStamp currentTime = TimeStamp::Now();
+
+  bool first = !gc->isIncrementalGCInProgress();
+  if (first) {
+    beginGC(options, currentTime);
+  }
+
+  JSRuntime* runtime = gc->rt;
+  if (!runtime->parentRuntime && !slices_.empty()) {
+    TimeDuration timeSinceLastSlice = currentTime - slices_.back().end;
+    runtime->metrics().GC_TIME_BETWEEN_SLICES_MS(timeSinceLastSlice);
+  }
+
+  Maybe<Trigger> trigger = recordedTrigger;
+  recordedTrigger.reset();
+
+  if (!slices_.emplaceBack(budget, trigger, reason, currentTime,
+                           GetPageFaultCount(), gc->state())) {
+    // If we are OOM, set a flag to indicate we have missing slice data.
+    aborted = true;
+    return;
+  }
+
+  runtime->metrics().GC_REASON_2(uint32_t(reason));
+  runtime->metrics().GC_BUDGET_WAS_INCREASED(budgetWasIncreased);
+
+  // Slice callbacks should only fire for the outermost level.
+  if (sliceCallback) {
+    JSContext* cx = context();
+    JS::GCDescription desc(!gc->fullGCRequested, false, options, reason);
+    if (first) {
+      (*sliceCallback)(cx, JS::GC_CYCLE_BEGIN, desc);
+    }
+    (*sliceCallback)(cx, JS::GC_SLICE_BEGIN, desc);
+  }
+
+  log("begin slice");
+}
+
+void Statistics::endSlice() {
+  MOZ_ASSERT(phaseStack.empty() ||
+             (phaseStack.length() == 1 && phaseStack[0] == Phase::MUTATOR));
+
+  if (!aborted) {
+    auto& slice = slices_.back();
+    slice.end = TimeStamp::Now();
+    slice.endFaults = GetPageFaultCount();
+    slice.finalState = gc->state();
+
+    log("end slice");
+
+    sendSliceTelemetry(slice);
+
+    sliceCount_++;
+
+    totalGCTime_ += slice.end - slice.start;
+  }
+
+  bool last = !gc->isIncrementalGCInProgress();
+  if (last) {
+    if (gcTimerFile) {
+      printStats();
+    }
+
+    if (!aborted) {
+      endGC();
+    }
+  }
+
+  if (!aborted &&
+      ShouldPrintProfile(gc->rt, enableProfiling_, profileWorkers_,
+                         profileThreshold_, slices_.back().duration())) {
+    printSliceProfile();
+  }
+
+  // Slice callbacks should only fire for the outermost level.
+  if (!aborted) {
+    if (sliceCallback) {
+      JSContext* cx = context();
+      JS::GCDescription desc(!gc->fullGCRequested, last, gcOptions,
+                             slices_.back().reason);
+      (*sliceCallback)(cx, JS::GC_SLICE_END, desc);
+      if (last) {
+        (*sliceCallback)(cx, JS::GC_CYCLE_END, desc);
+      }
+    }
+  }
+
+  // Do this after the slice callback since it uses these values.
+  if (last) {
+    for (auto& count : counts) {
+      count = 0;
+    }
+
+    // Clear the timers at the end of a GC, preserving the data for
+    // PhaseKind::MUTATOR.
+    auto mutatorStartTime = phaseStartTimes[Phase::MUTATOR];
+    auto mutatorTime = phaseTimes[Phase::MUTATOR];
+
+    phaseStartTimes = PhaseTimeStamps();
+#ifdef DEBUG
+    phaseEndTimes = PhaseTimeStamps();
+#endif
+    phaseTimes = PhaseTimes();
+
+    phaseStartTimes[Phase::MUTATOR] = mutatorStartTime;
+    phaseTimes[Phase::MUTATOR] = mutatorTime;
+  }
+
+  aborted = false;
+}
+
+void Statistics::sendSliceTelemetry(const SliceData& slice) {
+  JSRuntime* runtime = gc->rt;
+  TimeDuration sliceTime = slice.end - slice.start;
+  runtime->metrics().GC_SLICE_MS(sliceTime);
+
+  if (slice.budget.isTimeBudget()) {
+    TimeDuration budgetDuration = slice.budget.timeBudgetDuration();
+    runtime->metrics().GC_BUDGET_MS_2(budgetDuration);
+
+    if (IsCurrentlyAnimating(runtime->lastAnimationTime, slice.end)) {
+      runtime->metrics().GC_ANIMATION_MS(sliceTime);
+    }
+
+    bool wasLongSlice = false;
+    if (sliceTime > budgetDuration) {
+      // Record how long we went over budget.
+      TimeDuration overrun = sliceTime - budgetDuration;
+      runtime->metrics().GC_BUDGET_OVERRUN(overrun);
+
+      // Long GC slices are those that go 50% or 5ms over their budget.
+      wasLongSlice = (overrun > TimeDuration::FromMilliseconds(5)) ||
+                     (overrun > (budgetDuration / int64_t(2)));
+
+      // Record the longest phase in any long slice.
+      if (wasLongSlice) {
+        PhaseKind longest = LongestPhaseSelfTimeInMajorGC(slice.phaseTimes);
+        reportLongestPhaseInMajorGC(longest, [runtime](auto sample) {
+          runtime->metrics().GC_SLOW_PHASE(sample);
+        });
+
+        // If the longest phase was waiting for parallel tasks then record the
+        // longest task.
+        if (longest == PhaseKind::JOIN_PARALLEL_TASKS) {
+          PhaseKind longestParallel =
+              FindLongestPhaseKind(slice.maxParallelTimes);
+          reportLongestPhaseInMajorGC(longestParallel, [runtime](auto sample) {
+            runtime->metrics().GC_SLOW_TASK(sample);
+          });
+        }
+      }
+    }
+
+    // Record `wasLongSlice` for all TimeBudget slices.
+    runtime->metrics().GC_SLICE_WAS_LONG(wasLongSlice);
+  }
+}
+
+template <typename Fn>
+void Statistics::reportLongestPhaseInMajorGC(PhaseKind longest, Fn reportFn) {
+  if (longest != PhaseKind::NONE) {
+    uint8_t bucket = phaseKinds[longest].telemetryBucket;
+    reportFn(bucket);
+  }
+}
+
+bool Statistics::startTimingMutator() {
+  if (phaseStack.length() != 0) {
+    // Should only be called from outside of GC.
+    MOZ_ASSERT(phaseStack.length() == 1);
+    MOZ_ASSERT(phaseStack[0] == Phase::MUTATOR);
+    return false;
+  }
+
+  MOZ_ASSERT(suspendedPhases.empty());
+
+  timedGCTime = 0;
+  phaseStartTimes[Phase::MUTATOR] = TimeStamp();
+  phaseTimes[Phase::MUTATOR] = 0;
+  timedGCStart = TimeStamp();
+
+  beginPhase(PhaseKind::MUTATOR);
+  return true;
+}
+
+bool Statistics::stopTimingMutator(double& mutator_ms, double& gc_ms) {
+  // This should only be called from outside of GC, while timing the mutator.
+  if (phaseStack.length() != 1 || phaseStack[0] != Phase::MUTATOR) {
+    return false;
+  }
+
+  endPhase(PhaseKind::MUTATOR);
+  mutator_ms = t(phaseTimes[Phase::MUTATOR]);
+  gc_ms = t(timedGCTime);
+
+  return true;
+}
+
+void Statistics::suspendPhases(PhaseKind suspension) {
+  MOZ_ASSERT(suspension == PhaseKind::EXPLICIT_SUSPENSION ||
+             suspension == PhaseKind::IMPLICIT_SUSPENSION);
+  while (!phaseStack.empty()) {
+    MOZ_ASSERT(suspendedPhases.length() < MAX_SUSPENDED_PHASES);
+    Phase parent = phaseStack.back();
+    suspendedPhases.infallibleAppend(parent);
+    recordPhaseEnd(parent);
+  }
+  suspendedPhases.infallibleAppend(lookupChildPhase(suspension));
+}
+
+void Statistics::resumePhases() {
+  MOZ_ASSERT(suspendedPhases.back() == Phase::EXPLICIT_SUSPENSION ||
+             suspendedPhases.back() == Phase::IMPLICIT_SUSPENSION);
+  suspendedPhases.popBack();
+
+  while (!suspendedPhases.empty() &&
+         suspendedPhases.back() != Phase::EXPLICIT_SUSPENSION &&
+         suspendedPhases.back() != Phase::IMPLICIT_SUSPENSION) {
+    Phase resumePhase = suspendedPhases.popCopy();
+    if (resumePhase == Phase::MUTATOR) {
+      timedGCTime += TimeStamp::Now() - timedGCStart;
+    }
+    recordPhaseBegin(resumePhase);
+  }
+}
+
+void Statistics::beginPhase(PhaseKind phaseKind) {
+  // No longer timing these phases. We should never see these.
+  MOZ_ASSERT(phaseKind != PhaseKind::GC_BEGIN &&
+             phaseKind != PhaseKind::GC_END);
+
+  // PhaseKind::MUTATOR is suspended while performing GC.
+  if (currentPhase() == Phase::MUTATOR) {
+    suspendPhases(PhaseKind::IMPLICIT_SUSPENSION);
+  }
+
+  recordPhaseBegin(lookupChildPhase(phaseKind));
+}
+
+void Statistics::recordPhaseBegin(Phase phase) {
+  MOZ_ASSERT(CurrentThreadCanAccessRuntime(gc->rt));
+
+  // Guard against any other re-entry.
+  MOZ_ASSERT(!phaseStartTimes[phase]);
+
+  MOZ_ASSERT(phaseStack.length() < MAX_PHASE_NESTING);
+
+  Phase current = currentPhase();
+  MOZ_ASSERT(phases[phase].parent == current);
+
+  TimeStamp now = TimeStamp::Now();
+
+  if (current != Phase::NONE) {
+    MOZ_ASSERT(now >= phaseStartTimes[currentPhase()],
+               "Inconsistent time data; see bug 1400153");
+    if (now < phaseStartTimes[currentPhase()]) {
+      now = phaseStartTimes[currentPhase()];
+      aborted = true;
+    }
+  }
+
+  phaseStack.infallibleAppend(phase);
+  phaseStartTimes[phase] = now;
+  log("begin: %s", phases[phase].path);
+}
+
+void Statistics::recordPhaseEnd(Phase phase) {
+  MOZ_ASSERT(CurrentThreadCanAccessRuntime(gc->rt));
+
+  MOZ_ASSERT(phaseStartTimes[phase]);
+
+  TimeStamp now = TimeStamp::Now();
+
+  // Make sure this phase ends after it starts.
+  MOZ_ASSERT(now >= phaseStartTimes[phase],
+             "Inconsistent time data; see bug 1400153");
+
+#ifdef DEBUG
+  // Make sure this phase ends after all of its children. Note that some
+  // children might not have run in this instance, in which case they will
+  // have run in a previous instance of this parent or not at all.
+  for (Phase kid = phases[phase].firstChild; kid != Phase::NONE;
+       kid = phases[kid].nextSibling) {
+    if (phaseEndTimes[kid].IsNull()) {
+      continue;
+    }
+    if (phaseEndTimes[kid] > now) {
+      fprintf(stderr,
+              "Parent %s ended at %.3fms, before child %s ended at %.3fms?\n",
+              phases[phase].name, t(now - TimeStamp::FirstTimeStamp()),
+              phases[kid].name,
+              t(phaseEndTimes[kid] - TimeStamp::FirstTimeStamp()));
+    }
+    MOZ_ASSERT(phaseEndTimes[kid] <= now,
+               "Inconsistent time data; see bug 1400153");
+  }
+#endif
+
+  if (now < phaseStartTimes[phase]) {
+    now = phaseStartTimes[phase];
+    aborted = true;
+  }
+
+  if (phase == Phase::MUTATOR) {
+    timedGCStart = now;
+  }
+
+  phaseStack.popBack();
+
+  TimeDuration t = now - phaseStartTimes[phase];
+  if (!slices_.empty()) {
+    slices_.back().phaseTimes[phase] += t;
+  }
+  phaseTimes[phase] += t;
+  phaseStartTimes[phase] = TimeStamp();
+
+#ifdef DEBUG
+  phaseEndTimes[phase] = now;
+  log("end: %s", phases[phase].path);
+#endif
+}
+
+void Statistics::endPhase(PhaseKind phaseKind) {
+  Phase phase = currentPhase();
+  MOZ_ASSERT(phase != Phase::NONE);
+  MOZ_ASSERT(phases[phase].phaseKind == phaseKind);
+
+  recordPhaseEnd(phase);
+
+  // When emptying the stack, we may need to return to timing the mutator
+  // (PhaseKind::MUTATOR).
+  if (phaseStack.empty() && !suspendedPhases.empty() &&
+      suspendedPhases.back() == Phase::IMPLICIT_SUSPENSION) {
+    resumePhases();
+  }
+}
+
+void Statistics::recordParallelPhase(PhaseKind phaseKind,
+                                     TimeDuration duration) {
+  MOZ_ASSERT(CurrentThreadCanAccessRuntime(gc->rt));
+
+  if (aborted) {
+    return;
+  }
+
+  slices_.back().totalParallelTimes[phaseKind] += duration;
+
+  // Also record the maximum task time for each phase. Don't record times for
+  // parent phases.
+  TimeDuration& maxTime = slices_.back().maxParallelTimes[phaseKind];
+  maxTime = std::max(maxTime, duration);
+}
+
+TimeStamp Statistics::beginSCC() { return TimeStamp::Now(); }
+
+void Statistics::endSCC(unsigned scc, TimeStamp start) {
+  if (scc >= sccTimes.length() && !sccTimes.resize(scc + 1)) {
+    return;
+  }
+
+  sccTimes[scc] += TimeStamp::Now() - start;
+}
+
+/*
+ * MMU (minimum mutator utilization) is a measure of how much garbage collection
+ * is affecting the responsiveness of the system. MMU measurements are given
+ * with respect to a certain window size. If we report MMU(50ms) = 80%, then
+ * that means that, for any 50ms window of time, at least 80% of the window is
+ * devoted to the mutator. In other words, the GC is running for at most 20% of
+ * the window, or 10ms. The GC can run multiple slices during the 50ms window
+ * as long as the total time it spends is at most 10ms.
+ */
+double Statistics::computeMMU(TimeDuration window) const {
+  MOZ_ASSERT(!slices_.empty());
+
+  TimeDuration gc = slices_[0].end - slices_[0].start;
+  TimeDuration gcMax = gc;
+
+  if (gc >= window) {
+    return 0.0;
+  }
+
+  int startIndex = 0;
+  for (size_t endIndex = 1; endIndex < slices_.length(); endIndex++) {
+    auto* startSlice = &slices_[startIndex];
+    auto& endSlice = slices_[endIndex];
+    gc += endSlice.end - endSlice.start;
+
+    while (endSlice.end - startSlice->end >= window) {
+      gc -= startSlice->end - startSlice->start;
+      startSlice = &slices_[++startIndex];
+    }
+
+    TimeDuration cur = gc;
+    if (endSlice.end - startSlice->start > window) {
+      cur -= (endSlice.end - startSlice->start - window);
+    }
+    if (cur > gcMax) {
+      gcMax = cur;
+    }
+  }
+
+  return double((window - gcMax) / window);
+}
+
+void Statistics::maybePrintProfileHeaders() {
+  static int printedHeader = 0;
+  if ((printedHeader++ % 200) == 0) {
+    printProfileHeader();
+    if (gc->nursery().enableProfiling()) {
+      gc->nursery().printProfileHeader();
+    }
+  }
+}
+
+// The following macros define GC profile metadata fields that are printed
+// before the timing information defined by FOR_EACH_GC_PROFILE_TIME.
+
+#define FOR_EACH_GC_PROFILE_COMMON_METADATA(_) \
+  _("PID", 7, "%7zu", pid)                     \
+  _("Runtime", 14, "0x%12p", runtime)
+
+#define FOR_EACH_GC_PROFILE_SLICE_METADATA(_)         \
+  _("Timestamp", 10, "%10.6f", timestamp.ToSeconds()) \
+  _("Reason", 20, "%-20.20s", reason)                 \
+  _("States", 6, "%6s", formatGCStates(slice))        \
+  _("FSNR", 4, "%4s", formatGCFlags(slice))           \
+  _("SizeKB", 8, "%8zu", sizeKB)                      \
+  _("Budget", 6, "%6s", formatBudget(slice))
+
+#define FOR_EACH_GC_PROFILE_METADATA(_)  \
+  FOR_EACH_GC_PROFILE_COMMON_METADATA(_) \
+  FOR_EACH_GC_PROFILE_SLICE_METADATA(_)
+
+void Statistics::printProfileHeader() {
+  if (!enableProfiling_) {
+    return;
+  }
+
+  Sprinter sprinter;
+  if (!sprinter.init() || !sprinter.put(MajorGCProfilePrefix)) {
+    return;
+  }
+
+#define PRINT_METADATA_NAME(name, width, _1, _2)  \
+  if (!sprinter.jsprintf(" %-*s", width, name)) { \
+    return;                                       \
+  }
+  FOR_EACH_GC_PROFILE_METADATA(PRINT_METADATA_NAME)
+#undef PRINT_METADATA_NAME
+
+#define PRINT_PROFILE_NAME(_1, text, _2)     \
+  if (!sprinter.jsprintf(" %-6.6s", text)) { \
+    return;                                  \
+  }
+  FOR_EACH_GC_PROFILE_TIME(PRINT_PROFILE_NAME)
+#undef PRINT_PROFILE_NAME
+
+  if (!sprinter.put("\n")) {
+    return;
+  }
+
+  fputs(sprinter.string(), profileFile());
+}
+
+static TimeDuration SumAllPhaseKinds(const Statistics::PhaseKindTimes& times) {
+  TimeDuration sum;
+  for (PhaseKind kind : AllPhaseKinds()) {
+    sum += times[kind];
+  }
+  return sum;
+}
+
+void Statistics::printSliceProfile() {
+  maybePrintProfileHeaders();
+
+  const SliceData& slice = slices_.back();
+  ProfileDurations times = getProfileTimes(slice);
+  updateTotalProfileTimes(times);
+
+  Sprinter sprinter;
+  if (!sprinter.init() || !sprinter.put(MajorGCProfilePrefix)) {
+    return;
+  }
+
+  size_t pid = getpid();
+  JSRuntime* runtime = gc->rt;
+  TimeDuration timestamp = slice.end - creationTime();
+  const char* reason = ExplainGCReason(slice.reason);
+  size_t sizeKB = gc->heapSize.bytes() / 1024;
+
+#define PRINT_FIELD_VALUE(_1, _2, format, value) \
+  if (!sprinter.jsprintf(" " format, value)) {   \
+    return;                                      \
+  }
+  FOR_EACH_GC_PROFILE_METADATA(PRINT_FIELD_VALUE)
+#undef PRINT_FIELD_VALUE
+
+  if (!printProfileTimes(times, sprinter)) {
+    return;
+  }
+
+  fputs(sprinter.string(), profileFile());
+}
+
+Statistics::ProfileDurations Statistics::getProfileTimes(
+    const SliceData& slice) const {
+  ProfileDurations times;
+
+  times[ProfileKey::Total] = slice.duration();
+  times[ProfileKey::Background] = SumAllPhaseKinds(slice.totalParallelTimes);
+
+#define GET_PROFILE_TIME(name, text, phase)                      \
+  if (phase != PhaseKind::NONE) {                                \
+    times[ProfileKey::name] = SumPhase(phase, slice.phaseTimes); \
+  }
+  FOR_EACH_GC_PROFILE_TIME(GET_PROFILE_TIME)
+#undef GET_PROFILE_TIME
+
+  return times;
+}
+
+void Statistics::updateTotalProfileTimes(const ProfileDurations& times) {
+#define UPDATE_PROFILE_TIME(name, _, phase) \
+  totalTimes_[ProfileKey::name] += times[ProfileKey::name];
+  FOR_EACH_GC_PROFILE_TIME(UPDATE_PROFILE_TIME)
+#undef UPDATE_PROFILE_TIME
+}
+
+const char* Statistics::formatGCStates(const SliceData& slice) {
+  DebugOnly<int> r =
+      SprintfLiteral(formatBuffer_, "%1d -> %1d", int(slice.initialState),
+                     int(slice.finalState));
+  MOZ_ASSERT(r > 0 && r < FormatBufferLength);
+  return formatBuffer_;
+}
+
+const char* Statistics::formatGCFlags(const SliceData& slice) {
+  bool fullGC = gc->fullGCRequested;
+  bool shrinkingGC = gcOptions == JS::GCOptions::Shrink;
+  bool nonIncrementalGC = nonincrementalReason_ != GCAbortReason::None;
+  bool wasReset = slice.resetReason != GCAbortReason::None;
+
+  MOZ_ASSERT(FormatBufferLength >= 5);
+  formatBuffer_[0] = fullGC ? 'F' : ' ';
+  formatBuffer_[1] = shrinkingGC ? 'S' : ' ';
+  formatBuffer_[2] = nonIncrementalGC ? 'N' : ' ';
+  formatBuffer_[3] = wasReset ? 'R' : ' ';
+  formatBuffer_[4] = '\0';
+
+  return formatBuffer_;
+}
+
+const char* Statistics::formatBudget(const SliceData& slice) {
+  if (nonincrementalReason_ != GCAbortReason::None ||
+      !slice.budget.isTimeBudget()) {
+    formatBuffer_[0] = '\0';
+    return formatBuffer_;
+  }
+
+  DebugOnly<int> r =
+      SprintfLiteral(formatBuffer_, " %6" PRIi64, slice.budget.timeBudget());
+  MOZ_ASSERT(r > 0 && r < FormatBufferLength);
+  return formatBuffer_;
+}
+
+/* static */
+bool Statistics::printProfileTimes(const ProfileDurations& times,
+                                   Sprinter& sprinter) {
+  for (auto time : times) {
+    int64_t millis = int64_t(time.ToMilliseconds());
+    if (!sprinter.jsprintf(" %6" PRIi64, millis)) {
+      return false;
+    }
+  }
+
+  return sprinter.put("\n");
+}
+
+constexpr size_t SliceMetadataFormatWidth() {
+  size_t fieldCount = 0;
+  size_t totalWidth = 0;
+
+#define UPDATE_COUNT_AND_WIDTH(_1, width, _2, _3) \
+  fieldCount++;                                   \
+  totalWidth += width;
+  FOR_EACH_GC_PROFILE_SLICE_METADATA(UPDATE_COUNT_AND_WIDTH)
+#undef UPDATE_COUNT_AND_WIDTH
+
+  // Add padding between fields.
+  totalWidth += fieldCount - 1;
+
+  return totalWidth;
+}
+
+void Statistics::printTotalProfileTimes() {
+  if (!enableProfiling_) {
+    return;
+  }
+
+  Sprinter sprinter;
+  if (!sprinter.init() || !sprinter.put(MajorGCProfilePrefix)) {
+    return;
+  }
+
+  size_t pid = getpid();
+  JSRuntime* runtime = gc->rt;
+
+#define PRINT_FIELD_VALUE(_1, _2, format, value) \
+  if (!sprinter.jsprintf(" " format, value)) {   \
+    return;                                      \
+  }
+  FOR_EACH_GC_PROFILE_COMMON_METADATA(PRINT_FIELD_VALUE)
+#undef PRINT_FIELD_VALUE
+
+  // Use whole width of per-slice metadata to print total slices so the profile
+  // totals that follow line up.
+  size_t width = SliceMetadataFormatWidth();
+  if (!sprinter.jsprintf(" %-*s", int(width), formatTotalSlices())) {
+    return;
+  }
+
+  if (!printProfileTimes(totalTimes_, sprinter)) {
+    return;
+  }
+
+  fputs(sprinter.string(), profileFile());
+}
+
+const char* Statistics::formatTotalSlices() {
+  DebugOnly<int> r = SprintfLiteral(
+      formatBuffer_, "TOTALS: %7" PRIu64 " slices:", sliceCount_);
+  MOZ_ASSERT(r > 0 && r < FormatBufferLength);
+  return formatBuffer_;
+}