Export of internal Abseil changes

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5d6734366ec54997df5234ac3b7e21015d7d5fde by Martijn Vels <mvels@google.com>:

Increase slop for unit test to reduce flakiness of test

PiperOrigin-RevId: 371935786

--
6e97ff23e7f732ebf969bbc69102e5e677aae8cd by Martijn Vels <mvels@google.com>:

Add node and memory usage stats analysis to GetCordzStatistics.

PiperOrigin-RevId: 371893353

--
17f7443e6f988f25efa25c2291c1cde191af2bf2 by Martijn Vels <mvels@google.com>:

Add check on n == 0 in CordReader::ReadCord, which breaks invariants in the ring buffer code.

PiperOrigin-RevId: 371738207
GitOrigin-RevId: 5d6734366ec54997df5234ac3b7e21015d7d5fde
Change-Id: I0fc883f4f49f2380ab9afddbdfe6eb5ccc15dfc3

9 files changed, 738 insertions, 32 deletions

diff --git a/absl/strings/BUILD.bazel b/absl/strings/BUILD.bazel
index 15277de3..84d4bc4f 100644
--- a/absl/strings/BUILD.bazel
+++ b/absl/strings/BUILD.bazel
@@ -376,6 +376,7 @@ cc_library(
         "//absl/base:config",
         "//absl/base:core_headers",
         "//absl/base:raw_logging_internal",
+        "//absl/container:inlined_vector",
         "//absl/debugging:stacktrace",
         "//absl/synchronization",
         "//absl/types:span",
@@ -498,6 +499,26 @@ cc_test(
 )
 
 cc_test(
+    name = "cordz_info_statistics_test",
+    srcs = [
+        "internal/cordz_info_statistics_test.cc",
+    ],
+    deps = [
+        ":cord",
+        ":cord_internal",
+        ":cordz_info",
+        ":cordz_sample_token",
+        ":cordz_statistics",
+        ":cordz_update_scope",
+        ":cordz_update_tracker",
+        "//absl/base:config",
+        "//absl/synchronization",
+        "//absl/synchronization:thread_pool",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
     name = "cordz_sample_token_test",
     srcs = [
         "internal/cordz_sample_token_test.cc",
diff --git a/absl/strings/CMakeLists.txt b/absl/strings/CMakeLists.txt
index 1750f7af..92728d91 100644
--- a/absl/strings/CMakeLists.txt
+++ b/absl/strings/CMakeLists.txt
@@ -696,6 +696,7 @@ absl_cc_library(
     absl::cordz_statistics
     absl::cordz_update_tracker
     absl::core_headers
+    absl::inlined_vector
     absl::span
     absl::raw_logging_internal
     absl::stacktrace
@@ -722,6 +723,24 @@ absl_cc_test(
     gmock_main
 )
 
+absl_cc_test(
+  NAME
+    cordz_info_statistics_test
+  SRCS
+    "internal/cordz_info_statistics_test.cc"
+  DEPS
+    absl::config
+    absl::cord
+    absl::cord_internal
+    absl::cordz_info
+    absl::cordz_sample_token
+    absl::cordz_statistics
+    absl::cordz_update_scope
+    absl::cordz_update_tracker
+    absl::thread_pool
+    gmock_main
+)
+
 absl_cc_library(
   NAME
     cordz_sample_token
diff --git a/absl/strings/cord.h b/absl/strings/cord.h
index 8abc4742..5c80a5cb 100644
--- a/absl/strings/cord.h
+++ b/absl/strings/cord.h
@@ -1077,6 +1077,7 @@ inline cord_internal::CordRepFlat* Cord::InlineRep::MakeFlatWithExtraCapacity(
 
 inline void Cord::InlineRep::EmplaceTree(CordRep* rep,
                                          MethodIdentifier method) {
+  assert(rep);
   data_.make_tree(rep);
   CordzInfo::MaybeTrackCord(data_, method);
 }
diff --git a/absl/strings/internal/cordz_info.cc b/absl/strings/internal/cordz_info.cc
index 0f657aaf..e1fa6b6b 100644
--- a/absl/strings/internal/cordz_info.cc
+++ b/absl/strings/internal/cordz_info.cc
@@ -16,8 +16,10 @@
 
 #include "absl/base/config.h"
 #include "absl/base/internal/spinlock.h"
+#include "absl/container/inlined_vector.h"
 #include "absl/debugging/stacktrace.h"
 #include "absl/strings/internal/cord_internal.h"
+#include "absl/strings/internal/cord_rep_ring.h"
 #include "absl/strings/internal/cordz_handle.h"
 #include "absl/strings/internal/cordz_statistics.h"
 #include "absl/strings/internal/cordz_update_tracker.h"
@@ -34,6 +36,198 @@ constexpr int CordzInfo::kMaxStackDepth;
 
 ABSL_CONST_INIT CordzInfo::List CordzInfo::global_list_{absl::kConstInit};
 
+namespace {
+
+// CordRepAnalyzer performs the analysis of a cord.
+//
+// It computes absolute node counts and total memory usage, and an 'estimated
+// fair share memory usage` statistic.
+// Conceptually, it divides the 'memory usage' at each location in the 'cord
+// graph' by the cumulative reference count of that location. The cumulative
+// reference count is the factored total of all edges leading into that node.
+//
+// The top level node is treated specially: we assume the current thread
+// (typically called from the CordzHandler) to hold a reference purely to
+// perform a safe analysis, and not being part of the application. So we
+// substract 1 from the reference count of the top node to compute the
+// 'application fair share' excluding the reference of the current thread.
+//
+// An example of fair sharing, and why we multiply reference counts:
+// Assume we have 2 CordReps, both being a Substring referencing a Flat:
+//   CordSubstring A (refcount = 5) --> child Flat C (refcount = 2)
+//   CordSubstring B (refcount = 9) --> child Flat C (refcount = 2)
+//
+// Flat C has 2 incoming edges from the 2 substrings (refcount = 2) and is not
+// referenced directly anywhere else. Translated into a 'fair share', we then
+// attribute 50% of the memory (memory / refcount = 2) to each incoming edge.
+// Rep A has a refcount of 5, so we attribute each incoming edge 1 / 5th of the
+// memory cost below it, i.e.: the fair share of Rep A of the memory used by C
+// is then 'memory C / (refcount C * refcount A) + (memory A / refcount A)'.
+// It is also easy to see how all incoming edges add up to 100%.
+class CordRepAnalyzer {
+ public:
+  // Creates an analyzer instance binding to `statistics`.
+  explicit CordRepAnalyzer(CordzStatistics& statistics)
+      : statistics_(statistics) {}
+
+  // Analyzes the memory statistics and node counts for the provided `rep`, and
+  // adds the results to `statistics`. Note that node counts and memory sizes
+  // are not initialized, computed values are added to any existing values.
+  void AnalyzeCordRep(const CordRep* rep) {
+    // Process all linear nodes.
+    // As per the class comments, use refcout - 1 on the top level node, as the
+    // top level node is assumed to be referenced only for analysis purposes.
+    size_t refcount = rep->refcount.Get();
+    RepRef repref{rep, (refcount > 1) ? refcount - 1 : 1};
+
+    // Process all top level linear nodes (substrings and flats).
+    repref = CountLinearReps(repref, memory_usage_);
+
+    // We should have have either a concat or ring node node if not null.
+    if (repref.rep != nullptr) {
+      assert(repref.rep->tag == RING || repref.rep->tag == CONCAT);
+      if (repref.rep->tag == RING) {
+        AnalyzeRing(repref);
+      } else if (repref.rep->tag == CONCAT) {
+        AnalyzeConcat(repref);
+      }
+    }
+
+    // Adds values to output
+    statistics_.estimated_memory_usage += memory_usage_.total;
+    statistics_.estimated_fair_share_memory_usage += memory_usage_.fair_share;
+  }
+
+ private:
+  // RepRef identifies a CordRep* inside the Cord tree with its cumulative
+  // refcount including itself. For example, a tree consisting of a substring
+  // with a refcount of 3 and a child flat with a refcount of 4 will have RepRef
+  // refcounts of 3 and 12 respectively.
+  struct RepRef {
+    const CordRep* rep;
+    size_t refcount;
+
+    // Returns a 'child' RepRef which contains the cumulative reference count of
+    // this instance multiplied by the child's reference count.
+    RepRef Child(const CordRep* child) const {
+      return RepRef{child, refcount * child->refcount.Get()};
+    }
+  };
+
+  // Memory usage values
+  struct MemoryUsage {
+    size_t total = 0;
+    size_t fair_share = 0;
+
+    // Adds 'size` memory usage to this class, with a cumulative (recursive)
+    // reference count of `refcount`
+    void Add(size_t size, size_t refcount) {
+      total += size;
+      fair_share += size / refcount;
+    }
+  };
+
+  // Returns `rr` if `rr.rep` is not null and a CONCAT type.
+  // Asserts that `rr.rep` is a concat node or null.
+  static RepRef AssertConcat(RepRef repref) {
+    const CordRep* rep = repref.rep;
+    assert(rep == nullptr || rep->tag == CONCAT);
+    return (rep != nullptr && rep->tag == CONCAT) ? repref : RepRef{nullptr, 0};
+  }
+
+  // Processes 'linear' reps (substring, flat, external) not requiring iteration
+  // or recursion. Returns RefRep{null} if all reps were processed, else returns
+  // the top-most non-linear concat or ring cordrep.
+  // Node counts are updated into `statistics_`, memory usage is update into
+  // `memory_usage`, which typically references `memory_usage_` except for ring
+  // buffers where we count children unrounded.
+  RepRef CountLinearReps(RepRef rep, MemoryUsage& memory_usage) {
+    // Consume all substrings
+    while (rep.rep->tag == SUBSTRING) {
+      statistics_.node_count++;
+      statistics_.node_counts.substring++;
+      memory_usage.Add(sizeof(CordRepSubstring), rep.refcount);
+      rep = rep.Child(rep.rep->substring()->child);
+    }
+
+    // Consume possible FLAT
+    if (rep.rep->tag >= FLAT) {
+      statistics_.node_count++;
+      statistics_.node_counts.flat++;
+      memory_usage.Add(rep.rep->flat()->AllocatedSize(), rep.refcount);
+      return RepRef{nullptr, 0};
+    }
+
+    // Consume possible external
+    if (rep.rep->tag == EXTERNAL) {
+      statistics_.node_count++;
+      statistics_.node_counts.external++;
+      size_t size = rep.rep->length + sizeof(CordRepExternalImpl<intptr_t>);
+      memory_usage.Add(size, rep.refcount);
+      return RepRef{nullptr, 0};
+    }
+
+    return rep;
+  }
+
+  // Analyzes the provided concat node in a flattened recursive way.
+  void AnalyzeConcat(RepRef rep) {
+    absl::InlinedVector<RepRef, 47> pending;
+
+    while (rep.rep != nullptr) {
+      const CordRepConcat* concat = rep.rep->concat();
+      RepRef left = rep.Child(concat->left);
+      RepRef right = rep.Child(concat->right);
+
+      statistics_.node_count++;
+      statistics_.node_counts.concat++;
+      memory_usage_.Add(sizeof(CordRepConcat), rep.refcount);
+
+      right = AssertConcat(CountLinearReps(right, memory_usage_));
+      rep = AssertConcat(CountLinearReps(left, memory_usage_));
+      if (rep.rep != nullptr) {
+        if (right.rep != nullptr) {
+          pending.push_back(right);
+        }
+      } else if (right.rep != nullptr) {
+        rep = right;
+      } else if (!pending.empty()) {
+        rep = pending.back();
+        pending.pop_back();
+      }
+    }
+  }
+
+  // Counts the provided ring buffer child into `child_usage`.
+  void CountRingChild(const CordRep* child, MemoryUsage& child_usage) {
+    RepRef rep{child, static_cast<size_t>(child->refcount.Get())};
+    rep = CountLinearReps(rep, child_usage);
+    assert(rep.rep == nullptr);
+  }
+
+  // Analyzes the provided ring. As ring buffers can have many child nodes, the
+  // effect of rounding errors can become non trivial, so we compute the totals
+  // first at the ring level, and then divide the fair share of the total
+  // including children fair share totals.
+  void AnalyzeRing(RepRef rep) {
+    statistics_.node_count++;
+    statistics_.node_counts.ring++;
+    MemoryUsage ring_usage;
+    const CordRepRing* ring = rep.rep->ring();
+    ring_usage.Add(CordRepRing::AllocSize(ring->capacity()), 1);
+    ring->ForEach([&](CordRepRing::index_type pos) {
+      CountRingChild(ring->entry_child(pos), ring_usage);
+    });
+    memory_usage_.total += ring_usage.total;
+    memory_usage_.fair_share += ring_usage.fair_share / rep.refcount;
+  }
+
+  CordzStatistics& statistics_;
+  MemoryUsage memory_usage_;
+};
+
+}  // namespace
+
 CordzInfo* CordzInfo::Head(const CordzSnapshot& snapshot) {
   ABSL_ASSERT(snapshot.is_snapshot());
 
@@ -101,8 +295,7 @@ CordzInfo::CordzInfo(CordRep* rep, const CordzInfo* src,
       parent_stack_depth_(FillParentStack(src, parent_stack_)),
       method_(method),
       parent_method_(GetParentMethod(src)),
-      create_time_(absl::Now()),
-      size_(rep->length) {
+      create_time_(absl::Now()) {
   update_tracker_.LossyAdd(method);
 }
 
@@ -173,9 +366,6 @@ void CordzInfo::Lock(MethodIdentifier method)
 
 void CordzInfo::Unlock() ABSL_UNLOCK_FUNCTION(mutex_) {
   bool tracked = rep_ != nullptr;
-  if (rep_) {
-    size_.store(rep_->length);
-  }
   mutex_.Unlock();
   if (!tracked) {
     Untrack();
@@ -195,7 +385,12 @@ CordzStatistics CordzInfo::GetCordzStatistics() const {
   stats.method = method_;
   stats.parent_method = parent_method_;
   stats.update_tracker = update_tracker_;
-  stats.size = size_.load(std::memory_order_relaxed);
+  if (CordRep* rep = RefCordRep()) {
+    stats.size = rep->length;
+    CordRepAnalyzer analyzer(stats);
+    analyzer.AnalyzeCordRep(rep);
+    CordRep::Unref(rep);
+  }
   return stats;
 }
 
diff --git a/absl/strings/internal/cordz_info.h b/absl/strings/internal/cordz_info.h
index 1fe046ec..e84006c5 100644
--- a/absl/strings/internal/cordz_info.h
+++ b/absl/strings/internal/cordz_info.h
@@ -147,11 +147,6 @@ class ABSL_LOCKABLE CordzInfo : public CordzHandle {
   // or RemovePrefix.
   CordzStatistics GetCordzStatistics() const;
 
-  // Records size metric for this CordzInfo instance.
-  void RecordMetrics(int64_t size) {
-    size_.store(size, std::memory_order_relaxed);
-  }
-
  private:
   using SpinLock = absl::base_internal::SpinLock;
   using SpinLockHolder = ::absl::base_internal::SpinLockHolder;
@@ -215,9 +210,6 @@ class ABSL_LOCKABLE CordzInfo : public CordzHandle {
   const MethodIdentifier parent_method_;
   CordzUpdateTracker update_tracker_;
   const absl::Time create_time_;
-
-  // Last recorded size for the cord.
-  std::atomic<int64_t> size_{0};
 };
 
 inline ABSL_ATTRIBUTE_ALWAYS_INLINE void CordzInfo::MaybeTrackCord(
@@ -250,9 +242,6 @@ inline void CordzInfo::AssertHeld() ABSL_ASSERT_EXCLUSIVE_LOCK(mutex_) {
 inline void CordzInfo::SetCordRep(CordRep* rep) {
   AssertHeld();
   rep_ = rep;
-  if (rep) {
-    size_.store(rep->length);
-  }
 }
 
 inline void CordzInfo::UnsafeSetCordRep(CordRep* rep) { rep_ = rep; }
diff --git a/absl/strings/internal/cordz_info_statistics_test.cc b/absl/strings/internal/cordz_info_statistics_test.cc
new file mode 100644
index 00000000..d46d6d62
--- /dev/null
+++ b/absl/strings/internal/cordz_info_statistics_test.cc
@@ -0,0 +1,483 @@
+// Copyright 2021 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <iostream>
+#include <random>
+#include <vector>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/base/config.h"
+#include "absl/strings/cord.h"
+#include "absl/strings/internal/cord_internal.h"
+#include "absl/strings/internal/cord_rep_flat.h"
+#include "absl/strings/internal/cord_rep_ring.h"
+#include "absl/strings/internal/cordz_info.h"
+#include "absl/strings/internal/cordz_sample_token.h"
+#include "absl/strings/internal/cordz_statistics.h"
+#include "absl/strings/internal/cordz_update_scope.h"
+#include "absl/strings/internal/cordz_update_tracker.h"
+#include "absl/synchronization/internal/thread_pool.h"
+#include "absl/synchronization/notification.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace cord_internal {
+
+// Do not print statistics contents, the matcher prints them as needed.
+inline void PrintTo(const CordzStatistics& stats, std::ostream* s) {
+  if (s) *s << "CordzStatistics{...}";
+}
+
+namespace {
+
+// Creates a flat of the specified length
+CordRepFlat* Flat(int length = 512) {
+  auto* flat = CordRepFlat::New(length);
+  flat->length = length;
+  return flat;
+}
+
+// Creates an external of the specified length
+CordRepExternal* External(int length = 512) {
+  return static_cast<CordRepExternal*>(
+      NewExternalRep(absl::string_view("", length), [](absl::string_view) {}));
+}
+
+// Creates a substring on the provided rep of length - 1
+CordRepSubstring* Substring(CordRep* rep) {
+  auto* substring = new CordRepSubstring;
+  substring->length = rep->length - 1;
+  substring->tag = SUBSTRING;
+  substring->child = rep;
+  return substring;
+}
+
+// Creates a concat on the provided reps
+CordRepConcat* Concat(CordRep* left, CordRep* right) {
+  auto* concat = new CordRepConcat;
+  concat->length = left->length + right->length;
+  concat->tag = CONCAT;
+  concat->left = left;
+  concat->right = right;
+  return concat;
+}
+
+// Reference count helper
+struct RefHelper {
+  std::vector<CordRep*> refs;
+
+  ~RefHelper() {
+    for (CordRep* rep : refs) {
+      CordRep::Unref(rep);
+    }
+  }
+
+  // Invokes CordRep::Unref() on `rep` when this instance is destroyed.
+  template <typename T>
+  T* NeedsUnref(T* rep) {
+    refs.push_back(rep);
+    return rep;
+  }
+
+  // Adds `n` reference counts to `rep` which will be unreffed when this
+  // instance is destroyed.
+  template <typename T>
+  T* Ref(T* rep, size_t n = 1) {
+    while (n--) {
+      NeedsUnref(CordRep::Ref(rep));
+    }
+    return rep;
+  }
+};
+
+// Sizeof helper. Returns the allocated size of `p`, excluding any child
+// elements for substring, concat and ring cord reps.
+template <typename T>
+size_t SizeOf(const T* rep) {
+  return sizeof(T);
+}
+
+template <>
+size_t SizeOf(const CordRepFlat* rep) {
+  return rep->AllocatedSize();
+}
+
+template <>
+size_t SizeOf(const CordRepExternal* rep) {
+  // See cord.cc
+  return sizeof(CordRepExternalImpl<intptr_t>) + rep->length;
+}
+
+template <>
+size_t SizeOf(const CordRepRing* rep) {
+  return CordRepRing::AllocSize(rep->capacity());
+}
+
+// Computes fair share memory used in a naive 'we dare to recurse' way.
+size_t FairShare(CordRep* rep, size_t ref = 1) {
+  size_t self = 0, children = 0;
+  ref *= rep->refcount.Get();
+  if (rep->tag >= FLAT) {
+    self = SizeOf(rep->flat());
+  } else if (rep->tag == EXTERNAL) {
+    self = SizeOf(rep->external());
+  } else if (rep->tag == SUBSTRING) {
+    self = SizeOf(rep->substring());
+    children = FairShare(rep->substring()->child, ref);
+  } else if (rep->tag == RING) {
+    self = SizeOf(rep->ring());
+    rep->ring()->ForEach([&](CordRepRing::index_type i) {
+      self += FairShare(rep->ring()->entry_child(i));
+    });
+  } else if (rep->tag == CONCAT) {
+    self = SizeOf(rep->concat());
+    children = FairShare(rep->concat()->left, ref) +
+               FairShare(rep->concat()->right, ref);
+  } else {
+    assert(false);
+  }
+  return self / ref + children;
+}
+
+// Samples the cord and returns CordzInfo::GetStatistics()
+CordzStatistics SampleCord(CordRep* rep) {
+  InlineData cord(rep);
+  CordzInfo::TrackCord(cord, CordzUpdateTracker::kUnknown);
+  CordzStatistics stats = cord.cordz_info()->GetCordzStatistics();
+  cord.cordz_info()->Untrack();
+  return stats;
+}
+
+MATCHER_P(EqStatistics, stats, "Statistics equal expected values") {
+  bool ok = true;
+
+#define STATS_MATCHER_EXPECT_EQ(member)                              \
+  if (stats.member != arg.member) {                                  \
+    *result_listener << "\n    stats." << #member                    \
+                     << ": actual = " << arg.member << ", expected " \
+                     << stats.member;                                \
+    ok = false;                                                      \
+  }
+
+  STATS_MATCHER_EXPECT_EQ(size);
+  STATS_MATCHER_EXPECT_EQ(node_count);
+  STATS_MATCHER_EXPECT_EQ(node_counts.flat);
+  STATS_MATCHER_EXPECT_EQ(node_counts.external);
+  STATS_MATCHER_EXPECT_EQ(node_counts.concat);
+  STATS_MATCHER_EXPECT_EQ(node_counts.substring);
+  STATS_MATCHER_EXPECT_EQ(node_counts.ring);
+  STATS_MATCHER_EXPECT_EQ(estimated_memory_usage);
+  STATS_MATCHER_EXPECT_EQ(estimated_fair_share_memory_usage);
+
+#undef STATS_MATCHER_EXPECT_EQ
+
+  return ok;
+}
+
+TEST(CordzInfoStatisticsTest, Flat) {
+  RefHelper ref;
+  auto* flat = ref.NeedsUnref(Flat());
+
+  CordzStatistics expected;
+  expected.size = flat->length;
+  expected.estimated_memory_usage = SizeOf(flat);
+  expected.estimated_fair_share_memory_usage = expected.estimated_memory_usage;
+  expected.node_count = 1;
+  expected.node_counts.flat = 1;
+
+  EXPECT_THAT(SampleCord(flat), EqStatistics(expected));
+}
+
+TEST(CordzInfoStatisticsTest, SharedFlat) {
+  RefHelper ref;
+  auto* flat = ref.Ref(ref.NeedsUnref(Flat()));
+
+  CordzStatistics expected;
+  expected.size = flat->length;
+  expected.estimated_memory_usage = SizeOf(flat);
+  expected.estimated_fair_share_memory_usage = SizeOf(flat) / 2;
+  expected.node_count = 1;
+  expected.node_counts.flat = 1;
+
+  EXPECT_THAT(SampleCord(flat), EqStatistics(expected));
+}
+
+TEST(CordzInfoStatisticsTest, External) {
+  RefHelper ref;
+  auto* external = ref.NeedsUnref(External());
+
+  CordzStatistics expected;
+  expected.size = external->length;
+  expected.estimated_memory_usage = SizeOf(external);
+  expected.estimated_fair_share_memory_usage = SizeOf(external);
+  expected.node_count = 1;
+  expected.node_counts.external = 1;
+
+  EXPECT_THAT(SampleCord(external), EqStatistics(expected));
+}
+
+TEST(CordzInfoStatisticsTest, SharedExternal) {
+  RefHelper ref;
+  auto* external = ref.Ref(ref.NeedsUnref(External()));
+
+  CordzStatistics expected;
+  expected.size = external->length;
+  expected.estimated_memory_usage = SizeOf(external);
+  expected.estimated_fair_share_memory_usage = SizeOf(external) / 2;
+  expected.node_count = 1;
+  expected.node_counts.external = 1;
+
+  EXPECT_THAT(SampleCord(external), EqStatistics(expected));
+}
+
+TEST(CordzInfoStatisticsTest, Substring) {
+  RefHelper ref;
+  auto* flat = Flat();
+  auto* substring = ref.NeedsUnref(Substring(flat));
+
+  CordzStatistics expected;
+  expected.size = substring->length;
+  expected.estimated_memory_usage = SizeOf(substring) + SizeOf(flat);
+  expected.estimated_fair_share_memory_usage = expected.estimated_memory_usage;
+  expected.node_count = 2;
+  expected.node_counts.flat = 1;
+  expected.node_counts.substring = 1;
+
+  EXPECT_THAT(SampleCord(substring), EqStatistics(expected));
+}
+
+TEST(CordzInfoStatisticsTest, SharedSubstring) {
+  RefHelper ref;
+  auto* flat = ref.Ref(Flat(), 2);
+  auto* substring = ref.Ref(ref.NeedsUnref(Substring(flat)));
+
+  CordzStatistics expected;
+  expected.size = substring->length;
+  expected.estimated_memory_usage = SizeOf(flat) + SizeOf(substring);
+  expected.estimated_fair_share_memory_usage =
+      SizeOf(substring) / 2 + SizeOf(flat) / 6;
+  expected.node_count = 2;
+  expected.node_counts.flat = 1;
+  expected.node_counts.substring = 1;
+
+  EXPECT_THAT(SampleCord(substring), EqStatistics(expected));
+}
+
+TEST(CordzInfoStatisticsTest, Concat) {
+  RefHelper ref;
+  auto* flat1 = Flat(20);
+  auto* flat2 = Flat(2000);
+  auto* concat = ref.NeedsUnref(Concat(flat1, flat2));
+
+  CordzStatistics expected;
+  expected.size = concat->length;
+  expected.estimated_memory_usage =
+      SizeOf(concat) + SizeOf(flat1) + SizeOf(flat2);
+  expected.estimated_fair_share_memory_usage = expected.estimated_memory_usage;
+  expected.node_count = 3;
+  expected.node_counts.flat = 2;
+  expected.node_counts.concat = 1;
+
+  EXPECT_THAT(SampleCord(concat), EqStatistics(expected));
+}
+
+TEST(CordzInfoStatisticsTest, DeepConcat) {
+  RefHelper ref;
+  auto* flat1 = Flat(20);
+  auto* flat2 = Flat(2000);
+  auto* flat3 = Flat(30);
+  auto* external = External(3000);
+  auto* substring = Substring(external);
+  auto* concat1 = Concat(flat1, flat2);
+  auto* concat2 = Concat(flat3, substring);
+  auto* concat = ref.NeedsUnref(Concat(concat1, concat2));
+
+  CordzStatistics expected;
+  expected.size = concat->length;
+  expected.estimated_memory_usage = SizeOf(concat) * 3 + SizeOf(flat1) +
+                                    SizeOf(flat2) + SizeOf(flat3) +
+                                    SizeOf(external) + SizeOf(substring);
+  expected.estimated_fair_share_memory_usage = expected.estimated_memory_usage;
+
+  expected.node_count = 8;
+  expected.node_counts.flat = 3;
+  expected.node_counts.external = 1;
+  expected.node_counts.concat = 3;
+  expected.node_counts.substring = 1;
+
+  EXPECT_THAT(SampleCord(concat), EqStatistics(expected));
+}
+
+TEST(CordzInfoStatisticsTest, DeepSharedConcat) {
+  RefHelper ref;
+  auto* flat1 = Flat(20);
+  auto* flat2 = ref.Ref(Flat(2000), 4);
+  auto* flat3 = Flat(30);
+  auto* external = ref.Ref(External(3000));
+  auto* substring = ref.Ref(Substring(external), 3);
+  auto* concat1 = Concat(flat1, flat2);
+  auto* concat2 = Concat(flat3, substring);
+  auto* concat = ref.Ref(ref.NeedsUnref(Concat(concat1, concat2)));
+
+  CordzStatistics expected;
+  expected.size = concat->length;
+  expected.estimated_memory_usage = SizeOf(concat) * 3 + SizeOf(flat1) +
+                                    SizeOf(flat2) + SizeOf(flat3) +
+                                    SizeOf(external) + SizeOf(substring);
+  expected.estimated_fair_share_memory_usage = FairShare(concat);
+  expected.node_count = 8;
+  expected.node_counts.flat = 3;
+  expected.node_counts.external = 1;
+  expected.node_counts.concat = 3;
+  expected.node_counts.substring = 1;
+
+  EXPECT_THAT(SampleCord(concat), EqStatistics(expected));
+}
+
+TEST(CordzInfoStatisticsTest, Ring) {
+  RefHelper ref;
+  auto* flat1 = Flat(20);
+  auto* flat2 = Flat(2000);
+  auto* flat3 = Flat(30);
+  auto* external = External(3000);
+  CordRepRing* ring = CordRepRing::Create(flat1);
+  ring = CordRepRing::Append(ring, flat2);
+  ring = CordRepRing::Append(ring, flat3);
+  ring = ref.NeedsUnref(CordRepRing::Append(ring, external));
+
+  CordzStatistics expected;
+  expected.size = ring->length;
+  expected.estimated_memory_usage = SizeOf(ring) + SizeOf(flat1) +
+                                    SizeOf(flat2) + SizeOf(flat3) +
+                                    SizeOf(external);
+  expected.estimated_fair_share_memory_usage = expected.estimated_memory_usage;
+  expected.node_count = 5;
+  expected.node_counts.flat = 3;
+  expected.node_counts.external = 1;
+  expected.node_counts.ring = 1;
+
+  EXPECT_THAT(SampleCord(ring), EqStatistics(expected));
+}
+
+TEST(CordzInfoStatisticsTest, SharedSubstringRing) {
+  RefHelper ref;
+  auto* flat1 = ref.Ref(Flat(20));
+  auto* flat2 = Flat(200);
+  auto* flat3 = Flat(30);
+  auto* external = ref.Ref(External(3000), 5);
+  CordRepRing* ring = CordRepRing::Create(flat1);
+  ring = CordRepRing::Append(ring, flat2);
+  ring = CordRepRing::Append(ring, flat3);
+  ring = ref.Ref(CordRepRing::Append(ring, external), 4);
+  auto* substring = ref.Ref(ref.NeedsUnref(Substring(ring)));
+
+
+  CordzStatistics expected;
+  expected.size = substring->length;
+  expected.estimated_memory_usage = SizeOf(ring) + SizeOf(flat1) +
+                                    SizeOf(flat2) + SizeOf(flat3) +
+                                    SizeOf(external) + SizeOf(substring);
+  expected.estimated_fair_share_memory_usage = FairShare(substring);
+  expected.node_count = 6;
+  expected.node_counts.flat = 3;
+  expected.node_counts.external = 1;
+  expected.node_counts.ring = 1;
+  expected.node_counts.substring = 1;
+
+  EXPECT_THAT(SampleCord(substring), EqStatistics(expected));
+}
+
+TEST(CordzInfoStatisticsTest, ThreadSafety) {
+  Notification stop;
+  static constexpr int kNumThreads = 8;
+  int64_t sampled_node_count = 0;
+
+  {
+    absl::synchronization_internal::ThreadPool pool(kNumThreads);
+
+    // Run analyzer thread emulating a CordzHandler collection.
+    pool.Schedule([&]() {
+      while (!stop.HasBeenNotified()) {
+        // Run every 10us (about 100K total collections).
+        absl::SleepFor(absl::Microseconds(10));
+        CordzSampleToken token;
+        for (const CordzInfo& cord_info : token) {
+          CordzStatistics stats = cord_info.GetCordzStatistics();
+          sampled_node_count += stats.node_count;
+        }
+      }
+    });
+
+    // Run 'application threads'
+    for (int i = 0; i < kNumThreads; ++i) {
+      pool.Schedule([&]() {
+        // Track 0 - 2 cordz infos at a time, providing permutations of 0, 1
+        // and 2 CordzHandle and CordzInfo queues being active, with plenty of
+        // 'empty to non empty' transitions.
+        InlineData cords[2];
+        std::minstd_rand gen;
+        std::uniform_int_distribution<int> coin_toss(0, 1);
+
+        while (!stop.HasBeenNotified()) {
+          for (InlineData& cord : cords) {
+            // 50/50 flip the state of the cord
+            if (coin_toss(gen) != 0) {
+              if (cord.is_tree()) {
+                // 50/50 simulate delete (untrack) or 'edit to empty'
+                if (coin_toss(gen) != 0) {
+                  CordzInfo::MaybeUntrackCord(cord.cordz_info());
+                } else {
+                  CordzUpdateScope scope(cord.cordz_info(),
+                                         CordzUpdateTracker::kUnknown);
+                  scope.SetCordRep(nullptr);
+                }
+                CordRep::Unref(cord.as_tree());
+                cord.set_inline_size(0);
+              } else {
+                // 50/50 Ring or Flat coin toss
+                CordRep* rep = Flat();
+                rep = (coin_toss(gen) != 0) ? CordRepRing::Create(rep) : rep;
+                cord.make_tree(rep);
+
+                // 50/50 sample
+                if (coin_toss(gen) != 0) {
+                  CordzInfo::TrackCord(cord, CordzUpdateTracker::kUnknown);
+                }
+              }
+            }
+          }
+        }
+        for (InlineData& cord : cords) {
+          if (cord.is_tree()) {
+            CordzInfo::MaybeUntrackCord(cord.cordz_info());
+            CordRep::Unref(cord.as_tree());
+          }
+        }
+      });
+    }
+
+    // Run for 1 second to give memory and thread safety analyzers plenty of
+    // time to detect any mishaps or undefined behaviors.
+    absl::SleepFor(absl::Seconds(1));
+    stop.Notify();
+  }
+
+  std::cout << "Sampled " << sampled_node_count << " nodes\n";
+}
+
+}  // namespace
+}  // namespace cord_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/absl/strings/internal/cordz_info_test.cc b/absl/strings/internal/cordz_info_test.cc
index 5bb23e47..b7eb910d 100644
--- a/absl/strings/internal/cordz_info_test.cc
+++ b/absl/strings/internal/cordz_info_test.cc
@@ -304,20 +304,6 @@ TEST(CordzInfoTest, FromParentInlined) {
   info->Untrack();
 }
 
-TEST(CordzInfoTest, RecordMetrics) {
-  TestCordData data;
-  CordzInfo* info = TrackParentCord(data.data);
-
-  CordzStatistics expected;
-  expected.size = 100;
-  info->RecordMetrics(expected.size);
-
-  CordzStatistics actual = info->GetCordzStatistics();
-  EXPECT_EQ(actual.size, expected.size);
-
-  info->Untrack();
-}
-
 }  // namespace
 }  // namespace cord_internal
 ABSL_NAMESPACE_END
diff --git a/absl/strings/internal/cordz_statistics.h b/absl/strings/internal/cordz_statistics.h
index 6e335c0b..1c93dfd0 100644
--- a/absl/strings/internal/cordz_statistics.h
+++ b/absl/strings/internal/cordz_statistics.h
@@ -28,6 +28,15 @@ namespace cord_internal {
 struct CordzStatistics {
   using MethodIdentifier = CordzUpdateTracker::MethodIdentifier;
 
+  // Node counts information
+  struct NodeCounts {
+    size_t flat = 0;
+    size_t external = 0;
+    size_t substring = 0;
+    size_t concat = 0;
+    size_t ring = 0;
+  };
+
   // The size of the cord in bytes. This matches the result of Cord::size().
   int64_t size = 0;
 
@@ -50,6 +59,9 @@ struct CordzStatistics {
   // A value of 0 implies the property has not been recorded.
   int64_t node_count = 0;
 
+  // Detailed node counts per type
+  NodeCounts node_counts;
+
   // The cord method responsible for sampling the cord.
   MethodIdentifier method = MethodIdentifier::kUnknown;
 
diff --git a/absl/synchronization/internal/per_thread_sem_test.cc b/absl/synchronization/internal/per_thread_sem_test.cc
index 8cf59e64..db1184e6 100644
--- a/absl/synchronization/internal/per_thread_sem_test.cc
+++ b/absl/synchronization/internal/per_thread_sem_test.cc
@@ -159,7 +159,7 @@ TEST_F(PerThreadSemTest, Timeouts) {
   const absl::Duration elapsed = absl::Now() - start;
   // Allow for a slight early return, to account for quality of implementation
   // issues on various platforms.
-  const absl::Duration slop = absl::Microseconds(200);
+  const absl::Duration slop = absl::Milliseconds(1);
   EXPECT_LE(delay - slop, elapsed)
       << "Wait returned " << delay - elapsed
       << " early (with " << slop << " slop), start time was " << start;