Export of internal Abseil changes

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341670bce317dd6af8d3c066970230591a47e80c by Martijn Vels <mvels@google.com>:

Change GetStack() and GetParentStack() to return absl::Span

PiperOrigin-RevId: 368765721

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6aaab9536d6957303c7aba100c3afaa6fb0ea2c8 by Martijn Vels <mvels@google.com>:

Remove locking from parent stack.

This change removes the need to lock all access to `parent_stack' by making the 'copy constructor' logic specify the 'copied from' CordzInfo (where available) to the TrackCord function, after which parent_stack is immutable.

PiperOrigin-RevId: 368760630

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b19e2059cada35a8ede994833018edac94de6ddc by Martijn Vels <mvels@google.com>:

Add cordz instrumentation to Cord

PiperOrigin-RevId: 368746225

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67b8bbf980f0f4e1db79aa32968e9a715a09b51a by Martijn Vels <mvels@google.com>:

Create ABSL_INTERNAL_CORDZ_ENABLED define controlling when Cordz code is enabled

There are specific builds and condtions under which we don't support cordz sampling, which is per this change represented by ABSL_INTERNAL_CORDZ_ENABLED being defined.

PiperOrigin-RevId: 368731603

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8cbfe0e3169637a620f4b66ad2bc2ce340879cb0 by Martijn Vels <mvels@google.com>:

Add a `rep` property to CordzInfo to be managed by Cord logic.

This change adds a `rep` property to CordzInfo, which is intended to be used by collection logic.

Mini design:
Cord invokes TrackCord() providing the active 'root' cordrep of the newly sampled Cord, returning a CordzInfo with a weak (uncounted) reference to this root. Cord invokes `SetCordRep()` each time the root cordrep of the sampled Cord is updated while holding `mutex()`. Cord must also obtain `mutex()` _before_ removing a reference on the old root. i.e.: Cord must guarantee that the (weak) reference held in CordzInfo is at all times valid.

CordzInfo collection code can then safely obtain a (reference counted) rep pointer by adding a reference to `rep_` while holding `mutex()`. This requires only a very brief critical section inside CordzInfo logic, minimizing contention with concurrent Cord updates.

Cord code should typically obtain and hold `mutex()` for the entirety of each mutating Cord operation on a sampled cord. As Cord is thread compatible, it never competes on the lock with any other thread. The only possible concurrent access is from Cordz collection code, which should be a relatively rare event.

PiperOrigin-RevId: 368673758

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1255120dce2bdd6b4205a34a0e555e0b74b6152f by Martijn Vels <mvels@google.com>:

Remove 'depth' from active recorded metrics.

Going forward we do not 'live' record depth (and size), but will observe these at collection time only.

PiperOrigin-RevId: 368636572

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83e5146e35f221736b49e9f0a8805f8c159a51db by Martijn Vels <mvels@google.com>:

Make cordz targets visible in OSS

PiperOrigin-RevId: 368615010

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dcb16a4f1239151f0a8c70a8cfeb29dabbd113b8 by Martijn Vels <mvels@google.com>:

Internal cleanup

PiperOrigin-RevId: 368514666
GitOrigin-RevId: 341670bce317dd6af8d3c066970230591a47e80c
Change-Id: I94cecfbbd441eb386f99fc5186c468a7a5538862

1 files changed, 41 insertions, 0 deletions

diff --git a/absl/strings/cord.h b/absl/strings/cord.h
index 7ce938ca..de1470b2 100644
--- a/absl/strings/cord.h
+++ b/absl/strings/cord.h
@@ -70,6 +70,7 @@
 #include <string>
 #include <type_traits>
 
+#include "absl/base/config.h"
 #include "absl/base/internal/endian.h"
 #include "absl/base/internal/per_thread_tls.h"
 #include "absl/base/macros.h"
@@ -80,6 +81,9 @@
 #include "absl/strings/internal/cord_internal.h"
 #include "absl/strings/internal/cord_rep_ring.h"
 #include "absl/strings/internal/cord_rep_ring_reader.h"
+#include "absl/strings/internal/cordz_functions.h"
+#include "absl/strings/internal/cordz_info.h"
+#include "absl/strings/internal/cordz_statistics.h"
 #include "absl/strings/internal/resize_uninitialized.h"
 #include "absl/strings/internal/string_constant.h"
 #include "absl/strings/string_view.h"
@@ -772,6 +776,20 @@ class Cord {
     // Resets the current cordz_info to null / empty.
     void clear_cordz_info() { data_.clear_cordz_info(); }
 
+    // Starts profiling this cord.
+    void StartProfiling();
+
+    // Starts profiling this cord which has been copied from `src`.
+    void StartProfiling(const Cord::InlineRep& src);
+
+    // Returns true if a Cord should be profiled and false otherwise.
+    static bool should_profile();
+
+    // Updates the cordz statistics. info may be nullptr if the CordzInfo object
+    // is unknown.
+    void UpdateCordzStatistics();
+    void UpdateCordzStatisticsSlow();
+
    private:
     friend class Cord;
 
@@ -943,6 +961,9 @@ inline Cord::InlineRep::InlineRep(const Cord::InlineRep& src)
   if (is_tree()) {
     data_.clear_cordz_info();
     absl::cord_internal::CordRep::Ref(as_tree());
+    if (ABSL_PREDICT_FALSE(should_profile())) {
+      StartProfiling(src);
+    }
   }
 }
 
@@ -1004,6 +1025,9 @@ inline size_t Cord::InlineRep::size() const {
 
 inline void Cord::InlineRep::set_tree(absl::cord_internal::CordRep* rep) {
   if (rep == nullptr) {
+    if (ABSL_PREDICT_FALSE(is_profiled())) {
+      absl::cord_internal::CordzInfo::UntrackCord(cordz_info());
+    }
     ResetToEmpty();
   } else {
     if (data_.is_tree()) {
@@ -1013,7 +1037,11 @@ inline void Cord::InlineRep::set_tree(absl::cord_internal::CordRep* rep) {
     } else {
       // `data_` contains inlined data: initialize data_ to tree value `rep`.
       data_.make_tree(rep);
+      if (ABSL_PREDICT_FALSE(should_profile())) {
+        StartProfiling();
+      }
     }
+    UpdateCordzStatistics();
   }
 }
 
@@ -1024,9 +1052,13 @@ inline void Cord::InlineRep::replace_tree(absl::cord_internal::CordRep* rep) {
     return;
   }
   data_.set_tree(rep);
+  UpdateCordzStatistics();
 }
 
 inline absl::cord_internal::CordRep* Cord::InlineRep::clear() {
+  if (ABSL_PREDICT_FALSE(is_profiled())) {
+    absl::cord_internal::CordzInfo::UntrackCord(cordz_info());
+  }
   absl::cord_internal::CordRep* result = tree();
   ResetToEmpty();
   return result;
@@ -1039,6 +1071,15 @@ inline void Cord::InlineRep::CopyToArray(char* dst) const {
   cord_internal::SmallMemmove(dst, data_.as_chars(), n);
 }
 
+inline ABSL_ATTRIBUTE_ALWAYS_INLINE bool Cord::InlineRep::should_profile() {
+  return absl::cord_internal::cordz_should_profile();
+}
+
+inline void Cord::InlineRep::UpdateCordzStatistics() {
+  if (ABSL_PREDICT_TRUE(!is_profiled())) return;
+  UpdateCordzStatisticsSlow();
+}
+
 constexpr inline Cord::Cord() noexcept {}
 
 template <typename T>