Export of internal Abseil changes

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f6fbb03bff276e72123e8590519079e87732ae62 by Abseil Team <absl-team@google.com>:

Replace static absl::Mutex with SpinLock in absl::Cords

to avoid static initializers by absl::Mutex destructors

PiperOrigin-RevId: 370694199

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654b7d9edfdc24f226990b2b46cbf91451a1d92a by Martijn Vels <mvels@google.com>:

Implement global data for CordzInfo in an ODR hardened way

This change puts the global data into a global list structure, and stores a reference to the global list in the handle itself. This hardens the implementation against ODR violations where info pointers are crossing dynamic library boundaries which are privately loaded.

PiperOrigin-RevId: 370673045

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712dba768e66ee2ba85d6010829c617cd2af6ba7 by Martijn Vels <mvels@google.com>:

Intrument Cord::operator= for Cordz

PiperOrigin-RevId: 370659149

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c0b347a2289e151b72680269332e264b8fa989c0 by Matt Kulukundis <kfm@google.com>:

Fix test guards for ABSL_ATTRIBUTE_RETURNS_NONNULL

PiperOrigin-RevId: 370594807

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c2bedaa3472ef223f907de2604f9b9b58852ec5f by Martijn Vels <mvels@google.com>:

Add new Cordz instrumentation on GetAppendRegion.

PiperOrigin-RevId: 370587761

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84fbfcc852697d509f6094482b86e84743a6b331 by Martijn Vels <mvels@google.com>:

Add instrumentation on Cord::Apppend(string_view)

PiperOrigin-RevId: 370576590

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9e077390b8ca2239e1cb7bfbe1d5a04f2fc11d30 by Abseil Team <absl-team@google.com>:

Google-internal changes only.

PiperOrigin-RevId: 370558424

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fb53c149eb2364ea34e3a67235f873866618b8ac by Matt Kulukundis <kfm@google.com>:

Update config.h macros with a few useful helpers to simplify version checking

PiperOrigin-RevId: 370557684

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abf8142e99b9ff7e15f6528a357f1005461950b0 by Martijn Vels <mvels@google.com>:

clang-format cord

PiperOrigin-RevId: 370549371

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e555985eabe63fcf0e980e9c433dd84caffec191 by Martijn Vels <mvels@google.com>:

Add MaybeUntrackCord() function

This function is near identical to the old UntrackCord() but allows info to be null, moving the cord.is_profiled() branch into CordzInfo.

PiperOrigin-RevId: 370528447

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3883538efe4601f7864bda70a50d868bb383c63b by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 370503186

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a9514b65542fde1bc73584e6f3c1c4b3a05f215f by Derek Mauro <dmauro@google.com>:

Add -Winvalid-constexpr to warning options for LLVM

PiperOrigin-RevId: 370455171

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d8a3966de2cf15a2dc28e17e49a3d27d205eca92 by Martijn Vels <mvels@google.com>:

Add naive UniqueGenerator<T, kMaxValues, ...> to avoid flakes from dup random values.

PiperOrigin-RevId: 370179772

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46d0caa1a12b68a5998d4f919e20f0f83b9286f8 by Martijn Vels <mvels@google.com>:

Add new Cordz instrumentation on PrependTree.

PiperOrigin-RevId: 370138969
GitOrigin-RevId: f6fbb03bff276e72123e8590519079e87732ae62
Change-Id: Ifa4c00a5c7b01198ee367a3253bea6b66612135e

1 files changed, 40 insertions, 19 deletions

diff --git a/absl/strings/internal/cordz_info.h b/absl/strings/internal/cordz_info.h
index 4cf57664..f7682cb3 100644
--- a/absl/strings/internal/cordz_info.h
+++ b/absl/strings/internal/cordz_info.h
@@ -20,6 +20,8 @@
 #include <functional>
 
 #include "absl/base/config.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/spinlock.h"
 #include "absl/base/thread_annotations.h"
 #include "absl/strings/internal/cord_internal.h"
 #include "absl/strings/internal/cordz_functions.h"
@@ -79,17 +81,22 @@ class ABSL_LOCKABLE CordzInfo : public CordzHandle {
   // and before the root cordrep of the sampled cord is unreffed.
   // This function may extend the lifetime of the cordrep in cases where the
   // CordInfo instance is being held by a concurrent collection thread.
-  static void UntrackCord(CordzInfo* cordz_info);
+  void Untrack();
+
+  // Invokes UntrackCord() on `info` if `info` is not null.
+  static void MaybeUntrackCord(CordzInfo* info);
 
   CordzInfo() = delete;
   CordzInfo(const CordzInfo&) = delete;
   CordzInfo& operator=(const CordzInfo&) = delete;
 
   // Retrieves the oldest existing CordzInfo.
-  static CordzInfo* Head(const CordzSnapshot& snapshot);
+  static CordzInfo* Head(const CordzSnapshot& snapshot)
+      ABSL_NO_THREAD_SAFETY_ANALYSIS;
 
   // Retrieves the next oldest existing CordzInfo older than 'this' instance.
-  CordzInfo* Next(const CordzSnapshot& snapshot) const;
+  CordzInfo* Next(const CordzSnapshot& snapshot) const
+      ABSL_NO_THREAD_SAFETY_ANALYSIS;
 
   // Locks this instance for the update identified by `method`.
   // Increases the count for `method` in `update_tracker`.
@@ -141,6 +148,17 @@ class ABSL_LOCKABLE CordzInfo : public CordzHandle {
   }
 
  private:
+  // Global cordz info list. CordzInfo stores a pointer to the global list
+  // instance to harden against ODR violations.
+  struct List {
+    constexpr explicit List(absl::ConstInitType)
+        : mutex(absl::kConstInit,
+                absl::base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL) {}
+
+    absl::base_internal::SpinLock mutex;
+    std::atomic<CordzInfo*> head ABSL_GUARDED_BY(mutex){nullptr};
+  };
+
   static constexpr int kMaxStackDepth = 64;
 
   explicit CordzInfo(CordRep* rep, const CordzInfo* src,
@@ -148,7 +166,6 @@ class ABSL_LOCKABLE CordzInfo : public CordzHandle {
   ~CordzInfo() override;
 
   void Track();
-  void Untrack();
 
   // Returns the parent method from `src`, which is either `parent_method_` or
   // `method_` depending on `parent_method_` being kUnknown.
@@ -161,23 +178,20 @@ class ABSL_LOCKABLE CordzInfo : public CordzHandle {
   // Returns 0 if `src` is null.
   static int FillParentStack(const CordzInfo* src, void** stack);
 
-  // 'Unsafe' head/next/prev accessors not requiring the lock being held.
-  // These are used exclusively for iterations (Head / Next) where we enforce
-  // a token being held, so reading an 'old' / deleted pointer is fine.
-  static CordzInfo* ci_head_unsafe() ABSL_NO_THREAD_SAFETY_ANALYSIS {
-    return ci_head_.load(std::memory_order_acquire);
-  }
-  CordzInfo* ci_next_unsafe() const ABSL_NO_THREAD_SAFETY_ANALYSIS {
-    return ci_next_.load(std::memory_order_acquire);
-  }
-  CordzInfo* ci_prev_unsafe() const ABSL_NO_THREAD_SAFETY_ANALYSIS {
-    return ci_prev_.load(std::memory_order_acquire);
+  void ODRCheck() const {
+#ifndef NDEBUG
+    ABSL_RAW_CHECK(list_ == &global_list_, "ODR violation in Cord");
+#endif
   }
 
-  static absl::Mutex ci_mutex_;
-  static std::atomic<CordzInfo*> ci_head_ ABSL_GUARDED_BY(ci_mutex_);
-  std::atomic<CordzInfo*> ci_prev_ ABSL_GUARDED_BY(ci_mutex_){nullptr};
-  std::atomic<CordzInfo*> ci_next_ ABSL_GUARDED_BY(ci_mutex_){nullptr};
+  ABSL_CONST_INIT static List global_list_;
+  List* const list_ = &global_list_;
+
+  // ci_prev_ and ci_next_ require the global list mutex to be held.
+  // Unfortunately we can't use thread annotations such that the thread safety
+  // analysis understands that list_ and global_list_ are one and the same.
+  std::atomic<CordzInfo*> ci_prev_{nullptr};
+  std::atomic<CordzInfo*> ci_next_{nullptr};
 
   mutable absl::Mutex mutex_;
   CordRep* rep_ ABSL_GUARDED_BY(mutex_);
@@ -209,6 +223,13 @@ inline ABSL_ATTRIBUTE_ALWAYS_INLINE void CordzInfo::MaybeTrackCord(
   }
 }
 
+inline ABSL_ATTRIBUTE_ALWAYS_INLINE void CordzInfo::MaybeUntrackCord(
+    CordzInfo* info) {
+  if (ABSL_PREDICT_FALSE(info)) {
+    info->Untrack();
+  }
+}
+
 inline void CordzInfo::AssertHeld() ABSL_ASSERT_EXCLUSIVE_LOCK(mutex_) {
 #ifndef NDEBUG
   mutex_.AssertHeld();