Record sampling stride in cord profiling to facilitate unsampling.

The sampling rate may change over time, so this allows us to weight samples by
the value observed when we made the sampling decision.

PiperOrigin-RevId: 616900100
Change-Id: I9b1affdba93f5f48367cb7503916296b2d84709a

1 files changed, 9 insertions, 4 deletions

diff --git a/absl/strings/internal/cordz_info.h b/absl/strings/internal/cordz_info.h
index 17eaa91c..2dc9d16d 100644
--- a/absl/strings/internal/cordz_info.h
+++ b/absl/strings/internal/cordz_info.h
@@ -60,7 +60,8 @@ class ABSL_LOCKABLE CordzInfo : public CordzHandle {
   // and/or deleted. `method` identifies the Cord public API method initiating
   // the cord to be sampled.
   // Requires `cord` to hold a tree, and `cord.cordz_info()` to be null.
-  static void TrackCord(InlineData& cord, MethodIdentifier method);
+  static void TrackCord(InlineData& cord, MethodIdentifier method,
+                        int64_t sampling_stride);
 
   // Identical to TrackCord(), except that this function fills the
   // `parent_stack` and `parent_method` properties of the returned CordzInfo
@@ -181,6 +182,8 @@ class ABSL_LOCKABLE CordzInfo : public CordzHandle {
   // or RemovePrefix.
   CordzStatistics GetCordzStatistics() const;
 
+  int64_t sampling_stride() const { return sampling_stride_; }
+
  private:
   using SpinLock = absl::base_internal::SpinLock;
   using SpinLockHolder = ::absl::base_internal::SpinLockHolder;
@@ -199,7 +202,7 @@ class ABSL_LOCKABLE CordzInfo : public CordzHandle {
   static constexpr size_t kMaxStackDepth = 64;
 
   explicit CordzInfo(CordRep* rep, const CordzInfo* src,
-                     MethodIdentifier method);
+                     MethodIdentifier method, int64_t weight);
   ~CordzInfo() override;
 
   // Sets `rep_` without holding a lock.
@@ -250,12 +253,14 @@ class ABSL_LOCKABLE CordzInfo : public CordzHandle {
   const MethodIdentifier parent_method_;
   CordzUpdateTracker update_tracker_;
   const absl::Time create_time_;
+  const int64_t sampling_stride_;
 };
 
 inline ABSL_ATTRIBUTE_ALWAYS_INLINE void CordzInfo::MaybeTrackCord(
     InlineData& cord, MethodIdentifier method) {
-  if (ABSL_PREDICT_FALSE(cordz_should_profile())) {
-    TrackCord(cord, method);
+  auto stride = cordz_should_profile();
+  if (ABSL_PREDICT_FALSE(stride > 0)) {
+    TrackCord(cord, method, stride);
   }
 }