Introduce a kTotalMorePrecise accounting mode for Cord::EstimatedMemoryUsage(). This mode avoids double-counting blocks that a Cord references more than once; otherwise it is similar to the existing kTotal mode.

There's no change to the existing kTotal or kFairShare accounting modes.

PiperOrigin-RevId: 544378591
Change-Id: I7b4ae55cd93d631194e59a9cd0ff07f47611219e

1 files changed, 18 insertions, 0 deletions

diff --git a/absl/strings/cord_analysis.h b/absl/strings/cord_analysis.h
index 7041ad1a..9b9527a5 100644
--- a/absl/strings/cord_analysis.h
+++ b/absl/strings/cord_analysis.h
@@ -31,6 +31,24 @@ namespace cord_internal {
 size_t GetEstimatedMemoryUsage(const CordRep* rep);
 
 // Returns the *approximate* number of bytes held in full or in part by this
+// Cord for the distinct memory held by this cord. This is similar to
+// `GetEstimatedMemoryUsage()`, except that if the cord has multiple references
+// to the same memory, that memory is only counted once.
+//
+// For example:
+//   absl::Cord cord;
+//   cord.append(some_other_cord);
+//   cord.append(some_other_cord);
+//    // Calls GetEstimatedMemoryUsage() and counts `other_cord` twice:
+//   cord.EstimatedMemoryUsage(kTotal);
+//    // Calls GetMorePreciseMemoryUsage() and counts `other_cord` once:
+//   cord.EstimatedMemoryUsage(kTotalMorePrecise);
+//
+// This is more expensive than `GetEstimatedMemoryUsage()` as it requires
+// deduplicating all memory references.
+size_t GetMorePreciseMemoryUsage(const CordRep* rep);
+
+// Returns the *approximate* number of bytes held in full or in part by this
 // CordRep weighted by the sharing ratio of that data. For example, if some data
 // edge is shared by 4 different Cords, then each cord is attribute 1/4th of
 // the total memory usage as a 'fair share' of the total memory usage.