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, 38 insertions, 0 deletions

diff --git a/absl/strings/cord.cc b/absl/strings/cord.cc
index 8f0999f8..d33d6a0d 100644
--- a/absl/strings/cord.cc
+++ b/absl/strings/cord.cc
@@ -38,6 +38,7 @@
 #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_statistics.h"
 #include "absl/strings/internal/resize_uninitialized.h"
 #include "absl/strings/str_cat.h"
 #include "absl/strings/str_format.h"
@@ -426,6 +427,7 @@ void Cord::InlineRep::GetAppendRegion(char** region, size_t* size,
   CordRep* root = force_tree(max_length);
 
   if (PrepareAppendRegion(root, region, size, max_length)) {
+    UpdateCordzStatistics();
     return;
   }
 
@@ -460,6 +462,7 @@ void Cord::InlineRep::GetAppendRegion(char** region, size_t* size) {
   CordRep* root = force_tree(max_length);
 
   if (PrepareAppendRegion(root, region, size, max_length)) {
+    UpdateCordzStatistics();
     return;
   }
 
@@ -490,6 +493,27 @@ static bool RepMemoryUsageLeaf(const CordRep* rep, size_t* total_mem_usage) {
   return false;
 }
 
+void Cord::InlineRep::StartProfiling() {
+  CordRep* tree = as_tree();
+  auto* cordz_info = absl::cord_internal::CordzInfo::TrackCord(tree);
+  set_cordz_info(cordz_info);
+  cordz_info->RecordMetrics(size());
+}
+
+void Cord::InlineRep::StartProfiling(const Cord::InlineRep& src) {
+  CordRep* tree = as_tree();
+  absl::cord_internal::CordzInfo* parent =
+      src.is_profiled() ? src.cordz_info() : nullptr;
+  auto* cordz_info = absl::cord_internal::CordzInfo::TrackCord(tree, parent);
+  set_cordz_info(cordz_info);
+  cordz_info->RecordMetrics(size());
+}
+
+void Cord::InlineRep::UpdateCordzStatisticsSlow() {
+  CordRep* tree = as_tree();
+  data_.cordz_info()->RecordMetrics(tree->length);
+}
+
 void Cord::InlineRep::AssignSlow(const Cord::InlineRep& src) {
   UnrefTree();
 
@@ -497,11 +521,17 @@ void Cord::InlineRep::AssignSlow(const Cord::InlineRep& src) {
   if (is_tree()) {
     CordRep::Ref(tree());
     clear_cordz_info();
+    if (ABSL_PREDICT_FALSE(should_profile())) {
+      StartProfiling(src);
+    }
   }
 }
 
 void Cord::InlineRep::UnrefTree() {
   if (is_tree()) {
+    if (ABSL_PREDICT_FALSE(is_profiled())) {
+      absl::cord_internal::CordzInfo::UntrackCord(cordz_info());
+    }
     CordRep::Unref(tree());
   }
 }
@@ -552,6 +582,9 @@ template Cord::Cord(std::string&& src);
 // The destruction code is separate so that the compiler can determine
 // that it does not need to call the destructor on a moved-from Cord.
 void Cord::DestroyCordSlow() {
+  if (ABSL_PREDICT_FALSE(contents_.is_profiled())) {
+    absl::cord_internal::CordzInfo::UntrackCord(contents_.cordz_info());
+  }
   if (CordRep* tree = contents_.tree()) {
     CordRep::Unref(VerifyTree(tree));
   }
@@ -567,6 +600,10 @@ void Cord::Clear() {
 }
 
 Cord& Cord::operator=(absl::string_view src) {
+  if (ABSL_PREDICT_FALSE(contents_.is_profiled())) {
+    absl::cord_internal::CordzInfo::UntrackCord(contents_.cordz_info());
+    contents_.clear_cordz_info();
+  }
 
   const char* data = src.data();
   size_t length = src.size();
@@ -615,6 +652,7 @@ void Cord::InlineRep::AppendArray(const char* src_data, size_t src_size) {
     char* region;
     if (PrepareAppendRegion(root, &region, &appended, src_size)) {
       memcpy(region, src_data, appended);
+      UpdateCordzStatistics();
     }
   } else {
     // Try to fit in the inline buffer if possible.