Export of internal Abseil changes

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a9ea60e9c0ccd744b6f12fd021dbedfe826dfe84 by Matt Kulukundis <kfm@google.com>:

Add an internal hook to allow keeping flags in sync with global state.

Rollforward, except continue including hashtablez_flags.h in absl_flags.h so users don't break.

PiperOrigin-RevId: 412198044

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183e5c440b68c797ce4a82102f94f41c97a14674 by Martijn Vels <mvels@google.com>:

Internal cleanups and changes

PiperOrigin-RevId: 412083793

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3740faf7c5a2e1723e3c7e4d1b3f3db7cbec6e61 by Abseil Team <absl-team@google.com>:

Mark Cord::Clear() with the ABSL_ATTRIBUTE_REINITIALIZES attribute.

This prevents false positives in the clang-tidy check bugprone-use-after-move; it allows Clear() to be called on a moved-from Cord without any warnings, and the Cord will thereafter be regarded as initialized again.

PiperOrigin-RevId: 412082757

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a730d3f4ba06b55ae50386920a0544592069ac01 by Abseil Team <absl-team@google.com>:

StrJoin: Support iterators that do not have an `operator->`

Allows using `StrJoin` with iterators that do not have an `operator->`.
The `operator->` requirement for input iterators was dropped in C++20.

PiperOrigin-RevId: 412066130

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6773c0ced2caa6a7855898298faecc584f3997ec by Andy Soffer <asoffer@google.com>:

Rollback of internal hook for keeping flags in sync with global state.

PiperOrigin-RevId: 411895027

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4e7016a2fb88ce97853ef85ad5b4f76998eacca1 by Matt Kulukundis <kfm@google.com>:

Add an internal hook to allow keeping flags in sync with global state.

PiperOrigin-RevId: 411867376

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2a7d4056e467b6b5d8a7aa9398d6cb5454c10fc5 by Martijn Vels <mvels@google.com>:

Internal change

PiperOrigin-RevId: 411806932
GitOrigin-RevId: a9ea60e9c0ccd744b6f12fd021dbedfe826dfe84
Change-Id: Ib35bb7b40774979ed2ad205bbb1744b1085eae78

2 files changed, 46 insertions, 0 deletions

diff --git a/absl/container/internal/hashtablez_sampler.cc b/absl/container/internal/hashtablez_sampler.cc
index 40cce047..1a3ca7cc 100644
--- a/absl/container/internal/hashtablez_sampler.cc
+++ b/absl/container/internal/hashtablez_sampler.cc
@@ -38,12 +38,18 @@ ABSL_CONST_INIT std::atomic<bool> g_hashtablez_enabled{
     false
 };
 ABSL_CONST_INIT std::atomic<int32_t> g_hashtablez_sample_parameter{1 << 10};
+std::atomic<HashtablezConfigListener> g_hashtablez_config_listener{nullptr};
 
 #if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 ABSL_PER_THREAD_TLS_KEYWORD absl::profiling_internal::ExponentialBiased
     g_exponential_biased_generator;
 #endif
 
+void TriggerHashtablezConfigListener() {
+  auto* listener = g_hashtablez_config_listener.load(std::memory_order_acquire);
+  if (listener != nullptr) listener();
+}
+
 }  // namespace
 
 #if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
@@ -163,11 +169,33 @@ void RecordInsertSlow(HashtablezInfo* info, size_t hash,
   info->size.fetch_add(1, std::memory_order_relaxed);
 }
 
+void SetHashtablezConfigListener(HashtablezConfigListener l) {
+  g_hashtablez_config_listener.store(l, std::memory_order_release);
+}
+
+bool IsHashtablezEnabled() {
+  return g_hashtablez_enabled.load(std::memory_order_acquire);
+}
+
 void SetHashtablezEnabled(bool enabled) {
+  SetHashtablezEnabledInternal(enabled);
+  TriggerHashtablezConfigListener();
+}
+
+void SetHashtablezEnabledInternal(bool enabled) {
   g_hashtablez_enabled.store(enabled, std::memory_order_release);
 }
 
+int32_t GetHashtablezSampleParameter() {
+  return g_hashtablez_sample_parameter.load(std::memory_order_acquire);
+}
+
 void SetHashtablezSampleParameter(int32_t rate) {
+  SetHashtablezSampleParameterInternal(rate);
+  TriggerHashtablezConfigListener();
+}
+
+void SetHashtablezSampleParameterInternal(int32_t rate) {
   if (rate > 0) {
     g_hashtablez_sample_parameter.store(rate, std::memory_order_release);
   } else {
@@ -176,7 +204,16 @@ void SetHashtablezSampleParameter(int32_t rate) {
   }
 }
 
+int32_t GetHashtablezMaxSamples() {
+  return GlobalHashtablezSampler().GetMaxSamples();
+}
+
 void SetHashtablezMaxSamples(int32_t max) {
+  SetHashtablezMaxSamplesInternal(max);
+  TriggerHashtablezConfigListener();
+}
+
+void SetHashtablezMaxSamplesInternal(int32_t max) {
   if (max > 0) {
     GlobalHashtablezSampler().SetMaxSamples(max);
   } else {
diff --git a/absl/container/internal/hashtablez_sampler.h b/absl/container/internal/hashtablez_sampler.h
index 91fcdb34..ee4d293e 100644
--- a/absl/container/internal/hashtablez_sampler.h
+++ b/absl/container/internal/hashtablez_sampler.h
@@ -258,14 +258,23 @@ using HashtablezSampler =
 // Returns a global Sampler.
 HashtablezSampler& GlobalHashtablezSampler();
 
+using HashtablezConfigListener = void (*)();
+void SetHashtablezConfigListener(HashtablezConfigListener l);
+
 // Enables or disables sampling for Swiss tables.
+bool IsHashtablezEnabled();
 void SetHashtablezEnabled(bool enabled);
+void SetHashtablezEnabledInternal(bool enabled);
 
 // Sets the rate at which Swiss tables will be sampled.
+int32_t GetHashtablezSampleParameter();
 void SetHashtablezSampleParameter(int32_t rate);
+void SetHashtablezSampleParameterInternal(int32_t rate);
 
 // Sets a soft max for the number of samples that will be kept.
+int32_t GetHashtablezMaxSamples();
 void SetHashtablezMaxSamples(int32_t max);
+void SetHashtablezMaxSamplesInternal(int32_t max);
 
 // Configuration override.
 // This allows process-wide sampling without depending on order of