Export of internal Abseil changes

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7f5caec21a1a88db6486b8bc2e5f6d5baba076ed by Derek Mauro <dmauro@google.com>:

Tag absl::StatusOr with [[nodiscard]] when it is available

[[nodiscard]] provides better diagnostics on classes than the current
ABSL_MUST_USE_RESULT, which expands to
__attribute__((warn_unused_result))

Ideally we would make ABSL_MUST_USE_RESULT expand to [[nodiscard]], but
we would need to fix all code to build with [[nodiscard]] first.

PiperOrigin-RevId: 422628161

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236be69f0f34ccaa3adc831075613847797e6557 by Jorg Brown <jorg@google.com>:

Make sure all of absl/strings compiles even with -Wsign-compare and -Wconversion warnings.

PiperOrigin-RevId: 422573904

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005669883a8794e6d19dc4bbb4f0e18032e2fbc9 by Chris Kennelly <ckennelly@google.com>:

Include sampling stride in hashtable sampling data.

This allows us to weight each sample to control for our sampling rate.

PiperOrigin-RevId: 421886935

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78046ce6b429b9f5b6c97b05e8448a791db93bbe by Abseil Team <absl-team@google.com>:

Use __builtin_bit_cast for absl::bit_cast when possible

This makes absl::bit_cast match the requirements of the standard when compiler support exists.

PiperOrigin-RevId: 421883999

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f397461f4bbeabd32437df0f2275663aeb51adb2 by Derek Mauro <dmauro@google.com>:

Tag absl::Status with [[nodiscard]] when it is available

[[nodiscard]] provides better diagnostics on classes than the current
ABSL_MUST_USE_RESULT, which expands to
__attribute__((warn_unused_result))

Ideally we would make ABSL_MUST_USE_RESULT expand to [[nodiscard]], but
we would need to fix all code to build with [[nodiscard]] first.

PiperOrigin-RevId: 421825565
GitOrigin-RevId: 7f5caec21a1a88db6486b8bc2e5f6d5baba076ed
Change-Id: I760b45b68f6012809c70c2a584e4144a99f98733

1 files changed, 23 insertions, 11 deletions

diff --git a/absl/container/internal/hashtablez_sampler.cc b/absl/container/internal/hashtablez_sampler.cc
index 1d24db5f..322e0547 100644
--- a/absl/container/internal/hashtablez_sampler.cc
+++ b/absl/container/internal/hashtablez_sampler.cc
@@ -27,6 +27,7 @@
 #include "absl/profiling/internal/exponential_biased.h"
 #include "absl/profiling/internal/sample_recorder.h"
 #include "absl/synchronization/mutex.h"
+#include "absl/utility/utility.h"
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
@@ -53,7 +54,7 @@ void TriggerHashtablezConfigListener() {
 }  // namespace
 
 #if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
-ABSL_PER_THREAD_TLS_KEYWORD int64_t global_next_sample = 0;
+ABSL_PER_THREAD_TLS_KEYWORD SamplingState global_next_sample = {0, 0};
 #endif  // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 
 HashtablezSampler& GlobalHashtablezSampler() {
@@ -64,7 +65,8 @@ HashtablezSampler& GlobalHashtablezSampler() {
 HashtablezInfo::HashtablezInfo() = default;
 HashtablezInfo::~HashtablezInfo() = default;
 
-void HashtablezInfo::PrepareForSampling(size_t inline_element_size_value) {
+void HashtablezInfo::PrepareForSampling(int64_t stride,
+                                        size_t inline_element_size_value) {
   capacity.store(0, std::memory_order_relaxed);
   size.store(0, std::memory_order_relaxed);
   num_erases.store(0, std::memory_order_relaxed);
@@ -77,6 +79,7 @@ void HashtablezInfo::PrepareForSampling(size_t inline_element_size_value) {
   max_reserve.store(0, std::memory_order_relaxed);
 
   create_time = absl::Now();
+  weight = stride;
   // The inliner makes hardcoded skip_count difficult (especially when combined
   // with LTO).  We use the ability to exclude stacks by regex when encoding
   // instead.
@@ -105,23 +108,32 @@ static bool ShouldForceSampling() {
   return state == kForce;
 }
 
-HashtablezInfo* SampleSlow(int64_t* next_sample, size_t inline_element_size) {
+HashtablezInfo* SampleSlow(SamplingState& next_sample,
+                           size_t inline_element_size) {
   if (ABSL_PREDICT_FALSE(ShouldForceSampling())) {
-    *next_sample = 1;
+    next_sample.next_sample = 1;
+    const int64_t old_stride = exchange(next_sample.sample_stride, 1);
     HashtablezInfo* result =
-        GlobalHashtablezSampler().Register(inline_element_size);
+        GlobalHashtablezSampler().Register(old_stride, inline_element_size);
     return result;
   }
 
 #if !defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
-  *next_sample = std::numeric_limits<int64_t>::max();
+  next_sample = {
+      std::numeric_limits<int64_t>::max(),
+      std::numeric_limits<int64_t>::max(),
+  };
   return nullptr;
 #else
-  bool first = *next_sample < 0;
-  *next_sample = g_exponential_biased_generator.GetStride(
+  bool first = next_sample.next_sample < 0;
+
+  const int64_t next_stride = g_exponential_biased_generator.GetStride(
       g_hashtablez_sample_parameter.load(std::memory_order_relaxed));
+
+  next_sample.next_sample = next_stride;
+  const int64_t old_stride = exchange(next_sample.sample_stride, next_stride);
   // Small values of interval are equivalent to just sampling next time.
-  ABSL_ASSERT(*next_sample >= 1);
+  ABSL_ASSERT(next_stride >= 1);
 
   // g_hashtablez_enabled can be dynamically flipped, we need to set a threshold
   // low enough that we will start sampling in a reasonable time, so we just use
@@ -131,11 +143,11 @@ HashtablezInfo* SampleSlow(int64_t* next_sample, size_t inline_element_size) {
   // We will only be negative on our first count, so we should just retry in
   // that case.
   if (first) {
-    if (ABSL_PREDICT_TRUE(--*next_sample > 0)) return nullptr;
+    if (ABSL_PREDICT_TRUE(--next_sample.next_sample > 0)) return nullptr;
     return SampleSlow(next_sample, inline_element_size);
   }
 
-  return GlobalHashtablezSampler().Register(inline_element_size);
+  return GlobalHashtablezSampler().Register(old_stride, inline_element_size);
 #endif
 }