Export of internal Abseil changes

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f9476c95cf7625d7b0fc4661f253b0aac4341044 by Abseil Team <absl-team@google.com>:

Add a test to verify that the new checksum field in Hashtablez is calculated

PiperOrigin-RevId: 356744293

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ff8a3612463000e8c3d451e50367a3c65cb6cf21 by Abseil Team <absl-team@google.com>:

Remove the implied support comment for port.h, attributes.h, and integral_types.h's C compatibility from the header documentations.

Abseil-cpp is a C++ library; this brings port.h, attributes.h, and integral_types.h, into our stance for the rest of Abseil (aka, no assurance of C compatibility)

There is no guarantee that future changes to port.h, attributes.h, and integral_types.h, and their dependencies, will remain compatible with C, even for macros and definitions that currently are.

PiperOrigin-RevId: 356727505

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be62292016381deee628dbb3f36cb6009bcc0282 by Abseil Team <absl-team@google.com>:

internal change

PiperOrigin-RevId: 356608125

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13b35f17171df3d6853ea7088797b3be611505fc by Evan Brown <ezb@google.com>:

Clarify the comments for CapacityToGrowth/GrowthToLowerboundCapacity methods to specify the intent that capacity should equal growth when `capacity+1 < kWidth`.

Also add testing for this behavior.

PiperOrigin-RevId: 356579041
GitOrigin-RevId: f9476c95cf7625d7b0fc4661f253b0aac4341044
Change-Id: Iadd094d109b4869998f2427319ef66d1cf1e8eff

absl/base/attributes.h

@@ -18,8 +18,6 @@
 // These macros are used within Abseil and allow the compiler to optimize, where
 // applicable, certain function calls.
 //
-// This file is used for both C and C++!
-//
 // Most macros here are exposing GCC or Clang features, and are stubbed out for
 // other compilers.
 //

absl/base/port.h

@@ -14,7 +14,6 @@
 //
 // This files is a forwarding header for other headers containing various
 // portability macros and functions.
-// This file is used for both C and C++!
 
 #ifndef ABSL_BASE_PORT_H_
 #define ABSL_BASE_PORT_H_

absl/container/internal/raw_hash_set.h

@@ -468,8 +468,16 @@ inline size_t NormalizeCapacity(size_t n) {
   return n ? ~size_t{} >> countl_zero(n) : 1;
 }
 
-// We use 7/8th as maximum load factor.
-// For 16-wide groups, that gives an average of two empty slots per group.
+// General notes on capacity/growth methods below:
+// - We use 7/8th as maximum load factor. For 16-wide groups, that gives an
+//   average of two empty slots per group.
+// - For (capacity+1) >= Group::kWidth, growth is 7/8*capacity.
+// - For (capacity+1) < Group::kWidth, growth == capacity. In this case, we
+//   never need to probe (the whole table fits in one group) so we don't need a
+//   load factor less than 1.
+
+// Given `capacity` of the table, returns the size (i.e. number of full slots)
+// at which we should grow the capacity.
 inline size_t CapacityToGrowth(size_t capacity) {
   assert(IsValidCapacity(capacity));
   // `capacity*7/8`
@@ -480,7 +488,7 @@ inline size_t CapacityToGrowth(size_t capacity) {
   return capacity - capacity / 8;
 }
 // From desired "growth" to a lowerbound of the necessary capacity.
-// Might not be a valid one and required NormalizeCapacity().
+// Might not be a valid one and requires NormalizeCapacity().
 inline size_t GrowthToLowerboundCapacity(size_t growth) {
   // `growth*8/7`
   if (Group::kWidth == 8 && growth == 7) {

absl/container/internal/raw_hash_set_test.cc

@@ -14,6 +14,7 @@
 
 #include "absl/container/internal/raw_hash_set.h"
 
+#include <atomic>
 #include <cmath>
 #include <cstdint>
 #include <deque>
@@ -22,6 +23,8 @@
 #include <numeric>
 #include <random>
 #include <string>
+#include <unordered_map>
+#include <unordered_set>
 
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
@@ -48,11 +51,10 @@ struct RawHashSetTestOnlyAccess {
 
 namespace {
 
-using ::testing::DoubleNear;
 using ::testing::ElementsAre;
+using ::testing::Eq;
 using ::testing::Ge;
 using ::testing::Lt;
-using ::testing::Optional;
 using ::testing::Pair;
 using ::testing::UnorderedElementsAre;
 
@@ -75,8 +77,14 @@ TEST(Util, GrowthAndCapacity) {
   for (size_t growth = 0; growth < 10000; ++growth) {
     SCOPED_TRACE(growth);
     size_t capacity = NormalizeCapacity(GrowthToLowerboundCapacity(growth));
-    // The capacity is large enough for `growth`
+    // The capacity is large enough for `growth`.
     EXPECT_THAT(CapacityToGrowth(capacity), Ge(growth));
+    // For (capacity+1) < kWidth, growth should equal capacity.
+    if (capacity + 1 < Group::kWidth) {
+      EXPECT_THAT(CapacityToGrowth(capacity), Eq(capacity));
+    } else {
+      EXPECT_THAT(CapacityToGrowth(capacity), Lt(capacity));
+    }
     if (growth != 0 && capacity > 1) {
       // There is no smaller capacity that works.
       EXPECT_THAT(CapacityToGrowth(capacity / 2), Lt(growth));
@@ -1875,18 +1883,34 @@ TEST(RawHashSamplerTest, Sample) {
 
   auto& sampler = HashtablezSampler::Global();
   size_t start_size = 0;
-  start_size += sampler.Iterate([&](const HashtablezInfo&) { ++start_size; });
+  std::unordered_set<const HashtablezInfo*> preexisting_info;
+  start_size += sampler.Iterate([&](const HashtablezInfo& info) {
+    preexisting_info.insert(&info);
+    ++start_size;
+  });
 
   std::vector<IntTable> tables;
   for (int i = 0; i < 1000000; ++i) {
     tables.emplace_back();
     tables.back().insert(1);
+    tables.back().insert(i % 5);
   }
   size_t end_size = 0;
-  end_size += sampler.Iterate([&](const HashtablezInfo&) { ++end_size; });
+  std::unordered_map<size_t, int> observed_checksums;
+  end_size += sampler.Iterate([&](const HashtablezInfo& info) {
+    if (preexisting_info.count(&info) == 0) {
+      observed_checksums[info.hashes_bitwise_xor.load(
+          std::memory_order_relaxed)]++;
+    }
+    ++end_size;
+  });
 
   EXPECT_NEAR((end_size - start_size) / static_cast<double>(tables.size()),
               0.01, 0.005);
+  EXPECT_EQ(observed_checksums.size(), 5);
+  for (const auto& [_, count] : observed_checksums) {
+    EXPECT_NEAR((100 * count) / static_cast<double>(tables.size()), 0.2, 0.05);
+  }
 }
 #endif  // ABSL_INTERNAL_HASHTABLEZ_SAMPLE
 

absl/status/status_test.cc

@@ -460,5 +460,4 @@ TEST(Status, Swap) {
   test_swap(no_payload, with_payload);
   test_swap(with_payload, no_payload);
 }
-
 }  // namespace