Export of internal Abseil changes

--
9fc37c11b9e46287acef00ee06ed9adcba54dd13 by Greg Falcon <gfalcon@google.com>:

Rename absl::hash_internal::HashState to absl::hash_internal::MixingHashState.

Before this change, we had two classes named HashState: absl::HashState, the public API used for type erasure, and absl::hash_internal::HashState, the internal concrete implementation ordinarily used.

The internal class used to be named `CityHashState`, but we renamed it to `HashState` it when we changed underlying hash implementation to wyhash.  This inadvertent naming conflict made the code much harder to read, and this change intends to undo that.

PiperOrigin-RevId: 373481959

--
4aec55ffddebd085c239352a2e20721091f719a1 by Greg Falcon <gfalcon@google.com>:

Introduce absl::HashOf(), a convenience wrapper around absl::Hash that calculates hashes from the values of its arguments.

PiperOrigin-RevId: 373461406

--
86b5fd8db50bbc8bd0aa9258523527381fe0445d by Abseil Team <absl-team@google.com>:

Improve speed of BlockingCounter by making its most common path lock free.

With the new implementation, the fast path of BlockingCounter::DecrementCount()
is only a fetch_sub operation. This is most times much more efficient than the
previous implementation (full mutex lock/unlock). As a matter of fact, in most
actual usecases in practice, the waiter thread is already waiting on the
Wait() call when DecrementCount() is called, which makes Mutex::Unlock() take
the slow path as there's a waiter thread that it might need to wake up.

PiperOrigin-RevId: 373394164

--
65c876be5eac0cd32583ff8535ede4109d39cf3f by Martijn Vels <mvels@google.com>:

Move the 'sample copied cord' logic into MaybeTrackCord(),

This changes move the logic for selecting if a cord should remain being sampled from Cord to CordzInfo::MaybeTrackCord, and updates the documentation for the latter method.

PiperOrigin-RevId: 373363168

--
e84410bd0aada293a81dfb82656c952e209e21fb by Martijn Vels <mvels@google.com>:

Add check for the first call to cordz_should_profile() for each thread.

This prevents the first cord of a newly created thread to be always sampled, which is a 'bad' kind of determinism for sampling.

PiperOrigin-RevId: 373229768

--
bf09c589dc099ac8f4af780bf7e609c53c27574c by Samuel Benzaquen <sbenza@google.com>:

Refactor the Flags structure into an enum.
This gives us more control over the representation and allows for easier
merging during parsing.

PiperOrigin-RevId: 373163038

--
b947b0c51083b7b6508284b5d31819596c91729e by Derek Mauro <dmauro@google.com>:

Fixes warnings about shadowed variables
Fixes #956

PiperOrigin-RevId: 373158133
GitOrigin-RevId: 9fc37c11b9e46287acef00ee06ed9adcba54dd13
Change-Id: I91f35699f9bf439d1a870c6493946a310afe088c

4 files changed, 74 insertions, 30 deletions

diff --git a/absl/hash/hash.h b/absl/hash/hash.h
index 5de132ca..69c44fde 100644
--- a/absl/hash/hash.h
+++ b/absl/hash/hash.h
@@ -73,6 +73,8 @@
 #ifndef ABSL_HASH_HASH_H_
 #define ABSL_HASH_HASH_H_
 
+#include <tuple>
+
 #include "absl/hash/internal/hash.h"
 
 namespace absl {
@@ -214,6 +216,26 @@ ABSL_NAMESPACE_BEGIN
 template <typename T>
 using Hash = absl::hash_internal::Hash<T>;
 
+// HashOf
+//
+// absl::HashOf() is a helper that generates a hash from the values of its
+// arguments.  It dispatches to absl::Hash directly, as follows:
+//  * HashOf(t) == absl::Hash<T>{}(t)
+//  * HashOf(a, b, c) == HashOf(std::make_tuple(a, b, c))
+//
+// HashOf(a1, a2, ...) == HashOf(b1, b2, ...) is guaranteed when
+//  * The argument lists have pairwise identical C++ types
+//  * a1 == b1 && a2 == b2 && ...
+//
+// The requirement that the arguments match in both type and value is critical.
+// It means that `a == b` does not necessarily imply `HashOf(a) == HashOf(b)` if
+// `a` and `b` have different types. For example, `HashOf(2) != HashOf(2.0)`.
+template <typename... Types>
+size_t HashOf(const Types&... values) {
+  auto tuple = std::tie(values...);
+  return absl::Hash<decltype(tuple)>{}(tuple);
+}
+
 // HashState
 //
 // A type erased version of the hash state concept, for use in user-defined
diff --git a/absl/hash/hash_test.cc b/absl/hash/hash_test.cc
index 1d2e6cf0..02b7733d 100644
--- a/absl/hash/hash_test.cc
+++ b/absl/hash/hash_test.cc
@@ -973,4 +973,26 @@ TEST(HashTest, DoesNotUseImplicitConversionsToBool) {
             absl::Hash<ValueWithBoolConversion>()(ValueWithBoolConversion{1}));
 }
 
+TEST(HashOf, MatchesHashForSingleArgument) {
+  std::string s = "forty two";
+  int i = 42;
+  double d = 42.0;
+  std::tuple<int, int> t{4, 2};
+
+  EXPECT_EQ(absl::HashOf(s), absl::Hash<std::string>{}(s));
+  EXPECT_EQ(absl::HashOf(i), absl::Hash<int>{}(i));
+  EXPECT_EQ(absl::HashOf(d), absl::Hash<double>{}(d));
+  EXPECT_EQ(absl::HashOf(t), (absl::Hash<std::tuple<int, int>>{}(t)));
+}
+
+TEST(HashOf, MatchesHashOfTupleForMultipleArguments) {
+  std::string hello = "hello";
+  std::string world = "world";
+
+  EXPECT_EQ(absl::HashOf(), absl::HashOf(std::make_tuple()));
+  EXPECT_EQ(absl::HashOf(hello), absl::HashOf(std::make_tuple(hello)));
+  EXPECT_EQ(absl::HashOf(hello, world),
+            absl::HashOf(std::make_tuple(hello, world)));
+}
+
 }  // namespace
diff --git a/absl/hash/internal/hash.cc b/absl/hash/internal/hash.cc
index 1433eb9d..06f53a59 100644
--- a/absl/hash/internal/hash.cc
+++ b/absl/hash/internal/hash.cc
@@ -18,9 +18,8 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace hash_internal {
 
-uint64_t HashState::CombineLargeContiguousImpl32(uint64_t state,
-                                                 const unsigned char* first,
-                                                 size_t len) {
+uint64_t MixingHashState::CombineLargeContiguousImpl32(
+    uint64_t state, const unsigned char* first, size_t len) {
   while (len >= PiecewiseChunkSize()) {
     state =
         Mix(state, absl::hash_internal::CityHash32(reinterpret_cast<const char*>(first),
@@ -33,9 +32,8 @@ uint64_t HashState::CombineLargeContiguousImpl32(uint64_t state,
                                std::integral_constant<int, 4>{});
 }
 
-uint64_t HashState::CombineLargeContiguousImpl64(uint64_t state,
-                                                 const unsigned char* first,
-                                                 size_t len) {
+uint64_t MixingHashState::CombineLargeContiguousImpl64(
+    uint64_t state, const unsigned char* first, size_t len) {
   while (len >= PiecewiseChunkSize()) {
     state = Mix(state, Hash64(first, PiecewiseChunkSize()));
     len -= PiecewiseChunkSize();
@@ -46,7 +44,7 @@ uint64_t HashState::CombineLargeContiguousImpl64(uint64_t state,
                                std::integral_constant<int, 8>{});
 }
 
-ABSL_CONST_INIT const void* const HashState::kSeed = &kSeed;
+ABSL_CONST_INIT const void* const MixingHashState::kSeed = &kSeed;
 
 // The salt array used by Wyhash. This array is NOT the mechanism used to make
 // absl::Hash non-deterministic between program invocations.  See `Seed()` for
@@ -61,7 +59,7 @@ constexpr uint64_t kWyhashSalt[5] = {
     uint64_t{0x452821E638D01377},
 };
 
-uint64_t HashState::WyhashImpl(const unsigned char* data, size_t len) {
+uint64_t MixingHashState::WyhashImpl(const unsigned char* data, size_t len) {
   return Wyhash(data, len, Seed(), kWyhashSalt);
 }
 
diff --git a/absl/hash/internal/hash.h b/absl/hash/internal/hash.h
index 7fb0af0b..69dbbc6b 100644
--- a/absl/hash/internal/hash.h
+++ b/absl/hash/internal/hash.h
@@ -379,7 +379,7 @@ template <typename H, typename... Ts>
 // This SFINAE gets MSVC confused under some conditions. Let's just disable it
 // for now.
 H
-#else  // _MSC_VER
+#else   // _MSC_VER
 typename std::enable_if<absl::conjunction<is_hashable<Ts>...>::value, H>::type
 #endif  // _MSC_VER
 AbslHashValue(H hash_state, const std::tuple<Ts...>& t) {
@@ -714,8 +714,8 @@ template <typename T>
 struct is_hashable
     : std::integral_constant<bool, HashSelect::template Apply<T>::value> {};
 
-// HashState
-class ABSL_DLL HashState : public HashStateBase<HashState> {
+// MixingHashState
+class ABSL_DLL MixingHashState : public HashStateBase<MixingHashState> {
   // absl::uint128 is not an alias or a thin wrapper around the intrinsic.
   // We use the intrinsic when available to improve performance.
 #ifdef ABSL_HAVE_INTRINSIC_INT128
@@ -734,22 +734,23 @@ class ABSL_DLL HashState : public HashStateBase<HashState> {
 
  public:
   // Move only
-  HashState(HashState&&) = default;
-  HashState& operator=(HashState&&) = default;
+  MixingHashState(MixingHashState&&) = default;
+  MixingHashState& operator=(MixingHashState&&) = default;
 
-  // HashState::combine_contiguous()
+  // MixingHashState::combine_contiguous()
   //
   // Fundamental base case for hash recursion: mixes the given range of bytes
   // into the hash state.
-  static HashState combine_contiguous(HashState hash_state,
-                                      const unsigned char* first, size_t size) {
-    return HashState(
+  static MixingHashState combine_contiguous(MixingHashState hash_state,
+                                            const unsigned char* first,
+                                            size_t size) {
+    return MixingHashState(
         CombineContiguousImpl(hash_state.state_, first, size,
                               std::integral_constant<int, sizeof(size_t)>{}));
   }
-  using HashState::HashStateBase::combine_contiguous;
+  using MixingHashState::HashStateBase::combine_contiguous;
 
-  // HashState::hash()
+  // MixingHashState::hash()
   //
   // For performance reasons in non-opt mode, we specialize this for
   // integral types.
@@ -761,24 +762,24 @@ class ABSL_DLL HashState : public HashStateBase<HashState> {
     return static_cast<size_t>(Mix(Seed(), static_cast<uint64_t>(value)));
   }
 
-  // Overload of HashState::hash()
+  // Overload of MixingHashState::hash()
   template <typename T, absl::enable_if_t<!IntegralFastPath<T>::value, int> = 0>
   static size_t hash(const T& value) {
-    return static_cast<size_t>(combine(HashState{}, value).state_);
+    return static_cast<size_t>(combine(MixingHashState{}, value).state_);
   }
 
  private:
   // Invoked only once for a given argument; that plus the fact that this is
   // move-only ensures that there is only one non-moved-from object.
-  HashState() : state_(Seed()) {}
+  MixingHashState() : state_(Seed()) {}
 
   // Workaround for MSVC bug.
   // We make the type copyable to fix the calling convention, even though we
   // never actually copy it. Keep it private to not affect the public API of the
   // type.
-  HashState(const HashState&) = default;
+  MixingHashState(const MixingHashState&) = default;
 
-  explicit HashState(uint64_t state) : state_(state) {}
+  explicit MixingHashState(uint64_t state) : state_(state) {}
 
   // Implementation of the base case for combine_contiguous where we actually
   // mix the bytes into the state.
@@ -793,7 +794,6 @@ class ABSL_DLL HashState : public HashStateBase<HashState> {
                                         std::integral_constant<int, 8>
                                         /* sizeof_size_t */);
 
-
   // Slow dispatch path for calls to CombineContiguousImpl with a size argument
   // larger than PiecewiseChunkSize().  Has the same effect as calling
   // CombineContiguousImpl() repeatedly with the chunk stride size.
@@ -911,8 +911,8 @@ class ABSL_DLL HashState : public HashStateBase<HashState> {
   uint64_t state_;
 };
 
-// HashState::CombineContiguousImpl()
-inline uint64_t HashState::CombineContiguousImpl(
+// MixingHashState::CombineContiguousImpl()
+inline uint64_t MixingHashState::CombineContiguousImpl(
     uint64_t state, const unsigned char* first, size_t len,
     std::integral_constant<int, 4> /* sizeof_size_t */) {
   // For large values we use CityHash, for small ones we just use a
@@ -934,8 +934,8 @@ inline uint64_t HashState::CombineContiguousImpl(
   return Mix(state, v);
 }
 
-// Overload of HashState::CombineContiguousImpl()
-inline uint64_t HashState::CombineContiguousImpl(
+// Overload of MixingHashState::CombineContiguousImpl()
+inline uint64_t MixingHashState::CombineContiguousImpl(
     uint64_t state, const unsigned char* first, size_t len,
     std::integral_constant<int, 8> /* sizeof_size_t */) {
   // For large values we use Wyhash or CityHash depending on the platform, for
@@ -976,7 +976,9 @@ struct PoisonedHash : private AggregateBarrier {
 
 template <typename T>
 struct HashImpl {
-  size_t operator()(const T& value) const { return HashState::hash(value); }
+  size_t operator()(const T& value) const {
+    return MixingHashState::hash(value);
+  }
 };
 
 template <typename T>