Export of internal Abseil changes.

--
5804cc13b413412988248835459b90cd15ec43d9 by Abseil Team <absl-team@google.com>:

Mark raw_hash_set::clear() with the ABSL_ATTRIBUTE_REINITIALIZES attribute.

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

PiperOrigin-RevId: 230717196

--
ff5961a5600ae19b69a9cba6912126cdf2858f38 by CJ Johnson <johnsoncj@google.com>:

Swaps DisableIfIntegral<> for EnableIfInputIterator<> for Iterator member functions of InlinedVector

PiperOrigin-RevId: 230559521

--
3f9754ccbeecbd40f235c6f2465279e045ff51d9 by Derek Mauro <dmauro@google.com>:

Import GitHub PR 254
https://github.com/abseil/abseil-cpp/pull/254

Fixes warnings from -Wclass-memaccess (base_internal::ThreadIdentity?
with no trivial copy-assignment).

PiperOrigin-RevId: 230536048

--
8af03a654ce9a4a7f55384bc7eb1ed64878ac2ec by Chris Kennelly <ckennelly@google.com>:

absl: cap SpinLock backoff to 4ms

The current backoff logic has 3 problems:
1. It can produce too high values (up to 256ms), which can negatively
affect tail latency. The value was chosen long time ago and now it's
a good idea to reconsider it.
2. It does not have low bound, so on any iteration it can produce
a very small value that will lead to unnecessary cpu consumption.
3. It does not increase low bound with the number of iterations.
So if the SpinLock is actually somehow locked for a very prolonged time,
a waiter can still wake periodically.

Rework the logic to solve these problems.
Add lower bound of 128us, no code should rely on absence of episodic
delays in this range as they can occur everywhere.
Lower upper bound to 4ms. A thread sleeping for 4ms does not consume
significant cpu time (see below).
Grow lower bound with the number of iterations.

This is cpu consumption of a process doing usleep(x) in a loop
(sampled with ps):

    64us -> 4.0%
   128us -> 2.7%
   256us -> 3.5%
   512us -> 2.8%
  1024us -> 1.6%
  2048us -> 0.6%
  4096us -> 0.3%
  8192us -> 0.0%

Few millisecond sleeps do not consume significant time.

PiperOrigin-RevId: 230534015

--
37ebba92289ca556cb2412cd8b3cb4c1ead3def7 by Samuel Benzaquen <sbenza@google.com>:

Add override and dispose hooks to the hashtable sampler.

PiperOrigin-RevId: 230353438

--
89c8f90175233ce9964eb3412df04e8a3cff0c0f by Andy Getzendanner <durandal@google.com>:

Fix a comment typo.

PiperOrigin-RevId: 229986838
GitOrigin-RevId: 5804cc13b413412988248835459b90cd15ec43d9
Change-Id: Iedb5e2cc9c0b924635c1c87b537780ab6b5b899f

7 files changed, 168 insertions, 2 deletions

diff --git a/absl/container/internal/hashtablez_force_sampling.cc b/absl/container/internal/hashtablez_force_sampling.cc
new file mode 100644
index 00000000..868976ec
--- /dev/null
+++ b/absl/container/internal/hashtablez_force_sampling.cc
@@ -0,0 +1,24 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/container/internal/hashtablez_sampler.h"
+
+namespace absl {
+namespace container_internal {
+
+// See hashtablez_sampler.h for details.
+extern "C" const bool kAbslContainerInternalSampleEverything = true;
+
+}  // namespace container_internal
+}  // namespace absl
diff --git a/absl/container/internal/hashtablez_force_sampling_test.cc b/absl/container/internal/hashtablez_force_sampling_test.cc
new file mode 100644
index 00000000..9ff1046a
--- /dev/null
+++ b/absl/container/internal/hashtablez_force_sampling_test.cc
@@ -0,0 +1,60 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <cstddef>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/container/internal/hashtablez_sampler.h"
+
+namespace absl {
+namespace container_internal {
+
+class HashtablezInfoHandlePeer {
+ public:
+  static bool IsSampled(const HashtablezInfoHandle& h) {
+    return h.info_ != nullptr;
+  }
+};
+
+namespace {
+
+bool samples[3]{true, true, true};
+
+// We do this test in a global object to test that this works even before main.
+struct Global {
+  Global() {
+    // By default it is sampled.
+    samples[0] = HashtablezInfoHandlePeer::IsSampled(Sample());
+
+    // Even with a large parameter, it is sampled.
+    SetHashtablezSampleParameter(100);
+    samples[1] = HashtablezInfoHandlePeer::IsSampled(Sample());
+
+    // Even if we turn it off, it is still sampled.
+    SetHashtablezEnabled(false);
+    samples[2] = HashtablezInfoHandlePeer::IsSampled(Sample());
+  }
+} global;
+
+TEST(kAbslContainerInternalSampleEverything, Works) {
+  EXPECT_THAT(samples, testing::Each(true));
+  EXPECT_TRUE(kAbslContainerInternalSampleEverything);
+  // One more after main()
+  EXPECT_TRUE(HashtablezInfoHandlePeer::IsSampled(Sample()));
+}
+
+}  // namespace
+}  // namespace container_internal
+}  // namespace absl
diff --git a/absl/container/internal/hashtablez_sampler.cc b/absl/container/internal/hashtablez_sampler.cc
index 1ba95645..7c411140 100644
--- a/absl/container/internal/hashtablez_sampler.cc
+++ b/absl/container/internal/hashtablez_sampler.cc
@@ -116,6 +116,11 @@ HashtablezSampler& HashtablezSampler::Global() {
   return *sampler;
 }
 
+HashtablezSampler::DisposeCallback HashtablezSampler::SetDisposeCallback(
+    DisposeCallback f) {
+  return dispose_.exchange(f, std::memory_order_relaxed);
+}
+
 HashtablezInfo::HashtablezInfo() { PrepareForSampling(); }
 HashtablezInfo::~HashtablezInfo() = default;
 
@@ -138,7 +143,7 @@ void HashtablezInfo::PrepareForSampling() {
 }
 
 HashtablezSampler::HashtablezSampler()
-    : dropped_samples_(0), size_estimate_(0), all_(nullptr) {
+    : dropped_samples_(0), size_estimate_(0), all_(nullptr), dispose_(nullptr) {
   absl::MutexLock l(&graveyard_.init_mu);
   graveyard_.dead = &graveyard_;
 }
@@ -161,6 +166,10 @@ void HashtablezSampler::PushNew(HashtablezInfo* sample) {
 }
 
 void HashtablezSampler::PushDead(HashtablezInfo* sample) {
+  if (auto* dispose = dispose_.load(std::memory_order_relaxed)) {
+    dispose(*sample);
+  }
+
   absl::MutexLock graveyard_lock(&graveyard_.init_mu);
   absl::MutexLock sample_lock(&sample->init_mu);
   sample->dead = graveyard_.dead;
@@ -220,6 +229,11 @@ int64_t HashtablezSampler::Iterate(
 }
 
 HashtablezInfo* SampleSlow(int64_t* next_sample) {
+  if (kAbslContainerInternalSampleEverything) {
+    *next_sample = 1;
+    return HashtablezSampler::Global().Register();
+  }
+
   bool first = *next_sample < 0;
   *next_sample = GetGeometricVariable(
       g_hashtablez_sample_parameter.load(std::memory_order_relaxed));
diff --git a/absl/container/internal/hashtablez_sampler.h b/absl/container/internal/hashtablez_sampler.h
index c42f1842..126a0ade 100644
--- a/absl/container/internal/hashtablez_sampler.h
+++ b/absl/container/internal/hashtablez_sampler.h
@@ -183,6 +183,13 @@ class HashtablezSampler {
   // Unregisters the sample.
   void Unregister(HashtablezInfo* sample);
 
+  // The dispose callback will be called on all samples the moment they are
+  // being unregistered. Only affects samples that are unregistered after the
+  // callback has been set.
+  // Returns the previous callback.
+  using DisposeCallback = void (*)(const HashtablezInfo&);
+  DisposeCallback SetDisposeCallback(DisposeCallback f);
+
   // Iterates over all the registered `StackInfo`s.  Returning the number of
   // samples that have been dropped.
   int64_t Iterate(const std::function<void(const HashtablezInfo& stack)>& f);
@@ -222,6 +229,8 @@ class HashtablezSampler {
   //
   std::atomic<HashtablezInfo*> all_;
   HashtablezInfo graveyard_;
+
+  std::atomic<DisposeCallback> dispose_;
 };
 
 // Enables or disables sampling for Swiss tables.
@@ -233,6 +242,13 @@ void SetHashtablezSampleParameter(int32_t rate);
 // Sets a soft max for the number of samples that will be kept.
 void SetHashtablezMaxSamples(int32_t max);
 
+// Configuration override.
+// This allows process-wide sampling without depending on order of
+// initialization of static storage duration objects.
+// The definition of this constant is weak, which allows us to inject a
+// different value for it at link time.
+extern "C" const bool kAbslContainerInternalSampleEverything;
+
 }  // namespace container_internal
 }  // namespace absl
 
diff --git a/absl/container/internal/hashtablez_sampler_force_weak_definition.cc b/absl/container/internal/hashtablez_sampler_force_weak_definition.cc
new file mode 100644
index 00000000..38a3f260
--- /dev/null
+++ b/absl/container/internal/hashtablez_sampler_force_weak_definition.cc
@@ -0,0 +1,27 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/container/internal/hashtablez_sampler.h"
+
+#include "absl/base/attributes.h"
+
+namespace absl {
+namespace container_internal {
+
+// See hashtablez_sampler.h for details.
+extern "C" ABSL_ATTRIBUTE_WEAK const bool
+    kAbslContainerInternalSampleEverything = false;
+
+}  // namespace container_internal
+}  // namespace absl
diff --git a/absl/container/internal/hashtablez_sampler_test.cc b/absl/container/internal/hashtablez_sampler_test.cc
index 31e7641a..f9ee941a 100644
--- a/absl/container/internal/hashtablez_sampler_test.cc
+++ b/absl/container/internal/hashtablez_sampler_test.cc
@@ -302,6 +302,31 @@ TEST(HashtablezSamplerTest, MultiThreaded) {
   stop.Notify();
 }
 
+TEST(HashtablezSamplerTest, Callback) {
+  HashtablezSampler sampler;
+
+  auto* info1 = Register(&sampler, 1);
+  auto* info2 = Register(&sampler, 2);
+
+  static const HashtablezInfo* expected;
+
+  auto callback = [](const HashtablezInfo& info) {
+    // We can't use `info` outside of this callback because the object will be
+    // disposed as soon as we return from here.
+    EXPECT_EQ(&info, expected);
+  };
+
+  // Set the callback.
+  EXPECT_EQ(sampler.SetDisposeCallback(callback), nullptr);
+  expected = info1;
+  sampler.Unregister(info1);
+
+  // Unset the callback.
+  EXPECT_EQ(callback, sampler.SetDisposeCallback(nullptr));
+  expected = nullptr;  // no more calls.
+  sampler.Unregister(info2);
+}
+
 }  // namespace
 }  // namespace container_internal
 }  // namespace absl
diff --git a/absl/container/internal/raw_hash_set.h b/absl/container/internal/raw_hash_set.h
index 8f6469ff..8e3fa02d 100644
--- a/absl/container/internal/raw_hash_set.h
+++ b/absl/container/internal/raw_hash_set.h
@@ -1035,7 +1035,7 @@ class raw_hash_set {
   size_t capacity() const { return capacity_; }
   size_t max_size() const { return (std::numeric_limits<size_t>::max)(); }
 
-  void clear() {
+  ABSL_ATTRIBUTE_REINITIALIZES void clear() {
     // Iterating over this container is O(bucket_count()). When bucket_count()
     // is much greater than size(), iteration becomes prohibitively expensive.
     // For clear() it is more important to reuse the allocated array when the