Export of internal Abseil changes.

--
5f1cf6547231f1b1daad6d1b785df6b0b999b3c9 by Samuel Benzaquen <sbenza@google.com>:

Fix uninitialized member in the `iterator` class by using a union of the two
possible states of the iterator.
This silences a Wuninitialized warning in gcc>=7.

PiperOrigin-RevId: 228175148

--
98b4e3204c0ec3cfd4cb037e24d443ea4b63fc84 by CJ Johnson <johnsoncj@google.com>:

Factors out the implementation of InlinedVector::swap(...) into a private member function

PiperOrigin-RevId: 228173383

--
f1432ad3a8b05285c6d55bc4754cfae765485b7f by Abseil Team <absl-team@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 227891984

--
03fc00c7a4efc6000e6d9125cb2e252bffda76fe by Andy Getzendanner <durandal@google.com>:

Add a missing linebreak to a comment and markdownify two unordered lists.

PiperOrigin-RevId: 227861389

--
0d66c9afba4fc9aa52e61d9fb410e165018a7b48 by Abseil Team <absl-team@google.com>:

Add an API to register a new source for the cycle clock.

PiperOrigin-RevId: 227779218

--
14d3f9b70c8818b8541e5fb2f6ca4c59d479de31 by Andy Getzendanner <durandal@google.com>:

Correct a typo in a stripping marker.

PiperOrigin-RevId: 227750014

--
59df88740f4e315beb57a8772f8bcf7879440c74 by Matt Kulukundis <kfm@google.com>:

Switch thread local handling to be more cross platform

PiperOrigin-RevId: 227695133

--
75deed5bfcb5c42534e933f104aa7d94e11e348d by Abseil Team <absl-team@google.com>:

Rollback workaround toolchain bug for incorrect handling of thread_local in inline
functions

PiperOrigin-RevId: 227689133

--
54994bf0afec026e6e0e7a199df0bbb4b7d9a4aa by Derek Mauro <dmauro@google.com>:

Add -pthread to linkopts where it actually belongs, on the library
that uses it.
Fixes https://github.com/abseil/abseil-cpp/issues/240.

PiperOrigin-RevId: 227612492

--
893875f3536b7e0a1bad993aa6b2e083abb3b25a by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 227582833

--
506c9b8e9002ca3389c7040473b68d4cbf94bdcc by Matt Kulukundis <kfm@google.com>:

Workaround toolchain bug for incorrect handling of thread_local in inline
functions

PiperOrigin-RevId: 227561449

--
29ee90d96dfe3114cf93f9bb92ea0cc9e768a407 by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 227054634
GitOrigin-RevId: 5f1cf6547231f1b1daad6d1b785df6b0b999b3c9
Change-Id: Ibc90566d92ee6e0ad7e150f513ec7f5d22ec0a94

41 files changed, 253 insertions, 178 deletions

diff --git a/absl/UPGRADES.md b/absl/UPGRADES.md
deleted file mode 100644
index edbc4dc4dd32..000000000000
--- a/absl/UPGRADES.md
+++ /dev/null
@@ -1,17 +0,0 @@
-# C++ Upgrade Tools
-
-Abseil may occassionally release API-breaking changes. As noted in our
-[Compatibility Guidelines][compatibility-guide], we will aim to provide a tool
-to do the work of effecting such API-breaking changes, when absolutely
-necessary.
-
-These tools will be listed on the [C++ Upgrade Tools][upgrade-tools] guide on
-http://abseil.io.
-
-For more information, the [C++ Automated Upgrade Guide][api-upgrades-guide]
-outlines this process.
-
-[compatibility-guide]: https://abseil.io/about/compatibility
-[api-upgrades-guide]: https://abseil.io/docs/cpp/tools/api-upgrades
-[upgrade-tools]: https://abseil.io/docs/cpp/tools/upgrades/
-
diff --git a/absl/base/BUILD.bazel b/absl/base/BUILD.bazel
index 2717df0c93a1..49ae1824ffcb 100644
--- a/absl/base/BUILD.bazel
+++ b/absl/base/BUILD.bazel
@@ -89,6 +89,10 @@ cc_library(
         "internal/low_level_alloc.h",
     ],
     copts = ABSL_DEFAULT_COPTS,
+    linkopts = select({
+        "//absl:windows": [],
+        "//conditions:default": ["-pthread"],
+    }),
     visibility = [
         "//absl:__subpackages__",
     ],
@@ -142,6 +146,10 @@ cc_library(
         "log_severity.h",
     ],
     copts = ABSL_DEFAULT_COPTS,
+    linkopts = select({
+        "//absl:windows": [],
+        "//conditions:default": ["-pthread"],
+    }),
     deps = [
         ":base_internal",
         ":config",
@@ -423,10 +431,6 @@ cc_test(
     size = "small",
     srcs = ["internal/low_level_alloc_test.cc"],
     copts = ABSL_TEST_COPTS,
-    linkopts = select({
-        "//absl:windows": [],
-        "//conditions:default": ["-pthread"],
-    }),
     tags = ["no_test_ios_x86_64"],
     deps = [":malloc_internal"],
 )
@@ -436,10 +440,6 @@ cc_test(
     size = "small",
     srcs = ["internal/thread_identity_test.cc"],
     copts = ABSL_TEST_COPTS,
-    linkopts = select({
-        "//absl:windows": [],
-        "//conditions:default": ["-pthread"],
-    }),
     tags = [
         "no_test_wasm",
     ],
diff --git a/absl/base/internal/cycleclock.cc b/absl/base/internal/cycleclock.cc
index a742df01f94a..9eb13b8cb8c0 100644
--- a/absl/base/internal/cycleclock.cc
+++ b/absl/base/internal/cycleclock.cc
@@ -22,6 +22,7 @@
 
 #include "absl/base/internal/cycleclock.h"
 
+#include <atomic>
 #include <chrono>  // NOLINT(build/c++11)
 
 #include "absl/base/internal/unscaledcycleclock.h"
@@ -52,17 +53,26 @@ static constexpr int32_t kShift = 2;
 #endif
 
 static constexpr double kFrequencyScale = 1.0 / (1 << kShift);
+static std::atomic<CycleClockSourceFunc> cycle_clock_source;
 
 }  // namespace
 
 int64_t CycleClock::Now() {
-  return base_internal::UnscaledCycleClock::Now() >> kShift;
+  auto fn = cycle_clock_source.load(std::memory_order_relaxed);
+  if (fn == nullptr) {
+    return base_internal::UnscaledCycleClock::Now() >> kShift;
+  }
+  return fn() >> kShift;
 }
 
 double CycleClock::Frequency() {
   return kFrequencyScale * base_internal::UnscaledCycleClock::Frequency();
 }
 
+void CycleClockSource::Register(CycleClockSourceFunc source) {
+  cycle_clock_source.store(source, std::memory_order_relaxed);
+}
+
 #else
 
 int64_t CycleClock::Now() {
diff --git a/absl/base/internal/cycleclock.h b/absl/base/internal/cycleclock.h
index 60e971583c57..9853a66cefa6 100644
--- a/absl/base/internal/cycleclock.h
+++ b/absl/base/internal/cycleclock.h
@@ -71,6 +71,20 @@ class CycleClock {
   CycleClock& operator=(const CycleClock&) = delete;
 };
 
+using CycleClockSourceFunc = int64_t (*)();
+
+class CycleClockSource {
+ private:
+  // CycleClockSource::Register()
+  //
+  // Register a function that provides an alternate source for the unscaled CPU
+  // cycle count value. The source function must be async signal safe, must not
+  // call CycleClock::Now(), and must have a frequency that matches that of the
+  // unscaled clock used by CycleClock. A nullptr value resets CycleClock to use
+  // the default source.
+  static void Register(CycleClockSourceFunc source);
+};
+
 }  // namespace base_internal
 }  // namespace absl
 
diff --git a/absl/base/internal/per_thread_tls.h b/absl/base/internal/per_thread_tls.h
index 2428bdc1238e..56359853bcb5 100644
--- a/absl/base/internal/per_thread_tls.h
+++ b/absl/base/internal/per_thread_tls.h
@@ -16,13 +16,17 @@
 #define ABSL_BASE_INTERNAL_PER_THREAD_TLS_H_
 
 // This header defines two macros:
+//
 // If the platform supports thread-local storage:
-//   ABSL_PER_THREAD_TLS_KEYWORD is the C keyword needed to declare a
-//   thread-local variable ABSL_PER_THREAD_TLS is 1
+//
+// * ABSL_PER_THREAD_TLS_KEYWORD is the C keyword needed to declare a
+//   thread-local variable
+// * ABSL_PER_THREAD_TLS is 1
 //
 // Otherwise:
-//   ABSL_PER_THREAD_TLS_KEYWORD is empty
-//   ABSL_PER_THREAD_TLS is 0
+//
+// * ABSL_PER_THREAD_TLS_KEYWORD is empty
+// * ABSL_PER_THREAD_TLS is 0
 //
 // Microsoft C supports thread-local storage.
 // GCC supports it if the appropriate version of glibc is available,
diff --git a/absl/container/BUILD.bazel b/absl/container/BUILD.bazel
index e1880a8b546f..623faf4564b2 100644
--- a/absl/container/BUILD.bazel
+++ b/absl/container/BUILD.bazel
@@ -123,12 +123,21 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "counting_allocator",
+    testonly = 1,
+    hdrs = ["internal/counting_allocator.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    visibility = ["//visibility:private"],
+)
+
 cc_test(
     name = "inlined_vector_test",
     srcs = ["inlined_vector_test.cc"],
     copts = ABSL_TEST_COPTS + ABSL_EXCEPTIONS_FLAG,
     linkopts = ABSL_EXCEPTIONS_FLAG_LINKOPTS,
     deps = [
+        ":counting_allocator",
         ":inlined_vector",
         ":test_instance_tracker",
         "//absl/base",
@@ -146,6 +155,7 @@ cc_test(
     srcs = ["inlined_vector_test.cc"],
     copts = ABSL_TEST_COPTS,
     deps = [
+        ":counting_allocator",
         ":inlined_vector",
         ":test_instance_tracker",
         "//absl/base",
@@ -443,6 +453,7 @@ cc_library(
     copts = ABSL_DEFAULT_COPTS,
     deps = [
         ":have_sse",
+        "//absl/base",
         "//absl/base:core_headers",
         "//absl/debugging:stacktrace",
         "//absl/memory",
diff --git a/absl/container/CMakeLists.txt b/absl/container/CMakeLists.txt
index 4162d269ec2b..de9b22f7e5a7 100644
--- a/absl/container/CMakeLists.txt
+++ b/absl/container/CMakeLists.txt
@@ -122,6 +122,15 @@ absl_cc_library(
   PUBLIC
 )
 
+absl_cc_library(
+  NAME
+    counting_allocator
+  HDRS
+    "internal/counting_allocator.h"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+)
+
 absl_cc_test(
   NAME
     inlined_vector_test
@@ -132,6 +141,7 @@ absl_cc_test(
   LINKOPTS
     ${ABSL_EXCEPTIONS_FLAG_LINKOPTS}
   DEPS
+    absl::counting_allocator
     absl::inlined_vector
     absl::test_instance_tracker
     absl::base
@@ -437,6 +447,7 @@ absl_cc_library(
   COPTS
     ${ABSL_DEFAULT_COPTS}
   DEPS
+    absl::base
     absl::have_sse
     absl::synchronization
 )
diff --git a/absl/container/inlined_vector.h b/absl/container/inlined_vector.h
index fe228001bf2c..b6063441a0e9 100644
--- a/absl/container/inlined_vector.h
+++ b/absl/container/inlined_vector.h
@@ -795,79 +795,7 @@ class InlinedVector {
   void swap(InlinedVector& other) {
     if (ABSL_PREDICT_FALSE(this == &other)) return;
 
-    using std::swap;  // Augment ADL with `std::swap`.
-    if (allocated() && other.allocated()) {
-      // Both out of line, so just swap the tag, allocation, and allocator.
-      swap(tag(), other.tag());
-      swap(allocation(), other.allocation());
-      swap(allocator(), other.allocator());
-      return;
-    }
-    if (!allocated() && !other.allocated()) {
-      // Both inlined: swap up to smaller size, then move remaining elements.
-      InlinedVector* a = this;
-      InlinedVector* b = &other;
-      if (size() < other.size()) {
-        swap(a, b);
-      }
-
-      const size_type a_size = a->size();
-      const size_type b_size = b->size();
-      assert(a_size >= b_size);
-      // `a` is larger. Swap the elements up to the smaller array size.
-      std::swap_ranges(a->inlined_space(), a->inlined_space() + b_size,
-                       b->inlined_space());
-
-      // Move the remaining elements:
-      //   [`b_size`, `a_size`) from `a` -> [`b_size`, `a_size`) from `b`
-      b->UninitializedCopy(a->inlined_space() + b_size,
-                           a->inlined_space() + a_size,
-                           b->inlined_space() + b_size);
-      a->Destroy(a->inlined_space() + b_size, a->inlined_space() + a_size);
-
-      swap(a->tag(), b->tag());
-      swap(a->allocator(), b->allocator());
-      assert(b->size() == a_size);
-      assert(a->size() == b_size);
-      return;
-    }
-
-    // One is out of line, one is inline.
-    // We first move the elements from the inlined vector into the
-    // inlined space in the other vector.  We then put the other vector's
-    // pointer/capacity into the originally inlined vector and swap
-    // the tags.
-    InlinedVector* a = this;
-    InlinedVector* b = &other;
-    if (a->allocated()) {
-      swap(a, b);
-    }
-    assert(!a->allocated());
-    assert(b->allocated());
-    const size_type a_size = a->size();
-    const size_type b_size = b->size();
-    // In an optimized build, `b_size` would be unused.
-    static_cast<void>(b_size);
-
-    // Made Local copies of `size()`, don't need `tag()` accurate anymore
-    swap(a->tag(), b->tag());
-
-    // Copy `b_allocation` out before `b`'s union gets clobbered by
-    // `inline_space`
-    Allocation b_allocation = b->allocation();
-
-    b->UninitializedCopy(a->inlined_space(), a->inlined_space() + a_size,
-                         b->inlined_space());
-    a->Destroy(a->inlined_space(), a->inlined_space() + a_size);
-
-    a->allocation() = b_allocation;
-
-    if (a->allocator() != b->allocator()) {
-      swap(a->allocator(), b->allocator());
-    }
-
-    assert(b->size() == a_size);
-    assert(a->size() == b_size);
+    SwapImpl(other);
   }
 
  private:
@@ -1238,6 +1166,83 @@ class InlinedVector {
     return begin() + index;
   }
 
+  void SwapImpl(InlinedVector& other) {
+    using std::swap;  // Augment ADL with `std::swap`.
+
+    if (allocated() && other.allocated()) {
+      // Both out of line, so just swap the tag, allocation, and allocator.
+      swap(tag(), other.tag());
+      swap(allocation(), other.allocation());
+      swap(allocator(), other.allocator());
+      return;
+    }
+    if (!allocated() && !other.allocated()) {
+      // Both inlined: swap up to smaller size, then move remaining elements.
+      InlinedVector* a = this;
+      InlinedVector* b = &other;
+      if (size() < other.size()) {
+        swap(a, b);
+      }
+
+      const size_type a_size = a->size();
+      const size_type b_size = b->size();
+      assert(a_size >= b_size);
+      // `a` is larger. Swap the elements up to the smaller array size.
+      std::swap_ranges(a->inlined_space(), a->inlined_space() + b_size,
+                       b->inlined_space());
+
+      // Move the remaining elements:
+      //   [`b_size`, `a_size`) from `a` -> [`b_size`, `a_size`) from `b`
+      b->UninitializedCopy(a->inlined_space() + b_size,
+                           a->inlined_space() + a_size,
+                           b->inlined_space() + b_size);
+      a->Destroy(a->inlined_space() + b_size, a->inlined_space() + a_size);
+
+      swap(a->tag(), b->tag());
+      swap(a->allocator(), b->allocator());
+      assert(b->size() == a_size);
+      assert(a->size() == b_size);
+      return;
+    }
+
+    // One is out of line, one is inline.
+    // We first move the elements from the inlined vector into the
+    // inlined space in the other vector.  We then put the other vector's
+    // pointer/capacity into the originally inlined vector and swap
+    // the tags.
+    InlinedVector* a = this;
+    InlinedVector* b = &other;
+    if (a->allocated()) {
+      swap(a, b);
+    }
+    assert(!a->allocated());
+    assert(b->allocated());
+    const size_type a_size = a->size();
+    const size_type b_size = b->size();
+    // In an optimized build, `b_size` would be unused.
+    static_cast<void>(b_size);
+
+    // Made Local copies of `size()`, don't need `tag()` accurate anymore
+    swap(a->tag(), b->tag());
+
+    // Copy `b_allocation` out before `b`'s union gets clobbered by
+    // `inline_space`
+    Allocation b_allocation = b->allocation();
+
+    b->UninitializedCopy(a->inlined_space(), a->inlined_space() + a_size,
+                         b->inlined_space());
+    a->Destroy(a->inlined_space(), a->inlined_space() + a_size);
+
+    a->allocation() = b_allocation;
+
+    if (a->allocator() != b->allocator()) {
+      swap(a->allocator(), b->allocator());
+    }
+
+    assert(b->size() == a_size);
+    assert(a->size() == b_size);
+  }
+
   // Stores either the inlined or allocated representation
   union Rep {
     using ValueTypeBuffer =
diff --git a/absl/container/inlined_vector_test.cc b/absl/container/inlined_vector_test.cc
index 3a1ea8ac1de9..b3dcc7f0ad40 100644
--- a/absl/container/inlined_vector_test.cc
+++ b/absl/container/inlined_vector_test.cc
@@ -30,6 +30,7 @@
 #include "absl/base/internal/exception_testing.h"
 #include "absl/base/internal/raw_logging.h"
 #include "absl/base/macros.h"
+#include "absl/container/internal/counting_allocator.h"
 #include "absl/container/internal/test_instance_tracker.h"
 #include "absl/hash/hash_testing.h"
 #include "absl/memory/memory.h"
@@ -37,6 +38,7 @@
 
 namespace {
 
+using absl::container_internal::CountingAllocator;
 using absl::test_internal::CopyableMovableInstance;
 using absl::test_internal::CopyableOnlyInstance;
 using absl::test_internal::InstanceTracker;
@@ -138,57 +140,6 @@ static IntVec Fill(int len, int offset = 0) {
   return v;
 }
 
-// This is a stateful allocator, but the state lives outside of the
-// allocator (in whatever test is using the allocator). This is odd
-// but helps in tests where the allocator is propagated into nested
-// containers - that chain of allocators uses the same state and is
-// thus easier to query for aggregate allocation information.
-template <typename T>
-class CountingAllocator : public std::allocator<T> {
- public:
-  using Alloc = std::allocator<T>;
-  using pointer = typename Alloc::pointer;
-  using size_type = typename Alloc::size_type;
-
-  CountingAllocator() : bytes_used_(nullptr) {}
-  explicit CountingAllocator(int64_t* b) : bytes_used_(b) {}
-
-  template <typename U>
-  CountingAllocator(const CountingAllocator<U>& x)
-      : Alloc(x), bytes_used_(x.bytes_used_) {}
-
-  pointer allocate(size_type n,
-                   std::allocator<void>::const_pointer hint = nullptr) {
-    assert(bytes_used_ != nullptr);
-    *bytes_used_ += n * sizeof(T);
-    return Alloc::allocate(n, hint);
-  }
-
-  void deallocate(pointer p, size_type n) {
-    Alloc::deallocate(p, n);
-    assert(bytes_used_ != nullptr);
-    *bytes_used_ -= n * sizeof(T);
-  }
-
-  template<typename U>
-  class rebind {
-   public:
-    using other = CountingAllocator<U>;
-  };
-
-  friend bool operator==(const CountingAllocator& a,
-                         const CountingAllocator& b) {
-    return a.bytes_used_ == b.bytes_used_;
-  }
-
-  friend bool operator!=(const CountingAllocator& a,
-                         const CountingAllocator& b) {
-    return !(a == b);
-  }
-
-  int64_t* bytes_used_;
-};
-
 TEST(IntVec, SimpleOps) {
   for (int len = 0; len < 20; len++) {
     IntVec v;
diff --git a/absl/container/internal/counting_allocator.h b/absl/container/internal/counting_allocator.h
new file mode 100644
index 000000000000..f4e652d9600e
--- /dev/null
+++ b/absl/container/internal/counting_allocator.h
@@ -0,0 +1,79 @@
+// 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.
+
+#ifndef ABSL_CONTAINER_INTERNAL_COUNTING_ALLOCATOR_H_
+#define ABSL_CONTAINER_INTERNAL_COUNTING_ALLOCATOR_H_
+
+#include <cassert>
+#include <cstdint>
+#include <memory>
+
+namespace absl {
+namespace container_internal {
+
+// This is a stateful allocator, but the state lives outside of the
+// allocator (in whatever test is using the allocator). This is odd
+// but helps in tests where the allocator is propagated into nested
+// containers - that chain of allocators uses the same state and is
+// thus easier to query for aggregate allocation information.
+template <typename T>
+class CountingAllocator : public std::allocator<T> {
+ public:
+  using Alloc = std::allocator<T>;
+  using pointer = typename Alloc::pointer;
+  using size_type = typename Alloc::size_type;
+
+  CountingAllocator() : bytes_used_(nullptr) {}
+  explicit CountingAllocator(int64_t* b) : bytes_used_(b) {}
+
+  template <typename U>
+  CountingAllocator(const CountingAllocator<U>& x)
+      : Alloc(x), bytes_used_(x.bytes_used_) {}
+
+  pointer allocate(size_type n,
+                   std::allocator<void>::const_pointer hint = nullptr) {
+    assert(bytes_used_ != nullptr);
+    *bytes_used_ += n * sizeof(T);
+    return Alloc::allocate(n, hint);
+  }
+
+  void deallocate(pointer p, size_type n) {
+    Alloc::deallocate(p, n);
+    assert(bytes_used_ != nullptr);
+    *bytes_used_ -= n * sizeof(T);
+  }
+
+  template<typename U>
+  class rebind {
+   public:
+    using other = CountingAllocator<U>;
+  };
+
+  friend bool operator==(const CountingAllocator& a,
+                         const CountingAllocator& b) {
+    return a.bytes_used_ == b.bytes_used_;
+  }
+
+  friend bool operator!=(const CountingAllocator& a,
+                         const CountingAllocator& b) {
+    return !(a == b);
+  }
+
+  int64_t* bytes_used_;
+};
+
+}  // namespace container_internal
+}  // namespace absl
+
+#endif  // ABSL_CONTAINER_INTERNAL_COUNTING_ALLOCATOR_H_
diff --git a/absl/container/internal/hashtablez_sampler.cc b/absl/container/internal/hashtablez_sampler.cc
index 6cc10c201c34..e588f24c25c5 100644
--- a/absl/container/internal/hashtablez_sampler.cc
+++ b/absl/container/internal/hashtablez_sampler.cc
@@ -238,6 +238,10 @@ HashtablezInfo* SampleSlow(int64_t* next_sample) {
   return HashtablezSampler::Global().Register();
 }
 
+#if ABSL_PER_THREAD_TLS == 1
+ABSL_PER_THREAD_TLS_KEYWORD int64_t next_sample = 0;
+#endif  // ABSL_PER_THREAD_TLS == 1
+
 void UnsampleSlow(HashtablezInfo* info) {
   HashtablezSampler::Global().Unregister(info);
 }
diff --git a/absl/container/internal/hashtablez_sampler.h b/absl/container/internal/hashtablez_sampler.h
index 4aea3ffa67de..c42f1842ffe7 100644
--- a/absl/container/internal/hashtablez_sampler.h
+++ b/absl/container/internal/hashtablez_sampler.h
@@ -31,6 +31,7 @@
 #include <memory>
 #include <vector>
 
+#include "absl/base/internal/per_thread_tls.h"
 #include "absl/base/optimization.h"
 #include "absl/synchronization/mutex.h"
 #include "absl/utility/utility.h"
@@ -147,14 +148,16 @@ class HashtablezInfoHandle {
 
 // Returns an RAII sampling handle that manages registration and unregistation
 // with the global sampler.
+#if ABSL_PER_THREAD_TLS == 1
+extern ABSL_PER_THREAD_TLS_KEYWORD int64_t next_sample;
+#endif  // ABSL_PER_THREAD_TLS
+
 inline HashtablezInfoHandle Sample() {
-#if ABSL_HAVE_THREAD_LOCAL
-  thread_local int64_t next_sample = 0;
-#else   // ABSL_HAVE_THREAD_LOCAL
+#if ABSL_PER_THREAD_TLS == 0
   static auto* mu = new absl::Mutex;
   static int64_t next_sample = 0;
   absl::MutexLock l(mu);
-#endif  // ABSL_HAVE_THREAD_LOCAL
+#endif  // !ABSL_HAVE_THREAD_LOCAL
 
   if (ABSL_PREDICT_TRUE(--next_sample > 0)) {
     return HashtablezInfoHandle(nullptr);
diff --git a/absl/container/internal/raw_hash_set.h b/absl/container/internal/raw_hash_set.h
index 34d69d7af2fc..8cdea4ec8cd4 100644
--- a/absl/container/internal/raw_hash_set.h
+++ b/absl/container/internal/raw_hash_set.h
@@ -785,7 +785,11 @@ class raw_hash_set {
     }
 
     ctrl_t* ctrl_ = nullptr;
-    slot_type* slot_;
+    // To avoid uninitialized member warnigs, put slot_ in an anonymous union.
+    // The member is not initialized on singleton and end iterators.
+    union {
+      slot_type* slot_;
+    };
   };
 
   class const_iterator {
diff --git a/absl/copts/copts.py b/absl/copts/copts.py
index 40a8062f33b5..4da8442de028 100644
--- a/absl/copts/copts.py
+++ b/absl/copts/copts.py
@@ -10,8 +10,6 @@ compilation options:
 The generated copts are consumed by configure_copts.bzl and
 AbseilConfigureCopts.cmake.
 """
-
-import collections  # absl:google-only(used for internal flags)
 COPT_VARS = {
     "GCC_FLAGS": [
         "-Wall",
diff --git a/absl/synchronization/BUILD.bazel b/absl/synchronization/BUILD.bazel
index 53e7988457e9..43680046e796 100644
--- a/absl/synchronization/BUILD.bazel
+++ b/absl/synchronization/BUILD.bazel
@@ -69,6 +69,10 @@ cc_library(
         "notification.h",
     ],
     copts = ABSL_DEFAULT_COPTS,
+    linkopts = select({
+        "//absl:windows": [],
+        "//conditions:default": ["-pthread"],
+    }),
     deps = [
         ":graphcycles_internal",
         "//absl/base",
@@ -245,10 +249,6 @@ cc_test(
         "lifetime_test.cc",
     ],
     copts = ABSL_TEST_COPTS,
-    linkopts = select({
-        "//absl:windows": [],
-        "//conditions:default": ["-pthread"],
-    }),
     tags = ["no_test_ios_x86_64"],
     deps = [
         ":synchronization",
diff --git a/absl/time/internal/cctz/BUILD.bazel b/absl/time/internal/cctz/BUILD.bazel
index e2cfe801f23d..a2053c974203 100644
--- a/absl/time/internal/cctz/BUILD.bazel
+++ b/absl/time/internal/cctz/BUILD.bazel
@@ -98,13 +98,13 @@ cc_test(
 cc_test(
     name = "time_zone_lookup_test",
     size = "small",
+    timeout = "moderate",
     srcs = ["src/time_zone_lookup_test.cc"],
     data = [":zoneinfo"],
     tags = [
         "no_test_android_arm",
         "no_test_android_arm64",
         "no_test_android_x86",
-        "no_test_wasm",
     ],
     deps = [
         ":civil_time",
diff --git a/absl/time/internal/cctz/src/time_zone_format_test.cc b/absl/time/internal/cctz/src/time_zone_format_test.cc
index cd0ae23f3562..b99e1c6359af 100644
--- a/absl/time/internal/cctz/src/time_zone_format_test.cc
+++ b/absl/time/internal/cctz/src/time_zone_format_test.cc
@@ -64,17 +64,6 @@ void TestFormatSpecifier(time_point<D> tp, time_zone tz, const std::string& fmt,
   EXPECT_EQ("xxx " + ans + " yyy", format("xxx " + fmt + " yyy", tp, tz));
 }
 
-// These tests sometimes run on platforms that have zoneinfo data so old
-// that the transition we are attempting to check does not exist, most
-// notably Android emulators.  Fortunately, AndroidZoneInfoSource supports
-// time_zone::version() so, in cases where we've learned that it matters,
-// we can make the check conditionally.
-int VersionCmp(time_zone tz, const std::string& target) {
-  std::string version = tz.version();
-  if (version.empty() && !target.empty()) return 1;  // unknown > known
-  return version.compare(target);
-}
-
 }  // namespace
 
 //
@@ -174,7 +163,9 @@ TEST(Format, PosixConversions) {
   TestFormatSpecifier(tp, tz, "%M", "00");
   TestFormatSpecifier(tp, tz, "%S", "00");
   TestFormatSpecifier(tp, tz, "%U", "00");
+#if !defined(__EMSCRIPTEN__)
   TestFormatSpecifier(tp, tz, "%w", "4");  // 4=Thursday
+#endif
   TestFormatSpecifier(tp, tz, "%W", "00");
   TestFormatSpecifier(tp, tz, "%y", "70");
   TestFormatSpecifier(tp, tz, "%Y", "1970");
@@ -1464,6 +1455,10 @@ TEST(FormatParse, RoundTrip) {
 #if defined(_WIN32) || defined(_WIN64)
   // Initial investigations indicate the %c does not roundtrip on Windows.
   // TODO: Figure out what is going on here (perhaps a locale problem).
+#elif defined(__EMSCRIPTEN__)
+  // strftime() and strptime() use different defintions for "%c" under
+  // emscripten (see https://github.com/kripken/emscripten/pull/7491),
+  // causing its round-trip test to fail.
 #else
   // Even though we don't know what %c will produce, it should roundtrip,
   // but only in the 0-offset timezone.
diff --git a/absl/time/internal/cctz/src/time_zone_lookup_test.cc b/absl/time/internal/cctz/src/time_zone_lookup_test.cc
index e84b9469aa08..e9865659f268 100644
--- a/absl/time/internal/cctz/src/time_zone_lookup_test.cc
+++ b/absl/time/internal/cctz/src/time_zone_lookup_test.cc
@@ -666,6 +666,7 @@ int VersionCmp(time_zone tz, const std::string& target) {
 
 }  // namespace
 
+#if !defined(__EMSCRIPTEN__)
 TEST(TimeZones, LoadZonesConcurrently) {
   std::promise<void> ready_promise;
   std::shared_future<void> ready_future(ready_promise.get_future());
@@ -713,6 +714,7 @@ TEST(TimeZones, LoadZonesConcurrently) {
   }
   EXPECT_LE(failures.size(), max_failures) << testing::PrintToString(failures);
 }
+#endif
 
 TEST(TimeZone, NamedTimeZones) {
   const time_zone utc = utc_time_zone();
diff --git a/absl/time/internal/cctz/testdata/version b/absl/time/internal/cctz/testdata/version
index ac954d74f977..63f58006ee93 100644
--- a/absl/time/internal/cctz/testdata/version
+++ b/absl/time/internal/cctz/testdata/version
@@ -1 +1 @@
-2018g-9-gf0d2759
+2018i
diff --git a/absl/time/internal/cctz/testdata/zoneinfo/Africa/Sao_Tome b/absl/time/internal/cctz/testdata/zoneinfo/Africa/Sao_Tome
index d2a64bd1d3d5..59f3759c409a 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Africa/Sao_Tome
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Africa/Sao_Tome
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/America/Metlakatla b/absl/time/internal/cctz/testdata/zoneinfo/America/Metlakatla
index 26356078f8d1..85a7e16e165d 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/America/Metlakatla
+++ b/absl/time/internal/cctz/testdata/zoneinfo/America/Metlakatla
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Asia/Hong_Kong b/absl/time/internal/cctz/testdata/zoneinfo/Asia/Hong_Kong
index 8e5c5813666a..91eaff488f8c 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Asia/Hong_Kong
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Asia/Hong_Kong
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Asia/Qostanay b/absl/time/internal/cctz/testdata/zoneinfo/Asia/Qostanay
new file mode 100644
index 000000000000..cb6e2d90f813
--- /dev/null
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Asia/Qostanay
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Asia/Qyzylorda b/absl/time/internal/cctz/testdata/zoneinfo/Asia/Qyzylorda
index 00b278440592..fc636b3b868b 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Asia/Qyzylorda
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Asia/Qyzylorda
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Asia/Tehran b/absl/time/internal/cctz/testdata/zoneinfo/Asia/Tehran
index ad9058b4937b..0ae2f65fcdaa 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Asia/Tehran
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Asia/Tehran
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Hongkong b/absl/time/internal/cctz/testdata/zoneinfo/Hongkong
index 8e5c5813666a..91eaff488f8c 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Hongkong
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Hongkong
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Iran b/absl/time/internal/cctz/testdata/zoneinfo/Iran
index ad9058b4937b..0ae2f65fcdaa 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Iran
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Iran
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Kwajalein b/absl/time/internal/cctz/testdata/zoneinfo/Kwajalein
index 54bd71ff2dc7..d6413577f980 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Kwajalein
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Kwajalein
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Chuuk b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Chuuk
index e79bca2dafa7..8004d65bbe56 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Chuuk
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Chuuk
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Guam b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Guam
index ffdf8c24b862..e22424758f8d 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Guam
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Guam
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Kosrae b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Kosrae
index b6bd4b089416..11583b13e468 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Kosrae
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Kosrae
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Kwajalein b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Kwajalein
index 54bd71ff2dc7..d6413577f980 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Kwajalein
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Kwajalein
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Majuro b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Majuro
index 53f32886d081..65990cbba941 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Majuro
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Majuro
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Nauru b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Nauru
index 7e7d920e1139..86d3b7d1e72f 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Nauru
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Nauru
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Palau b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Palau
index 968f1956c8ee..05633b88e720 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Palau
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Palau
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Pohnpei b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Pohnpei
index d3393a20d852..090429c09e76 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Pohnpei
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Pohnpei
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Ponape b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Ponape
index d3393a20d852..090429c09e76 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Ponape
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Ponape
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Saipan b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Saipan
index ffdf8c24b862..e22424758f8d 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Saipan
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Saipan
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Truk b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Truk
index e79bca2dafa7..8004d65bbe56 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Truk
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Truk
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Yap b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Yap
index e79bca2dafa7..8004d65bbe56 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Yap
+++ b/absl/time/internal/cctz/testdata/zoneinfo/Pacific/Yap
Binary files differdiff --git a/absl/time/internal/cctz/testdata/zoneinfo/zone1970.tab b/absl/time/internal/cctz/testdata/zoneinfo/zone1970.tab
index 2729e6e8f9aa..9a8e4244fa30 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/zone1970.tab
+++ b/absl/time/internal/cctz/testdata/zoneinfo/zone1970.tab
@@ -211,6 +211,7 @@ KP	+3901+12545	Asia/Pyongyang
 KR	+3733+12658	Asia/Seoul
 KZ	+4315+07657	Asia/Almaty	Kazakhstan (most areas)
 KZ	+4448+06528	Asia/Qyzylorda	Qyzylorda/Kyzylorda/Kzyl-Orda
+KZ	+5312+06337	Asia/Qostanay	Qostanay/Kostanay/Kustanay
 KZ	+5017+05710	Asia/Aqtobe	Aqtöbe/Aktobe
 KZ	+4431+05016	Asia/Aqtau	Mangghystaū/Mankistau
 KZ	+4707+05156	Asia/Atyrau	Atyraū/Atirau/Gur'yev