Export of internal Abseil changes.

--
cd076f55c1fa600131f6dda392533dfe61679fc0 by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 224008762

--
e05f62b01286d51044ff86ec6ef565749b9faf82 by Abseil Team <absl-team@google.com>:

Create a pow10() test helper function to compute guaranteed-precise double values of 10^x. Not all standard libraries ship bit-accurate pow() functions, causing tests to fail that rely on expected values generated by it.

PiperOrigin-RevId: 223883762

--
fd88e5e3f7ab80f7f5df9fd1488cd58b4573be69 by Abseil Team <absl-team@google.com>:

Remove some absl:: qualifications to work around inline namespace bugs on MSVC 2015.

PiperOrigin-RevId: 223869642

--
6276cfff969d596edd36a2bbaba65ee045808903 by Abseil Team <absl-team@google.com>:

Update absl/memory/CMakeLists.txt to use new functions
i.e. absl_cc_(library|test)

PiperOrigin-RevId: 223854224

--
359de9afc7a34c975fd3e0cbc52afd96637d97bd by Chris Kennelly <ckennelly@google.com>:

Mark spinlock_benchmark_common as alwayslink = 1.

PiperOrigin-RevId: 223844536

--
450cd8cbe2789a6d54ed1eb87170259bb334f8b9 by Abseil Team <absl-team@google.com>:

Support .* (pointer-to-member dereference) expressions in demangle.cc.

PiperOrigin-RevId: 223826797

--
772ca92179c3634f3e31a80bbc272ed8022e3572 by Abseil Team <absl-team@google.com>:

Fix misspellings in absl::variant comments and replace a ' with a `.

PiperOrigin-RevId: 223807911

--
35dcdc2fbf299d195658aac101887f6dcad1de2f by Abseil Team <absl-team@google.com>:

Bug fix in CMakeLists.txt file (SRCS --> HDRS).

The compressed_tuple header-only library is being defined
with the SRCS parameter instead of the HDRS parameter and
this has been observed to cause some builds on some platforms
to attempt to create a static library from it which fails
since there are no .cc sources.

PiperOrigin-RevId: 223805367

--
4a57a3d2045bb137c0c97958e45ce425190b8d3e by Chris Kennelly <ckennelly@google.com>:

Add test that absl::make_unique value initializes memory.

PiperOrigin-RevId: 223801819

--
dfe8289d7f4dcc6bb568a26aaf192a89e896bdfd by Chris Kennelly <ckennelly@google.com>:

SpinLock: Use exchange to avoid missing wakeups.

The default fast path for SpinLock::Unlock does not use an atomic.  If the
SpinLock becomes contended while we are unlocking between lockword_.load and
lockword_.store, we will fail to wake up the new waiter.  This can cause
unexpected latency spikes.

PiperOrigin-RevId: 223800369

--
9b9d35df786482f0016f77dd31691eff81503d23 by Abseil Team <absl-team@google.com>:

Update absl/hash/CMakeLists.txt to use new functions
i.e. absl_cc_(library|test)

PiperOrigin-RevId: 223755819

--
c2014e2704b87e7cdce2d2a0287c7e2397752296 by Abseil Team <absl-team@google.com>:

Update absl/debugging/CMakeLists.txt to use new functions
i.e. absl_cc_(library|test)

PiperOrigin-RevId: 223751986

--
d83a4e09126400e3fd80645cb03ee558f532271e by Derek Mauro <dmauro@google.com>:

Cleanup synchronization benchmarks.

PiperOrigin-RevId: 223589416

--
fad140b473586531b5b12843f942ec27dfcf5e93 by CJ Johnson <johnsoncj@google.com>:

Makes unifies the order of forward_iterator and input_iterator overloads

PiperOrigin-RevId: 223580660

--
6cd7c96faa7cc5f79f574e35a1b13837ef187d05 by Abseil Team <absl-team@google.com>:

Internal Change.

PiperOrigin-RevId: 223561629

--
bd2e545356b0f548af0e3c14bb2f7f0e712e49d0 by Shaindel Schwartz <shaindel@google.com>:

Remove misleading comments. try_emplace() does not exist for the hash_set containers.

PiperOrigin-RevId: 223543089

--
0cd380a53b587eb7aacc4003a4a3bbb6c78d7c10 by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 223512551

--
7156dfee599cb72e9adddfe0e6ae07a95ddf10bb by Greg Miller <jgm@google.com>:

Fixes UB that would result from constructing, multiplying, or dividing a
Duration with a double "NaN" value. This CL changes the absl::Duration
*implementation* to return an InfiniteDuration value that has the same sign as
the given NaN.

PiperOrigin-RevId: 223407499

--
196b7d18609958267951882baf7f9429e49bcafa by CJ Johnson <johnsoncj@google.com>:

Addresses NVCC+MSVC compilation bug where `inlined_capacity()` was not considered valid in constexpr

PiperOrigin-RevId: 223397718
GitOrigin-RevId: cd076f55c1fa600131f6dda392533dfe61679fc0
Change-Id: I5423ca6470f661a7c6f73aa8fee49990446f157f

3 files changed, 82 insertions, 2 deletions

diff --git a/absl/base/BUILD.bazel b/absl/base/BUILD.bazel
index 44de05e3..4566c697 100644
--- a/absl/base/BUILD.bazel
+++ b/absl/base/BUILD.bazel
@@ -107,6 +107,7 @@ cc_library(
         "internal/identity.h",
         "internal/inline_variable.h",
         "internal/invoke.h",
+        "internal/scheduling_mode.h",
     ],
     copts = ABSL_DEFAULT_COPTS,
     visibility = [
@@ -314,6 +315,33 @@ cc_test(
 )
 
 cc_library(
+    name = "spinlock_benchmark_common",
+    testonly = 1,
+    srcs = ["internal/spinlock_benchmark.cc"],
+    copts = ABSL_DEFAULT_COPTS,
+    visibility = [
+        "//absl/base:__pkg__",
+    ],
+    deps = [
+        ":base",
+        ":base_internal",
+        "//absl/synchronization",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+    alwayslink = 1,
+)
+
+cc_binary(
+    name = "spinlock_benchmark",
+    testonly = 1,
+    copts = ABSL_DEFAULT_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":spinlock_benchmark_common",
+    ],
+)
+
+cc_library(
     name = "endian",
     hdrs = [
         "internal/endian.h",
diff --git a/absl/base/internal/spinlock.h b/absl/base/internal/spinlock.h
index dcce0109..eb3eec9c 100644
--- a/absl/base/internal/spinlock.h
+++ b/absl/base/internal/spinlock.h
@@ -101,8 +101,8 @@ class LOCKABLE SpinLock {
   inline void Unlock() UNLOCK_FUNCTION() {
     ABSL_TSAN_MUTEX_PRE_UNLOCK(this, 0);
     uint32_t lock_value = lockword_.load(std::memory_order_relaxed);
-    lockword_.store(lock_value & kSpinLockCooperative,
-                    std::memory_order_release);
+    lock_value = lockword_.exchange(lock_value & kSpinLockCooperative,
+                                    std::memory_order_release);
 
     if ((lock_value & kSpinLockDisabledScheduling) != 0) {
       base_internal::SchedulingGuard::EnableRescheduling(true);
diff --git a/absl/base/internal/spinlock_benchmark.cc b/absl/base/internal/spinlock_benchmark.cc
new file mode 100644
index 00000000..907d3e27
--- /dev/null
+++ b/absl/base/internal/spinlock_benchmark.cc
@@ -0,0 +1,52 @@
+// 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.
+
+// See also //absl/synchronization:mutex_benchmark for a comparison of SpinLock
+// and Mutex performance under varying levels of contention.
+
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/scheduling_mode.h"
+#include "absl/base/internal/spinlock.h"
+#include "absl/synchronization/internal/create_thread_identity.h"
+#include "benchmark/benchmark.h"
+
+namespace {
+
+template <absl::base_internal::SchedulingMode scheduling_mode>
+static void BM_SpinLock(benchmark::State& state) {
+  // Ensure a ThreadIdentity is installed.
+  ABSL_INTERNAL_CHECK(
+      absl::synchronization_internal::GetOrCreateCurrentThreadIdentity() !=
+          nullptr,
+      "GetOrCreateCurrentThreadIdentity() failed");
+
+  static auto* spinlock = new absl::base_internal::SpinLock(scheduling_mode);
+  for (auto _ : state) {
+    absl::base_internal::SpinLockHolder holder(spinlock);
+  }
+}
+
+BENCHMARK_TEMPLATE(BM_SpinLock,
+                   absl::base_internal::SCHEDULE_KERNEL_ONLY)
+    ->UseRealTime()
+    ->Threads(1)
+    ->ThreadPerCpu();
+
+BENCHMARK_TEMPLATE(BM_SpinLock,
+                   absl::base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL)
+    ->UseRealTime()
+    ->Threads(1)
+    ->ThreadPerCpu();
+
+}  // namespace