Export of internal Abseil changes

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daf5a2b9ab3507ad5fb9aebe9165933f33098b83 by Abseil Team <absl-team@google.com>:

Absl flat containers reserve enough space even in the presence of tombstones.

PiperOrigin-RevId: 372339945

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9a61504867ba0eccc5046d7333090fbe3439cdd9 by Abseil Team <absl-team@google.com>:

Add benchmark for BlockingCounter

PiperOrigin-RevId: 372246068

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91ee87e6de09fc62970667ee52654c9dcf7c478d by Evan Brown <ezb@google.com>:

In absl::StrSplit, support btree_multimap, and other non-std::multimap-multimaps by supporting any map type that returns iterator from insert().

Also:
- Use emplace() instead of insert() when available, not just for std::(multi)map - we can potentially change some string copies to moves this way.
- We no longer need the Insert class so remove it.
PiperOrigin-RevId: 372209653
GitOrigin-RevId: daf5a2b9ab3507ad5fb9aebe9165933f33098b83
Change-Id: I83098fde4a722cd4b682f024d3bfa56c613f960c

2 files changed, 98 insertions, 0 deletions

diff --git a/absl/synchronization/BUILD.bazel b/absl/synchronization/BUILD.bazel
index 5ce16958..92e2448d 100644
--- a/absl/synchronization/BUILD.bazel
+++ b/absl/synchronization/BUILD.bazel
@@ -136,6 +136,21 @@ cc_test(
     ],
 )
 
+cc_binary(
+    name = "blocking_counter_benchmark",
+    testonly = 1,
+    srcs = ["blocking_counter_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":synchronization",
+        ":thread_pool",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
 cc_test(
     name = "graphcycles_test",
     size = "medium",
diff --git a/absl/synchronization/blocking_counter_benchmark.cc b/absl/synchronization/blocking_counter_benchmark.cc
new file mode 100644
index 00000000..b504d1a5
--- /dev/null
+++ b/absl/synchronization/blocking_counter_benchmark.cc
@@ -0,0 +1,83 @@
+// Copyright 2021 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
+//
+//      https://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 <limits>
+
+#include "absl/synchronization/blocking_counter.h"
+#include "absl/synchronization/internal/thread_pool.h"
+#include "benchmark/benchmark.h"
+
+namespace {
+
+void BM_BlockingCounter_SingleThread(benchmark::State& state) {
+  for (auto _ : state) {
+    int iterations = state.range(0);
+    absl::BlockingCounter counter{iterations};
+    for (int i = 0; i < iterations; ++i) {
+      counter.DecrementCount();
+    }
+    counter.Wait();
+  }
+}
+BENCHMARK(BM_BlockingCounter_SingleThread)
+    ->ArgName("iterations")
+    ->Arg(2)
+    ->Arg(4)
+    ->Arg(16)
+    ->Arg(64)
+    ->Arg(256);
+
+void BM_BlockingCounter_DecrementCount(benchmark::State& state) {
+  static absl::BlockingCounter* counter =
+      new absl::BlockingCounter{std::numeric_limits<int>::max()};
+  for (auto _ : state) {
+    counter->DecrementCount();
+  }
+}
+BENCHMARK(BM_BlockingCounter_DecrementCount)
+    ->Threads(2)
+    ->Threads(4)
+    ->Threads(6)
+    ->Threads(8)
+    ->Threads(10)
+    ->Threads(12)
+    ->Threads(16)
+    ->Threads(32)
+    ->Threads(64)
+    ->Threads(128);
+
+void BM_BlockingCounter_Wait(benchmark::State& state) {
+  int num_threads = state.range(0);
+  absl::synchronization_internal::ThreadPool pool(num_threads);
+  for (auto _ : state) {
+    absl::BlockingCounter counter{num_threads};
+    pool.Schedule([num_threads, &counter, &pool]() {
+      for (int i = 0; i < num_threads; ++i) {
+        pool.Schedule([&counter]() { counter.DecrementCount(); });
+      }
+    });
+    counter.Wait();
+  }
+}
+BENCHMARK(BM_BlockingCounter_Wait)
+    ->ArgName("threads")
+    ->Arg(2)
+    ->Arg(4)
+    ->Arg(8)
+    ->Arg(16)
+    ->Arg(32)
+    ->Arg(64)
+    ->Arg(128);
+
+}  // namespace