- a4e14440b870dbf7b36975eaebf783a70a7fcee4 Release string_view...

  - a4e14440b870dbf7b36975eaebf783a70a7fcee4 Release string_view microbenchmarks. by Alex Strelnikov <strel@google.com>
  - 7cec68e37e16fb4e266368236ae1de6419f6946a Increase Abseil's minimum supported cmake version to 3.1.... by Jon Cohen <cohenjon@google.com>
  - b977456175c8db380676bd56c44b32efbfc6f606 Fix a typo in the mutex.h comments. by Abseil Team <absl-team@google.com>
  - 3d30cec131d08b066bc1cf877e4f661e8ee0584c Release StrSplit microbenchmarks. by Alex Strelnikov <strel@google.com>
  - dddece6031feac1cca4689e623462f895f28d019 Release StrReplace microbenchmarks. by Alex Strelnikov <strel@google.com>
  - ac3b40e1694f74bdcf31b8d1152481e92edfd441 Internal Change by Abseil Team <absl-team@google.com>
  - d0e69ad6ddf0e59596a02ccab0253967f2909cdb Release StrCat microbenchmarks. by Alex Strelnikov <strel@google.com>
  - db4d471030fa320d2b9d2ce241610333f0eb7a50 Release StrJoin microbenchmarks. by Alex Strelnikov <strel@google.com>

GitOrigin-RevId: a4e14440b870dbf7b36975eaebf783a70a7fcee4
Change-Id: I3f12700aafce677049f4d1a6e09ea821963a8c9e

CMakeLists.txt

@@ -13,7 +13,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-cmake_minimum_required(VERSION 2.8.12)
+
+# We require 3.0 for modern, target-based CMake.  We require 3.1 for the use of
+# CXX_STANDARD in our targets.
+cmake_minimum_required(VERSION 3.1)
 project(absl)
 
 list(APPEND CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/CMake)

absl/strings/BUILD.bazel

@@ -172,6 +172,20 @@ cc_test(
     ],
 )
 
+cc_test(
+    name = "string_view_benchmark",
+    srcs = ["string_view_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base",
+        "//absl/base:core_headers",
+        "@com_github_google_benchmark//:benchmark",
+    ],
+)
+
 cc_test(
     name = "string_view_test",
     size = "small",
@@ -200,6 +214,19 @@ cc_test(
     ],
 )
 
+cc_test(
+    name = "str_replace_benchmark",
+    srcs = ["str_replace_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base",
+        "@com_github_google_benchmark//:benchmark",
+    ],
+)
+
 cc_test(
     name = "str_replace_test",
     size = "small",
@@ -225,6 +252,19 @@ cc_test(
     ],
 )
 
+cc_test(
+    name = "str_split_benchmark",
+    srcs = ["str_split_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base",
+        "@com_github_google_benchmark//:benchmark",
+    ],
+)
+
 cc_test(
     name = "ostringstream_test",
     size = "small",
@@ -267,6 +307,19 @@ cc_test(
     ],
 )
 
+cc_test(
+    name = "str_join_benchmark",
+    srcs = ["str_join_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/memory",
+        "@com_github_google_benchmark//:benchmark",
+    ],
+)
+
 cc_test(
     name = "str_cat_test",
     size = "small",
@@ -280,6 +333,18 @@ cc_test(
     ],
 )
 
+cc_test(
+    name = "str_cat_benchmark",
+    srcs = ["str_cat_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "@com_github_google_benchmark//:benchmark",
+    ],
+)
+
 cc_test(
     name = "numbers_test",
     size = "small",

absl/strings/str_cat_benchmark.cc

+// 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/strings/str_cat.h"
+
+#include <cstdint>
+#include <string>
+
+#include "benchmark/benchmark.h"
+#include "absl/strings/substitute.h"
+
+namespace {
+
+const char kStringOne[] = "Once Upon A Time, ";
+const char kStringTwo[] = "There was a std::string benchmark";
+
+// We want to include negative numbers in the benchmark, so this function
+// is used to count 0, 1, -1, 2, -2, 3, -3, ...
+inline int IncrementAlternatingSign(int i) {
+  return i > 0 ? -i : 1 - i;
+}
+
+void BM_Sum_By_StrCat(benchmark::State& state) {
+  int i = 0;
+  char foo[100];
+  for (auto _ : state) {
+    // NOLINTNEXTLINE(runtime/printf)
+    strcpy(foo, absl::StrCat(kStringOne, i, kStringTwo, i * 65536ULL).c_str());
+    int sum = 0;
+    for (char* f = &foo[0]; *f != 0; ++f) {
+      sum += *f;
+    }
+    benchmark::DoNotOptimize(sum);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_Sum_By_StrCat);
+
+void BM_StrCat_By_snprintf(benchmark::State& state) {
+  int i = 0;
+  char on_stack[1000];
+  for (auto _ : state) {
+    snprintf(on_stack, sizeof(on_stack), "%s %s:%d", kStringOne, kStringTwo, i);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_StrCat_By_snprintf);
+
+void BM_StrCat_By_Strings(benchmark::State& state) {
+  int i = 0;
+  for (auto _ : state) {
+    std::string result =
+        std::string(kStringOne) + " " + kStringTwo + ":" + absl::StrCat(i);
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_StrCat_By_Strings);
+
+void BM_StrCat_By_StringOpPlus(benchmark::State& state) {
+  int i = 0;
+  for (auto _ : state) {
+    std::string result = kStringOne;
+    result += " ";
+    result += kStringTwo;
+    result += ":";
+    result += absl::StrCat(i);
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_StrCat_By_StringOpPlus);
+
+void BM_StrCat_By_StrCat(benchmark::State& state) {
+  int i = 0;
+  for (auto _ : state) {
+    std::string result = absl::StrCat(kStringOne, " ", kStringTwo, ":", i);
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_StrCat_By_StrCat);
+
+void BM_HexCat_By_StrCat(benchmark::State& state) {
+  int i = 0;
+  for (auto _ : state) {
+    std::string result =
+        absl::StrCat(kStringOne, " ", absl::Hex(int64_t{i} + 0x10000000));
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_HexCat_By_StrCat);
+
+void BM_HexCat_By_Substitute(benchmark::State& state) {
+  int i = 0;
+  for (auto _ : state) {
+    std::string result = absl::Substitute(
+        "$0 $1", kStringOne, reinterpret_cast<void*>(int64_t{i} + 0x10000000));
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_HexCat_By_Substitute);
+
+void BM_FloatToString_By_StrCat(benchmark::State& state) {
+  int i = 0;
+  float foo = 0.0f;
+  for (auto _ : state) {
+    std::string result = absl::StrCat(foo += 1.001f, " != ", int64_t{i});
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_FloatToString_By_StrCat);
+
+void BM_DoubleToString_By_SixDigits(benchmark::State& state) {
+  int i = 0;
+  double foo = 0.0;
+  for (auto _ : state) {
+    std::string result =
+        absl::StrCat(absl::SixDigits(foo += 1.001), " != ", int64_t{i});
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_DoubleToString_By_SixDigits);
+
+}  // namespace
+
+BENCHMARK_MAIN();

absl/strings/str_join_benchmark.cc

+//
+// 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/strings/str_join.h"
+
+#include <string>
+#include <vector>
+#include <utility>
+
+#include "benchmark/benchmark.h"
+
+namespace {
+
+void BM_Join2_Strings(benchmark::State& state) {
+  const int string_len = state.range(0);
+  const int num_strings = state.range(1);
+  const std::string s(string_len, 'x');
+  const std::vector<std::string> v(num_strings, s);
+  for (auto _ : state) {
+    std::string s = absl::StrJoin(v, "-");
+    benchmark::DoNotOptimize(s);
+  }
+}
+BENCHMARK(BM_Join2_Strings)
+    ->ArgPair(1 << 0, 1 << 3)
+    ->ArgPair(1 << 10, 1 << 3)
+    ->ArgPair(1 << 13, 1 << 3)
+    ->ArgPair(1 << 0, 1 << 10)
+    ->ArgPair(1 << 10, 1 << 10)
+    ->ArgPair(1 << 13, 1 << 10)
+    ->ArgPair(1 << 0, 1 << 13)
+    ->ArgPair(1 << 10, 1 << 13)
+    ->ArgPair(1 << 13, 1 << 13);
+
+void BM_Join2_Ints(benchmark::State& state) {
+  const int num_ints = state.range(0);
+  const std::vector<int> v(num_ints, 42);
+  for (auto _ : state) {
+    std::string s = absl::StrJoin(v, "-");
+    benchmark::DoNotOptimize(s);
+  }
+}
+BENCHMARK(BM_Join2_Ints)->Range(0, 1 << 13);
+
+void BM_Join2_KeysAndValues(benchmark::State& state) {
+  const int string_len = state.range(0);
+  const int num_pairs = state.range(1);
+  const std::string s(string_len, 'x');
+  const std::vector<std::pair<std::string, int>> v(num_pairs, std::make_pair(s, 42));
+  for (auto _ : state) {
+    std::string s = absl::StrJoin(v, ",", absl::PairFormatter("="));
+    benchmark::DoNotOptimize(s);
+  }
+}
+BENCHMARK(BM_Join2_KeysAndValues)
+    ->ArgPair(1 << 0, 1 << 3)
+    ->ArgPair(1 << 10, 1 << 3)
+    ->ArgPair(1 << 13, 1 << 3)
+    ->ArgPair(1 << 0, 1 << 10)
+    ->ArgPair(1 << 10, 1 << 10)
+    ->ArgPair(1 << 13, 1 << 10)
+    ->ArgPair(1 << 0, 1 << 13)
+    ->ArgPair(1 << 10, 1 << 13)
+    ->ArgPair(1 << 13, 1 << 13);
+
+void BM_JoinStreamable(benchmark::State& state) {
+  const int string_len = state.range(0);
+  const int num_strings = state.range(1);
+  const std::vector<std::string> v(num_strings, std::string(string_len, 'x'));
+  for (auto _ : state) {
+    std::string s = absl::StrJoin(v, "", absl::StreamFormatter());
+    benchmark::DoNotOptimize(s);
+  }
+}
+BENCHMARK(BM_JoinStreamable)
+    ->ArgPair(0, 0)
+    ->ArgPair(16, 1)
+    ->ArgPair(256, 1)
+    ->ArgPair(16, 16)
+    ->ArgPair(256, 16)
+    ->ArgPair(16, 256)
+    ->ArgPair(256, 256);
+
+}  // namespace
+
+BENCHMARK_MAIN();

absl/strings/str_replace_benchmark.cc

+// 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/strings/str_replace.h"
+
+#include <cstring>
+#include <string>
+
+#include "benchmark/benchmark.h"
+#include "absl/base/internal/raw_logging.h"
+
+namespace {
+
+std::string* big_string;
+std::string* after_replacing_the;
+std::string* after_replacing_many;
+
+struct Replacement {
+  const char* needle;
+  const char* replacement;
+} replacements[] = {
+    {"the", "box"},          //
+    {"brown", "quick"},      //
+    {"jumped", "liquored"},  //
+    {"dozen", "brown"},      //
+    {"lazy", "pack"},        //
+    {"liquor", "shakes"},    //
+};
+
+// Here, we set up a std::string for use in global-replace benchmarks.
+// We started with a million blanks, and then deterministically insert
+// 10,000 copies each of two pangrams.  The result is a std::string that is
+// 40% blank space and 60% these words.  'the' occurs 18,247 times and
+// all the substitutions together occur 49,004 times.
+//
+// We then create "after_replacing_the" to be a std::string that is a result of
+// replacing "the" with "box" in big_string.
+//
+// And then we create "after_replacing_many" to be a std::string that is result
+// of preferring several substitutions.
+void SetUpStrings() {
+  if (big_string == nullptr) {
+    size_t r = 0;
+    big_string = new std::string(1000 * 1000, ' ');
+    for (std::string phrase : {"the quick brown fox jumped over the lazy dogs",
+                          "pack my box with the five dozen liquor jugs"}) {
+      for (int i = 0; i < 10 * 1000; ++i) {
+        r = r * 237 + 41;  // not very random.
+        memcpy(&(*big_string)[r % (big_string->size() - phrase.size())],
+               phrase.data(), phrase.size());
+      }
+    }
+    // big_string->resize(50);
+    // OK, we've set up the std::string, now let's set up expectations - first by
+    // just replacing "the" with "box"
+    after_replacing_the = new std::string(*big_string);
+    for (size_t pos = 0;
+         (pos = after_replacing_the->find("the", pos)) != std::string::npos;) {
+      memcpy(&(*after_replacing_the)[pos], "box", 3);
+    }
+    // And then with all the replacements.
+    after_replacing_many = new std::string(*big_string);
+    for (size_t pos = 0;;) {
+      size_t next_pos = static_cast<size_t>(-1);
+      const char* needle_string = nullptr;
+      const char* replacement_string = nullptr;
+      for (const auto& r : replacements) {
+        auto needlepos = after_replacing_many->find(r.needle, pos);
+        if (needlepos != std::string::npos && needlepos < next_pos) {
+          next_pos = needlepos;
+          needle_string = r.needle;
+          replacement_string = r.replacement;
+        }
+      }
+      if (next_pos > after_replacing_many->size()) break;
+      after_replacing_many->replace(next_pos, strlen(needle_string),
+                                    replacement_string);
+      next_pos += strlen(replacement_string);
+      pos = next_pos;
+    }
+  }
+}
+
+void BM_StrReplaceAllOneReplacement(benchmark::State& state) {
+  SetUpStrings();
+  std::string src = *big_string;
+  for (auto _ : state) {
+    std::string dest = absl::StrReplaceAll(src, {{"the", "box"}});
+    ABSL_RAW_CHECK(dest == *after_replacing_the,
+                   "not benchmarking intended behavior");
+  }
+}
+BENCHMARK(BM_StrReplaceAllOneReplacement);
+
+void BM_StrReplaceAll(benchmark::State& state) {
+  SetUpStrings();
+  std::string src = *big_string;
+  for (auto _ : state) {
+    std::string dest = absl::StrReplaceAll(src, {{"the", "box"},
+                                            {"brown", "quick"},
+                                            {"jumped", "liquored"},
+                                            {"dozen", "brown"},
+                                            {"lazy", "pack"},
+                                            {"liquor", "shakes"}});
+    ABSL_RAW_CHECK(dest == *after_replacing_many,
+                   "not benchmarking intended behavior");
+  }
+}
+BENCHMARK(BM_StrReplaceAll);
+
+}  // namespace
+
+BENCHMARK_MAIN();

absl/strings/str_split_benchmark.cc

+// 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/strings/str_split.h"
+
+#include <iterator>
+#include <string>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+#include "benchmark/benchmark.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/strings/string_view.h"
+
+namespace {
+
+std::string MakeTestString(int desired_length) {
+  static const int kAverageValueLen = 25;
+  std::string test(desired_length * kAverageValueLen, 'x');
+  for (int i = 1; i < test.size(); i += kAverageValueLen) {
+    test[i] = ';';
+  }
+  return test;
+}
+
+void BM_Split2StringPiece(benchmark::State& state) {
+  std::string test = MakeTestString(state.range(0));
+  for (auto _ : state) {
+    std::vector<absl::string_view> result = absl::StrSplit(test, ';');
+    benchmark::DoNotOptimize(result);
+  }
+}
+BENCHMARK_RANGE(BM_Split2StringPiece, 0, 1 << 20);
+
+void BM_Split2StringPieceLifted(benchmark::State& state) {
+  std::string test = MakeTestString(state.range(0));
+  std::vector<absl::string_view> result;
+  for (auto _ : state) {
+    result = absl::StrSplit(test, ';');
+  }
+  benchmark::DoNotOptimize(result);
+}
+BENCHMARK_RANGE(BM_Split2StringPieceLifted, 0, 1 << 20);
+
+void BM_Split2String(benchmark::State& state) {
+  std::string test = MakeTestString(state.range(0));
+  for (auto _ : state) {
+    std::vector<std::string> result = absl::StrSplit(test, ';');
+    benchmark::DoNotOptimize(result);
+  }
+}
+BENCHMARK_RANGE(BM_Split2String, 0, 1 << 20);
+
+// This benchmark is for comparing Split2 to Split1 (SplitStringUsing). In
+// particular, this benchmark uses SkipEmpty() to match SplitStringUsing's
+// behavior.
+void BM_Split2SplitStringUsing(benchmark::State& state) {
+  std::string test = MakeTestString(state.range(0));
+  for (auto _ : state) {
+    std::vector<std::string> result = absl::StrSplit(test, ';', absl::SkipEmpty());
+    benchmark::DoNotOptimize(result);
+  }
+}
+BENCHMARK_RANGE(BM_Split2SplitStringUsing, 0, 1 << 20);
+
+void BM_SplitStringToUnorderedSet(benchmark::State& state) {
+  const int len = state.range(0);
+  std::string test(len, 'x');
+  for (int i = 1; i < len; i += 2) {
+    test[i] = ';';
+  }
+  for (auto _ : state) {
+    std::unordered_set<std::string> result =
+        absl::StrSplit(test, ':', absl::SkipEmpty());
+    benchmark::DoNotOptimize(result);
+  }
+}
+BENCHMARK_RANGE(BM_SplitStringToUnorderedSet, 0, 1 << 20);
+
+void BM_SplitStringToUnorderedMap(benchmark::State& state) {
+  const int len = state.range(0);
+  std::string test(len, 'x');
+  for (int i = 1; i < len; i += 2) {
+    test[i] = ';';
+  }
+  for (auto _ : state) {
+    std::unordered_map<std::string, std::string> result =
+        absl::StrSplit(test, ':', absl::SkipEmpty());
+    benchmark::DoNotOptimize(result);
+  }
+}
+BENCHMARK_RANGE(BM_SplitStringToUnorderedMap, 0, 1 << 20);
+
+void BM_SplitStringAllowEmpty(benchmark::State& state) {
+  const int len = state.range(0);
+  std::string test(len, 'x');
+  for (int i = 1; i < len; i += 2) {
+    test[i] = ';';
+  }
+  for (auto _ : state) {
+    std::vector<std::string> result = absl::StrSplit(test, ';');
+    benchmark::DoNotOptimize(result);
+  }
+}
+BENCHMARK_RANGE(BM_SplitStringAllowEmpty, 0, 1 << 20);
+
+struct OneCharLiteral {
+  char operator()() const { return 'X'; }
+};
+
+struct OneCharStringLiteral {
+  const char* operator()() const { return "X"; }
+};
+
+template <typename DelimiterFactory>
+void BM_SplitStringWithOneChar(benchmark::State& state) {
+  const auto delimiter = DelimiterFactory()();
+  std::vector<absl::string_view> pieces;
+  size_t v = 0;
+  for (auto _ : state) {
+    pieces = absl::StrSplit("The quick brown fox jumps over the lazy dog",
+                            delimiter);
+    v += pieces.size();
+  }
+  ABSL_RAW_CHECK(v == state.iterations(), "");
+}
+BENCHMARK_TEMPLATE(BM_SplitStringWithOneChar, OneCharLiteral);
+BENCHMARK_TEMPLATE(BM_SplitStringWithOneChar, OneCharStringLiteral);
+
+template <typename DelimiterFactory>
+void BM_SplitStringWithOneCharNoVector(benchmark::State& state) {
+  const auto delimiter = DelimiterFactory()();
+  size_t v = 0;
+  for (auto _ : state) {
+    auto splitter = absl::StrSplit(
+        "The quick brown fox jumps over the lazy dog", delimiter);
+    v += std::distance(splitter.begin(), splitter.end());
+  }
+  ABSL_RAW_CHECK(v == state.iterations(), "");
+}
+BENCHMARK_TEMPLATE(BM_SplitStringWithOneCharNoVector, OneCharLiteral);
+BENCHMARK_TEMPLATE(BM_SplitStringWithOneCharNoVector, OneCharStringLiteral);
+
+}  // namespace
+
+BENCHMARK_MAIN();

absl/strings/string_view_benchmark.cc

+// 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/strings/string_view.h"
+
+#include <algorithm>
+#include <cstdint>
+#include <map>
+#include <random>
+#include <string>
+#include <unordered_set>
+#include <vector>
+
+#include "benchmark/benchmark.h"
+#include "absl/base/attributes.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/macros.h"
+#include "absl/strings/str_cat.h"
+
+namespace {
+
+// Provide a forcibly out-of-line wrapper for operator== that can be used in
+// benchmarks to measure the impact of inlining.
+ABSL_ATTRIBUTE_NOINLINE
+bool NonInlinedEq(absl::string_view a, absl::string_view b) { return a == b; }
+
+// We use functions that cannot be inlined to perform the comparison loops so
+// that inlining of the operator== can't optimize away *everything*.
+ABSL_ATTRIBUTE_NOINLINE
+void DoEqualityComparisons(benchmark::State& state, absl::string_view a,
+                           absl::string_view b) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(a == b);
+  }
+}
+
+void BM_EqualIdentical(benchmark::State& state) {
+  std::string x(state.range(0), 'a');
+  DoEqualityComparisons(state, x, x);
+}
+BENCHMARK(BM_EqualIdentical)->DenseRange(0, 3)->Range(4, 1 << 10);
+
+void BM_EqualSame(benchmark::State& state) {
+  std::string x(state.range(0), 'a');
+  std::string y = x;
+  DoEqualityComparisons(state, x, y);
+}
+BENCHMARK(BM_EqualSame)
+    ->DenseRange(0, 10)
+    ->Arg(20)
+    ->Arg(40)
+    ->Arg(70)
+    ->Arg(110)
+    ->Range(160, 4096);
+
+void BM_EqualDifferent(benchmark::State& state) {
+  const int len = state.range(0);
+  std::string x(len, 'a');
+  std::string y = x;
+  if (len > 0) {
+    y[len - 1] = 'b';
+  }
+  DoEqualityComparisons(state, x, y);
+}
+BENCHMARK(BM_EqualDifferent)->DenseRange(0, 3)->Range(4, 1 << 10);
+
+// This benchmark is intended to check that important simplifications can be
+// made with absl::string_view comparisons against constant strings. The idea is
+// that if constant strings cause redundant components of the comparison, the
+// compiler should detect and eliminate them. Here we use 8 different strings,
+// each with the same size. Provided our comparison makes the implementation
+// inline-able by the compiler, it should fold all of these away into a single
+// size check once per loop iteration.
+ABSL_ATTRIBUTE_NOINLINE
+void DoConstantSizeInlinedEqualityComparisons(benchmark::State& state,
+                                              absl::string_view a) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(a == "aaa");
+    benchmark::DoNotOptimize(a == "bbb");
+    benchmark::DoNotOptimize(a == "ccc");
+    benchmark::DoNotOptimize(a == "ddd");
+    benchmark::DoNotOptimize(a == "eee");
+    benchmark::DoNotOptimize(a == "fff");
+    benchmark::DoNotOptimize(a == "ggg");
+    benchmark::DoNotOptimize(a == "hhh");
+  }
+}
+void BM_EqualConstantSizeInlined(benchmark::State& state) {
+  std::string x(state.range(0), 'a');
+  DoConstantSizeInlinedEqualityComparisons(state, x);
+}
+// We only need to check for size of 3, and <> 3 as this benchmark only has to
+// do with size differences.
+BENCHMARK(BM_EqualConstantSizeInlined)->DenseRange(2, 4);
+
+// This benchmark exists purely to give context to the above timings: this is
+// what they would look like if the compiler is completely unable to simplify
+// between two comparisons when they are comparing against constant strings.
+ABSL_ATTRIBUTE_NOINLINE
+void DoConstantSizeNonInlinedEqualityComparisons(benchmark::State& state,
+                                                 absl::string_view a) {
+  for (auto _ : state) {
+    // Force these out-of-line to compare with the above function.
+    benchmark::DoNotOptimize(NonInlinedEq(a, "aaa"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "bbb"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "ccc"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "ddd"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "eee"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "fff"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "ggg"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "hhh"));
+  }
+}
+
+void BM_EqualConstantSizeNonInlined(benchmark::State& state) {
+  std::string x(state.range(0), 'a');
+  DoConstantSizeNonInlinedEqualityComparisons(state, x);
+}
+// We only need to check for size of 3, and <> 3 as this benchmark only has to
+// do with size differences.
+BENCHMARK(BM_EqualConstantSizeNonInlined)->DenseRange(2, 4);
+
+void BM_CompareSame(benchmark::State& state) {
+  const int len = state.range(0);
+  std::string x;
+  for (int i = 0; i < len; i++) {
+    x += 'a';
+  }
+  std::string y = x;
+  absl::string_view a = x;
+  absl::string_view b = y;
+
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(a.compare(b));
+  }
+}
+BENCHMARK(BM_CompareSame)->DenseRange(0, 3)->Range(4, 1 << 10);
+
+void BM_find_string_view_len_one(benchmark::State& state) {
+  std::string haystack(state.range(0), '0');
+  absl::string_view s(haystack);
+  for (auto _ : state) {
+    s.find("x");  // not present; length 1
+  }
+}
+BENCHMARK(BM_find_string_view_len_one)->Range(1, 1 << 20);
+
+void BM_find_string_view_len_two(benchmark::State& state) {
+  std::string haystack(state.range(0), '0');
+  absl::string_view s(haystack);
+  for (auto _ : state) {
+    s.find("xx");  // not present; length 2
+  }
+}
+BENCHMARK(BM_find_string_view_len_two)->Range(1, 1 << 20);
+
+void BM_find_one_char(benchmark::State& state) {
+  std::string haystack(state.range(0), '0');
+  absl::string_view s(haystack);
+  for (auto _ : state) {
+    s.find('x');  // not present
+  }
+}
+BENCHMARK(BM_find_one_char)->Range(1, 1 << 20);
+
+void BM_rfind_one_char(benchmark::State& state) {
+  std::string haystack(state.range(0), '0');
+  absl::string_view s(haystack);
+  for (auto _ : state) {
+    s.rfind('x');  // not present
+  }
+}
+BENCHMARK(BM_rfind_one_char)->Range(1, 1 << 20);
+
+void BM_worst_case_find_first_of(benchmark::State& state, int haystack_len) {
+  const int needle_len = state.range(0);
+  std::string needle;
+  for (int i = 0; i < needle_len; ++i) {
+    needle += 'a' + i;
+  }
+  std::string haystack(haystack_len, '0');  // 1000 zeros.
+
+  absl::string_view s(haystack);
+  for (auto _ : state) {
+    s.find_first_of(needle);
+  }
+}
+
+void BM_find_first_of_short(benchmark::State& state) {
+  BM_worst_case_find_first_of(state, 10);
+}
+
+void BM_find_first_of_medium(benchmark::State& state) {
+  BM_worst_case_find_first_of(state, 100);
+}
+
+void BM_find_first_of_long(benchmark::State& state) {
+  BM_worst_case_find_first_of(state, 1000);
+}
+
+BENCHMARK(BM_find_first_of_short)->DenseRange(0, 4)->Arg(8)->Arg(16)->Arg(32);
+BENCHMARK(BM_find_first_of_medium)->DenseRange(0, 4)->Arg(8)->Arg(16)->Arg(32);
+BENCHMARK(BM_find_first_of_long)->DenseRange(0, 4)->Arg(8)->Arg(16)->Arg(32);
+
+struct EasyMap : public std::map<absl::string_view, uint64_t> {
+  explicit EasyMap(size_t) {}
+};
+
+// This templated benchmark helper function is intended to stress operator== or
+// operator< in a realistic test.  It surely isn't entirely realistic, but it's
+// a start.  The test creates a map of type Map, a template arg, and populates
+// it with table_size key/value pairs. Each key has WordsPerKey words.  After
+// creating the map, a number of lookups are done in random order.  Some keys
+// are used much more frequently than others in this phase of the test.
+template <typename Map, int WordsPerKey>
+void StringViewMapBenchmark(benchmark::State& state) {
+  const int table_size = state.range(0);
+  const double kFractionOfKeysThatAreHot = 0.2;
+  const int kNumLookupsOfHotKeys = 20;
+  const int kNumLookupsOfColdKeys = 1;
+  const char* words[] = {"the",   "quick",  "brown",    "fox",      "jumped",
+                         "over",  "the",    "lazy",     "dog",      "and",
+                         "found", "a",      "large",    "mushroom", "and",
+                         "a",     "couple", "crickets", "eating",   "pie"};
+  // Create some keys that consist of words in random order.
+  std::random_device r;
+  std::seed_seq seed({r(), r(), r(), r(), r(), r(), r(), r()});
+  std::mt19937 rng(seed);
+  std::vector<std::string> keys(table_size);
+  std::vector<int> all_indices;
+  const int kBlockSize = 1 << 12;
+  std::unordered_set<std::string> t(kBlockSize);
+  std::uniform_int_distribution<int> uniform(0, ABSL_ARRAYSIZE(words) - 1);
+  for (int i = 0; i < table_size; i++) {
+    all_indices.push_back(i);
+    do {
+      keys[i].clear();
+      for (int j = 0; j < WordsPerKey; j++) {
+        absl::StrAppend(&keys[i], j > 0 ? " " : "", words[uniform(rng)]);
+      }
+    } while (!t.insert(keys[i]).second);
+  }
+
+  // Create a list of strings to lookup: a permutation of the array of
+  // keys we just created, with repeats.  "Hot" keys get repeated more.
+  std::shuffle(all_indices.begin(), all_indices.end(), rng);
+  const int num_hot = table_size * kFractionOfKeysThatAreHot;
+  const int num_cold = table_size - num_hot;
+  std::vector<int> hot_indices(all_indices.begin(),
+                               all_indices.begin() + num_hot);
+  std::vector<int> indices;
+  for (int i = 0; i < kNumLookupsOfColdKeys; i++) {
+    indices.insert(indices.end(), all_indices.begin(), all_indices.end());
+  }
+  for (int i = 0; i < kNumLookupsOfHotKeys - kNumLookupsOfColdKeys; i++) {
+    indices.insert(indices.end(), hot_indices.begin(), hot_indices.end());
+  }
+  std::shuffle(indices.begin(), indices.end(), rng);
+  ABSL_RAW_CHECK(
+      num_cold * kNumLookupsOfColdKeys + num_hot * kNumLookupsOfHotKeys ==
+          indices.size(),
+      "");
+  // After constructing the array we probe it with absl::string_views built from
+  // test_strings.  This means operator== won't see equal pointers, so
+  // it'll have to check for equal lengths and equal characters.
+  std::vector<std::string> test_strings(indices.size());
+  for (int i = 0; i < indices.size(); i++) {
+    test_strings[i] = keys[indices[i]];
+  }
+
+  // Run the benchmark. It includes map construction but is mostly
+  // map lookups.
+  for (auto _ : state) {
+    Map h(table_size);
+    for (int i = 0; i < table_size; i++) {
+      h[keys[i]] = i * 2;
+    }
+    ABSL_RAW_CHECK(h.size() == table_size, "");
+    uint64_t sum = 0;
+    for (int i = 0; i < indices.size(); i++) {
+      sum += h[test_strings[i]];
+    }
+    benchmark::DoNotOptimize(sum);
+  }
+}
+
+void BM_StdMap_4(benchmark::State& state) {
+  StringViewMapBenchmark<EasyMap, 4>(state);
+}
+BENCHMARK(BM_StdMap_4)->Range(1 << 10, 1 << 16);
+
+void BM_StdMap_8(benchmark::State& state) {
+  StringViewMapBenchmark<EasyMap, 8>(state);
+}
+BENCHMARK(BM_StdMap_8)->Range(1 << 10, 1 << 16);
+
+void BM_CopyToStringNative(benchmark::State& state) {
+  std::string src(state.range(0), 'x');
+  absl::string_view sv(src);
+  std::string dst;
+  for (auto _ : state) {
+    dst.assign(sv.begin(), sv.end());
+  }
+}
+BENCHMARK(BM_CopyToStringNative)->Range(1 << 3, 1 << 12);
+
+void BM_AppendToStringNative(benchmark::State& state) {
+  std::string src(state.range(0), 'x');
+  absl::string_view sv(src);
+  std::string dst;
+  for (auto _ : state) {
+    dst.clear();
+    dst.insert(dst.end(), sv.begin(), sv.end());
+  }
+}
+BENCHMARK(BM_AppendToStringNative)->Range(1 << 3, 1 << 12);
+
+}  // namespace
+
+BENCHMARK_MAIN();

absl/synchronization/mutex.h

@@ -854,7 +854,7 @@ class SCOPED_LOCKABLE MutexLockMaybe {
   MutexLockMaybe& operator=(MutexLockMaybe&&) = delete;
 };
 
-// ReleaseableMutexLock
+// ReleasableMutexLock
 //
 // ReleasableMutexLock is like MutexLock, but permits `Release()` of its
 // mutex before destruction. `Release()` may be called at most once.