1 files changed, 105 insertions, 0 deletions
diff --git a/fcp/base/wall_clock_stopwatch.cc b/fcp/base/wall_clock_stopwatch.cc
new file mode 100644
index 0000000..b328554
--- /dev/null
+++ b/fcp/base/wall_clock_stopwatch.cc
@@ -0,0 +1,105 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * 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 "fcp/base/wall_clock_stopwatch.h"
+
+#include <memory>
+
+#include "absl/synchronization/mutex.h"
+#include "absl/time/time.h"
+#include "fcp/base/monitoring.h"
+
+namespace fcp {
+
+namespace internal {
+class RealWallClockStopwatch : public WallClockStopwatch {
+ public:
+  RealWallClockStopwatch() = default;
+
+  Handle Start() override ABSL_LOCKS_EXCLUDED(mutex_) {
+    return WallClockStopwatch::Handle(this);
+  }
+  absl::Duration GetTotalDuration() const override ABSL_LOCKS_EXCLUDED(mutex_) {
+    absl::MutexLock lock(&mutex_);
+    FCP_CHECK(started_count_ >= 0);
+    if (latest_start_time_ == absl::InfiniteFuture()) {
+      return previous_durations_;
+    }
+    return previous_durations_ + (absl::Now() - latest_start_time_);
+  }
+
+ private:
+  void StartInternal() override ABSL_LOCKS_EXCLUDED(mutex_) {
+    absl::MutexLock lock(&mutex_);
+    FCP_CHECK(started_count_ >= 0);
+    started_count_++;
+    if (started_count_ == 1) {
+      latest_start_time_ = absl::Now();
+    }
+  }
+  void StopInternal() override ABSL_LOCKS_EXCLUDED(mutex_) {
+    absl::MutexLock lock(&mutex_);
+    FCP_CHECK(started_count_ >= 1);
+    started_count_--;
+    if (started_count_ == 0) {
+      previous_durations_ += absl::Now() - latest_start_time_;
+      latest_start_time_ = absl::InfiniteFuture();
+    }
+  }
+
+  mutable absl::Mutex mutex_;
+  int started_count_ ABSL_GUARDED_BY(mutex_) = 0;
+  absl::Time latest_start_time_ ABSL_GUARDED_BY(mutex_) =
+      absl::InfiniteFuture();
+  absl::Duration previous_durations_ ABSL_GUARDED_BY(mutex_) =
+      absl::ZeroDuration();
+};
+
+// A noop stopwatch that does nothing (e.g. for use in tests or to
+// flag-off the measurement of something).
+class NoopWallClockStopwatch : public WallClockStopwatch {
+ public:
+  NoopWallClockStopwatch() = default;
+
+  Handle Start() override { return Handle(nullptr); }
+  absl::Duration GetTotalDuration() const override {
+    return absl::ZeroDuration();
+  }
+};
+}  // namespace internal
+
+WallClockStopwatch::Handle::Handle(WallClockStopwatch* stopwatch)
+    : stopwatch_(stopwatch) {
+  if (stopwatch_ != nullptr) {
+    stopwatch_->StartInternal();
+  }
+}
+
+WallClockStopwatch::Handle::~Handle() {
+  if (stopwatch_ != nullptr) {
+    stopwatch_->StopInternal();
+  }
+}
+
+std::unique_ptr<WallClockStopwatch> WallClockStopwatch::Create() {
+  return std::make_unique<internal::RealWallClockStopwatch>();
+}
+
+std::unique_ptr<WallClockStopwatch> WallClockStopwatch::CreateNoop() {
+  return std::make_unique<internal::NoopWallClockStopwatch>();
+}
+
+}  // namespace fcp