1 files changed, 57 insertions, 0 deletions
diff --git a/storage/rocksdb/rocksdb/third-party/folly/folly/synchronization/detail/Sleeper.h b/storage/rocksdb/rocksdb/third-party/folly/folly/synchronization/detail/Sleeper.h
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+++ b/storage/rocksdb/rocksdb/third-party/folly/folly/synchronization/detail/Sleeper.h
@@ -0,0 +1,57 @@
+//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+
+#pragma once
+
+/*
+ * @author Keith Adams <kma@fb.com>
+ * @author Jordan DeLong <delong.j@fb.com>
+ */
+
+#include <cstdint>
+#include <thread>
+
+#include <folly/portability/Asm.h>
+
+namespace folly {
+
+//////////////////////////////////////////////////////////////////////
+
+namespace detail {
+
+/*
+ * A helper object for the contended case. Starts off with eager
+ * spinning, and falls back to sleeping for small quantums.
+ */
+class Sleeper {
+  static const uint32_t kMaxActiveSpin = 4000;
+
+  uint32_t spinCount;
+
+ public:
+  Sleeper() noexcept : spinCount(0) {}
+
+  static void sleep() noexcept {
+    /*
+     * Always sleep 0.5ms, assuming this will make the kernel put
+     * us down for whatever its minimum timer resolution is (in
+     * linux this varies by kernel version from 1ms to 10ms).
+     */
+    std::this_thread::sleep_for(std::chrono::microseconds{500});
+  }
+
+  void wait() noexcept {
+    if (spinCount < kMaxActiveSpin) {
+      ++spinCount;
+      asm_volatile_pause();
+    } else {
+      sleep();
+    }
+  }
+};
+
+} // namespace detail
+} // namespace folly
+