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tdutils/td/utils/SpinLock.h

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+/*
+    This file is part of TON Blockchain Library.
+
+    TON Blockchain Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    TON Blockchain Library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with TON Blockchain Library.  If not, see <http://www.gnu.org/licenses/>.
+
+    Copyright 2017-2019 Telegram Systems LLP
+*/
+#pragma once
+
+#include "td/utils/port/thread.h"
+
+#include <atomic>
+#include <memory>
+
+namespace td {
+
+class SpinLock {
+  struct Unlock {
+    void operator()(SpinLock *ptr) {
+      ptr->unlock();
+    }
+  };
+
+  class InfBackoff {
+    int cnt = 0;
+
+   public:
+    bool next() {
+      cnt++;
+      if (cnt < 50) {
+        //TODO pause
+        return true;
+      } else {
+        td::this_thread::yield();
+        return true;
+      }
+    }
+  };
+
+ public:
+  using Lock = std::unique_ptr<SpinLock, Unlock>;
+
+  Lock lock() {
+    InfBackoff backoff;
+    while (!try_lock()) {
+      backoff.next();
+    }
+    return Lock(this);
+  }
+  bool try_lock() {
+    return !flag_.test_and_set(std::memory_order_acquire);
+  }
+
+ private:
+  std::atomic_flag flag_ = ATOMIC_FLAG_INIT;
+  void unlock() {
+    flag_.clear(std::memory_order_release);
+  }
+};
+
+}  // namespace td