1 files changed, 80 insertions, 0 deletions
diff --git a/src/common/fair_mutex.h b/src/common/fair_mutex.h
new file mode 100644
index 000000000..9baa04400
--- /dev/null
+++ b/src/common/fair_mutex.h
@@ -0,0 +1,80 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:nil -*-
+
+#pragma once
+
+#include "common/ceph_mutex.h"
+
+#include <thread>
+#include <string>
+
+namespace ceph {
+/// a FIFO mutex
+class fair_mutex {
+public:
+  fair_mutex(const std::string& name)
+    : mutex{ceph::make_mutex(name)}
+  {}
+  ~fair_mutex() = default;
+  fair_mutex(const fair_mutex&) = delete;
+  fair_mutex& operator=(const fair_mutex&) = delete;
+
+  void lock()
+  {
+    std::unique_lock lock(mutex);
+    const unsigned my_id = next_id++;
+    cond.wait(lock, [&] {
+      return my_id == unblock_id;
+    });
+    _set_locked_by();
+  }
+
+  bool try_lock()
+  {
+    std::lock_guard lock(mutex);
+    if (is_locked()) {
+      return false;
+    }
+    ++next_id;
+    _set_locked_by();
+    return true;
+  }
+
+  void unlock()
+  {
+    std::lock_guard lock(mutex);
+    ++unblock_id;
+    _reset_locked_by();
+    cond.notify_all();
+  }
+
+  bool is_locked() const
+  {
+    return next_id != unblock_id;
+  }
+
+#ifdef CEPH_DEBUG_MUTEX
+  bool is_locked_by_me() const {
+    return is_locked() && locked_by == std::this_thread::get_id();
+  }
+private:
+  void _set_locked_by() {
+    locked_by = std::this_thread::get_id();
+  }
+  void _reset_locked_by() {
+    locked_by = {};
+  }
+#else
+  void _set_locked_by() {}
+  void _reset_locked_by() {}
+#endif
+
+private:
+  unsigned next_id = 0;
+  unsigned unblock_id = 0;
+  ceph::condition_variable cond;
+  ceph::mutex mutex;
+#ifdef CEPH_DEBUG_MUTEX
+  std::thread::id locked_by = {};
+#endif
+};
+} // namespace ceph