hierarchical_mutex.cpp

#include "hierarchical_mutex.h"

thread_local unsigned long HierarchicalMutex::this_thread_hierarchical_value = ULONG_MAX;

hierarchical_mutex.h

#include <limits.h>
#include <stdint.h>

#include <mutex>
#include <thread>

class HierarchicalMutex {
 public:
  explicit HierarchicalMutex(unsigned long value)
      : hierarchical_value(value), previous_hierarchical_value(0) {}
  void lock() {
    CheckViolation();
    mtx_.lock();
    UpdateValue();
  }
  bool try_lock() {
    CheckViolation();
    if (!mtx_.try_lock()) {
      return false;
    }
    UpdateValue();
    return true;
  }
  void unlock() {
    this_thread_hierarchical_value = previous_hierarchical_value;
    mtx_.unlock();
  }

 private:
  void CheckViolation() {
    if (this_thread_hierarchical_value <= hierarchical_value) {
      throw std::logic_error("Hierarchical value vialates");
    }
  }
  void UpdateValue() {
    this_thread_hierarchical_value = hierarchical_value;
    previous_hierarchical_value = this_thread_hierarchical_value;
  }

 private:
  std::mutex mtx_;
  const unsigned long hierarchical_value;
  unsigned long previous_hierarchical_value;
  static thread_local unsigned long this_thread_hierarchical_value;
};