#ifndef RESOURCE_LOCK_H
#define RESOURCE_LOCK_H

#include <cassert>
#include <condition_variable>
#include <mutex>

class ResourceLock {
   public:
      ResourceLock(unsigned int capacity_) : capacity(capacity_), used(0) {
      }
      void lock() {
	 std::unique_lock<std::mutex> lock(mutex);
	 if (used == capacity) {
	    released.wait(lock);
	 }
	 ++used;
      }
      void unlock() {
	 std::unique_lock<std::mutex> lock(mutex);
	 assert(used > 0);
	 --used;
	 released.notify_one();
      }
   private:
      const unsigned int capacity;
      unsigned int used;
      std::mutex mutex;
      std::condition_variable released;
};

#endif