semaphore.hpp

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#pragma once
 
#include <vector>
#include <mutex>
 
#include "declarations.hpp"
 
namespace tf {
 
// ----------------------------------------------------------------------------
// Semaphore
// ----------------------------------------------------------------------------
 
class Semaphore {
 
  friend class Node;
 
  public:
 
    explicit Semaphore(size_t max_workers);
 
    size_t count() const;
 
  private:
 
    std::mutex _mtx;
 
    size_t _counter;
 
    std::vector<Node*> _waiters;
 
    bool _try_acquire_or_wait(Node*);
 
    std::vector<Node*> _release();
};
 
inline Semaphore::Semaphore(size_t max_workers) :
  _counter(max_workers) {
}
 
inline bool Semaphore::_try_acquire_or_wait(Node* me) {
  std::lock_guard<std::mutex> lock(_mtx);
  if(_counter > 0) {
    --_counter;
    return true;
  }
  else {
    _waiters.push_back(me);
    return false;
  }
}
 
inline std::vector<Node*> Semaphore::_release() {
  std::lock_guard<std::mutex> lock(_mtx);
  ++_counter;
  std::vector<Node*> r{std::move(_waiters)};
  return r;
}
 
inline size_t Semaphore::count() const {
  return _counter;
}
 
}  // end of namespace tf. ---------------------------------------------------