atexit-impl.h

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#ifndef ATEXIT_IMPL_H
#define ATEXIT_IMPL_H
 
#include <cstdint>
 
namespace __impl {
 
struct ExitFunctionStorage {
  void (*m_functionptr)(void *);
  void *m_userdata;
 
  void operator()() const { m_functionptr(m_userdata); }
};
 
/* Exit functions are registered in a singly-linked list of blocks of
 * registrations. Each block contains 32 exit registrations, and additional
 * space for registrations is allocated on the heap, as needed.*/
class RegistrationList {
  // FnBlock is an array of function pointers and their arguments.
  // The logical "front" of the block is the last item appended to
  // the array.
  struct FnBlock {
    static constexpr std::uint8_t BLOCK_SZ = 32;
 
    ExitFunctionStorage m_funcs[BLOCK_SZ];
    std::uint8_t m_sz;
 
    bool empty() const { return !m_sz; }
    bool full() const { return m_sz == BLOCK_SZ; }
 
    void push_front(const ExitFunctionStorage &newfn) {
      m_funcs[m_sz++] = newfn;
    }
 
    const ExitFunctionStorage &back() const { return m_funcs[m_sz - 1]; }
    void pop_back() { m_sz--; }
  };
 
  struct FnNode : public FnBlock {
    FnNode(FnBlock *next) : m_next{next} {}
 
    FnBlock *const m_next = nullptr;
  };
 
  // The initial base node allows 32 exit registrations (1 block)
  // of exit functions, without allocating.  So the minumum required
  // 32 exit functions will always be available.
  FnBlock m_tail;
  FnBlock *m_list = &m_tail;
 
public:
  bool push_front(const ExitFunctionStorage &new_exit);
  void run_all_exits();
};
 
} // namespace __impl
 
#endif // not ATEXIT_IMPL_H