fd_poller.hpp

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#pragma once
 
/// @file userver/engine/io/fd_poller.hpp
/// @brief Low-level file descriptor r/w poller
 
#include <memory>
#include <optional>
 
#include <userver/engine/deadline.hpp>
#include <userver/utils/fast_pimpl.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace engine::io {
 
namespace impl {
class Direction;
}
 
/// @brief Low-level poller that can wait for read, write, and read/write
/// operations on a file descriptor. It does not provide read/write operations.
/// @note FdPoller is not thread safe and its methods must not be called from
/// multiple threads simultaneously.
class FdPoller final {
 public:
  /// @brief Operation kind to wait for
  enum class Kind {
    kRead = 1,       /// < wait for read availability
    kWrite = 2,      /// < wait for write availability
    kReadWrite = 3,  /// < wait for either read or write availability
  };
 
  FdPoller();
  FdPoller(const FdPoller&) = delete;
  FdPoller(FdPoller&&) = delete;
  FdPoller& operator=(const FdPoller&) = delete;
  FdPoller& operator=(FdPoller&&) = delete;
  ~FdPoller();
 
  /// The same as `IsValid()`.
  explicit operator bool() const noexcept;
  /// Whether the file descriptor is valid.
  bool IsValid() const noexcept;
 
  /// If IsValid(), get file descriptor.
  int GetFd() const;
 
  /// When you're done with fd, call Invalidate(). It unregisters the fd, after
  /// that you have to call close(2) by yourself. After Invalidate() you may not
  /// call Wait().
  void Invalidate();
 
  /// Setup fd and kind to wait for. After Reset() you may call Wait().
  /// FdPoller does not take the ownership of `fd`, you still have to close `fd`
  /// when you're done.
  void Reset(int fd, Kind kind);
 
  /// Wait for an event kind that was passed in the latest Reset() call. If the
  /// operation (read/write) can already be handled, Wait() returns
  /// immediately. You have to call Reset() at least once before call to
  /// Wait().
  [[nodiscard]] std::optional<Kind> Wait(Deadline);
 
 private:
  friend class impl::Direction;
 
  enum class State : int {
    kInvalid,
    kReadyToUse,
    kInUse,  /// < used only in debug to detect invalid concurrent usage
  };
 
  void WakeupWaiters();
  void SwitchStateToInUse();
  void SwitchStateToReadyToUse();
 
  struct Impl;
  utils::FastPimpl<Impl, 144, 16> pimpl_;
};
 
}  // namespace engine::io
 
USERVER_NAMESPACE_END