Poll — Poll handle

class pyuv.Poll(loop, fd)
  • loop (Loop) – loop object where this handle runs (accessible through Poll.loop).
  • fd (int) – File descriptor to be monitored for readability or writability.
Poll handles can be used to monitor an arbitrary file descriptor for readability or writability.

On Unix any file descriptor is supported but on Windows only sockets are supported.


(From the libuv documentation) The uv_poll watcher is used to watch file descriptors for readability and writability, similar to the purpose of poll(2).

The purpose of uv_poll is to enable integrating external libraries that rely on the event loop to signal it about the socket status changes, like c-ares or libssh2. Using uv_poll_t for any other other purpose is not recommended; uv_tcp_t, uv_udp_t, etc. provide an implementation that is much faster and more scalable than what can be achieved with uv_poll_t, especially on Windows.

It is possible that uv_poll occasionally signals that a file descriptor is readable or writable even when it isn’t. The user should therefore always be prepared to handle EAGAIN or equivalent when it attempts to read from or write to the fd.

It is not okay to have multiple active uv_poll watchers for the same socket. This can cause libuv to busyloop or otherwise malfunction.

The user should not close a file descriptor while it is being polled by an active uv_poll watcher. This can cause the poll watcher to report an error, but it might also start polling another socket. However the fd can be safely closed immediately after a call to uv_poll_stop() or uv_close().

On windows only sockets can be polled with uv_poll. On unix any file descriptor that would be accepted by poll(2) can be used with uv_poll.

start(events, callback)
  • events (int) – Mask of events that will be detected. The possible events are pyuv.UV_READABLE or pyuv.UV_WRITABLE.
  • callback (callable) – Function that will be called when the Poll handle receives events.

Start or update the event mask of the Poll handle.

Callback signature: callback(poll_handle, events, errorno).


Stop the Poll handle.


Returns the file descriptor being monitored or -1 if the handle is closed.

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