select – Waiting for I/O efficiently

This module implements the corresponding CPython a subset of modules, as follows, refers to CPython document for details: select

This module provides the function of waiting for multiple events ``streams``（Ready to operate selection flow）.

Function

select.poll()

Create an instance of the Poll class.

select.select(rlist, wlist, xlist[, timeout])

When the monitoring object is readable or writable, once the status of the monitored object changes, the result (blocking thread) is returned. This function is for compatible but inefficient. It is recommended to use the poll function.

  • rlist：Array of file descriptors waiting to be read ready
  • wlist：Array of file descriptors waiting to be written
  • xlist：Array waiting for exception
  • timeout：Waiting time in seconds
Poll class

method

poll.register(obj[, eventmask])

Register an object for monitoring, eventmask is logic OR：stream

  • obj :Monitored objects

    • select.POLLIN - Read available data
    • select.POLLOUT - Write more data
    • select.POLLERR - Error occurred
    • select.POLLHUP - Flow end / connection end detection

    Attention to signs like uselect.POLLHUP and uselect. Is POLLERR valid for input eventmask (These are the unsolicited events from return poll(), whether they are requested or not）. This semantics is based on POSIX.

eventmask defaults to select.POLLIN | select.POLLOUT.

This function can be called multiple times for the same obj . Continuous call will update the value of eventmask to eventmask of OBJ（It will be shown as modify() ）.

poll.unregister(obj)

Unregister OBJ from polling.

poll.modify(obj, eventmask)

Modify registered object obj , If OBJ is not registered, an ENOENT error occurs for OSErrorr.

poll.poll([timeout])

Optional timeout waiting for at least one registered object to be ready or with exception conditions（in milliseconds）（If timeout Arg or - 1 is not specified, there is no timeout）.

Returns a tuple ( obj, event, …)of the list. There may be other elements in the tuple, depending on the platform and version, so don’t assume its size is 2.

The event element specifies the event that occurs in the flow, And it’s uselect.POLL* a combination of the above constants. What needs to be noted is the logo uselect.POLLHUP , and uselect.POLLERR can be returned at any time (even if not required), Appropriate action must be taken (from investigating unregistered and potentially closed flows), Otherwise, all further calls to poll() can use these flag settings to immediately return to this stream again.

If it times out, an empty list is returned.

Difference to CPython

The returned tuple may contain more than 2 elements, as described above.

poll.ipoll([timeout])

and poll.poll() similar, but returns an iterator that produces all tuples of the called function. This function provides an efficient, non location polling method in the stream.

differences with CPython

This function is an extension of MicroPython.