New Select Module

TableOfContents(3)

Introduction

There is now select support in the [http://www.jython.org/Project/download.html jython distribution], as of version 2.2rc1.

The new module presents an API which is as close as possible to the [http://www.python.org/doc/lib/module-select.html cpython select module], Jython supports both the

1. select.select function

2. [http://www.python.org/doc/lib/poll-objects.html select.poll objects].

When using the select module, you should be guided by the cpython documentation: any deviation from the behaviour described in that documentation should be considered a bug and [http://www.jython.org/bugs reported] as such.

Differences between cpython and jython

However, due to fundamental differences in the behaviour of java and C on various platforms, there are differences between the cpython and jython select modules which are not possible to code around. Those differences will be listed here.

Only sockets in non-blocking mode can be multiplexed

On cpython, when a socket is passed to select.select or select.poll, it can either be in blocking or non-blocking mode.

However, [http://java.sun.com/j2se/1.4.2/docs/api/java/nio/channels/SelectableChannel.html#register(java.nio.channels.Selector,%20int) java will only permit multiplex operations on sockets that are in non-blocking mode]; any attempt to pass a socket in blocking mode to either select.select or select.poll().register will fail with an exception.

To summarise

1. You must set a socket in non-blocking mode before passing it to the select function or registering it with a poll object
2. Any attempt to register a blocking socket for multiplex will raise a select.error exception, with an error code of errno.ESOCKISBLOCKING
3. If a socket is currently registered with a select.poll object, an attempt to change it to blocking mode will give rise to the same exception.

4. A socket can only be placed in blocking mode if it is not registered with a select.poll object.