Apache HTTP Server Version 2.2

Apache > HTTP Server > Documentation > Version 2.2 > Modules

# Apache MPM event

Available Languages: en

Description: | An experimental variant of the standard `worker` MPM
Status: | MPM
Module Identifier: | mpm_event_module
Source File: | event.c

### Summary

### Warning

This MPM is experimental, so it may or may not work as expected.

The `event` Multi-Processing Module (MPM) is designed to allow more requests to be served simultaneously by passing off some processing work to supporting threads, freeing up the main threads to work on new requests. It is based on the `worker` MPM, which implements a hybrid multi-process multi-threaded server. Run-time configuration directives are identical to those provided by `worker`.

To use the `event` MPM, add `--with-mpm=event` to the `configure` script's arguments when building the `httpd`.

### Directives

### Topics

- How it Works
- Requirements
- Issues

### See also

- The worker MPM

## How it Works

This MPM tries to fix the 'keep alive problem' in HTTP. After a client completes the first request, the client can keep the connection open, and send further requests using the same socket. This can save signifigant overhead in creating TCP connections. However, Apache traditionally keeps an entire child process/thread waiting for data from the client, which brings its own disadvantages. To solve this problem, this MPM uses a dedicated thread to handle both the Listening sockets, and all sockets that are in a Keep Alive state.

The MPM assumes that the underlying `apr_pollset` implementation is reasonably threadsafe. This enables the MPM to avoid excessive high level locking, or having to wake up the listener thread in order to send it a keep-alive socket. This is currently only compatible with KQueue and EPoll.

## Requirements

This MPM depends on APR's atomic compare-and-swap operations for thread synchronization. If you are compiling for an x86 target and you don't need to support 386s, or you are compiling for a SPARC and you don't need to run on pre-UltraSPARC chips, add `--enable-nonportable-atomics=yes` to the `configure` script's arguments. This will cause APR to implement atomic operations using efficient opcodes not available in older CPUs.

This MPM does not perform well on older platforms which lack good threading, but the requirement for EPoll or KQueue makes this moot.

- To use this MPM on FreeBSD, FreeBSD 5.3 or higher is recommended. However, it is possible to run this MPM on FreeBSD 5.2.1, if you use `libkse` (see `man libmap.conf`).
- For NetBSD, at least version 2.0 is recommended.
- For Linux, a 2.6 kernel is recommended. It is also necessary to ensure that your version of `glibc` has been compiled with support for EPoll.

## Issues

At present, this MPM is incompatible with `mod_ssl`, and other input filters.

Available Languages: en