# Multi-Processing Module threaded

This Multi-Processing Module implements a hybrid multi-threaded multi-process web server.

Status: MPM
Source File: threaded.c
Module Identifier: mpm_threaded_module

## Summary

This Multi-Processing Module (MPM) is the default for most unix-like operating systems. It implements a hybrid multi-process multi-threaded server. Each process has a fixed number of threads. The server adjusts to handle load by increasing or decreasing the number of processes.

A single control process is responsible for launching child processes. Each child process creates a fixed number of threads as specified in the `ThreadsPerChild` directive. The individual threads then listen for connections and serve them when they arrive.

Apache always tries to maintain a pool of spare or idle server threads, which stand ready to serve incoming requests. In this way, clients do not need to wait for a new threads or processes to be created before their requests can be served. Apache assesses the total number of idle threads in all processes, and forks or kills processes to keep this number within the boundaries specified by `MinSpareThreads` and `MaxSpareThreads`. Since this process is very self-regulating, it is rarely necessary to modify these directives from their default values. The maximum number of clients that may be served simultaneously is determined by multiplying the maximum number of server processes that will be created (`MaxClients`) by the number of threads created in each process (`ThreadsPerChild`).

While the parent process is usually started as root under Unix in order to bind to port 80, the child processes and threads are launched by Apache as a less-privileged user. The `User` and `Group` directives are used to set the privileges of the Apache child processes. The child processes must be able to read all the content that will be served, but should have as few privileges beyond that as possible. In addition, unless suexec is used, these directives also set the privileges which will be inherited by CGI scripts.

`MaxRequestsPerChild` controls how frequently the server recycles processes by killing old ones and launching new ones.

See also: Setting which addresses and ports Apache uses.

## Directives

- CoreDumpDirectory
- Group
- PidFile
- Listen
- ListenBacklog
- LockFile
- MaxClients
- MaxRequestsPerChild
- MaxSpareThreads
- MinSpareThreads
- ScoreBoardFile
- SendBufferSize
- StartServers
- ThreadsPerChild
- User