/Apache HTTP Server

Apache MPM winnt

Description: Multi-Processing Module optimized for Windows NT.
Status: MPM
ModuleIdentifier: mpm_winnt_module
SourceFile: mpm_winnt.c


This Multi-Processing Module (MPM) is the default for the Windows NT operating systems. It uses a single control process which launches a single child process which in turn creates threads to handle requests

Capacity is configured using the ThreadsPerChild directive, which sets the maximum number of concurrent client connections.

By default, this MPM uses advanced Windows APIs for accepting new client connections. In some configurations, third-party products may interfere with this implementation, with the following messages written to the web server log:

Child: Encountered too many AcceptEx faults accepting client connections.
winnt_mpm: falling back to 'AcceptFilter none'.

The MPM falls back to a safer implementation, but some client requests were not processed correctly. In order to avoid this error, use AcceptFilter with accept filter none.

AcceptFilter http none
AcceptFilter https none

In Apache httpd 2.0 and 2.2, Win32DisableAcceptEx was used for this purpose.

The WinNT MPM differs from the Unix MPMs such as worker and event in several areas:

  • When a child process is exiting due to shutdown, restart, or MaxConnectionsPerChild, active requests in the exiting process have TimeOut seconds to finish before processing is aborted. Alternate types of restart and shutdown are not implemented.
  • New child processes read the configuration files instead of inheriting the configuration from the parent. The behavior will be the same as on Unix if the child process is created at startup or restart, but if a child process is created because the prior one crashed or reached MaxConnectionsPerChild, any pending changes to the configuration will become active in the child at that point, and the parent and child will be using a different configuration. If planned configuration changes have been partially implemented and the current configuration cannot be parsed, the replacement child process cannot start up and the server will halt. Because of this behavior, configuration files should not be changed until the time of a server restart.
  • The monitor and fatal_exception hooks are not currently implemented.
  • AcceptFilter is implemented in the MPM and has a different type of control over handling of new connections. (Refer to the AcceptFilter documentation for details.)

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Licensed under the Apache License, Version 2.0.