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Q74528: INFO: "Power-Friendly" Applications

Article: Q74528
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s): 
Keyword(s): kb16bitonly kbSDKPlatform kbSysSettings
Last Modified: 10-JUN-1999

3.00 3.10
WINDOWS
kbprg

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) 3.1 
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SUMMARY
=======

Power-managed personal computers, such as some battery-powered notebook
computers, are designed to conserve power during periods of CPU inactivity or
"idle time." Although most power-saving measures should occur transparently to
an application, developers should be aware of several attributes that make an
application "power friendly."

To qualify as "power-friendly," an application must use the PeekMessage and Yield
functions carefully, preferably only for temporary background tasks. As long as
an application is in a PeekMessage loop, the Windows system cannot go idle.
Therefore, an application should not remain in a PeekMessage loop after its
background processing has completed.

MORE INFORMATION
================

Traditionally, an application running in the Windows multitasking environment
needed only to ensure that once it was finished with its processing it yielded
the processor to other applications in the system. However, the increased
popularity of battery-powered systems imposes another responsibility on
applications: to allow Windows to "go idle" as often as possible.

To Windows, the system appears idle when all executing programs are awaiting
input. All applications have called the GetMessage or WaitMessage function, and
no pending messages are in any application queue. At such times, the Windows
kernel broadcasts an idle notification by using an MS-DOS interrupt. A
power-managed PC can use this notification as a signal to take power-saving
measures.

When an application is in a PeekMessage or Yield loop, it prevents Windows from
going idle, thus thwarting attempts by power-managed PCs to save power.

An application's main message handler should use a GetMessage loop or equivalent
structure (such as the combined use of the PeekMessage and WaitMessage
functions) when no background processing is required. This allows Windows to go
idle and power-saving measures to take effect.

Applications that must periodically service a task (for example, a communications
connection) should poll, in response to a message from a timer, if there is no
other way to determine when the status of the device changes.

Additional query words: 3.00 3.10 APM

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Keywords          : kb16bitonly kbSDKPlatform kbSysSettings 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1
Issue type        : kbinfo

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