ID Number: Q74528
3.00 3.10
WINDOWS
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 functions, 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
will allow 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.
For more information about PeekMessage loops and idle time, query the
Microsoft Knowledge Base on the following words:
prod(winsdk) and peekmessage and idle
For more information about background processing in applications
running in the Windows environment, including references to sample
source code, query the Microsoft Knowledge Base on the following
words:
prod(winsdk) and backproc
Additional reference words: 3.00 3.10 APM backproc