Detecting Idle Time in Windows (96422)
The information in this article applies to:
- Microsoft Windows Software Development Kit (SDK) 3.1
This article was previously published under Q96422 SUMMARY
When the system goes idle under Microsoft Windows version 3.1, Kernel
issues a single Interrupt 2Fh function 1689h call. This interrupt can be
used by a Windows-based application to detect idle time.
MORE INFORMATION
Listed as "Windows kernel idle call" in the INT2FAPI.INC file of the
Windows Device Development Kit (DDK) version 3.1, Interrupt 2Fh
function 1689h is the system-idle notification. To be notified when
the system becomes idle, a Windows-based application must put an interrupt
service routine (ISR) in the Interrupt 2Fh chain using the MS-DOS Set
Interrupt Vector call (Interrupt 21h function 25h), and look for AX
register equal to 1689h. The ISR must call the address of the old
handler to pass the control down the Interrupt 2Fh chain. The address
of the old handler can be retrieved using the MS-DOS Get Interrupt
Vector call (Interrupt 21h function 35h).
The ISR must be part of a device driver, dynamic-link library (DLL),
or installable device driver. Furthermore, the ISR is required to be
in a fixed segment. This can be accomplished by marking the segment of
the ISR as PRELOAD FIXED in the module definition (.DEF) file for the
DLL.
Hooking Interrupt 2Fh function 1689h to detect idle time can result in
performance degradation. Therefore, if a Windows-based application only
needs to perform background processing, it must use the PeekMessage()
and WaitMessage() functions. Only those applications that need to detect
idle time (for example, benchmarking applications) should use
Interrupt 2Fh.
| Modification Type: | Minor | Last Reviewed: | 8/2/2004 |
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| Keywords: | kb16bitonly KB96422 |
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