雖然我們大多數人可能很少考慮每次關閉電腦時發生的所有事情，但在關閉過程中到底發生了什麼？今天的超級使用者問答帖子回答了一位好奇的讀者的問題。

今天的問答環節是由SuperUser提供的，SuperUser是Stack Exchange的一個分支，是一個由社群驅動的問答網站分組。

問題

超級使用者閱讀器RACING121想知道Windows計算機關閉時實際發生的情況：

When I click the shutdown button on my Windows system, it gives me another screen saying Shutting down:

What is actually going on during this stage?

If I recall correctly, in Windows XP it would say something like Saving Settings before powering off. However, what settings are there to actually save here? For example,  if you have applied a theme or completed some other action, it has already been “saved” when you clicked Apply or Ok.

If it is unmounting the hard drive, then surely it would be the same as forcing a shutdown by pulling the plug, right?

當一臺Windows計算機經歷關機過程時，實際發生了什麼？

答案

超級使用者貢獻者Keltari和zzarzzur為我們提供了答案。首先，凱爾塔裡：

There are a lot of things happening during the shutdown process. Here are just a few examples:

• Checking to see if any user applicati*** have not been closed yet (like an unsaved document) and prompt the user if necessary
• Stopping background services
• Waiting for the termination signal from services and applicati*** that are open or running
• Flushing the cache to disk
• Writing log files
• All users are logged out
• Ending the shell
• Start installing Windows updates and tell the system to finish the update process during the next system start-up if necessary
• Send the ACPI shutdown signal (this is what turns the machine off)

然後是扎爾祖爾的回答：

The system registry is (maybe?) written to the disk. Back when I used Windows XP, I noticed that if you made any changes to the registry then pulled the power, the changes would not be saved. I am not quite sure about this one, just pointing it out.

Here is an excerpt from a document that Microsoft released:

• System session shutdown. This phase includes the pre-shutdown notification and shutdown notification sub-phases.
• Pre-shutdown notification. Windows serially shuts down all services that registered to receive pre-shutdown notificati***. Ordered services—services that have set up the shutdown order of dependent services—are shut down before non-ordered services.
• Shutdown notification. All services that registered to receive shutdown notificati*** are shut down in parallel. If all services have not exited after 20 seconds (in Windows Vista) or 12 seconds (in Windows 7 client operating systems), the system continues the shutdown. Processes and services that do not shut down in a timely manner are left running as the system shuts down.
• Kernel shutdown. The remainder of the system, such as all devices and drivers, are shut down during the kernel shutdown phase.

Basically, what you are waiting on is each individual service to clean up and exit. Each service is given 12 seconds to exit before it is killed.

Half of the shutdown time is dedicated to shutting down system services. If you are really interesting in seeing what time is dedicated to whatever during a shutdown, Windows includes a tool for tracing shutdown time.

• xbootmgr -trace shutdown -numRuns 3 -resultPath %systemdrive%\traces -postBootDelay 180 -traceFlags base

And to make sense of the generated file (be sure to run in %systemdrive%\traces)

• xperf -i trace.etl -o summary.xml -a shutdown

Sources

Windows On/Off Transition Performance Analysis Document [Microsoft]

Windows On/Off Transiti*** Soluti*** Guide Document [Microsoft]

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