如何监视文件的更改？

Question

How do I monitor rtf file to check if it is updated for a while (lets say 15 min). If not updating then let the main thread know that file is not updated. I am thinking of using WaitforSingleObject function to wait for any changes in last 15 minute. how can I implement this funcationality?

Answer 1

我相信正在寻找的是文件更改通知，例如FindFirstChangeNotification ， FindNextChangeNotification和ReadDirectoryChangesW您可以监视文件或目录的更改，重命名，写入等。

Answer 2

Presumably your platform is Windows since you mention WaitForSingleObject. In which case the function you are looking for is ReadDirectoryChangesW . This will allow you to be notified as soon as changes are made, without you performing any polling.

Jim Beveridge has an excellent pair of articles that go into some depth:

• http://qualapps.blogspot.com/2010/05/understanding-readdirectorychangesw.html
• http://qualapps.blogspot.com/2010/05/understanding-readdirectorychangesw_19.html

Answer 3

You can stat() the file, check its modification date and act appropriately.

You can also periodically compute a checksum of the file and compare it to the previous one.

For RTF files you can also take the size of the file and compare it to the previous size; if it's been modified it's very likely the size will be different.

All those methods will probably introduce more overhead than the system calls mentioned by others.

Answer 4

In my opinion, you can achieve this in two ways. You can write a file filter driver that can monitor write operation on the file. However this is little bit stretching.

Another way is simple one. In your main thread, create a hash of your RTF file and cache it. Create an event in non-signaled state, create a callback function, create a worker thread. Wait in the worker thread on event for 15 min. After timout, again generate hash of your file and compare it with cached hash. If mismatch, notify your main thread through callback function.