Solved

ReadDirectoryChangesW

Posted on 1998-11-20
6
1,341 Views
Last Modified: 2013-11-20
My application watches for change in specific file using ReadDirectoryChangesW Windows NT API function. Changes include file creation and last write. I user OVERLAPPED structure woth non signalled event. The structure is passed to ReadDirectoryChangesW function which immediately returns. Then I wait on event using WaitForSingleObject. When change in waching directory occurs ReadDirectoryChangesW signals event and WaitForSingleObject exits blocking state. Then I reset event and restart watch.
My problem is second time after I reset event ReadDirectoryChangesW immediately returns signaling event so I get two changes in the same file with the same parameters despite only one actual chnage (i.e. file was added to the directory) occured.
Could some one explain to me why ReadDirectoryChangesW notifies about file change twice?
0
Comment
Question by:galkin
  • 3
  • 2
6 Comments
 
LVL 86

Expert Comment

by:jkr
Comment Utility
I assume that the first notification is due to the 'file was added to directory' incident, whilst the second notification is related to the 'last time modified changed' incident for the directory itself...
0
 
LVL 7

Author Comment

by:galkin
Comment Utility
Maybe, but I am actually interested in getting one notification, namely last write to file if it exists or creating file if it does not. Action filed of FILE_NOTIFY_INFORMATION structure has FILE_ACTION_MOFIFIED value in both cases. I need somehow to distinguish and omit case when time stamp chnaged.
0
 
LVL 3

Accepted Solution

by:
vinniew earned 200 total points
Comment Utility
The problem is in the way ReadDirectoryChanges works underneath.  The NtCreateFile() function (in NTDLL.DLL) gets called twice and triggers it.
0
What Should I Do With This Threat Intelligence?

Are you wondering if you actually need threat intelligence? The answer is yes. We explain the basics for creating useful threat intelligence.

 
LVL 3

Expert Comment

by:vinniew
Comment Utility
Here are the flags for that api...

                                    FILE_NOTIFY_CHANGE_FILE_NAME      |      // filter conditions to watch for
                                          FILE_NOTIFY_CHANGE_DIR_NAME            |
                                          FILE_NOTIFY_CHANGE_ATTRIBUTES      |
                                          FILE_NOTIFY_CHANGE_SIZE                  |
                                          FILE_NOTIFY_CHANGE_LAST_WRITE      |
                                          FILE_NOTIFY_CHANGE_LAST_ACCESS      |
                                          FILE_NOTIFY_CHANGE_CREATION            |
                                          FILE_NOTIFY_CHANGE_SECURITY,



If you want to get file creation - specific notification, you can call readdirectorychanges multiple times, once for the notification of creation and once for the others, and use the event handle in WaitForMultipleObjects()... The event that triggers is the one that will have the notification you want.  E-mail your readdirectorychanges snippet to me and I can code what I'm talking about...
0
 
LVL 7

Author Comment

by:galkin
Comment Utility
Thank's for explanation. But i need to folter only one call. My another problem with ReadDirectoryChangesW is that it locks directory. I try from Explorer to duplicate file using copy/paste in directory wached but I have an error "Sharing valuation. Source or target may be in use"
0
 
LVL 7

Author Comment

by:galkin
Comment Utility
The problem  is ReadDirectoryChangesW with FILE_NOTIFY_CHANGE_LAST_WRITE notifies twice about change and there is no way do distinguish between chnage for instance in last write and time stampt as they are reffered in the same FILE_ACTION_MOFIFIED bit.
0

Featured Post

Why You Should Analyze Threat Actor TTPs

After years of analyzing threat actor behavior, it’s become clear that at any given time there are specific tactics, techniques, and procedures (TTPs) that are particularly prevalent. By analyzing and understanding these TTPs, you can dramatically enhance your security program.

Join & Write a Comment

Introduction: Dialogs (2) modeless dialog and a worker thread.  Handling data shared between threads.  Recursive functions. Continuing from the tenth article about sudoku.   Last article we worked with a modal dialog to help maintain informat…
Exception Handling is in the core of any application that is able to dignify its name. In this article, I'll guide you through the process of writing a DRY (Don't Repeat Yourself) Exception Handling mechanism, using Aspect Oriented Programming.
This video will show you how to get GIT to work in Eclipse.   It will walk you through how to install the EGit plugin in eclipse and how to checkout an existing repository.
This video shows how to remove a single email address from the Outlook 2010 Auto Suggestion memory. NOTE: For Outlook 2016 and 2013 perform the exact same steps. Open a new email: Click the New email button in Outlook. Start typing the address: …

763 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

14 Experts available now in Live!

Get 1:1 Help Now