Re: FileSystemWatcher Created() delay
- From: "Michael D. Ober" <obermd.@.alum.mit.edu.nospam>
- Date: Sat, 21 Jan 2006 19:24:21 GMT
It's using FindFirstChangeNotification. The flag options correspond
one-to-one with this API. However, FSW does some additional work to ensure
the file that triggered the event matches you file template. In the API,
any file will end the wait state and return.
Mike Ober.
"Tushar" <xxTushar.Karsan@xxxxxxxxxx> wrote in message
news:OmHlwHeHGHA.2036@xxxxxxxxxxxxxxxxxxxxxxx
> I get the following...
>
> The process cannot access the file "C:\...\log-Wed.txt" because it is
being
> used by another process IOException.
>
> Behind the scenes .Net must be using
>
> HANDLE FindFirstChangeNotification(
> LPCTSTR lpPathName, // pointer to name of directory to watch
> BOOL bWatchSubtree, // flag for monitoring directory or directory
tree
> DWORD dwNotifyFilter // filter conditions to watch for
> );
>
> or
>
> BOOL ReadDirectoryChangesW(
> HANDLE hDirectory, // handle to the directory to be watched
> LPVOID lpBuffer, // pointer to the buffer to receive the read
results
> DWORD nBufferLength, // length of lpBuffer
> BOOL bWatchSubtree, // flag for monitoring directory or directory tree
> DWORD dwNotifyFilter, // filter conditions to watch for
> LPDWORD lpBytesReturned, // number of bytes returned
> LPOVERLAPPED lpOverlapped, // pointer to structure needed for overlapped
> I/O
> LPOVERLAPPED_COMPLETION_ROUTINE lpCompletionRoutine // pointer to
> completion routine
> );
>
> Please help
>
> "Kevin Spencer" <kevin@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
> news:usY5QldHGHA.3896@xxxxxxxxxxxxxxxxxxxxxxx
> Hi Tushar,
>
> My apologies. After thinking about it, I realized that an event *may* be
> raised when the file handle is created. I have scoured the .Net
> documentation, and Google to find an answer, but there is no indication in
> the .Net docs as to what events exactly the FileSystemWatcher is
subscribing
> to.
>
> Therefore, I may be in error with my first statement.
>
> So, let me back up a bit and see if I can be more helpful. Since it is not
> documented anywhere exactly what event the FileSystemWatcher is monitoring
> when a file is created, and we cannot know, perhaps we can look at your
> requirements and figure out a workaround.
>
> Your original message read:
>
> >> the problem I'm having is that the file does not seem to be available
> >> when
> >> I
> >> receive this event.
>
> So, my first question is, what do you need to do with the file? It
certainly
> does seem that one of your requirements is that you do something with the
> file. Assuming that you do need to access the file, and you state that it
> "does not seem to be available," how do you know that it is not available?
> That is, are you getting some kind of error? For example, if you are
trying
> to open the file while it is in use by another process, an exception will
be
> raised.
>
> If so, I do know (this time!) that there is no way to easily tell if a
file
> is in use by another process. It is actually less expensive to use a
> try/catch to figure this out (it could be done with unmanage API calls,
but
> again, that's a lot of trouble). So, one solution would be to create a
loop
> that has a try/catch in it. The try clause would end by exiting the loop.
> The catch would put the thread to sleep for a few cycles, and continue the
> loop. Something like:
>
> int timeout = 30; // seconds to wait before giving up
> while (true)
> {
> try
> {
> using (FileStream fs = new FileStream(filePath, FileMode.Open,
> FileAccess.Read))
> {
> // do something here
> }
> break;
> }
> catch
> {
> if (--i == 0)
> throw new Exception("Unable to open file '" + filePath + "'");
> Thread.Sleep(1000);
> }
> }
>
> --
> HTH,
>
> Kevin Spencer
> Microsoft MVP
> .Net Developer
> Who is Mighty Abbott?
> A twin turret scalawag.
>
> "Tushar" <xxTushar.Karsan@xxxxxxxxxx> wrote in message
> news:%23kxQS6cHGHA.3176@xxxxxxxxxxxxxxxxxxxxxxx
> > Very cleaver. I suppose my question is whether 'created' means:
> >
> > 1) Created directory entry (but file has no data whatsoever)
> > 2) Completed creating the file (which is written to and closed)
> >
> > I think you are suggesting it is 2) but then why is it not avilable for
> > reading at that stage on my PC? Why is it available after 3 seconds?
> >
> >
> > "Kevin Spencer" <kevin@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
> > news:Oskum1bHGHA.140@xxxxxxxxxxxxxxxxxxxxxxx
> >> Does anyone know when is this event raised, is it:
> >> 1) When the file is created but may not have been closed
> >> 2) When the file is created AND it has been closed
> >
> > Is a house created when you start digging the foundation?
> >
> > When you "create" a file in software, all you have done is opened a
stream
> > to the disk for writing. You have written nothing to the disk. While you
> > are
> > writing to the disk, the file is *being* created. When you close the
> > handle,
> > the file *has been* created. Completed. Finished. Remember that
"created"
> > is
> > the *past* tense of the verb "create." I will create. I do create. I am
> > creating. I created.
> >
> > --
> > HTH,
> >
> > Kevin Spencer
> > Microsoft MVP
> > .Net Developer
> > Who is Mighty Abbott?
> > A twin turret scalawag.
> >
> > "Tushar" <xxTushar.Karsan@xxxxxxxx> wrote in message
> > news:uDU$QjaHGHA.1032@xxxxxxxxxxxxxxxxxxxxxxx
> >> Followup-To: microsoft.public.dotnet.general
> >>
> >> Does anyone know when is this event raised, is it:
> >> 1) When the file is created but may not have been closed
> >> 2) When the file is created AND it has been closed
> >>
> >> I am using this control in a Windows-Service I've developed. It works
> >> hoever
> >> the problem I'm having is that the file does not seem to be available
> >> when
> >> I
> >> receive this event. If I include a delay of a few seconds using
> >> Sleep(3000)
> >> for example in the event method then the file does become available. It
> >> is
> >> as if the application that created the file has not finished with the
> >> file
> >> when the event is raised.
> >>
> >> Could it be that the Anti-Virus gets hold of it also and checking when
I
> >> receive the event. I do not have the rights to stop the AV and
therefore
> >> I
> >> could not test. If it is not the AV then I see no point if having this
> >> API
> >> if one is having to poll for the file to become availabe (to be closed
by
> >> the creating application) for it to be processed by the event receiving
> >> application.
> >>
> >> Please help.
> >>
> >>
> >
> >
> >
>
>
>
.
- References:
- Re: FileSystemWatcher Created() delay
- From: Kevin Spencer
- Re: FileSystemWatcher Created() delay
- From: Tushar
- Re: FileSystemWatcher Created() delay
- Prev by Date: Re: Exception Logging With Visual Studio 2005
- Next by Date: sending mouse events to other applications' windows in .net/c#
- Previous by thread: Re: FileSystemWatcher Created() delay
- Next by thread: Re: FileSystemWatcher Created() delay
- Index(es):
Relevant Pages
|
