WatchService

[Alan Bateman]

wolfgang.baltes wrote:
>
> Hi,
>
> I have started to use the WatchService and would like to get 
> confirmation for some of my observations. At least one of them is not 
> in agreement with the documentation.
>
> My system is Windows 7 Ultimate 64bit with JDK7-b121 32bit and using 
> Eclipse 3.61 32bit as the development platform. I am writing a piece 
> of code that watches one or several directories recursively or not for 
> file additions and deletions.
>
> My observations are for a directory tree where all 
> directories/subdirectories are being watched. I use Windows Explorer 
> to copy files and directory trees into this directory tree and to 
> delete them.
>
> 1 - If I delete a file at any level in the tree, then I get the 
> ENTRY_DELETE event for the file and an ENTRY_MODIFIED event for its 
> parent directory. - This should be normal.
>
> 2 - If I delete a subdirectory that contains files but no further 
> subdirectories, then I receive an ENTRY_DELETE event for the 
> subdirectory and an ENTRY_MODIFIED event for its parent directory. In 
> addition - and only sometimes - I also receieve ENTRY_DELETE events 
> for the files within the subdirectory. - I assume that this is normal, 
> although I don't understand the random behavior of getting or not 
> getting events regarding the files.
>
> 3 - If I try to delete a subdirectory tree - that is a subdirectory 
> with nested directories - then Windows Explorer does not let me delete 
> the tree. The WatchService seems to block this. I can however, delete 
> this tree by starting at the bottom (leaf) directories and delete them 
> one at a time. This corresponds essentially to the scenario described 
> in 2. - This may be normal, but is certainly not convenient. Is this a 
> Windows feature?
>
> 4 - Contrary to the documentation (tutorial on WatchService), the 
> WatchKey remains valid (isValid()) after deletion of the associated 
> directory. That is, the expression (dir.notExists() && key.isValid()), 
> where key is the WatchKey associated with dir is true. The first part 
> of the expression confirms that dir is deleted, and the second part 
> should be false if the key is automatically cancelled. - I don' think 
> this is normal at all!
>
> Thanks for any comments you may have,
>
For item 3, yes, unfortunately if you are watching a directory then 
Windows prevents you deleting or moving the directory's parent. It's not 
a problem deleting the directory that is being watched, it's the parent 
that is the issue.  We have a bug tracking it:
    
http://bugs.sun.com/view_bug.do?bug_id=6972833

but I don't think there is anything we can do because it seems to be a 
Windows limitation.

I'm interested if you can create a test case to demonstrate item 4. When 
a watched directory is deleted then we get a notification from Windows 
(via a completion port) and that causes the key to be invalidated. We 
have various test cases for this and I'm not aware of any issues.

-Alan