Re: [equinox-dev] [prov] directory watcher

[Jeff McAffer <Jeff_McAffer@xxxxxxxxxx>]

For the most part the DirectoryWatcher
is very similar to what Peter did originally.  That is, it just polls
using a configurable delay.  It certainly could be extended to hook
the filesystem to get change notifications.  We have all the required
infrastructure in the resources plugins so it should be relatively easy.

The DirectoryWatcher also notices changes
(based on File.lastModified()) and file deletions.  The "JARListener"
translates file timestamp changes into BundleContext.update() and file
deletions into BundleContext.uninstall().  In some cases a file might
be locked (e.g., if you installed a bundle by reference: and a classloader
has it open).  In that case you can "virtually delete" the
file by adding a sibling file of the same name but with ".del"
appended.  The DirectoryWatcher will notice this and process the base
file (the one without .del) as though it had been removed (e.g., the corresponding
bundle would be uninstalled).  Then, at the end of each polling cycle
the DirectoryWatcher attempts to delete all "virtually deleted"
base files as well as the corresponding delete marker files (.del files).
 I'm sure there are holes in the actual implementation but initial
testing shows that it works quite handily.

Some notes:
- currently bundles are installed using
standard OSGi installBundle().  That is, they are not installed by
reference so you end up with two copies of the bundle on disk.  Worse,
you get one copy per configuration that used this technique.   We
should look at having an option to install by reference.
- The real intention is to have this
be a replacement for Update Manager's promiscuous install behaviour.  People
have grown quite used to dropping some files in the plugins dir and having
them show up in Eclipse on next run.   With p2 that will not happen
natively.  With the DirectoryWatcher and a p2 listener, users should
be able to identify as many directories as they want and have bundles added
and removed from them *dynamically* installed/uninstalled/updated.  So
in the end users get enhanced functionality.

Jeff

"Alex Blewitt" <alex.blewitt@xxxxxxxxx>
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08/30/2007 03:58 AM

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Subject	Re: [equinox-dev] [prov] directory watcher

Interesting. Does it periodically scan for changes,
or does it hook in
with the underlying file system notifications to receive changes? I
believe that the Win32 resources API has the ability to pick up
changes; it would be good if that worked for other systems too.

Does it do the reverse, uninstalling a bundle if the corresponding
file is deleted?

Alex.

On 30/08/2007, Jeff McAffer <Jeff_McAffer@xxxxxxxxxx> wrote:
>
> I finally did something that has been on my list for quite some time.
>  Inspired by Peter Kriens' FileInstall bundle, I made a DirectoryWatcher
> that, as the name implies, watches a directory and installs, uninstalls,
> configures, ... things that are dropped into/removed from/changed
in the
> dir.  The current working support directly calls installBundle()
etc but I
> have also been working on one that calls p2 API to effect and install.
 The
> design consists of a DirectoryWatcher with which you can register
listeners.
>  The listeners then get added, removed and changed events for
the files of
> interest in the directory being watched.  It is quite easy to
create a new
> listener that does your own thing.
>
> Keeping in mind that this is quite early, take a look at
>         org.eclipse.equinox.p2.directorywatcher
> I have added not this to the PSF files yet as there are some compile
errors
> in the provisioning listener as I have not completed enhancing the
metadata
> generator to work on individual files rather than directories.  More
to come
> later...
>
> Jeff
>
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>
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