Multiple SHChangeNotify's: Shell ignores most of them?

[Hein]

I've written a shell extension displaying overlay icons for files, and I'm
trying to get Explorer to update the file icon, displaying a changed
overlay. I use "SHChangeNotify(SHCNE_UPDATEITEM,...", but it only works when
I send very few notifycations at a time. When I try to update 10 or more
files at once, Explorer ignores (most of ) the notifications. Anyone
experiencing the same behavior, and knows how to work around it?

-Hartmut

[Jim Barry]

This is a well-known limitation of the shell update mechanism. You should be able to find some discussion about it by searching past messages from this group (http://groups.google.com).

--
Jim Barry, MVP for Windows SDK
"Honor Bound to Defend Freedom" - slogan displayed at the gates of Camp
Delta, Guantanamo Bay, Cuba, where over 600 prisoners are held indefinitely
by the U.S. military, without trial, in defiance of international law.

[Raymond Chen]

SHChangeNotify is not a general-purpose IPC mechanism. For perf reasons, if
you generate lots of notifications at once, the shell tries to combine them
to reduce message traffic. E.g., if you send out fifty "update items", the
shell will combine them into a single "update directory".

Otherwise you could launch a denial of service attack by going to a
directory and continuously updating files. Each one would create a separate
notification and soon explorer would run out of memory.

"Jim Barry" <j...@mvps.org> wrote in message
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bynt-T U.S. military, without trial, in defiance of international law.

[David Lowndes]

>SHChangeNotify is not a general-purpose IPC mechanism. For perf reasons, if
>you generate lots of notifications at once, the shell tries to combine them
>to reduce message traffic. E.g., if you send out fifty "update items", the
>shell will combine them into a single "update directory".

Raymond,

That sounds reasonable, but where's the documentation of this
behaviour?

Dave
--
MVP VC++ FAQ: http://www.mvps.org/vcfaq

[Raymond Chen]

This is one of those things you're not supposed to notice. If you send a lot
of file update notifications, they get combined into a single "directory
update" notification, and Explorer refreshes the entire directory - so the
operation still succeeds; the items you sent notifications on did get
updated. (as did a bunch of files that you didn't send notifications on, but
no harm done there)

"David Lowndes" <dav...@mvps.org> wrote in message
news:i6skovs0t5udhr93q...@4ax.com...

[David Lowndes]

>This is one of those things you're not supposed to notice. If you send a lot
>of file update notifications, they get combined into a single "directory
>update" notification, and Explorer refreshes the entire directory - so the
>operation still succeeds; the items you sent notifications on did get
>updated. (as did a bunch of files that you didn't send notifications on, but
>no harm done there)

It's OK that Explorer will refresh, but a 3'rd party application using
SHChangeNotifyRegister that doesn't know these rules may not be
monitoring for the amalgamated notification.

So, what do you think - shouldn't this behaviour be documented?

[Raymond Chen]

Good point - I had forgotten that SHChangeNotifyRegister is now a documented
function.

"David Lowndes" <dav...@mvps.org> wrote in message

news:a5t1pvo46fd1iqf77...@4ax.com...

[Patrick Walsh]

The workaround for preventing the shell of collapsing your events is to
include the flag SHCNF_FLUSH when you call ShChangeNotify. this will
garantee that the message will be delivered. See ShChangeNotify
documentation

"Hein" <m...@temp.com> wrote in message
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