This turned out to be a race between the dashboard's dataset db
subscriber being initialised and the applet "embed" request, with
artiq.applet.simple not being able to handle the unexpected "mod"
message. We were only handling the other ordering outcome of this
race before.
I had introduced this in f11aef74b as a means of quickly cleaning up
after e.g. an exploratory session where a lot of transient applets were
opened from ndscan, or for a dashboard that has been running for a while
with CCBs enabled but without anybody actually working there.
It turns out that one usually wants the few docked applets to stay open,
as they were necessarily arranged manually at some prior point. And as a
corollary to the latter, if one did want to close them as well, doing so
manually would not be too onerous either.
This allows ndscan v0.3+ to use the IPC interface for efficiency;
previously, the non-upstreamed RID dataset namespace feature allowed
the applets to somewhat efficient subscribe directly to the master
process via the socket interface.
Quickly closing/reopening applets (e.g. quickly clicking the checkbox
on an entire folder of applets) would previously lead to an occasional
KeyError on the self.dock_to_item access in on_dock_closed, as close()
would be invoked more than once.
The geometry/checked state handling can potentially be cleaned up
further, but at least this avoid the crash.
True to itself, Qt did not miss the opportunity to trash widgets inside
QTreeWidgetItems when they are moved by drag-and-drop. Problem known for
more than 6 years and still not fixed as of Qt 5.7.
This only makes a difference on POSIX. It prevents subprocesses
from receiving the signals that the parent receives. For ctlmgr
and master is cuts down on spam on the console (KeyboardInterrupt
tracebacks from all controllers) and enforces that proper
termination is followed.
This does not help if the parent gets SIGKILL (subprocesses
may linger).
