On 7/30/2022 3:53 PM, Paul Dupuis via use-livecode wrote:
My understanding of 'wait 0 with messages' is that it will cause any
pending messages, that are not scheduled for a time later than the
current time, in the pendingMessages queue to be processed before
continuing. Messages later than the current time (when the statement
is executed) will not be processed (yet).
Is this correct?
First, than you to those that have responded.
The reason I got curious about 'wait 0 with messages' (or even just
'wait 0') is because of an epiphany I had just last week regarding a bug
a customer reported in our software. The customer experienced and
execution error and our software presents a custom dialog that allows
them to email out support account some information, including the
'executionContexts' so we have some code debugging information.
The problem as a 'can't find object' error. In reviewing the code, I
could see no way that the error should have occurred. The code was using
the ChartMaker library to create a graph. It all looked good per
documentation and we could not reproduce the error in house. I then
noticed a 'wait 0 with messages' prior to the line the error occurred on
and noticed that the line that had the error used object references
relative to the current stack (which the defaultStack was explicitly set
to much prior).
My epiphany was realizing - for the first time, despite LiveCodeing
since HyperCard and having a Masters in Computer Science and my entire
career being in the IT/software development space for over 40 years -
that when the 'wait 0 with messages' is executed, if there was a pending
USER click on another window, the defaultStack could change and then the
relative object references would not be able to find their target objects.
Perhaps I should have realized that a 'wait 0 with messages' COULD
result in the defaultStack changing much sooner OR perhaps I should
always fully qualify all object references (which I have been doing for
quite a few years, but this was old code), but it is a 'gotcha' of using
wait with messages I had never thought of.
The Dictionary Entry (LC 9.6.8) does state "If the wait..with messages
form is used, LiveCode continues normal processing during the wait. The
current handler is frozen, but the user can start other handlers and
perform other actions such as switching cards." and 'switching cards'
does imply changing the context of relative object references even if
the defaultStack does not change, so perhaps I should have realized, but
didn't until just last week.
Now I am very curious about exactly what wait 0 with messages does and
also about what actions change the defaultStack. Does anyone know of an
article or something someone has done to identify all the messages,
commands, or functions that change (or potentially change) the defaultStack?
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