Looking to trigger the end of a loop by the creation of a file.
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Don Green
Oct 2, 2021, 7:25:01 PM10/2/21
to Racket Users
Looking to trigger the end of a loop by the creation of a file.
Is this possible? Is this advisable?
Currently using:
a 'for' loop with
a 'for' loop guard expression to test for the existence of a file.
Tried file-exists? but that does not seem appropriate.
Tried using Racket function: filesystem-change-evt but that did not seem appropriate.
Is it possible to trigger an end condition on a 'for' loop by the creation of a file?
I suspect my problem is that it takes a significant amount of time for the operating system to register the creation of a file.
So maybe the best that can be done is to use file-exists? as it works but there a many loops of the 'for' loop before the end condition takes effect.
Any comments?
Is this possible? Is this advisable?
Currently using:
a 'for' loop with
a 'for' loop guard expression to test for the existence of a file.
Tried file-exists? but that does not seem appropriate.
Tried using Racket function: filesystem-change-evt but that did not seem appropriate.
Is it possible to trigger an end condition on a 'for' loop by the creation of a file?
I suspect my problem is that it takes a significant amount of time for the operating system to register the creation of a file.
So maybe the best that can be done is to use file-exists? as it works but there a many loops of the 'for' loop before the end condition takes effect.
Any comments?
Sorawee Porncharoenwase
Oct 2, 2021, 7:39:13 PM10/2/21
to Don Green, Racket Users
What do you mean by "Tried using Racket function: filesystem-change-evt but that did not seem appropriate."? What's inappropriate about it?
My first thought is to initialize a variable with `#f`. Spawn a thread before the loop that uses `filesystem-change-evt` so that when the event that you are interested in occurs, mutate the variable to `#t`. In the loop, break from the loop when the variable is `#t`.
I guess you can also poll `file-exists?` yourself in the thread, with some `sleep` between each polling.
Related library: https://github.com/zyrolasting/file-watchers/
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George Neuner
Oct 2, 2021, 10:49:56 PM10/2/21
to racket users
Is the loop doing something else while it waits? If not, you might as
well use filesystem-change-evt.
A polling loop /may/ respond faster than waiting on an event, but at the
level of user applications that is /not/ guaranteed. Is there some
reason you (think you) need to respond very quickly when the file is
created?
George
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