How to check if a Task is already running?

Honitos · 16 December 2019, 09:41

I want to check, if my program has been started before to prevent another instance by double clicking the icon again by mistake.

I cannot use FindTask() as it will always find itself, so I cannot find the other task that MAY be started before.

deimos · 16 December 2019, 09:58

AttemptSemaphore?

daxb · 16 December 2019, 11:24

Check if program message port is open or not maybe?

ross · 16 December 2019, 11:47

I check with

jsr (_LVOFindPort,a6)

if there is already a named port, possibly added with a precedent

jsr (_LVOAddPort,a6)

.

There are probably better methods but this works, in every kickstart, and is very simple.

BastyCDGS · 23 December 2019, 08:22

Another possibility is to Lock() your program's executable with exclusive access mode straight after start.

This way you get a meaningful error message via IoErr() (202: object is busy), if it's opened again.
However, there is a caveat, if your program crashes, the lock might remain open forever, so prepare special cleanup code for this.

The FindPort solution is nice, too, but you should be careful about name collisions with other applications running.

And beware of race conditions occuring by both methods! Always sempahore protect such code!

Wilsom1992 · 28 February 2020, 10:30

Quote:

Originally Posted by BastyCDGS

Another possibility is to Lock() your program's executable with exclusive access mode straight after start.

This way you get a meaningful error message via IoErr() (202: object is busy), if it's opened again.
However, there is a caveat, if your program crashes, the lock might remain open forever, so prepare special cleanup code for this.

The FindPort solution is nice, too, but you should be careful about name collisions with other applications running.

And beware of race conditions occuring by both methods! Always sempahore protect such code!

wanted to advice the same.

sparhawk · 29 February 2020, 21:05

Ia the port introduces race conditions, and has to be protected with a semaphore, then wouldn't it make more sense to use AttemptSemaphore already mentioned by deimos?

After all you will need a semaphore anyway, and this is a exactly the purpose this is for.

16 December 2019, 09:41	#1
Honitos Registered User Join Date: Nov 2019 Location: Celle / Germany Posts: 145	How to check if a Task is already running? I want to check, if my program has been started before to prevent another instance by double clicking the icon again by mistake. I cannot use FindTask() as it will always find itself, so I cannot find the other task that MAY be started before.

16 December 2019, 11:47	#4
ross Defendit numerus Join Date: Mar 2017 Location: Crossing the Rubicon Age: 53 Posts: 4,468	I check with jsr (_LVOFindPort,a6) if there is already a named port, possibly added with a precedent jsr (_LVOAddPort,a6) . There are probably better methods but this works, in every kickstart, and is very simple.

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16 December 2019, 09:58	#2
deimos It's coming back! Join Date: Jul 2018 Location: comp.sys.amiga Posts: 762	AttemptSemaphore?

16 December 2019, 11:24	#3
daxb Registered User Join Date: Oct 2009 Location: Germany Posts: 3,303	Check if program message port is open or not maybe?

23 December 2019, 08:22	#5
BastyCDGS Registered User Join Date: Nov 2015 Location: Freiburg / Germany Age: 44 Posts: 200	Another possibility is to Lock() your program's executable with exclusive access mode straight after start. This way you get a meaningful error message via IoErr() (202: object is busy), if it's opened again. However, there is a caveat, if your program crashes, the lock might remain open forever, so prepare special cleanup code for this. The FindPort solution is nice, too, but you should be careful about name collisions with other applications running. And beware of race conditions occuring by both methods! Always sempahore protect such code!

29 February 2020, 21:05	#7
sparhawk Registered User Join Date: Sep 2019 Location: Essen/Germany Age: 55 Posts: 463	Ia the port introduces race conditions, and has to be protected with a semaphore, then wouldn't it make more sense to use AttemptSemaphore already mentioned by deimos? After all you will need a semaphore anyway, and this is a exactly the purpose this is for.

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