Allow to cancel a task

[aschempp]

It must be possible to cancel a task using the API. Maybe by setting a CANCELLED state in the JSON file?

[discordier]

Problem is yet again, how shall the running process read the cancelled state.
This would only be possible by registering a tick function which will scan the file (and therefore slow down overall execution).

If we could assume to have process control available, we could kill the process, sadly this is not the case for various shared hosters and Windows.

[aschempp]

One idea would be to use a Composer Plugin (or script handler) to check the cancelled state on each event.

[discordier]

This would of course only capture the composer tasks (and of those even only these triggering various events).
We would also have to determine a way to inject an embedded plugin always.

[backbone87]

a simple way would be to have a controller process, that launches the runtask.

So basically the following workflow:

• REST API launches controller command
• controller command forks itself to background and returns
• controller fork launches runtask
• runtask is doin its thing
• controller process goes into a sleep loop waiting for runtask to finish
• controller process is checking an input file regularly for a termination request (or any other control op)
• controller process uses proc_terminate/kill/killtask to terminate runtask, if requested

lets call this the "supervised" workflow.

there may be another workflow called "manual" workflow, where an admin executes runtask from commandline and is in charge of canceling it.

this would require following changes:

• remove forking logic from runtask
• change runAction from TaskController to launch the controller process and wait for it to return (it will return immediately because it forks itself to background or launches itself with "force background" or uses a "start"-bat on windows)
• create the controller command with background logic, and sleep loop logic