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Running QGIS (using currently 3.14.1, but this happens in older versions as well) on Windows 10, I sometimes encounter the problem of a task (algorithm) running endlessly without the possibility to stop it. The only workaround is to force QGIS to close, losing temporary layers.

In this specific case, I started vectorize - it's running for two hours and I don't know for how long it will continue. I would like to change parameters and start it again. However, the Cancel button is not active.

enter image description here

There are other cases of tasks that I canceled, but they still continue to run in the background. So it seems to be a general issue of QGIS.

Is there a solution to cancel running algorithms without closing the program?

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    I have once seen the suggestion to use the "qgis task manager", it is located at the bottom center of the qgis window and only visible when tasks are running. However, at least for me this does not work as well. So this would be a really needed feature, maybe worth pushing another request at github.
    – MrXsquared
    Commented Aug 13, 2020 at 11:46

1 Answer 1

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We see on your screenshot that you are using gdal_polygonize algorithm. There is currently no way to cancel GDAL/OGR based algorithms.

It works for QGIS based algorithms (provider native or qgis). Algorithms must check regularly if the user has cancelled the operation, so it can take some time, depending of the background algorithm how it is built.

You can read this topic on the QGIS Dev mailing list explaining the situation : http://osgeo-org.1560.x6.nabble.com/QGIS-Developer-Cancelling-a-running-processing-model-td5443718.html#none

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    in the mailing list they say you have to kill the whole QGIS session to terminate a gdal task, but instead I found you can just kill the gdal process in Task Manager. Commented Jun 9, 2021 at 13:12
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    This indeed new. GDAL algorithms can now be cancelled.
    – etrimaille
    Commented Jun 10, 2021 at 10:08

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