What does this error message mean?

[Geoff]

I got the attached error message for the first time ever.  Not sure what action to take.  There was only one image open and no processes open except for STF.  My only option was to close PI in spite of dire warnings.
Geoff

[pfile]

i have seen this too throughout the 1.8 cycle - basically there's a bug somewhere that's causing a view to remain locked after some process is applied to it - maybe STF. then when you try to close it you get that error.

i think you can force close an image from the console by activating it and then typing "close --force" in the console window.

rob

[Geoff]

Thanks Rob.  I'll try this if it happens again.
Does anybody know if there is a way to actually identify the locking process and then terminate it? Seems like the right thing to do.

[Juan Conejero]

PixInsight is a multithreaded environment, where data access has to be synchronized among the core applications and the different modules installed. Before a module can change an image, it must lock it for read/write operations, so nobody else can access the image. When the module finishes working with the image, it must unlock it.

This error message means that an image was left locked by a module, which is a serious implementation error. Hopefully it is not one of the standard modules (that is, the set of modules that are included in the standard PixInsight distribution). Have you installed an unofficial module? Can you identify some process that you normally don't use but you did use before this error happened?

As Rob says, the best thing you can do is issuing this command from the Process Console window:

close --force <name_of_the_locked_image>

where you replace <name_of_the_locked_image> with the actual image identifier. The --force argument will close the image unconditionally, ignoring lock states. If the image is important, you can try to duplicate it before doing this.

[Geoff]

Hi Juan
I was experimenting with PixelMath to learn more about it, being guided by your tutorial http://pixinsight.com/tutorials/PixelMath/en.html and some of Gerald Wechselberger's video tutorials.  I would have duplicated images and applied masks. During the course of this I used STF, Curves and HistogramTransformation and lots of PixelMath--certainly nothing that I hadn't used before and nothing unofficial.  I will keep a more detailed track of things if it happens again.
Geoff
Note added: I recall that the image that was locked was an experimental mask I was constructing.  I used PixelMath to construct a preliminary mask, then applied NoiseGenerator, but that was a mistake, so I undid, then applied Convolution with a Gaussian11 blur several times and that was about it.