[Paraview-developers] Lifecycle / Workflow of a Plugin

[Matthias Sonntag]

Hello,

we are developing a Paraview-Plugin to read state files written by our 
CFD flow solver (https://www.flexi-project.org/). We managed to get it 
somehow running, but the internal logic of ParaView how the plugin is 
accessed, created and deleted is not totally clear to us.
We observed the following (a commented logfile is listed below):

1. When opening a file with our plugin, ParaView first creates two 
instances of the plugin and directly destroys them, without calling the 
RequestInformation or RequestData routines. Why?
2. The third instance (lets call it instanceA) of the plugin finally 
executes the RequestInformation routine (but 2 times!) and the file 
becomes visible in the pipeline browser.
3. When pressing 'Apply' the RequestInformation is executed again. Why? 
And then RequestData routine is called once and everything works as 
expected and the data is visualized.
4. Loading a second file leads to the following behaviour:
Steps 1. and 2. are the same for the second file. But additionally the 
RequestData routine of the first file (instanceA) is called again. Why?
5. Pressing 'Apply' for the second file shows the same behavior as in 
step 3. for the first file.

Basically it works, but we get an additional RequestData call of the 
already visualized first file, when loading a second file. In our case 
this is quite expensive and we would like to avoid it.

LogFile for the above example:
* Loading first file
    visu3DReader  0x431c2e0
    ~visu3DReader 0x431c2e0
    visu3DReader  0x431c2e0
    ~visu3DReader 0x431c2e0
    visu3DReader  0x431c2e0
    RequestInformation 0x431c2e0
    RequestInformation 0x431c2e0
* Pressing Apply
    RequestInformation 0x431c2e0
    RequestData0x431c2e0
* Loading second file
    visu3DReader  0x736f950
    ~visu3DReader 0x736f950
    visu3DReader  0x74662f0
    ~visu3DReader 0x74662f0
    visu3DReader  0x74662f0
    RequestInformation 0x74662f0
    RequestInformation 0x74662f0
    RequestData 0x431c2e0    <<<<<< Why called again for first file?
* Pressing Apply
    RequestInformation 0x74662f0
    RequestData 0x74662f0

Can anyone explain/reproduce this behavior? Is there any source of 
information how the internal logic of requesting information / data 
works? Does anyone know the respective parts in the paraview source code?

Regards,
Matthias Sonntag