Better responsiveness when loading remote plugins

[armislv]

Edited by @tresf April 13th, 2015, adjusted original post to reflect actual problem.

Lukas-W wrote Apr 15, 2014: "While it is normal that loading a VST takes a few seconds, it should not cause LMMS to freeze. Instead, the loading process should take place in a separate thread so that the UI stays responsive. I don't know the architecture well enough, so I can't say if this is possible."

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LMMS often hangs when loading vst dll. The system is linux. It becomes very unresponsive when it happens. Seems it is looping in while (1) at the end of RemoteVstPlugin::RemoteVstPlugin. I am not an expert of programming threads, but maybe some QThread::msleep can help here?

[diizy]

I don't know... can someone test this and see what happens?

[musikBear]

dont have linux, but armislv, you write " when loading vst dll." -Is that then meant generally, eg ALL vsts, ot ONE specific vst? -What is the behavior with the vst Synth1. Synth1 is kind of a MustWork, and at the same time very cpu friendly. That is in NO way a general rule for vsts
How does Synth1 do for you?

[armislv]

Exactly the synth1 it is. But this happens with other vsts as well.

[Sti2nd]

but hangs... of course it hangs when your CPU is running high... it does with everyone, but hangs... I wouldn't call it hang, I'll call it working.

[musikBear]

Oo 'hangs' is that the 'please wait' for 2-4 skd? As Sti2nd says- thats normal. A lot of data shifts and all always has a little 'break' at that time. Hangs is when you have time for a coffebreak. Serious hangs is when you have time to buy the coffee :p
No sorry seriously, its a pc issue, not a lmms. But you dont describe hw, so any bottleneck is not idenfiable. ..How -long- do you wait?

[armislv]

This happens on 3 different pcs. The most powerful one have E8400 3 GHz dual core CPU. On this pc this happens less often, of course. Sometimes dll get loaded, but sometimes not, especially when loading some project. I tried to wait ~ hour couple of times, then killed lmms.

[lukas-w]

While it is normal that loading a VST takes a few seconds, it should not cause LMMS to freeze.
Instead, the loading process should take place in a separate thread so that the UI stays responsive. I don't know the architecture well enough, so I can't say if this is possible.

[armislv]

Probably the while loop takes too much of cpu.

[musikBear]

~hour is of cause rediculous, and not ok - and thats with Synth1? Could it be that you installed it wrongly, or that some component is flawed (could be a kit??) -then lmms helplessly would loop while trying to find the piece. If it was a general problem, other would have reported it , i think - Synth1 loads for me (win32) < 2 sekd. -Need other linux users input here

[Sti2nd]

Obviously this is a bug, I was wrong. It should maximum hang for some seconds with synth1. Now: "system is linux" isn't enough information. And LMMS probably does it wrong as far as I have experienced @lukas-w cause LMMS' GUI often become unresponsive when it is working.

[tresf]

@armislv if you find a place where the code could improve, please test it out and send over a pull request.

[tresf]

I'm pretty sure this is due to a while loop in RemoteVstPlugin.cpp#L405

We should instead use a method which scheduled a periodic check of the plugin as this while loop will use every CPU cycle until the plugin is loaded, potentially blocking other operations.

Edit zonkmachine: fixed broken link