Safe way to set many Params at once? (VST3 threading issue)

[PolyVector]

Hello!
I'm working on a preset browser for my second NIH-plug + egui plugin, and I'm running into issues trying to restore a preset from the UI thread. Many VST3 hosts seem to crash when modifying ~150 plugin params all at once. I've seen it so far in Waveform11/12, Ardour, and Bitwig Studio.

My initial attempt used ParamSetter:

for (param, value) in list_of_params {
        setter.begin_set_parameter(param);
        setter.set_parameter(param, value);
        setter.end_set_parameter(param);
}

... that appeared to work in Standalone and CLAP, but VST3 crashes in the hosts I tried.

My second attempt used the GuiContext directly like this:

let ctx = &setter.raw_context;
let mut state = ctx.get_state().clone();
// Update the state.params here...
ctx.set_state(state);

... that had the same outcome, but also appeared to be executing on the wrong thread according to this Carla error:

JUCE Assertion failure in juce_VST3PluginFormat.cpp:3636

Is there a safe way to set all these parameters?

[robbert-vdh]

Don't try to load presets using automation. Hosts definitely shouldn't crash, but they won't appreciate it either. Load the preset the normal way instead: https://nih-plug.robbertvanderhelm.nl/nih_plug/context/gui/trait.GuiContext.html#tymethod.set_state

[PolyVector]

set_state crashes the same way for me when used in VST3, so maybe I'm doing something else wrong. I'll have to figure out my debugger this weekend, heh. Thank you.

[PolyVector]

Hey Robbert,
I switched to set_state() for everything, thanks for the guidance, but I've still been having issues with various Linux hosts. After a ton of head scratching and digging around, I believe I was hitting 3 separate issues. I put together a quick repro project for you, and I'll try to explain things here.

1. There's a race condition that is crashing Linux Bitwig when using set_state() to swap presets.
   In src/wrapper/vst3/view.rs in the post_task() function, it appears that the task is pushed
   before the data is written. I see there's a comment about exactly this, but in my tests pushing the
   task at the end of the function is much safer:

let notify_value = 1i8;
const NOTIFY_VALUE_SIZE: usize = std::mem::size_of::<i8>();
assert_eq!(
    unsafe {
        libc::write(
            self.socket_write_fd,
            &notify_value as *const _ as *const c_void,
            NOTIFY_VALUE_SIZE,
        )
    },
    NOTIFY_VALUE_SIZE as isize
);

self.tasks.push(task)?; // Seems to be much safer here

Ok(())

When I make this change, Bitwig is totally stable.

2. Task::TriggerRestart(kParamValuesChanged) is called on the wrong thread on Linux, causing a warning in Carla/JUCE
   In src/wrapper/vst3/inner.rs at the end of the set_state_object_from_gui() function:

// After the state has been updated, notify the host about the new parameter values
let task_posted =
    self.schedule_gui(Task::TriggerRestart( // This makes Carla/JUCE happy
            RestartFlags::kParamValuesChanged as i32,
        ));   

I believe this should call self.schedule_gui() and not the event_loop.schedule_gui() directly.
When I make that change, Carla no longer complains.

3. Perhapse not an issue, but I was getting allocation assertions (that I mistook for bugs) when running my tests.
   in src/wrapper/vst3/wrapper.rs and src/wrapper/standalone/wrapper.rs there are similar lines:

        // We'll pass the state object back to the GUI thread so deallocation can happen
        // there without potentially blocking the audio thread
        if let Err(err) = self.inner.updated_state_sender.send(state) {
            nih_debug_assert_failure!(
                "Failed to send state object back to GUI thread: {}",
                err
            );
        };

I think the updated_state_sender.send() command is allocating, and wrapping it in a permit_alloc() helped.

Anyways, I hope some of this is useful.

NIH-plug Repro SetState.zip