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fix: avoid audio-thread stalls on model eviction and AU bypass toggle #627

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fix: avoid audio-thread stalls on model eviction and AU bypass toggle #627

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19 changes: 15 additions & 4 deletions NeuralAmpModeler/NeuralAmpModeler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -409,14 +409,24 @@ void NeuralAmpModeler::OnReset()
SetTailSize(tailCycles * (int)(sampleRate / kDCBlockerFrequency));
mInputSender.Reset(sampleRate);
mOutputSender.Reset(sampleRate);
// If there is a model or IR loaded, they need to be checked for resampling.
_ResetModelAndIR(sampleRate, GetBlockSize());
// Only reset the model when the format actually changed. iPlug2 also calls OnReset() in
// response to kAudioUnitProperty_BypassEffect (the AU bypass / power-button toggle), which
// would trigger prewarm() on the audio thread and cause an audible dropout. Sample rate and
// block size are unchanged on a bypass toggle, so skipping _ResetModelAndIR() is safe there.
if (sampleRate != mLastResetSampleRate || maxBlockSize != mLastResetBlockSize)
{
_ResetModelAndIR(sampleRate, maxBlockSize);
mLastResetSampleRate = sampleRate;
mLastResetBlockSize = maxBlockSize;
}
mToneStack->Reset(sampleRate, maxBlockSize);
_UpdateLatency();
}

void NeuralAmpModeler::OnIdle()
{
delete mModelPendingDeletion.exchange(nullptr, std::memory_order_acquire);

mInputSender.TransmitData(*this);
mOutputSender.TransmitData(*this);

Expand Down Expand Up @@ -597,7 +607,7 @@ void NeuralAmpModeler::_ApplyDSPStaging()
// Remove marked modules
if (mShouldRemoveModel)
{
mModel = nullptr;
mModelPendingDeletion.store(mModel.release(), std::memory_order_release);
mNAMPath.Set("");
mShouldRemoveModel = false;
mModelCleared = true;
Expand All @@ -614,8 +624,9 @@ void NeuralAmpModeler::_ApplyDSPStaging()
// Move things from staged to live
if (mStagedModel != nullptr)
{
ResamplingNAM* old = mModel.release();
mModel = std::move(mStagedModel);
mStagedModel = nullptr;
mModelPendingDeletion.store(old, std::memory_order_release);
mNewModelLoadedInDSP = true;
_UpdateLatency();
_SetInputGain();
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8 changes: 8 additions & 0 deletions NeuralAmpModeler/NeuralAmpModeler.h
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Expand Up @@ -306,6 +306,14 @@ class NeuralAmpModeler final : public iplug::Plugin

std::atomic<bool> mNewModelLoadedInDSP = false;
std::atomic<bool> mModelCleared = false;
// Holds a model evicted from mModel that must be deleted on the UI thread (OnIdle) rather
// than the audio thread, to avoid freeing large Eigen weight matrices inside ProcessBlock
// and causing a buffer-deadline miss.
std::atomic<ResamplingNAM*> mModelPendingDeletion{nullptr};

// Last format seen by OnReset(). Used to guard _ResetModelAndIR() — see OnReset() for rationale.
double mLastResetSampleRate{0.0};
int mLastResetBlockSize{0};

// Tone stack modules
std::unique_ptr<dsp::tone_stack::AbstractToneStack> mToneStack;
Expand Down