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Fix thread safety in fast_tanh toggle #178

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Fix thread safety in fast_tanh toggle #178

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30 changes: 12 additions & 18 deletions NAM/activations.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7,39 +7,33 @@ nam::activations::ActivationReLU _RELU = nam::activations::ActivationReLU();
nam::activations::ActivationLeakyReLU _LEAKY_RELU = nam::activations::ActivationLeakyReLU();
nam::activations::ActivationSigmoid _SIGMOID = nam::activations::ActivationSigmoid();

bool nam::activations::Activation::using_fast_tanh = false;
std::atomic<bool> nam::activations::Activation::using_fast_tanh{false};

std::unordered_map<std::string, nam::activations::Activation*> nam::activations::Activation::_activations = {
{"Tanh", &_TANH}, {"Hardtanh", &_HARD_TANH}, {"Fasttanh", &_FAST_TANH},
{"ReLU", &_RELU}, {"LeakyReLU", &_LEAKY_RELU}, {"Sigmoid", &_SIGMOID}};

nam::activations::Activation* tanh_bak = nullptr;

nam::activations::Activation* nam::activations::Activation::get_activation(const std::string name)
{
if (_activations.find(name) == _activations.end())
// Return FastTanh when Tanh is requested and fast_tanh mode is enabled
if (name == "Tanh" && using_fast_tanh.load(std::memory_order_relaxed))
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@sdatkinson sdatkinson Jan 14, 2026

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Does this change make the WaveNet's getting of the sigmoid activation for its gating activation no longer real-time safe?

NeuralAmpModelerCore/NAM/wavenet.cpp

Line 56 in 6ea03b1

activations::Activation::get_activation("Sigmoid")->apply(this->_z.block(channels, i, channels, 1));

{
return _activations.at("Fasttanh");
}

auto it = _activations.find(name);
if (it == _activations.end())
return nullptr;

return _activations[name];
return it->second;
}

void nam::activations::Activation::enable_fast_tanh()
{
nam::activations::Activation::using_fast_tanh = true;

if (_activations["Tanh"] != _activations["Fasttanh"])
{
tanh_bak = _activations["Tanh"];
_activations["Tanh"] = _activations["Fasttanh"];
}
using_fast_tanh.store(true, std::memory_order_relaxed);
}

void nam::activations::Activation::disable_fast_tanh()
{
nam::activations::Activation::using_fast_tanh = false;

if (_activations["Tanh"] == _activations["Fasttanh"])
{
_activations["Tanh"] = tanh_bak;
}
using_fast_tanh.store(false, std::memory_order_relaxed);
}
5 changes: 3 additions & 2 deletions NAM/activations.h
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Original file line number Diff line number Diff line change
@@ -1,7 +1,8 @@
#pragma once

#include <string>
#include <atomic>
#include <cmath> // expf
#include <string>
#include <unordered_map>
#include <Eigen/Dense>

Expand Down Expand Up @@ -63,7 +64,7 @@ class Activation
static Activation* get_activation(const std::string name);
static void enable_fast_tanh();
static void disable_fast_tanh();
static bool using_fast_tanh;
static std::atomic<bool> using_fast_tanh;

protected:
static std::unordered_map<std::string, Activation*> _activations;
Expand Down