Worker thread per plugin instance.

src/IHost.hpp

@@ -46,7 +46,6 @@ namespace pipedal {
         virtual int GetNumberOfInputAudioChannels() const = 0;
         virtual int GetNumberOfOutputAudioChannels() const = 0;
         virtual std::shared_ptr<Lv2PluginInfo> GetPluginInfo(const std::string &uri) const = 0;
-        virtual std::shared_ptr<HostWorkerThread> GetHostWorkerThread() = 0;
 
         virtual IEffect *CreateEffect(PedalboardItem &pedalboard) = 0;
 

src/Lv2Effect.cpp

@@ -41,6 +41,7 @@
 #include "AudioHost.hpp"
 #include <exception>
 #include "RingBufferReader.hpp"
+#include "Worker.hpp"
 
 using namespace pipedal;
 namespace fs = std::filesystem;
@@ -70,6 +71,11 @@ Lv2Effect::Lv2Effect(
 
     this->bypass = pedalboardItem.isEnabled();
 
+    this->workerThread = std::make_unique<HostWorkerThread>();
+    if (info_->WantsWorkerThread())
+    {
+        workerThread->StartThread();
+    }
     // stash a list of known file properties that we want to keep synced.
     if (info->piPedalUI())
     {
@@ -179,10 +185,8 @@ Lv2Effect::Lv2Effect(
     const LV2_Worker_Interface *worker_interface =
         (const LV2_Worker_Interface *)lilv_instance_get_extension_data(pInstance,
                                                                        LV2_WORKER__interface);
-    if (worker_interface)
-    {
-        this->worker = std::make_unique<Worker>(pHost->GetHostWorkerThread(), pInstance, worker_interface);
-    }
+    this->worker = std::make_unique<Worker>(workerThread, pInstance, worker_interface);
+    
     const LV2_State_Interface *state_interface =
         (const LV2_State_Interface *)lilv_instance_get_extension_data(pInstance,
                                                                       LV2_STATE__interface);

src/Lv2Effect.hpp

@@ -40,12 +40,12 @@
 #include "StateInterface.hpp"
 #include "LogFeature.hpp"
 
-
 namespace pipedal
 {
 
     class RealtimeRingBufferWriter;    
     class IPatchWriterCallback;
+    class HostWorkerThread;
 
     class Lv2Effect : public IEffect, private LogFeature::LogMessageListener
     {
@@ -57,6 +57,10 @@ namespace pipedal
 
     private:
         
+
+        std::shared_ptr<HostWorkerThread> workerThread;
+        std::unique_ptr<Worker> worker;
+
         std::unordered_map<std::string,int> controlIndex;
 
         FileBrowserFilesFeature fileBrowserFilesFeature;
@@ -70,7 +74,6 @@ namespace pipedal
         int numberOfOutputs = 0;
         int numberOfMidiInputs = 0;
 
-        std::unique_ptr<Worker> worker;
         LilvInstance *pInstance;
         std::shared_ptr<Lv2PluginInfo> info;
         std::vector<float> controlValues;

src/PluginHost.cpp

@@ -47,6 +47,7 @@
 #include "StdErrorCapture.hpp"
 #include "util.hpp"
 #include "ModFileTypes.hpp"
+#include  <algorithm>
 
 #include "Locale.hpp"
 
@@ -301,7 +302,6 @@ PluginHost::PluginHost()
 
     this->urids = new Urids(mapFeature);
 
-    pHostWorkerThread = std::make_shared<HostWorkerThread>();
 }
 
 void PluginHost::OnConfigurationChanged(const JackConfiguration &configuration, const JackChannelSelection &settings)
@@ -1668,10 +1668,6 @@ bool Lv2PluginInfo::isSplit() const
 {
     return uri_ == SPLIT_PEDALBOARD_ITEM_URI;
 }
-std::shared_ptr<HostWorkerThread> PluginHost::GetHostWorkerThread()
-{
-    return pHostWorkerThread;
-}
 
 class ResourceInfo
 {
@@ -1883,6 +1879,13 @@ Lv2PatchPropertyInfo::Lv2PatchPropertyInfo(PluginHost *pluginHost, const LilvNod
     }
 }
 
+// ffs.
+static inline bool contains(const std::vector<std::string> &vec, const std::string &value) {
+    return std::find(vec.begin(),vec.end(),value) != vec.end();
+}
+bool Lv2PluginInfo::WantsWorkerThread() const {
+    return contains(this->required_features_,LV2_WORKER__schedule) || contains(this->supported_features_,LV2_WORKER__schedule);
+}
 // void PiPedalHostLogError(const std::string &error)
 // {
 //     Lv2Log::error("%s",error.c_str());

src/PluginHost.hpp

@@ -454,6 +454,8 @@ namespace pipedal
         LV2_PROPERTY_GETSET(patchProperties)
         LV2_PROPERTY_GETSET(hasDefaultState)
 
+        bool WantsWorkerThread() const;
+
         const Lv2PortInfo &getPort(const std::string &symbol)
         {
             for (size_t i = 0; i < ports_.size(); ++i)
@@ -913,7 +915,6 @@ namespace pipedal
         }
 
     private:
-        std::shared_ptr<HostWorkerThread> pHostWorkerThread;
         // IHost implementation.
         virtual void SetMaxAudioBufferSize(size_t size) { maxBufferSize = size; }
         virtual size_t GetMaxAudioBufferSize() const { return maxBufferSize; }
@@ -922,7 +923,6 @@ namespace pipedal
         virtual int GetNumberOfInputAudioChannels() const { return numberOfAudioInputChannels; }
         virtual int GetNumberOfOutputAudioChannels() const { return numberOfAudioOutputChannels; }
         virtual LV2_Feature *const *GetLv2Features() const { return (LV2_Feature *const *)&(this->lv2Features[0]); }
-        virtual std::shared_ptr<HostWorkerThread> GetHostWorkerThread();
 
     public:
         virtual MapFeature &GetMapFeature() override { return this->mapFeature; }

src/Worker.cpp

@@ -15,7 +15,7 @@
 */
 // (Borrows heavily from worker.c by David Robillard.)
 
-// Copyright (c) 2022 Robin Davies
+// Copyright (c) 2024 Robin Davies
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy of
 // this software and associated documentation files (the "Software"), to deal in
@@ -242,8 +242,19 @@ void HostWorkerThread::ThreadProc() noexcept
 HostWorkerThread::HostWorkerThread()
 {
     this->dataBuffer.resize(16*1024);
-    pThread = std::make_unique<std::thread>([this]()
-                                            { this->ThreadProc(); });
+}
+
+bool HostWorkerThread::StartThread()
+{
+    if (!pThread)
+    {
+        if (closed) {
+            return false;
+        }
+        pThread = std::make_unique<std::thread>([this]()
+                                                { this->ThreadProc(); });
+    }    
+    return true;
 }
 
 void HostWorkerThread::Close()
@@ -252,10 +263,12 @@ void HostWorkerThread::Close()
     bool sendClose = false;
     {
         std::lock_guard lock{submitMutex};
-        if (!closed)
-        {
-            closed = true;
-            sendClose = true;
+        if (pThread) {
+            if (!closed)
+            {
+                closed = true;
+                sendClose = true;
+            }
         }
     }
     if (sendClose)
@@ -278,7 +291,10 @@ LV2_Worker_Status HostWorkerThread::ScheduleWork(Worker *worker, size_t size, co
 {
     std::lock_guard lock(submitMutex);
 
-    if (exiting)
+    if (!StartThread()) { // ensures thread is running, when plugins haven't declared they want a worker thread.
+        return LV2_Worker_Status::LV2_WORKER_ERR_NO_SPACE;
+    }
+    if (exiting )
     {
         return LV2_Worker_Status::LV2_WORKER_ERR_NO_SPACE;
     }

src/Worker.hpp

@@ -1,4 +1,4 @@
-// Copyright (c) 2022 Robin Davies
+// Copyright (c) 2025 Robin Davies
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy of
 // this software and associated documentation files (the "Software"), to deal in
@@ -32,6 +32,7 @@
 #include "lv2/atom/atom.h"
 #include "lv2/worker/worker.h"
 #include "condition_variable"
+#include <atomic>
 
 #include <map>
 #include <string>
@@ -51,10 +52,12 @@ namespace pipedal {
         HostWorkerThread();
         ~HostWorkerThread();
 
+        bool StartThread();
         void Close();
+        bool Closed() const { return closed || pThread == nullptr; }
         LV2_Worker_Status ScheduleWork(Worker*worker, size_t size, const void*data);
     private:
-        bool closed = false;
+        std::atomic<bool> closed = false;
         std::unique_ptr<std::thread> pThread;
         void ThreadProc() noexcept;
 
@@ -64,8 +67,6 @@ namespace pipedal {
 
         std::vector<uint8_t> dataBuffer;
 
-        
-
     };
 
 	class Worker {
@@ -75,8 +76,8 @@ namespace pipedal {
         LilvInstance*lilvInstance;
         const LV2_Worker_Interface*workerInterface;
 
-        bool closed = false;
-        bool exiting = false;
+        std::atomic<bool> closed = false;
+        std::atomic<bool> exiting = false;
         RingBuffer<true,false> responseRingBuffer;
 
         std::vector<uint8_t> responseBuffer;
@@ -94,6 +95,7 @@ namespace pipedal {
 	public:
 		Worker(const std::shared_ptr<HostWorkerThread>& pHostWorker,LilvInstance *instance, const LV2_Worker_Interface *iface);
         ~Worker();
+        
         void Close();
 
         LV2_Worker_Status ScheduleWork(