NGSPICE as a singleton

One cannot call ngSpice_Init() twice without unloading the dll. When calling
ngSpice_Init, we pass a pointer to a NGSPICE instance and thus it cannot be changed.
When any of the callback function is called with a stale pointer everything crashes.

eeschema/sim/ngspice.cpp

@@ -45,7 +45,6 @@ NGSPICE::~NGSPICE()
 
 void NGSPICE::Init()
 {
-    init();
     Command( "reset" );
 }
 

eeschema/sim/sim_plot_frame.cpp

@@ -109,6 +109,19 @@ SIM_PLOT_FRAME::SIM_PLOT_FRAME( KIWAY* aKiway, wxWindow* aParent )
     if( m_schematicFrame == NULL )
         throw std::runtime_error( "There is no schematic window" );
 
+    m_simulator = SPICE_SIMULATOR::CreateInstance( "ngspice" );
+
+    if( !m_simulator )
+    {
+        throw std::runtime_error( "Could not create simulator instance" );
+        return;
+    }
+
+    m_simulator->Init();
+
+    m_reporter = new SIM_THREAD_REPORTER( this );
+    m_simulator->SetReporter( m_reporter );
+
     updateNetlistExporter();
 
     Connect( wxEVT_CLOSE_WINDOW, wxCloseEventHandler( SIM_PLOT_FRAME::onClose ), NULL, this );
@@ -145,12 +158,13 @@ SIM_PLOT_FRAME::SIM_PLOT_FRAME( KIWAY* aKiway, wxWindow* aParent )
 
     m_toolBar->Realize();
     m_plotNotebook->SetPageText( 0, _( "Welcome!" ) );
-    m_simulator.reset( SPICE_SIMULATOR::CreateInstance( "ngspice" ) );
 }
 
 
 SIM_PLOT_FRAME::~SIM_PLOT_FRAME()
 {
+    delete m_simulator;
+    delete m_reporter;
 }
 
 
@@ -159,12 +173,6 @@ void SIM_PLOT_FRAME::StartSimulation()
     STRING_FORMATTER formatter;
     SIM_PLOT_PANEL* plotPanel = CurrentPlot();
 
-    if( !m_simulator )
-    {
-        DisplayError( this, wxT( "Could not create simulator instance" ) );
-        return;
-    }
-
     m_simConsole->Clear();
     updateNetlistExporter();
 
@@ -183,8 +191,6 @@ void SIM_PLOT_FRAME::StartSimulation()
         return;
     }
 
-    m_simulator->SetReporter( new SIM_THREAD_REPORTER( this ) );
-    m_simulator->Init();
     m_simulator->LoadNetlist( formatter.GetString() );
     updateTuners();
     applyTuners();
@@ -194,8 +200,7 @@ void SIM_PLOT_FRAME::StartSimulation()
 
 void SIM_PLOT_FRAME::StopSimulation()
 {
-    if( m_simulator )
-        m_simulator->Stop();
+    m_simulator->Stop();
 }
 
 
@@ -367,9 +372,6 @@ void SIM_PLOT_FRAME::updateNetlistExporter()
 
 bool SIM_PLOT_FRAME::updatePlot( const TRACE_DESC& aDescriptor, SIM_PLOT_PANEL* aPanel )
 {
-    if( !m_simulator )
-        return false;
-
     SIM_TYPE simType = m_exporter->GetSimType();
     wxString spiceVector = m_exporter->GetSpiceVector( aDescriptor.GetName(),
             aDescriptor.GetType(), aDescriptor.GetParam() );
@@ -494,6 +496,7 @@ void SIM_PLOT_FRAME::applyTuners()
         /// @todo no ngspice hardcoding
         std::string command( "alter @" + tuner->GetSpiceName()
                 + "=" + tuner->GetValue().ToSpiceString() );
+
         m_simulator->Command( command );
     }
 }
@@ -1015,9 +1018,6 @@ void SIM_PLOT_FRAME::onSimFinished( wxCommandEvent& aEvent )
 
 void SIM_PLOT_FRAME::onSimUpdate( wxCommandEvent& aEvent )
 {
-    if( !m_simulator )
-        return;
-
     if( IsSimulationRunning() )
         StopSimulation();
 

eeschema/sim/sim_plot_frame.h

@@ -48,6 +48,7 @@ class SCH_COMPONENT;
 class SPICE_SIMULATOR;
 class NETLIST_EXPORTER_PSPICE_SIM;
 class SIM_PLOT_PANEL;
+class SIM_THREAD_REPORTER;
 class TUNER_SLIDER;
 
 ///> Trace descriptor class
@@ -271,7 +272,8 @@ private:
 
     SCH_EDIT_FRAME* m_schematicFrame;
     std::unique_ptr<NETLIST_EXPORTER_PSPICE_SIM> m_exporter;
-    std::unique_ptr<SPICE_SIMULATOR> m_simulator;
+    SPICE_SIMULATOR* m_simulator;
+    SIM_THREAD_REPORTER* m_reporter;
 
     typedef std::map<wxString, TRACE_DESC> TRACE_MAP;
 

eeschema/sim/spice_simulator.cpp

@@ -30,7 +30,12 @@ SPICE_SIMULATOR* SPICE_SIMULATOR::CreateInstance( const std::string& )
 {
     try
     {
-        return new NGSPICE;
+        static NGSPICE* ngspiceInstance = nullptr;
+
+        if( !ngspiceInstance )
+            ngspiceInstance = new NGSPICE;
+
+        return ngspiceInstance;
     }
     catch( std::exception& e )
     {