Mixer: Fix plugin bypass and plugin insertion broken by 8b9ef85.

mixer/src/Module.H

@@ -351,8 +351,8 @@ public:
             return control_output.size();
         }
 
-    bool bypass ( void ) const { return _bypass; }
-    void bypass ( bool v ) { _bypass = v; redraw(); }
+    virtual bool bypass ( void ) const { return _bypass; }
+    virtual void bypass ( bool v ) { _bypass = v; redraw(); }
 
     int control_input_port_index ( Port *p )
         {

mixer/src/Plugin_Module.C

@@ -669,10 +669,13 @@ Plugin_Module::set_output_buffer ( int n, void *buf )
 void
 Plugin_Module::activate ( void )
 {
+    DMESSAGE( "Activating plugin \"%s\"", label() );
+
     if ( _active )
         FATAL( "Attempt to activate already active plugin" );
 
-    chain()->engine()->lock();
+    if ( chain() )
+        chain()->engine()->lock();
 
     if ( _idata->descriptor->activate )
         for ( unsigned int i = 0; i < _idata->handle.size(); ++i )
@@ -680,13 +683,17 @@ Plugin_Module::activate ( void )
 
     _active = true;
 
-    chain()->engine()->unlock();
+    if ( chain() )
+        chain()->engine()->unlock();
 }
 
 void
 Plugin_Module::deactivate( void )
 {
-    chain()->engine()->lock();
+    DMESSAGE( "Deactivating plugin \"%s\"", label() );
+
+    if ( chain() )
+        chain()->engine()->lock();
 
     _active = false;
    
@@ -694,7 +701,8 @@ Plugin_Module::deactivate( void )
         for ( unsigned int i = 0; i < _idata->handle.size(); ++i )
             _idata->descriptor->deactivate( _idata->handle[i] );
 
-    chain()->engine()->unlock();
+    if ( chain() )
+        chain()->engine()->unlock();
 }
 
 void

mixer/src/Plugin_Module.H

@@ -66,7 +66,7 @@ private:
 
     ImplementationData *_idata;
 
-    bool _active;
+    volatile bool _active;
     int _plugin_ins;
     int _plugin_outs;
     bool _crosswire;