optimistic bundle lock avoidance in sim thread

logisim-evolution · Jan 31, 2019 · aae0c4e · aae0c4e
1 parent b310161
commit aae0c4e
Show file tree

Hide file tree

Showing 2 changed files with 49 additions and 14 deletions.
diff --git a/src/com/cburch/logisim/circuit/CircuitWires.java b/src/com/cburch/logisim/circuit/CircuitWires.java
@@ -193,7 +193,7 @@ private static Value pullValue(Value base, Value pullTo) {
   // derived data
   private Bounds bounds = Bounds.EMPTY_BOUNDS;
 
-  private BundleMap masterBundleMap = null;
+  private volatile BundleMap masterBundleMap = null;
 
   CircuitWires() {
   }
@@ -595,15 +595,23 @@ void draw(ComponentDrawContext context, Collection<Component> hidden) {
   // the components and wires, so to avoid deadlock, only the AWT should
   // create the new bundle map.
 
+  private class BundleMapGetter implements Runnable {
+    BundleMap result;
+    public void run() {
+      result = getBundleMap();
+    }
+  }
+
   /*synchronized*/ private BundleMap getBundleMap() {
+    BundleMap ret = masterBundleMap; // volatile read by AWT or simulation thread
+    if (ret != null)
+      return ret;
     if (SwingUtilities.isEventDispatchThread()) {
       // AWT event thread.
-      if (masterBundleMap != null)
-        return masterBundleMap;
-      BundleMap ret = new BundleMap();
+      ret = new BundleMap();
       try {
         computeBundleMap(ret);
-        masterBundleMap = ret;
+        masterBundleMap = ret; // volatile write by AWT thread
       } catch (Exception t) {
         ret.invalidate();
         System.err.println(t.getLocalizedMessage());
@@ -612,13 +620,12 @@ void draw(ComponentDrawContext context, Collection<Component> hidden) {
     } else {
       // Simulation thread.
       try {
-        final BundleMap ret[] = new BundleMap[1];
-        SwingUtilities.invokeAndWait(new Runnable() {
-          public void run() { ret[0] = getBundleMap(); }
-        });
-        return ret[0];
-      } catch (Exception e) {
-        BundleMap ret = new BundleMap();
+        BundleMapGetter awtThread = new BundleMapGetter();
+        SwingUtilities.invokeAndWait(awtThread);
+        return awtThread.result;
+      } catch (Exception t) {
+        System.err.println(t.getLocalizedMessage());
+        ret = new BundleMap();
         ret.invalidate();
         return ret;
       }
@@ -725,7 +732,7 @@ WireSet getWireSet(Wire start) {
   // query methods
   //
   boolean isMapVoided() {
-    return masterBundleMap == null;
+    return masterBundleMap == null; // volatile read by simulation thread
   }
 
   //
@@ -903,6 +910,6 @@ private void voidBundleMap() {
     // This should really only be called by AWT thread, but main() also
     // calls it during startup. It should not be called by the simulation
     // thread.
-    masterBundleMap = null;
+    masterBundleMap = null; // volatile write by AWT thread (and sometimes main/startup)
   }
 }
diff --git a/src/com/cburch/logisim/circuit/Simulator.java b/src/com/cburch/logisim/circuit/Simulator.java
@@ -416,14 +416,42 @@ public void run() {
   private ArrayList<Listener> listeners = new ArrayList<>();
   private Object lock = new Object();
 
+  // private class Dummy extends UniquelyNamedThread {
+  //   Dummy() { super("dummy"); }
+  //   public void run() {
+  //     try {
+  //       while(true) {
+  //         Thread.sleep(6000);
+  //         long t = System.currentTimeMillis();
+  //         long e = t + 6000;
+  //         long sum = 0;
+  //         while (t < e) {
+  //           t = System.currentTimeMillis();
+  //           sum += (t % 100);
+  //         }
+  //         System.out.printf("t=%d sum=%d\n", t, sum);
+  //       }
+  //     } catch (Exception e) { }
+  //   }
+  // }
+
   public Simulator() {
     simThread = new SimThread(this);
+    // UniquelyNamedThread dummy1= new Dummy();
+    // UniquelyNamedThread dummy2 = new Dummy();
+    // UniquelyNamedThread dummy3 = new Dummy();
 
     try {
       simThread.setPriority(simThread.getPriority() - 1);
+    //   dummy1.setPriority(dummy1.getPriority() - 1);
+    //   dummy2.setPriority(dummy2.getPriority() - 1);
+    //   dummy3.setPriority(dummy3.getPriority() - 1);
     } catch (IllegalArgumentException | SecurityException e) { }
 
     simThread.start();
+    // dummy1.start();
+    // dummy2.start();
+    // dummy3.start();
 
     setTickFrequency(AppPreferences.TICK_FREQUENCY.get().doubleValue());
   }