Bugfix for concurrent garbage collection in Java API.

Relates to #205 and #245

src/api/java/Context.java

@@ -18,6 +18,7 @@ Notes:
 package com.microsoft.z3;
 
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import com.microsoft.z3.enumerations.Z3_ast_print_mode;
 
@@ -3761,29 +3762,42 @@ public class Context extends IDisposable
         return m_Optimize_DRQ;
     }
 
-    protected long m_refCount = 0;
+    protected AtomicInteger m_refCount = new AtomicInteger(0);
 
     /**
      * Finalizer.
+     * @throws Throwable 
      **/
-    protected void finalize()
+    protected void finalize() throws Throwable
     {
-        dispose();
+        try {            
-
+            dispose();
-        if (m_refCount == 0)
+    
-        {
+            if (m_refCount.get() == 0)
-            try
             {
-                Native.delContext(m_ctx);
+                try
-            } catch (Z3Exception e)
+                {
+                    Native.delContext(m_ctx);
+                } catch (Z3Exception e)
+                {
+                    // OK.
+                }
+                m_ctx = 0;
+                System.out.println("> disposed OK.");
+            } 
+            else if (m_refCount.get() < 0)
+                System.out.println("XXX negative ref count");
+            else
             {
-                // OK.
+                System.out.println("XXX context not disposed");
             }
-            m_ctx = 0;
+        }
-        } 
+        catch (Throwable t) {
-        /*
+            throw t;
-        else
+        }
-            CMW: re-queue the finalizer? */
+        finally {
+            super.finalize();
+        }
     }
 
     /**
@@ -3791,6 +3805,7 @@ public class Context extends IDisposable
      **/
     public void dispose()
     {
+        System.out.println("> context disposing.");
         m_AST_DRQ.clear(this);
         m_ASTMap_DRQ.clear(this);
         m_ASTVector_DRQ.clear(this);

src/api/java/Z3Object.java

@@ -43,8 +43,8 @@ public class Z3Object extends IDisposable
         }
 
         if (m_ctx != null)
-        {
+        {            
-            m_ctx.m_refCount--;
+            m_ctx.m_refCount.decrementAndGet();
             m_ctx = null;
         }
     }
@@ -54,13 +54,13 @@ public class Z3Object extends IDisposable
 
     Z3Object(Context ctx)
     {
-        ctx.m_refCount++;
+        ctx.m_refCount.incrementAndGet();
         m_ctx = ctx;
     }
 
     Z3Object(Context ctx, long obj)
     {
-        ctx.m_refCount++;
+        ctx.m_refCount.incrementAndGet();
         m_ctx = ctx;
         incRef(obj);
         m_n_obj = obj;