Guard concurrent access to _outbound

src/main/java/org/syndicate_lang/actors/Actor.java

@@ -105,16 +105,22 @@ public class Actor implements Executor {
         }
     }
 
-    public void _injectOutbound(Long handle, Ref peer) {
+    void _injectOutbound(Long handle, Ref peer) {
-        _outbound.put(handle, peer);
+        synchronized (_outbound) {
+            _outbound.put(handle, peer);
+        }
     }
 
-    public Ref _lookupOutbound(Long handle) {
+    Ref _lookupOutbound(Long handle) {
-        return _outbound.get(handle);
+        synchronized (_outbound) {
+            return _outbound.get(handle);
+        }
     }
 
-    public Ref _extractOutbound(Long handle) {
+    Ref _extractOutbound(Long handle) {
-        return _outbound.remove(handle);
+        synchronized (_outbound) {
+            return _outbound.remove(handle);
+        }
     }
 
     public String toString() {
@@ -168,7 +174,11 @@ public class Actor implements Executor {
             } else {
                 log().log(Level.SEVERE, "Actor terminated with error", reason);
             }
-            Turn._forActor(this, t -> _outbound.forEach(t::_retract_));
+            Turn._forActor(this, t -> {
+                synchronized(_outbound) {
+                    _outbound.forEach(t::_retract_);
+                }
+            });
             _releaseCount();
         }
     }