add missing truffle boundaries

Author: cosminbasca

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/ThreadModuleBuiltins.java

@@ -114,6 +114,7 @@ long getId() {
     @GenerateNodeFactory
     abstract static class GetThreadCountNode extends PythonBuiltinNode {
         @Specialization
+        @TruffleBoundary
         long getCount() {
             return getContext().getThreadGroup().activeCount();
         }

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/thread/PThread.java

@@ -42,6 +42,7 @@
 
 import com.oracle.graal.python.builtins.objects.object.PythonBuiltinObject;
 import com.oracle.graal.python.builtins.objects.type.PythonClass;
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 
 public class PThread extends PythonBuiltinObject {
     public final static String GRAALPYTHON_THREADS = "GRAALPYTHON_THREADS";
@@ -56,6 +57,7 @@ public PThread(PythonClass cls, ThreadGroup group, long stackSize, Runnable runn
         this.thread = new Thread(group, runnable, "graalpython-thread-" + group.activeCount(), stackSize);
     }
 
+    @TruffleBoundary
     public void start() {
         if (!this.thread.isAlive()) {
             thread.start();