--- /dev/null	2015-10-06 23:29:51.451421828 +0200
+++ new/src/share/vm/gc/shenandoah/shenandoahJNICritical.cpp	2015-10-14 13:54:53.011951424 +0200
@@ -0,0 +1,121 @@
+/*
+ * Copyright (c) 2015, Red Hat, Inc. and/or its affiliates.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "gc/shenandoah/shenandoahJNICritical.hpp"
+#include "gc/shenandoah/shenandoahHeap.hpp"
+
+#include "gc/shared/gcLocker.hpp"
+#include "runtime/mutexLocker.hpp"
+#include "runtime/thread.hpp"
+#include "runtime/vmThread.hpp"
+
+class VM_ShenandoahJNICriticalOperation : public VM_Operation {
+private:
+  VM_Operation* _target;
+public:
+  VM_ShenandoahJNICriticalOperation(VM_Operation* target);
+  VMOp_Type type() const;
+  bool doit_prologue();
+  void doit_epilogue();
+  void doit();
+  const char* name() const;
+};
+
+ShenandoahJNICritical::ShenandoahJNICritical() : _op_waiting_for_jni_critical(NULL) {
+}
+
+/*
+ * This is called by the Java thread who leaves the last JNI critical block.
+ */
+void ShenandoahJNICritical::notify_jni_critical() {
+  assert(Thread::current()->is_Java_thread(), "call only from Java thread");
+  assert(_op_waiting_for_jni_critical != NULL, "must be waiting for jni critical notification");
+
+  MonitorLockerEx ml(ShenandoahJNICritical_lock, true);
+
+  VMThread::execute(_op_waiting_for_jni_critical);
+  _op_waiting_for_jni_critical = NULL;
+
+  ml.notify_all();
+
+}
+
+/*
+ * This is called by the VM thread, if it determines that the task must wait
+ * for JNI critical regions to be left.
+ */
+void ShenandoahJNICritical::set_waiting_for_jni_before_gc(VM_Operation* op) {
+  assert(Thread::current()->is_VM_thread(), "call only from VM thread");
+  _op_waiting_for_jni_critical = op;
+}
+
+/**
+ * This is called by the Shenandoah concurrent thread in order
+ * to execute a VM_Operation on the VM thread, that needs to perform
+ * a JNI critical region check.
+ */
+void ShenandoahJNICritical::execute_in_vm_thread(VM_Operation* op) {
+  MonitorLockerEx ml(ShenandoahJNICritical_lock, true);
+  VM_ShenandoahJNICriticalOperation jni_op(op);
+  VMThread::execute(&jni_op);
+  while (_op_waiting_for_jni_critical != NULL) {
+    ml.wait(true);
+  }
+}
+
+
+VM_ShenandoahJNICriticalOperation::VM_ShenandoahJNICriticalOperation(VM_Operation* target)
+  : _target(target) {
+}
+
+VM_Operation::VMOp_Type VM_ShenandoahJNICriticalOperation::type() const {
+  return _target->type();
+}
+
+const char* VM_ShenandoahJNICriticalOperation::name() const {
+  return _target->name();
+}
+
+bool VM_ShenandoahJNICriticalOperation::doit_prologue() {
+  return _target->doit_prologue();
+}
+
+void VM_ShenandoahJNICriticalOperation::doit_epilogue() {
+  _target->doit_epilogue();
+}
+
+void VM_ShenandoahJNICriticalOperation::doit() {
+  if (! GC_locker::check_active_before_gc()) {
+    _target->doit();
+  } else {
+
+    if (ShenandoahTraceJNICritical) {
+      gclog_or_tty->print_cr("Deferring JNI critical op because of active JNI critical regions");
+    }
+
+    // This makes the GC background thread wait, and kick off evacuation as
+    // soon as JNI notifies us that critical regions have all been left.
+    ShenandoahHeap *sh = ShenandoahHeap::heap();
+    sh->jni_critical()->set_waiting_for_jni_before_gc(this);
+  }
+}