--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/shenandoah/shenandoahEvacOOMHandler.cpp	Mon Dec 10 15:47:44 2018 +0100
@@ -0,0 +1,134 @@
+/*
+ * Copyright (c) 2018, Red Hat, Inc. All rights reserved.
+ *
+ * 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 "precompiled.hpp"
+
+#include "gc/shenandoah/shenandoahHeap.hpp"
+#include "gc/shenandoah/shenandoahUtils.hpp"
+#include "gc/shenandoah/shenandoahEvacOOMHandler.hpp"
+#include "gc/shenandoah/shenandoahThreadLocalData.hpp"
+#include "runtime/orderAccess.hpp"
+#include "runtime/os.hpp"
+#include "runtime/thread.hpp"
+
+const jint ShenandoahEvacOOMHandler::OOM_MARKER_MASK = 0x80000000;
+
+ShenandoahEvacOOMHandler::ShenandoahEvacOOMHandler() :
+  _threads_in_evac(0) {
+}
+
+void ShenandoahEvacOOMHandler::wait_for_no_evac_threads() {
+  while ((OrderAccess::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) != 0) {
+    os::naked_short_sleep(1);
+  }
+  // At this point we are sure that no threads can evacuate anything. Raise
+  // the thread-local oom_during_evac flag to indicate that any attempt
+  // to evacuate should simply return the forwarding pointer instead (which is safe now).
+  ShenandoahThreadLocalData::set_oom_during_evac(Thread::current(), true);
+}
+
+void ShenandoahEvacOOMHandler::enter_evacuation() {
+  jint threads_in_evac = OrderAccess::load_acquire(&_threads_in_evac);
+
+  assert(!ShenandoahThreadLocalData::is_evac_allowed(Thread::current()), "sanity");
+  assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must not be set");
+
+  if ((threads_in_evac & OOM_MARKER_MASK) != 0) {
+    wait_for_no_evac_threads();
+    return;
+  }
+
+  while (true) {
+    jint other = Atomic::cmpxchg(threads_in_evac + 1, &_threads_in_evac, threads_in_evac);
+    if (other == threads_in_evac) {
+      // Success: caller may safely enter evacuation
+      DEBUG_ONLY(ShenandoahThreadLocalData::set_evac_allowed(Thread::current(), true));
+      return;
+    } else {
+      // Failure:
+      //  - if offender has OOM_MARKER_MASK, then loop until no more threads in evac
+      //  - otherwise re-try CAS
+      if ((other & OOM_MARKER_MASK) != 0) {
+        wait_for_no_evac_threads();
+        return;
+      }
+      threads_in_evac = other;
+    }
+  }
+}
+
+void ShenandoahEvacOOMHandler::leave_evacuation() {
+  if (!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current())) {
+    assert((OrderAccess::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) > 0, "sanity");
+    // NOTE: It's ok to simply decrement, even with mask set, because unmasked value is positive.
+    Atomic::dec(&_threads_in_evac);
+  } else {
+    // If we get here, the current thread has already gone through the
+    // OOM-during-evac protocol and has thus either never entered or successfully left
+    // the evacuation region. Simply flip its TL oom-during-evac flag back off.
+    ShenandoahThreadLocalData::set_oom_during_evac(Thread::current(), false);
+  }
+  DEBUG_ONLY(ShenandoahThreadLocalData::set_evac_allowed(Thread::current(), false));
+  assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must be turned off");
+}
+
+void ShenandoahEvacOOMHandler::handle_out_of_memory_during_evacuation() {
+  assert(ShenandoahThreadLocalData::is_evac_allowed(Thread::current()), "sanity");
+  assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must not be set");
+
+  jint threads_in_evac = OrderAccess::load_acquire(&_threads_in_evac);
+  while (true) {
+    jint other = Atomic::cmpxchg((threads_in_evac - 1) | OOM_MARKER_MASK,
+                                  &_threads_in_evac, threads_in_evac);
+    if (other == threads_in_evac) {
+      // Success: wait for other threads to get out of the protocol and return.
+      wait_for_no_evac_threads();
+      return;
+    } else {
+      // Failure: try again with updated new value.
+      threads_in_evac = other;
+    }
+  }
+}
+
+void ShenandoahEvacOOMHandler::clear() {
+  assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
+  assert((OrderAccess::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) == 0, "sanity");
+  OrderAccess::release_store_fence<jint>(&_threads_in_evac, 0);
+}
+
+ShenandoahEvacOOMScope::ShenandoahEvacOOMScope() {
+  ShenandoahHeap::heap()->enter_evacuation();
+}
+
+ShenandoahEvacOOMScope::~ShenandoahEvacOOMScope() {
+  ShenandoahHeap::heap()->leave_evacuation();
+}
+
+ShenandoahEvacOOMScopeLeaver::ShenandoahEvacOOMScopeLeaver() {
+  ShenandoahHeap::heap()->leave_evacuation();
+}
+
+ShenandoahEvacOOMScopeLeaver::~ShenandoahEvacOOMScopeLeaver() {
+  ShenandoahHeap::heap()->enter_evacuation();
+}