1 /*
   2  * Copyright (c) 2016, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "jfr/recorder/checkpoint/types/traceid/jfrTraceIdEpoch.hpp"
  27 #include "runtime/safepoint.hpp"
  28 #include "runtime/orderAccess.hpp"
  29 
  30 // Alternating epochs on each rotation allow for concurrent tagging.
  31 // The regular epoch shift happens only during a safepoint.
  32 // The fence is there only for the emergency dump case which happens outside of safepoint.
  33 bool JfrTraceIdEpoch::_epoch_state = false;
  34 void JfrTraceIdEpoch::shift_epoch() {
  35   _epoch_state = !_epoch_state;
  36   if (!SafepointSynchronize::is_at_safepoint()) {
  37     OrderAccess::fence();
  38   }
  39 }