8138920: Refactor the sampling thread from ConcurrentG1RefineThread

Helps enable running without concurrent refinement threads

Reviewed-by: brutisso, pliden

hotspot/src/share/vm/gc/g1/g1YoungRemSetSamplingThread.cpp

@@ -0,0 +1,122 @@
+/*
+ * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * 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/g1/g1CollectedHeap.inline.hpp"
+#include "gc/g1/g1CollectorPolicy.hpp"
+#include "gc/g1/g1YoungRemSetSamplingThread.hpp"
+#include "gc/g1/suspendibleThreadSet.hpp"
+#include "runtime/mutexLocker.hpp"
+
+void G1YoungRemSetSamplingThread::run() {
+  initialize_in_thread();
+  wait_for_universe_init();
+
+  run_service();
+
+  terminate();
+}
+
+void G1YoungRemSetSamplingThread::stop() {
+  // it is ok to take late safepoints here, if needed
+  {
+    MutexLockerEx mu(Terminator_lock);
+    _should_terminate = true;
+  }
+
+  stop_service();
+
+  {
+    MutexLockerEx mu(Terminator_lock);
+    while (!_has_terminated) {
+      Terminator_lock->wait();
+    }
+  }
+}
+
+G1YoungRemSetSamplingThread::G1YoungRemSetSamplingThread() : ConcurrentGCThread() {
+  _monitor = new Monitor(Mutex::nonleaf,
+                         "G1YoungRemSetSamplingThread monitor",
+                         true,
+                         Monitor::_safepoint_check_never);
+
+  create_and_start();
+
+  set_name("G1 Young RemSet Sampling");
+}
+
+void G1YoungRemSetSamplingThread::sleep_before_next_cycle() {
+  MutexLockerEx x(_monitor, Mutex::_no_safepoint_check_flag);
+  if (!_should_terminate) {
+    intx waitms = G1ConcRefinementServiceIntervalMillis; // 300, really should be?
+    _monitor->wait(Mutex::_no_safepoint_check_flag, waitms);
+  }
+}
+
+void G1YoungRemSetSamplingThread::run_service() {
+  double vtime_start = os::elapsedVTime();
+
+  while (!_should_terminate) {
+    sample_young_list_rs_lengths();
+
+    if (os::supports_vtime()) {
+      _vtime_accum = (os::elapsedVTime() - vtime_start);
+    } else {
+      _vtime_accum = 0.0;
+    }
+
+    sleep_before_next_cycle();
+  }
+}
+
+void G1YoungRemSetSamplingThread::stop_service() {
+  MutexLockerEx x(_monitor, Mutex::_no_safepoint_check_flag);
+  _monitor->notify();
+}
+
+void G1YoungRemSetSamplingThread::sample_young_list_rs_lengths() {
+  SuspendibleThreadSetJoiner sts;
+  G1CollectedHeap* g1h = G1CollectedHeap::heap();
+  G1CollectorPolicy* g1p = g1h->g1_policy();
+  if (g1p->adaptive_young_list_length()) {
+    int regions_visited = 0;
+    g1h->young_list()->rs_length_sampling_init();
+    while (g1h->young_list()->rs_length_sampling_more()) {
+      g1h->young_list()->rs_length_sampling_next();
+      ++regions_visited;
+
+      // we try to yield every time we visit 10 regions
+      if (regions_visited == 10) {
+        if (sts.should_yield()) {
+          sts.yield();
+          // we just abandon the iteration
+          break;
+        }
+        regions_visited = 0;
+      }
+    }
+
+    g1p->revise_young_list_target_length_if_necessary();
+  }
+}