--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/shared/gcLocker.cpp	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,228 @@
+/*
+ * Copyright (c) 1997, 2016, 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/shared/collectedHeap.hpp"
+#include "gc/shared/gcLocker.inline.hpp"
+#include "memory/resourceArea.hpp"
+#include "logging/log.hpp"
+#include "runtime/atomic.hpp"
+#include "runtime/thread.inline.hpp"
+
+volatile jint GCLocker::_jni_lock_count = 0;
+volatile bool GCLocker::_needs_gc       = false;
+volatile bool GCLocker::_doing_gc       = false;
+
+#ifdef ASSERT
+volatile jint GCLocker::_debug_jni_lock_count = 0;
+#endif
+
+
+#ifdef ASSERT
+void GCLocker::verify_critical_count() {
+  if (SafepointSynchronize::is_at_safepoint()) {
+    assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree");
+    int count = 0;
+    // Count the number of threads with critical operations in progress
+    for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
+      if (thr->in_critical()) {
+        count++;
+      }
+    }
+    if (_jni_lock_count != count) {
+      log_error(gc, verify)("critical counts don't match: %d != %d", _jni_lock_count, count);
+      for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
+        if (thr->in_critical()) {
+          log_error(gc, verify)(INTPTR_FORMAT " in_critical %d", p2i(thr), thr->in_critical());
+        }
+      }
+    }
+    assert(_jni_lock_count == count, "must be equal");
+  }
+}
+
+// In debug mode track the locking state at all times
+void GCLocker::increment_debug_jni_lock_count() {
+  assert(_debug_jni_lock_count >= 0, "bad value");
+  Atomic::inc(&_debug_jni_lock_count);
+}
+
+void GCLocker::decrement_debug_jni_lock_count() {
+  assert(_debug_jni_lock_count > 0, "bad value");
+  Atomic::dec(&_debug_jni_lock_count);
+}
+#endif
+
+void GCLocker::log_debug_jni(const char* msg) {
+  Log(gc, jni) log;
+  if (log.is_debug()) {
+    ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
+    log.debug("%s Thread \"%s\" %d locked.", msg, Thread::current()->name(), _jni_lock_count);
+  }
+}
+
+bool GCLocker::check_active_before_gc() {
+  assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint");
+  if (is_active() && !_needs_gc) {
+    verify_critical_count();
+    _needs_gc = true;
+    log_debug_jni("Setting _needs_gc.");
+  }
+  return is_active();
+}
+
+void GCLocker::stall_until_clear() {
+  assert(!JavaThread::current()->in_critical(), "Would deadlock");
+  MutexLocker   ml(JNICritical_lock);
+
+  if (needs_gc()) {
+    log_debug_jni("Allocation failed. Thread stalled by JNI critical section.");
+  }
+
+  // Wait for _needs_gc  to be cleared
+  while (needs_gc()) {
+    JNICritical_lock->wait();
+  }
+}
+
+void GCLocker::jni_lock(JavaThread* thread) {
+  assert(!thread->in_critical(), "shouldn't currently be in a critical region");
+  MutexLocker mu(JNICritical_lock);
+  // Block entering threads if we know at least one thread is in a
+  // JNI critical region and we need a GC.
+  // We check that at least one thread is in a critical region before
+  // blocking because blocked threads are woken up by a thread exiting
+  // a JNI critical region.
+  while (is_active_and_needs_gc() || _doing_gc) {
+    JNICritical_lock->wait();
+  }
+  thread->enter_critical();
+  _jni_lock_count++;
+  increment_debug_jni_lock_count();
+}
+
+void GCLocker::jni_unlock(JavaThread* thread) {
+  assert(thread->in_last_critical(), "should be exiting critical region");
+  MutexLocker mu(JNICritical_lock);
+  _jni_lock_count--;
+  decrement_debug_jni_lock_count();
+  thread->exit_critical();
+  if (needs_gc() && !is_active_internal()) {
+    // We're the last thread out. Cause a GC to occur.
+    _doing_gc = true;
+    {
+      // Must give up the lock while at a safepoint
+      MutexUnlocker munlock(JNICritical_lock);
+      log_debug_jni("Performing GC after exiting critical section.");
+      Universe::heap()->collect(GCCause::_gc_locker);
+    }
+    _doing_gc = false;
+    _needs_gc = false;
+    JNICritical_lock->notify_all();
+  }
+}
+
+// Implementation of NoGCVerifier
+
+#ifdef ASSERT
+
+NoGCVerifier::NoGCVerifier(bool verifygc) {
+  _verifygc = verifygc;
+  if (_verifygc) {
+    CollectedHeap* h = Universe::heap();
+    assert(!h->is_gc_active(), "GC active during NoGCVerifier");
+    _old_invocations = h->total_collections();
+  }
+}
+
+
+NoGCVerifier::~NoGCVerifier() {
+  if (_verifygc) {
+    CollectedHeap* h = Universe::heap();
+    assert(!h->is_gc_active(), "GC active during NoGCVerifier");
+    if (_old_invocations != h->total_collections()) {
+      fatal("collection in a NoGCVerifier secured function");
+    }
+  }
+}
+
+PauseNoGCVerifier::PauseNoGCVerifier(NoGCVerifier * ngcv) {
+  _ngcv = ngcv;
+  if (_ngcv->_verifygc) {
+    // if we were verifying, then make sure that nothing is
+    // wrong before we "pause" verification
+    CollectedHeap* h = Universe::heap();
+    assert(!h->is_gc_active(), "GC active during NoGCVerifier");
+    if (_ngcv->_old_invocations != h->total_collections()) {
+      fatal("collection in a NoGCVerifier secured function");
+    }
+  }
+}
+
+
+PauseNoGCVerifier::~PauseNoGCVerifier() {
+  if (_ngcv->_verifygc) {
+    // if we were verifying before, then reenable verification
+    CollectedHeap* h = Universe::heap();
+    assert(!h->is_gc_active(), "GC active during NoGCVerifier");
+    _ngcv->_old_invocations = h->total_collections();
+  }
+}
+
+
+// JRT_LEAF rules:
+// A JRT_LEAF method may not interfere with safepointing by
+//   1) acquiring or blocking on a Mutex or JavaLock - checked
+//   2) allocating heap memory - checked
+//   3) executing a VM operation - checked
+//   4) executing a system call (including malloc) that could block or grab a lock
+//   5) invoking GC
+//   6) reaching a safepoint
+//   7) running too long
+// Nor may any method it calls.
+JRTLeafVerifier::JRTLeafVerifier()
+  : NoSafepointVerifier(true, JRTLeafVerifier::should_verify_GC())
+{
+}
+
+JRTLeafVerifier::~JRTLeafVerifier()
+{
+}
+
+bool JRTLeafVerifier::should_verify_GC() {
+  switch (JavaThread::current()->thread_state()) {
+  case _thread_in_Java:
+    // is in a leaf routine, there must be no safepoint.
+    return true;
+  case _thread_in_native:
+    // A native thread is not subject to safepoints.
+    // Even while it is in a leaf routine, GC is ok
+    return false;
+  default:
+    // Leaf routines cannot be called from other contexts.
+    ShouldNotReachHere();
+    return false;
+  }
+}
+#endif