8253064: monitor list simplifications and getting rid of TSM

Co-authored-by: Erik Österlund <eosterlund@openjdk.org>
Reviewed-by: eosterlund, rehn, coleenp

Author: Daniel D. Daugherty

src/hotspot/share/oops/markWord.cpp

@@ -25,9 +25,42 @@
 #include "precompiled.hpp"
 #include "oops/markWord.hpp"
 #include "runtime/thread.inline.hpp"
-#include "runtime/objectMonitor.hpp"
+#include "runtime/objectMonitor.inline.hpp"
 #include "utilities/ostream.hpp"
 
+markWord markWord::displaced_mark_helper() const {
+  assert(has_displaced_mark_helper(), "check");
+  if (has_monitor()) {
+    // Has an inflated monitor. Must be checked before has_locker().
+    ObjectMonitor* monitor = this->monitor();
+    return monitor->header();
+  }
+  if (has_locker()) {  // has a stack lock
+    BasicLock* locker = this->locker();
+    return locker->displaced_header();
+  }
+  // This should never happen:
+  fatal("bad header=" INTPTR_FORMAT, value());
+  return markWord(value());
+}
+
+void markWord::set_displaced_mark_helper(markWord m) const {
+  assert(has_displaced_mark_helper(), "check");
+  if (has_monitor()) {
+    // Has an inflated monitor. Must be checked before has_locker().
+    ObjectMonitor* monitor = this->monitor();
+    monitor->set_header(m);
+    return;
+  }
+  if (has_locker()) {  // has a stack lock
+    BasicLock* locker = this->locker();
+    locker->set_displaced_header(m);
+    return;
+  }
+  // This should never happen:
+  fatal("bad header=" INTPTR_FORMAT, value());
+}
+
 void markWord::print_on(outputStream* st, bool print_monitor_info) const {
   if (is_marked()) {  // last bits = 11
     st->print(" marked(" INTPTR_FORMAT ")", value());

src/hotspot/share/oops/markWord.hpp

@@ -286,16 +286,8 @@ class markWord {
   bool has_displaced_mark_helper() const {
     return ((value() & unlocked_value) == 0);
   }
-  markWord displaced_mark_helper() const {
-    assert(has_displaced_mark_helper(), "check");
-    uintptr_t ptr = (value() & ~monitor_value);
-    return *(markWord*)ptr;
-  }
-  void set_displaced_mark_helper(markWord m) const {
-    assert(has_displaced_mark_helper(), "check");
-    uintptr_t ptr = (value() & ~monitor_value);
-    ((markWord*)ptr)->_value = m._value;
-  }
+  markWord displaced_mark_helper() const;
+  void set_displaced_mark_helper(markWord m) const;
   markWord copy_set_hash(intptr_t hash) const {
     uintptr_t tmp = value() & (~hash_mask_in_place);
     tmp |= ((hash & hash_mask) << hash_shift);

src/hotspot/share/runtime/globals.hpp

@@ -728,6 +728,20 @@ const intx ObjectAlignmentInBytes = 8;
           "MonitorUsedDeflationThreshold is exceeded (0 is off).")          \
           range(0, max_jint)                                                \
                                                                             \
+  /* notice: the max range value here is max_jint, not max_intx  */         \
+  /* because of overflow issue                                   */         \
+  product(intx, AvgMonitorsPerThreadEstimate, 1024, DIAGNOSTIC,             \
+          "Used to estimate a variable ceiling based on number of threads " \
+          "for use with MonitorUsedDeflationThreshold (0 is off).")         \
+          range(0, max_jint)                                                \
+                                                                            \
+  /* notice: the max range value here is max_jint, not max_intx  */         \
+  /* because of overflow issue                                   */         \
+  product(intx, MonitorDeflationMax, 1000000, DIAGNOSTIC,                   \
+          "The maximum number of monitors to deflate, unlink and delete "   \
+          "at one time (minimum is 1024).")                      \
+          range(1024, max_jint)                                             \
+                                                                            \
   product(intx, MonitorUsedDeflationThreshold, 90, EXPERIMENTAL,            \
           "Percentage of used monitors before triggering deflation (0 is "  \
           "off). The check is performed on GuaranteedSafepointInterval "    \

src/hotspot/share/runtime/monitorDeflationThread.cpp

@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2020, 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 "classfile/javaClasses.hpp"
+#include "runtime/interfaceSupport.inline.hpp"
+#include "runtime/java.hpp"
+#include "runtime/javaCalls.hpp"
+#include "runtime/monitorDeflationThread.hpp"
+#include "runtime/mutexLocker.hpp"
+
+MonitorDeflationThread* MonitorDeflationThread::_instance = NULL;
+
+void MonitorDeflationThread::initialize() {
+  EXCEPTION_MARK;
+
+  const char* name = "Monitor Deflation Thread";
+  Handle string = java_lang_String::create_from_str(name, CHECK);
+
+  // Initialize thread_oop to put it into the system threadGroup
+  Handle thread_group (THREAD, Universe::system_thread_group());
+  Handle thread_oop = JavaCalls::construct_new_instance(
+                          SystemDictionary::Thread_klass(),
+                          vmSymbols::threadgroup_string_void_signature(),
+                          thread_group,
+                          string,
+                          CHECK);
+
+  {
+    MutexLocker mu(THREAD, Threads_lock);
+    MonitorDeflationThread* thread =  new MonitorDeflationThread(&monitor_deflation_thread_entry);
+
+    // At this point it may be possible that no osthread was created for the
+    // JavaThread due to lack of memory. We would have to throw an exception
+    // in that case. However, since this must work and we do not allow
+    // exceptions anyway, check and abort if this fails.
+    if (thread == NULL || thread->osthread() == NULL) {
+      vm_exit_during_initialization("java.lang.OutOfMemoryError",
+                                    os::native_thread_creation_failed_msg());
+    }
+
+    java_lang_Thread::set_thread(thread_oop(), thread);
+    java_lang_Thread::set_priority(thread_oop(), NearMaxPriority);
+    java_lang_Thread::set_daemon(thread_oop());
+    thread->set_threadObj(thread_oop());
+    _instance = thread;
+
+    Threads::add(thread);
+    Thread::start(thread);
+  }
+}
+
+void MonitorDeflationThread::monitor_deflation_thread_entry(JavaThread* jt, TRAPS) {
+  while (true) {
+    {
+      // Need state transition ThreadBlockInVM so that this thread
+      // will be handled by safepoint correctly when this thread is
+      // notified at a safepoint.
+
+      // This ThreadBlockInVM object is not also considered to be
+      // suspend-equivalent because MonitorDeflationThread is not
+      // visible to external suspension.
+
+      ThreadBlockInVM tbivm(jt);
+
+      MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
+      while (!ObjectSynchronizer::is_async_deflation_needed()) {
+        // Wait until notified that there is some work to do.
+        // We wait for GuaranteedSafepointInterval so that
+        // is_async_deflation_needed() is checked at the same interval.
+        ml.wait(GuaranteedSafepointInterval);
+      }
+    }
+
+    (void)ObjectSynchronizer::deflate_idle_monitors();
+  }
+}

src/hotspot/share/runtime/monitorDeflationThread.hpp

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2020, 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.
+ *
+ */
+
+#ifndef SHARE_RUNTIME_MONITORDEFLATIONTHREAD_HPP
+#define SHARE_RUNTIME_MONITORDEFLATIONTHREAD_HPP
+
+#include "runtime/thread.hpp"
+
+// A hidden from external view JavaThread for deflating idle monitors.
+
+class MonitorDeflationThread : public JavaThread {
+  friend class VMStructs;
+ private:
+  static MonitorDeflationThread* _instance;
+
+  static void monitor_deflation_thread_entry(JavaThread* thread, TRAPS);
+  MonitorDeflationThread(ThreadFunction entry_point) : JavaThread(entry_point) {};
+
+ public:
+  static void initialize();
+
+  // Hide this thread from external view.
+  bool is_hidden_from_external_view() const { return true; }
+  bool is_monitor_deflation_thread() const { return true; }
+};
+
+#endif // SHARE_RUNTIME_MONITORDEFLATIONTHREAD_HPP

src/hotspot/share/runtime/mutexLocker.cpp

@@ -116,6 +116,7 @@ Mutex*   OldSets_lock                 = NULL;
 Monitor* RootRegionScan_lock          = NULL;
 
 Mutex*   Management_lock              = NULL;
+Monitor* MonitorDeflation_lock        = NULL;
 Monitor* Service_lock                 = NULL;
 Monitor* Notification_lock            = NULL;
 Monitor* PeriodicTask_lock            = NULL;
@@ -244,6 +245,7 @@ void mutex_init() {
 
   def(Patching_lock                , PaddedMutex  , special,     true,  _safepoint_check_never);      // used for safepointing and code patching.
   def(CompiledMethod_lock          , PaddedMutex  , special-1,   true,  _safepoint_check_never);
+  def(MonitorDeflation_lock        , PaddedMonitor, tty-2,       true,  _safepoint_check_never);      // used for monitor deflation thread operations
   def(Service_lock                 , PaddedMonitor, tty-2,       true,  _safepoint_check_never);      // used for service thread operations
 
   if (UseNotificationThread) {

src/hotspot/share/runtime/mutexLocker.hpp

@@ -111,6 +111,7 @@ extern Mutex*   OldSets_lock;                    // protects the old region sets
 extern Monitor* RootRegionScan_lock;             // used to notify that the CM threads have finished scanning the IM snapshot regions
 
 extern Mutex*   Management_lock;                 // a lock used to serialize JVM management
+extern Monitor* MonitorDeflation_lock;           // a lock used for monitor deflation thread operation
 extern Monitor* Service_lock;                    // a lock used for service thread operation
 extern Monitor* Notification_lock;               // a lock used for notification thread operation
 extern Monitor* PeriodicTask_lock;               // protects the periodic task structure