src/hotspot/share/services/threadService.cpp

rev 59077 : 8153224.v2.09b.patch combined with 8153224.v2.10.patch; merge with jdk-15+21.
rev 59078 : eosterlund v2.10 CR: reorganize deflate_monitor_using_JT() to use "early exit" style; dcubed - clarify/fix/rearrange a few comments in deflate_monitor_using_JT(); eosterlund v2.10 CR: simplify install_displaced_markword_in_object() and save_om_ptr(); save_om_ptr()'s call to install_displaced_markword_in_object() can race with the deflater thread's clearing of the object field so handle that; fold 8153224.OMHandle_experiment into 8153224.v2.11.patch; merge with jdk-15+21.

*** 1,7 ****
  /*
!  * Copyright (c) 2003, 2019, 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.
--- 1,7 ----
  /*
!  * Copyright (c) 2003, 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.
*** 35,44 ****
--- 35,45 ----
  #include "prims/jvmtiRawMonitor.hpp"
  #include "runtime/atomic.hpp"
  #include "runtime/handles.inline.hpp"
  #include "runtime/init.hpp"
  #include "runtime/objectMonitor.inline.hpp"
+ #include "runtime/safepointVerifiers.hpp"
  #include "runtime/thread.inline.hpp"
  #include "runtime/threadSMR.inline.hpp"
  #include "runtime/vframe.hpp"
  #include "runtime/vmThread.hpp"
  #include "runtime/vmOperations.hpp"
*** 206,228 ****
  // FIXME: JVMTI should call this function
  Handle ThreadService::get_current_contended_monitor(JavaThread* thread) {
    assert(thread != NULL, "should be non-NULL");
    debug_only(Thread::check_for_dangling_thread_pointer(thread);)
  
    ObjectMonitor *wait_obj = thread->current_waiting_monitor();
  
    oop obj = NULL;
    if (wait_obj != NULL) {
      // thread is doing an Object.wait() call
      obj = (oop) wait_obj->object();
!     assert(obj != NULL, "Object.wait() should have an object");
    } else {
      ObjectMonitor *enter_obj = thread->current_pending_monitor();
      if (enter_obj != NULL) {
        // thread is trying to enter() an ObjectMonitor.
        obj = (oop) enter_obj->object();
!       assert(obj != NULL, "ObjectMonitor should have an associated object!");
      }
    }
  
    Handle h(Thread::current(), obj);
    return h;
--- 207,237 ----
  // FIXME: JVMTI should call this function
  Handle ThreadService::get_current_contended_monitor(JavaThread* thread) {
    assert(thread != NULL, "should be non-NULL");
    debug_only(Thread::check_for_dangling_thread_pointer(thread);)
  
+   // This function can be called on a target JavaThread that is not
+   // the caller and we are not at a safepoint. So it is possible for
+   // the waiting or pending condition to be over/stale and for the
+   // first stage of async deflation to clear the object field in
+   // the ObjectMonitor. It is also possible for the object to be
+   // inflated again and to be associated with a completely different
+   // ObjectMonitor by the time this object reference is processed
+   // by the caller.
    ObjectMonitor *wait_obj = thread->current_waiting_monitor();
  
    oop obj = NULL;
    if (wait_obj != NULL) {
      // thread is doing an Object.wait() call
      obj = (oop) wait_obj->object();
!     assert(AsyncDeflateIdleMonitors || obj != NULL, "Object.wait() should have an object");
    } else {
      ObjectMonitor *enter_obj = thread->current_pending_monitor();
      if (enter_obj != NULL) {
        // thread is trying to enter() an ObjectMonitor.
        obj = (oop) enter_obj->object();
!       assert(AsyncDeflateIdleMonitors || obj != NULL, "ObjectMonitor should have an associated object!");
      }
    }
  
    Handle h(Thread::current(), obj);
    return h;
*** 389,398 ****
--- 398,408 ----
      previousThread = jt;
      currentThread = jt;
  
      cycle->reset();
  
+     // The ObjectMonitor* can't be async deflated since we are at a safepoint.
      // When there is a deadlock, all the monitors involved in the dependency
      // cycle must be contended and heavyweight. So we only care about the
      // heavyweight monitor a thread is waiting to lock.
      waitingToLockMonitor = jt->current_pending_monitor();
      // JVM TI raw monitors can also be involved in deadlocks, and we can be
*** 965,981 ****
    st->cr();
    st->print_cr("Found one Java-level deadlock:");
    st->print("=============================");
  
    JavaThread* currentThread;
-   ObjectMonitor* waitingToLockMonitor;
    JvmtiRawMonitor* waitingToLockRawMonitor;
    oop waitingToLockBlocker;
    int len = _threads->length();
    for (int i = 0; i < len; i++) {
      currentThread = _threads->at(i);
!     waitingToLockMonitor = currentThread->current_pending_monitor();
      waitingToLockRawMonitor = currentThread->current_pending_raw_monitor();
      waitingToLockBlocker = currentThread->current_park_blocker();
      st->cr();
      st->print_cr("\"%s\":", currentThread->get_thread_name());
      const char* owner_desc = ",\n  which is held by";
--- 975,991 ----
    st->cr();
    st->print_cr("Found one Java-level deadlock:");
    st->print("=============================");
  
    JavaThread* currentThread;
    JvmtiRawMonitor* waitingToLockRawMonitor;
    oop waitingToLockBlocker;
    int len = _threads->length();
    for (int i = 0; i < len; i++) {
      currentThread = _threads->at(i);
!     // The ObjectMonitor* can't be async deflated since we are at a safepoint.
!     ObjectMonitor* waitingToLockMonitor = currentThread->current_pending_monitor();
      waitingToLockRawMonitor = currentThread->current_pending_raw_monitor();
      waitingToLockBlocker = currentThread->current_park_blocker();
      st->cr();
      st->print_cr("\"%s\":", currentThread->get_thread_name());
      const char* owner_desc = ",\n  which is held by";