8256306: ObjectMonitor::_contentions field should not be 'jint'

Reviewed-by: dholmes, stuefe, dcubed

Author: coleenp

src/hotspot/share/runtime/objectMonitor.cpp

@@ -485,7 +485,7 @@ bool ObjectMonitor::enter(JavaThread* current) {
     // just exited the monitor.
   }
   if (event.should_commit()) {
-    event.set_previousOwner((uintptr_t)_previous_owner_tid);
+    event.set_previousOwner(_previous_owner_tid);
     event.commit();
   }
   OM_PERFDATA_OP(ContendedLockAttempts, inc());
@@ -545,7 +545,7 @@ bool ObjectMonitor::deflate_monitor() {
     // Java threads. The GC already broke the association with the object.
     set_owner_from(NULL, DEFLATER_MARKER);
     assert(contentions() >= 0, "must be non-negative: contentions=%d", contentions());
-    _contentions = -max_jint;
+    _contentions = INT_MIN; // minimum negative int
   } else {
     // Attempt async deflation protocol.
 
@@ -572,7 +572,7 @@ bool ObjectMonitor::deflate_monitor() {
 
     // Make a zero contentions field negative to force any contending threads
     // to retry. This is the second part of the async deflation dance.
-    if (Atomic::cmpxchg(&_contentions, (jint)0, -max_jint) != 0) {
+    if (Atomic::cmpxchg(&_contentions, 0, INT_MIN) != 0) {
       // Contentions was no longer 0 so we lost the race since the
       // ObjectMonitor is now busy. Restore owner to NULL if it is
       // still DEFLATER_MARKER:
@@ -2243,7 +2243,7 @@ void ObjectMonitor::print_debug_style_on(outputStream* st) const {
   st->print_cr("    [%d] = '\\0'", (int)sizeof(_pad_buf0) - 1);
   st->print_cr("  }");
   st->print_cr("  _owner = " INTPTR_FORMAT, p2i(owner_raw()));
-  st->print_cr("  _previous_owner_tid = " JLONG_FORMAT, _previous_owner_tid);
+  st->print_cr("  _previous_owner_tid = " INTPTR_FORMAT, _previous_owner_tid);
   st->print_cr("  _pad_buf1 = {");
   st->print_cr("    [0] = '\\0'");
   st->print_cr("    ...");

src/hotspot/share/runtime/objectMonitor.hpp

@@ -148,13 +148,13 @@ class ObjectMonitor : public CHeapObj<mtInternal> {
   // Used by async deflation as a marker in the _owner field:
   #define DEFLATER_MARKER reinterpret_cast<void*>(-1)
   void* volatile _owner;            // pointer to owning thread OR BasicLock
-  volatile jlong _previous_owner_tid;  // thread id of the previous owner of the monitor
+  volatile uintptr_t _previous_owner_tid;  // thread id of the previous owner of the monitor
   // Separate _owner and _next_om on different cache lines since
   // both can have busy multi-threaded access. _previous_owner_tid is only
   // changed by ObjectMonitor::exit() so it is a good choice to share the
   // cache line with _owner.
   DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(void* volatile) +
-                        sizeof(volatile jlong));
+                        sizeof(volatile uintptr_t));
   ObjectMonitor* _next_om;          // Next ObjectMonitor* linkage
   volatile intx _recursions;        // recursion count, 0 for first entry
   ObjectWaiter* volatile _EntryList;  // Threads blocked on entry or reentry.
@@ -168,13 +168,13 @@ class ObjectMonitor : public CHeapObj<mtInternal> {
   volatile int _Spinner;            // for exit->spinner handoff optimization
   volatile int _SpinDuration;
 
-  jint  _contentions;               // Number of active contentions in enter(). It is used by is_busy()
+  int _contentions;                 // Number of active contentions in enter(). It is used by is_busy()
                                     // along with other fields to determine if an ObjectMonitor can be
                                     // deflated. It is also used by the async deflation protocol. See
                                     // ObjectMonitor::deflate_monitor().
  protected:
   ObjectWaiter* volatile _WaitSet;  // LL of threads wait()ing on the monitor
-  volatile jint  _waiters;          // number of waiting threads
+  volatile int  _waiters;           // number of waiting threads
  private:
   volatile int _WaitSetLock;        // protects Wait Queue - simple spinlock
 
@@ -238,9 +238,10 @@ class ObjectMonitor : public CHeapObj<mtInternal> {
 
   bool is_busy() const {
     // TODO-FIXME: assert _owner == null implies _recursions = 0
-    intptr_t ret_code = _waiters | intptr_t(_cxq) | intptr_t(_EntryList);
-    if (contentions() > 0) {
-      ret_code |= contentions();
+    intptr_t ret_code = intptr_t(_waiters) | intptr_t(_cxq) | intptr_t(_EntryList);
+    int cnts = contentions(); // read once
+    if (cnts > 0) {
+      ret_code |= intptr_t(cnts);
     }
     if (!owner_is_DEFLATER_MARKER()) {
       ret_code |= intptr_t(owner_raw());
@@ -281,10 +282,10 @@ class ObjectMonitor : public CHeapObj<mtInternal> {
   // _next_om field. Returns the prior value of the _next_om field.
   ObjectMonitor* try_set_next_om(ObjectMonitor* old_value, ObjectMonitor* new_value);
 
-  jint      waiters() const;
+  int       waiters() const;
 
-  jint      contentions() const;
-  void      add_to_contentions(jint value);
+  int       contentions() const;
+  void      add_to_contentions(int value);
   intx      recursions() const                                         { return _recursions; }
 
   // JVM/TI GetObjectMonitorUsage() needs this:

src/hotspot/share/runtime/objectMonitor.inline.hpp

@@ -52,7 +52,7 @@ inline void ObjectMonitor::set_header(markWord hdr) {
   Atomic::store(&_header, hdr);
 }
 
-inline jint ObjectMonitor::waiters() const {
+inline int ObjectMonitor::waiters() const {
   return _waiters;
 }
 
@@ -79,12 +79,12 @@ inline bool ObjectMonitor::is_being_async_deflated() {
 }
 
 // Return number of threads contending for this monitor.
-inline jint ObjectMonitor::contentions() const {
+inline int ObjectMonitor::contentions() const {
   return Atomic::load(&_contentions);
 }
 
 // Add value to the contentions field.
-inline void ObjectMonitor::add_to_contentions(jint value) {
+inline void ObjectMonitor::add_to_contentions(int value) {
   Atomic::add(&_contentions, value);
 }
 

src/hotspot/share/runtime/vmStructs.cpp

@@ -881,8 +881,8 @@ typedef HashtableEntry<InstanceKlass*, mtClass>  KlassHashtableEntry;
   unchecked_nonstatic_field(ObjectMonitor,     _owner,                                        sizeof(void *)) /* NOTE: no type */    \
   volatile_nonstatic_field(ObjectMonitor,      _next_om,                                      ObjectMonitor*)                        \
   volatile_nonstatic_field(BasicLock,          _displaced_header,                             markWord)                              \
-  nonstatic_field(ObjectMonitor,               _contentions,                                  jint)                                  \
-  volatile_nonstatic_field(ObjectMonitor,      _waiters,                                      jint)                                  \
+  nonstatic_field(ObjectMonitor,               _contentions,                                  int)                                   \
+  volatile_nonstatic_field(ObjectMonitor,      _waiters,                                      int)                                   \
   volatile_nonstatic_field(ObjectMonitor,      _recursions,                                   intx)                                  \
   nonstatic_field(BasicObjectLock,             _lock,                                         BasicLock)                             \
   nonstatic_field(BasicObjectLock,             _obj,                                          oop)                                   \

src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/runtime/ObjectMonitor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2021, 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
@@ -52,9 +52,9 @@ private static synchronized void initialize(TypeDataBase db) throws WrongTypeExc
     ownerFieldOffset = f.getOffset();
     f = type.getField("_next_om");
     nextOMFieldOffset = f.getOffset();
-    contentionsField  = type.getJIntField("_contentions");
-    waitersField = type.getJIntField("_waiters");
-    recursionsField = type.getCIntegerField("_recursions");
+    contentionsField  = new CIntField(type.getCIntegerField("_contentions"), 0);
+    waitersField      = new CIntField(type.getCIntegerField("_waiters"), 0);
+    recursionsField   = type.getCIntegerField("_recursions");
   }
 
   public ObjectMonitor(Address addr) {
@@ -83,7 +83,7 @@ public boolean isEntered(sun.jvm.hotspot.runtime.Thread current) {
   // FIXME
   //  void      set_owner(void* owner);
 
-  public int    waiters() { return waitersField.getValue(addr); }
+  public int    waiters() { return (int)waitersField.getValue(this); }
 
   public Address nextOM() { return addr.getAddressAt(nextOMFieldOffset); }
   // FIXME
@@ -100,7 +100,7 @@ public OopHandle object() {
   }
 
   public int contentions() {
-      return contentionsField.getValue(addr);
+      return (int)contentionsField.getValue(this);
   }
 
   // The following four either aren't expressed as typed fields in
@@ -111,8 +111,8 @@ public int contentions() {
   private static long          objectFieldOffset;
   private static long          ownerFieldOffset;
   private static long          nextOMFieldOffset;
-  private static JIntField     contentionsField;
-  private static JIntField     waitersField;
+  private static CIntField     contentionsField;
+  private static CIntField     waitersField;
   private static CIntegerField recursionsField;
   // FIXME: expose platform-dependent stuff
 }