src/hotspot/share/runtime/sharedRuntime.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.

@@ -63,10 +63,11 @@
 #include "runtime/interfaceSupport.inline.hpp"
 #include "runtime/java.hpp"
 #include "runtime/javaCalls.hpp"
 #include "runtime/sharedRuntime.hpp"
 #include "runtime/stubRoutines.hpp"
+#include "runtime/synchronizer.hpp"
 #include "runtime/vframe.inline.hpp"
 #include "runtime/vframeArray.hpp"
 #include "utilities/copy.hpp"
 #include "utilities/dtrace.hpp"
 #include "utilities/events.hpp"

@@ -3068,14 +3069,19 @@
   for (BasicObjectLock *kptr2 = fr.interpreter_frame_monitor_end();
        kptr2 < fr.interpreter_frame_monitor_begin();
        kptr2 = fr.next_monitor_in_interpreter_frame(kptr2) ) {
     if (kptr2->obj() != NULL) {         // Avoid 'holes' in the monitor array
       BasicLock *lock = kptr2->lock();
-      // Inflate so the displaced header becomes position-independent
-      if (lock->displaced_header().is_unlocked())
+      // Inflate so the object's header no longer refers to the BasicLock.
+      if (lock->displaced_header().is_unlocked()) {
+        // The object is locked and the resulting ObjectMonitor* will also be
+        // locked so it can't be async deflated until ownership is dropped.
+        // See the big comment in basicLock.cpp: BasicLock::move_to().
         ObjectSynchronizer::inflate_helper(kptr2->obj());
-      // Now the displaced header is free to move
+      }
+      // Now the displaced header is free to move because the
+      // object's header no longer refers to it.
       buf[i++] = (intptr_t)lock->displaced_header().value();
       buf[i++] = cast_from_oop<intptr_t>(kptr2->obj());
     }
   }
   assert(i - max_locals == active_monitor_count*2, "found the expected number of monitors");