src/hotspot/share/runtime/basicLock.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) 1997, 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) 1997, 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.
*** 34,72 ****
  }
  
  void BasicLock::move_to(oop obj, BasicLock* dest) {
    // Check to see if we need to inflate the lock. This is only needed
    // if an object is locked using "this" lightweight monitor. In that
!   // case, the displaced_header() is unlocked, because the
    // displaced_header() contains the header for the originally unlocked
!   // object. However the object could have already been inflated. But it
!   // does not matter, the inflation will just a no-op. For other cases,
    // the displaced header will be either 0x0 or 0x3, which are location
    // independent, therefore the BasicLock is free to move.
    //
    // During OSR we may need to relocate a BasicLock (which contains a
    // displaced word) from a location in an interpreter frame to a
    // new location in a compiled frame.  "this" refers to the source
!   // basiclock in the interpreter frame.  "dest" refers to the destination
!   // basiclock in the new compiled frame.  We *always* inflate in move_to().
!   // The always-Inflate policy works properly, but in 1.5.0 it can sometimes
!   // cause performance problems in code that makes heavy use of a small # of
!   // uncontended locks.   (We'd inflate during OSR, and then sync performance
!   // would subsequently plummet because the thread would be forced thru the slow-path).
!   // This problem has been made largely moot on IA32 by inlining the inflated fast-path
!   // operations in Fast_Lock and Fast_Unlock in i486.ad.
    //
    // Note that there is a way to safely swing the object's markword from
    // one stack location to another.  This avoids inflation.  Obviously,
    // we need to ensure that both locations refer to the current thread's stack.
    // There are some subtle concurrency issues, however, and since the benefit is
    // is small (given the support for inflated fast-path locking in the fast_lock, etc)
    // we'll leave that optimization for another time.
  
    if (displaced_header().is_neutral()) {
      ObjectSynchronizer::inflate_helper(obj);
!     // WARNING: We can not put check here, because the inflation
      // will not update the displaced header. Once BasicLock is inflated,
      // no one should ever look at its content.
    } else {
      // Typically the displaced header will be 0 (recursive stack lock) or
      // unused_mark.  Naively we'd like to assert that the displaced mark
--- 34,74 ----
  }
  
  void BasicLock::move_to(oop obj, BasicLock* dest) {
    // Check to see if we need to inflate the lock. This is only needed
    // if an object is locked using "this" lightweight monitor. In that
!   // case, the displaced_header() is unlocked/is_neutral, because the
    // displaced_header() contains the header for the originally unlocked
!   // object. However the lock could have already been inflated. But it
!   // does not matter, this inflation will just a no-op. For other cases,
    // the displaced header will be either 0x0 or 0x3, which are location
    // independent, therefore the BasicLock is free to move.
    //
    // During OSR we may need to relocate a BasicLock (which contains a
    // displaced word) from a location in an interpreter frame to a
    // new location in a compiled frame.  "this" refers to the source
!   // BasicLock in the interpreter frame.  "dest" refers to the destination
!   // BasicLock in the new compiled frame.  We *always* inflate in move_to()
!   // when the object is locked using "this" lightweight monitor.
!   //
!   // The always-Inflate policy works properly, but it depends on the
!   // inflated fast-path operations in fast_lock and fast_unlock to avoid
!   // performance problems. See x86/macroAssembler_x86.cpp: fast_lock()
!   // and fast_unlock() for examples.
    //
    // Note that there is a way to safely swing the object's markword from
    // one stack location to another.  This avoids inflation.  Obviously,
    // we need to ensure that both locations refer to the current thread's stack.
    // There are some subtle concurrency issues, however, and since the benefit is
    // is small (given the support for inflated fast-path locking in the fast_lock, etc)
    // we'll leave that optimization for another time.
  
    if (displaced_header().is_neutral()) {
+     // The object is locked and the resulting ObjectMonitor* will also be
+     // locked so it can't be async deflated until ownership is dropped.
      ObjectSynchronizer::inflate_helper(obj);
!     // WARNING: We cannot put a check here, because the inflation
      // will not update the displaced header. Once BasicLock is inflated,
      // no one should ever look at its content.
    } else {
      // Typically the displaced header will be 0 (recursive stack lock) or
      // unused_mark.  Naively we'd like to assert that the displaced mark