/*

 * 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.

 *

 * 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.

 *

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 */

#include "precompiled.hpp"

#include "runtime/basicLock.hpp"

#include "runtime/synchronizer.hpp"

void BasicLock::print_on(outputStream* st) const {

  st->print("monitor");

  markWord mark_word = displaced_header();

  if (mark_word.value() != 0)

    mark_word.print_on(st);

}

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

    // value is either 0, neutral, or 3.  But with the advent of the

    // store-before-CAS avoidance in fast_lock/compiler_lock_object

    // we can find any flavor mark in the displaced mark.

  }

  dest->set_displaced_header(displaced_header());

}