Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright (c) 1997, 2010, 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.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  *

  */

 #include "precompiled.hpp"

 #include "runtime/basicLock.hpp"

 #include "runtime/synchronizer.hpp"

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

   st->print("monitor");

 }

 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.

   }

 // [RGV] The next line appears to do nothing!

   intptr_t dh = (intptr_t) displaced_header();

   dest->set_displaced_header(displaced_header());

 }