acorn@2233: /*
acorn@2233:  * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.
acorn@2233:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
acorn@2233:  *
acorn@2233:  * This code is free software; you can redistribute it and/or modify it
acorn@2233:  * under the terms of the GNU General Public License version 2 only, as
acorn@2233:  * published by the Free Software Foundation.
acorn@2233:  *
acorn@2233:  * This code is distributed in the hope that it will be useful, but WITHOUT
acorn@2233:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
acorn@2233:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
acorn@2233:  * version 2 for more details (a copy is included in the LICENSE file that
acorn@2233:  * accompanied this code).
acorn@2233:  *
acorn@2233:  * You should have received a copy of the GNU General Public License version
acorn@2233:  * 2 along with this work; if not, write to the Free Software Foundation,
acorn@2233:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
acorn@2233:  *
acorn@2233:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
acorn@2233:  * or visit www.oracle.com if you need additional information or have any
acorn@2233:  * questions.
acorn@2233:  *
acorn@2233:  */
acorn@2233: 
stefank@2314: #include "precompiled.hpp"
stefank@2314: #include "runtime/basicLock.hpp"
stefank@2314: #include "runtime/synchronizer.hpp"
acorn@2233: 
acorn@2233: void BasicLock::print_on(outputStream* st) const {
acorn@2233:   st->print("monitor");
acorn@2233: }
acorn@2233: 
acorn@2233: void BasicLock::move_to(oop obj, BasicLock* dest) {
acorn@2233:   // Check to see if we need to inflate the lock. This is only needed
acorn@2233:   // if an object is locked using "this" lightweight monitor. In that
acorn@2233:   // case, the displaced_header() is unlocked, because the
acorn@2233:   // displaced_header() contains the header for the originally unlocked
acorn@2233:   // object. However the object could have already been inflated. But it
acorn@2233:   // does not matter, the inflation will just a no-op. For other cases,
acorn@2233:   // the displaced header will be either 0x0 or 0x3, which are location
acorn@2233:   // independent, therefore the BasicLock is free to move.
acorn@2233:   //
acorn@2233:   // During OSR we may need to relocate a BasicLock (which contains a
acorn@2233:   // displaced word) from a location in an interpreter frame to a
acorn@2233:   // new location in a compiled frame.  "this" refers to the source
acorn@2233:   // basiclock in the interpreter frame.  "dest" refers to the destination
acorn@2233:   // basiclock in the new compiled frame.  We *always* inflate in move_to().
acorn@2233:   // The always-Inflate policy works properly, but in 1.5.0 it can sometimes
acorn@2233:   // cause performance problems in code that makes heavy use of a small # of
acorn@2233:   // uncontended locks.   (We'd inflate during OSR, and then sync performance
acorn@2233:   // would subsequently plummet because the thread would be forced thru the slow-path).
acorn@2233:   // This problem has been made largely moot on IA32 by inlining the inflated fast-path
acorn@2233:   // operations in Fast_Lock and Fast_Unlock in i486.ad.
acorn@2233:   //
acorn@2233:   // Note that there is a way to safely swing the object's markword from
acorn@2233:   // one stack location to another.  This avoids inflation.  Obviously,
acorn@2233:   // we need to ensure that both locations refer to the current thread's stack.
acorn@2233:   // There are some subtle concurrency issues, however, and since the benefit is
acorn@2233:   // is small (given the support for inflated fast-path locking in the fast_lock, etc)
acorn@2233:   // we'll leave that optimization for another time.
acorn@2233: 
acorn@2233:   if (displaced_header()->is_neutral()) {
acorn@2233:     ObjectSynchronizer::inflate_helper(obj);
acorn@2233:     // WARNING: We can not put check here, because the inflation
acorn@2233:     // will not update the displaced header. Once BasicLock is inflated,
acorn@2233:     // no one should ever look at its content.
acorn@2233:   } else {
acorn@2233:     // Typically the displaced header will be 0 (recursive stack lock) or
acorn@2233:     // unused_mark.  Naively we'd like to assert that the displaced mark
acorn@2233:     // value is either 0, neutral, or 3.  But with the advent of the
acorn@2233:     // store-before-CAS avoidance in fast_lock/compiler_lock_object
acorn@2233:     // we can find any flavor mark in the displaced mark.
acorn@2233:   }
acorn@2233: // [RGV] The next line appears to do nothing!
acorn@2233:   intptr_t dh = (intptr_t) displaced_header();
acorn@2233:   dest->set_displaced_header(displaced_header());
acorn@2233: }