1 /*

     2  * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.

     8  *

     9  * This code is distributed in the hope that it will be useful, but WITHOUT

    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    12  * version 2 for more details (a copy is included in the LICENSE file that

    13  * accompanied this code).

    14  *

    15  * You should have received a copy of the GNU General Public License version

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    18  *

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

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

    21  * questions.

    22  *

    23  */

    24 

    25 # include "incls/_precompiled.incl"

    26 # include "incls/_basicLock.cpp.incl"

    27 

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

    29   st->print("monitor");

    30 }

    31 

    32 void BasicLock::move_to(oop obj, BasicLock* dest) {

    33   // Check to see if we need to inflate the lock. This is only needed

    34   // if an object is locked using "this" lightweight monitor. In that

    35   // case, the displaced_header() is unlocked, because the

    36   // displaced_header() contains the header for the originally unlocked

    37   // object. However the object could have already been inflated. But it

    38   // does not matter, the inflation will just a no-op. For other cases,

    39   // the displaced header will be either 0x0 or 0x3, which are location

    40   // independent, therefore the BasicLock is free to move.

    41   //

    42   // During OSR we may need to relocate a BasicLock (which contains a

    43   // displaced word) from a location in an interpreter frame to a

    44   // new location in a compiled frame.  "this" refers to the source

    45   // basiclock in the interpreter frame.  "dest" refers to the destination

    46   // basiclock in the new compiled frame.  We *always* inflate in move_to().

    47   // The always-Inflate policy works properly, but in 1.5.0 it can sometimes

    48   // cause performance problems in code that makes heavy use of a small # of

    49   // uncontended locks.   (We'd inflate during OSR, and then sync performance

    50   // would subsequently plummet because the thread would be forced thru the slow-path).

    51   // This problem has been made largely moot on IA32 by inlining the inflated fast-path

    52   // operations in Fast_Lock and Fast_Unlock in i486.ad.

    53   //

    54   // Note that there is a way to safely swing the object's markword from

    55   // one stack location to another.  This avoids inflation.  Obviously,

    56   // we need to ensure that both locations refer to the current thread's stack.

    57   // There are some subtle concurrency issues, however, and since the benefit is

    58   // is small (given the support for inflated fast-path locking in the fast_lock, etc)

    59   // we'll leave that optimization for another time.

    60 

    61   if (displaced_header()->is_neutral()) {

    62     ObjectSynchronizer::inflate_helper(obj);

    63     // WARNING: We can not put check here, because the inflation

    64     // will not update the displaced header. Once BasicLock is inflated,

    65     // no one should ever look at its content.

    66   } else {

    67     // Typically the displaced header will be 0 (recursive stack lock) or

    68     // unused_mark.  Naively we'd like to assert that the displaced mark

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

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

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

    72   }

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

    74   intptr_t dh = (intptr_t) displaced_header();

    75   dest->set_displaced_header(displaced_header());

    76 }