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comparison src/share/vm/runtime/basicLock.cpp @ 1878:fa83ab460c54

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6988353: refactor contended sync subsystem Summary: reduce complexity by factoring synchronizer.cpp Reviewed-by: dholmes, never, coleenp
author acorn
date Fri, 22 Oct 2010 15:59:34 -0400
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1874:75ab0162aa84 1878:fa83ab460c54
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 }