| /* |
| * Copyright (c) 1997, 2015, 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"); |
| markOop moop = displaced_header(); |
| if (moop != NULL) |
| moop->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. |
| } |
| // [RGV] The next line appears to do nothing! |
| intptr_t dh = (intptr_t) displaced_header(); |
| dest->set_displaced_header(displaced_header()); |
| } |