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 "precompiled.hpp" 26 #include "runtime/basicLock.hpp" 27 #include "runtime/synchronizer.hpp" 28 29 void BasicLock::print_on(outputStream* st) const { 30 st->print("monitor"); 31 } 32 33 void BasicLock::move_to(oop obj, BasicLock* dest) { 34 // Check to see if we need to inflate the lock. This is only needed 35 // if an object is locked using "this" lightweight monitor. In that 36 // case, the displaced_header() is unlocked, because the 37 // displaced_header() contains the header for the originally unlocked 38 // object. However the object could have already been inflated. But it 39 // does not matter, the inflation will just a no-op. For other cases, 40 // the displaced header will be either 0x0 or 0x3, which are location 41 // independent, therefore the BasicLock is free to move. 42 // 43 // During OSR we may need to relocate a BasicLock (which contains a 44 // displaced word) from a location in an interpreter frame to a 45 // new location in a compiled frame. "this" refers to the source 46 // basiclock in the interpreter frame. "dest" refers to the destination 47 // basiclock in the new compiled frame. We *always* inflate in move_to(). 48 // The always-Inflate policy works properly, but in 1.5.0 it can sometimes 49 // cause performance problems in code that makes heavy use of a small # of 50 // uncontended locks. (We'd inflate during OSR, and then sync performance 51 // would subsequently plummet because the thread would be forced thru the slow-path). 52 // This problem has been made largely moot on IA32 by inlining the inflated fast-path 53 // operations in Fast_Lock and Fast_Unlock in i486.ad. 54 // 55 // Note that there is a way to safely swing the object's markword from 56 // one stack location to another. This avoids inflation. Obviously, 57 // we need to ensure that both locations refer to the current thread's stack. 58 // There are some subtle concurrency issues, however, and since the benefit is 59 // is small (given the support for inflated fast-path locking in the fast_lock, etc) 60 // we'll leave that optimization for another time. 61 62 if (displaced_header()->is_neutral()) { 63 ObjectSynchronizer::inflate_helper(obj); 64 // WARNING: We can not put check here, because the inflation 65 // will not update the displaced header. Once BasicLock is inflated, 66 // no one should ever look at its content. 67 } else { 68 // Typically the displaced header will be 0 (recursive stack lock) or 69 // unused_mark. Naively we'd like to assert that the displaced mark 70 // value is either 0, neutral, or 3. But with the advent of the 71 // store-before-CAS avoidance in fast_lock/compiler_lock_object 72 // we can find any flavor mark in the displaced mark. 73 } 74 // [RGV] The next line appears to do nothing! 75 intptr_t dh = (intptr_t) displaced_header(); 76 dest->set_displaced_header(displaced_header()); 77 }