1 /* 2 * Copyright (c) 1997, 2024, 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 "oops/oop.inline.hpp" 27 #include "runtime/basicLock.inline.hpp" 28 #include "runtime/objectMonitor.hpp" 29 #include "runtime/synchronizer.hpp" 30 #include "utilities/globalDefinitions.hpp" 31 32 void BasicLock::print_on(outputStream* st, oop owner) const { 33 st->print("monitor"); 34 if (LockingMode == LM_LIGHTWEIGHT) { 35 ObjectMonitor* mon = object_monitor_cache(); 36 if (mon != nullptr) { 37 mon->print_on(st); 38 } 39 } else { 40 markWord mark_word = displaced_header(); 41 if (mark_word.value() != 0) { 42 // Print monitor info if there's an owning oop and it refers to this BasicLock. 43 bool print_monitor_info = (owner != nullptr) && (owner->mark() == markWord::from_pointer((void*)this)); 44 mark_word.print_on(st, print_monitor_info); 45 } 46 } 47 } 48 49 void BasicLock::move_to(oop obj, BasicLock* dest) { 50 // Check to see if we need to inflate the lock. This is only needed 51 // if an object is locked using "this" lightweight monitor. In that 52 // case, the displaced_header() is unlocked/neutral, because the 53 // displaced_header() contains the header for the originally unlocked 54 // object. However the lock could have already been inflated. But it 55 // does not matter, this inflation will just be a no-op. For other cases, 56 // the displaced header will be either 0x0 or 0x3, which are location 57 // independent, therefore the BasicLock is free to move. 58 // 59 // During OSR we may need to relocate a BasicLock (which contains a 60 // displaced word) from a location in an interpreter frame to a 61 // new location in a compiled frame. "this" refers to the source 62 // BasicLock in the interpreter frame. "dest" refers to the destination 63 // BasicLock in the new compiled frame. We *always* inflate in move_to() 64 // when the object is locked using "this" lightweight monitor. 65 // 66 // The always-Inflate policy works properly, but it depends on the 67 // inflated fast-path operations in fast_lock and fast_unlock to avoid 68 // performance problems. See x86/macroAssembler_x86.cpp: fast_lock() 69 // and fast_unlock() for examples. 70 // 71 // Note that there is a way to safely swing the object's markword from 72 // one stack location to another. This avoids inflation. Obviously, 73 // we need to ensure that both locations refer to the current thread's stack. 74 // There are some subtle concurrency issues, however, and since the benefit is 75 // small (given the support for inflated fast-path locking in the fast_lock, etc) 76 // we'll leave that optimization for another time. 77 78 if (LockingMode == LM_LEGACY) { 79 if (displaced_header().is_neutral()) { 80 // The object is locked and the resulting ObjectMonitor* will also be 81 // locked so it can't be async deflated until ownership is dropped. 82 ObjectSynchronizer::inflate_helper(obj); 83 // WARNING: We cannot put a check here, because the inflation 84 // will not update the displaced header. Once BasicLock is inflated, 85 // no one should ever look at its content. 86 } else { 87 // Typically the displaced header will be 0 (recursive stack lock) or 88 // unused_mark. Naively we'd like to assert that the displaced mark 89 // value is either 0, neutral, or 3. But with the advent of the 90 // store-before-CAS avoidance in fast_lock/compiler_lock_object 91 // we can find any flavor mark in the displaced mark. 92 } 93 dest->set_displaced_header(displaced_header()); 94 } else if (LockingMode == LM_LIGHTWEIGHT) { 95 // Preserve the ObjectMonitor*, the cache is cleared when a box is reused 96 // and only read while the lock is held, so no stale ObjectMonitor* is 97 // encountered. 98 dest->set_object_monitor_cache(object_monitor_cache()); 99 } 100 #ifdef ASSERT 101 else { 102 dest->set_bad_metadata_deopt(); 103 } 104 #endif 105 }