1 /*
 2  * Copyright (c) 1997, 2020, 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.hpp"
28 #include "runtime/synchronizer.hpp"
29 
30 void BasicLock::print_on(outputStream* st, oop owner) const {
31   st->print("monitor");
32   markWord mark_word = displaced_header();
33   if (mark_word.value() != 0) {
34     // Print monitor info if there's an owning oop and it refers to this BasicLock.
35     bool print_monitor_info = (owner != NULL) && (owner->mark() == markWord::from_pointer((void*)this));
36     mark_word.print_on(st, print_monitor_info);
37   }
38 }
39 
40 void BasicLock::move_to(oop obj, BasicLock* dest) {
41   // Check to see if we need to inflate the lock. This is only needed
42   // if an object is locked using "this" lightweight monitor. In that
43   // case, the displaced_header() is unlocked/is_neutral, because the
44   // displaced_header() contains the header for the originally unlocked
45   // object. However the lock could have already been inflated. But it
46   // does not matter, this inflation will just a no-op. For other cases,
47   // the displaced header will be either 0x0 or 0x3, which are location
48   // independent, therefore the BasicLock is free to move.
49   //
50   // During OSR we may need to relocate a BasicLock (which contains a
51   // displaced word) from a location in an interpreter frame to a
52   // new location in a compiled frame.  "this" refers to the source
53   // BasicLock in the interpreter frame.  "dest" refers to the destination
54   // BasicLock in the new compiled frame.  We *always* inflate in move_to()
55   // when the object is locked using "this" lightweight monitor.
56   //
57   // The always-Inflate policy works properly, but it depends on the
58   // inflated fast-path operations in fast_lock and fast_unlock to avoid
59   // performance problems. See x86/macroAssembler_x86.cpp: fast_lock()
60   // and fast_unlock() for examples.
61   //
62   // Note that there is a way to safely swing the object's markword from
63   // one stack location to another.  This avoids inflation.  Obviously,
64   // we need to ensure that both locations refer to the current thread's stack.
65   // There are some subtle concurrency issues, however, and since the benefit is
66   // is small (given the support for inflated fast-path locking in the fast_lock, etc)
67   // we'll leave that optimization for another time.
68 
69   if (LockingMode == LM_LEGACY) {
70     if (displaced_header().is_neutral()) {
71       // The object is locked and the resulting ObjectMonitor* will also be
72       // locked so it can't be async deflated until ownership is dropped.
73       ObjectSynchronizer::inflate_helper(obj);
74       // WARNING: We cannot put a check here, because the inflation
75       // will not update the displaced header. Once BasicLock is inflated,
76       // no one should ever look at its content.
77     } else {
78       // Typically the displaced header will be 0 (recursive stack lock) or
79       // unused_mark.  Naively we'd like to assert that the displaced mark
80       // value is either 0, neutral, or 3.  But with the advent of the
81       // store-before-CAS avoidance in fast_lock/compiler_lock_object
82       // we can find any flavor mark in the displaced mark.
83     }
84     dest->set_displaced_header(displaced_header());
85   }
86 #ifdef ASSERT
87   else {
88     dest->set_displaced_header(markWord(badDispHeaderDeopt));
89   }
90 #endif
91 }
--- EOF ---