1 /*
2 * Copyright (c) 1998, 2008, 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 // The SplitWord construct allows us to colocate the contention queue
26 // (cxq) with the lock-byte. The queue elements are ParkEvents, which are
27 // always aligned on 256-byte addresses - the least significant byte of
28 // a ParkEvent is always 0. Colocating the lock-byte with the queue
29 // allows us to easily avoid what would otherwise be a race in lock()
30 // if we were to use two completely separate fields for the contention queue
31 // and the lock indicator. Specifically, colocation renders us immune
32 // from the race where a thread might enqueue itself in the lock() slow-path
33 // immediately after the lock holder drops the outer lock in the unlock()
34 // fast-path.
35 //
36 // Colocation allows us to use a fast-path unlock() form that uses
37 // A MEMBAR instead of a CAS. MEMBAR has lower local latency than CAS
38 // on many platforms.
39 //
40 // See:
41 // + http://blogs.sun.com/dave/entry/biased_locking_in_hotspot
42 // + http://blogs.sun.com/dave/resource/synchronization-public2.pdf
43 //
44 // Note that we're *not* using word-tearing the classic sense.
248 // there may have been some benefit to having distinct mutexes and monitors, but that time
249 // has past.
250 //
251 // The Mutex/Monitor design parallels that of Java-monitors, being based on
252 // thread-specific park-unpark platform-specific primitives.
253
254
255 class Mutex : public Monitor { // degenerate Monitor
256 public:
257 Mutex (int rank, const char *name, bool allow_vm_block=false);
258 ~Mutex () ;
259 private:
260 bool notify () { ShouldNotReachHere(); return false; }
261 bool notify_all() { ShouldNotReachHere(); return false; }
262 bool wait (bool no_safepoint_check, long timeout, bool as_suspend_equivalent) {
263 ShouldNotReachHere() ;
264 return false ;
265 }
266 };
267
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1 /*
2 * Copyright (c) 1998, 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 #ifndef SHARE_VM_RUNTIME_MUTEX_HPP
26 #define SHARE_VM_RUNTIME_MUTEX_HPP
27
28 #include "memory/allocation.hpp"
29 #include "runtime/os.hpp"
30 #include "utilities/histogram.hpp"
31
32 // The SplitWord construct allows us to colocate the contention queue
33 // (cxq) with the lock-byte. The queue elements are ParkEvents, which are
34 // always aligned on 256-byte addresses - the least significant byte of
35 // a ParkEvent is always 0. Colocating the lock-byte with the queue
36 // allows us to easily avoid what would otherwise be a race in lock()
37 // if we were to use two completely separate fields for the contention queue
38 // and the lock indicator. Specifically, colocation renders us immune
39 // from the race where a thread might enqueue itself in the lock() slow-path
40 // immediately after the lock holder drops the outer lock in the unlock()
41 // fast-path.
42 //
43 // Colocation allows us to use a fast-path unlock() form that uses
44 // A MEMBAR instead of a CAS. MEMBAR has lower local latency than CAS
45 // on many platforms.
46 //
47 // See:
48 // + http://blogs.sun.com/dave/entry/biased_locking_in_hotspot
49 // + http://blogs.sun.com/dave/resource/synchronization-public2.pdf
50 //
51 // Note that we're *not* using word-tearing the classic sense.
255 // there may have been some benefit to having distinct mutexes and monitors, but that time
256 // has past.
257 //
258 // The Mutex/Monitor design parallels that of Java-monitors, being based on
259 // thread-specific park-unpark platform-specific primitives.
260
261
262 class Mutex : public Monitor { // degenerate Monitor
263 public:
264 Mutex (int rank, const char *name, bool allow_vm_block=false);
265 ~Mutex () ;
266 private:
267 bool notify () { ShouldNotReachHere(); return false; }
268 bool notify_all() { ShouldNotReachHere(); return false; }
269 bool wait (bool no_safepoint_check, long timeout, bool as_suspend_equivalent) {
270 ShouldNotReachHere() ;
271 return false ;
272 }
273 };
274
275
276 #endif // SHARE_VM_RUNTIME_MUTEX_HPP
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