Thu, 02 Apr 2009 18:17:03 -0400
Merge
1 /*
2 * Copyright 1998-2008 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
22 *
23 */
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.
45 // The lock() fast-path will CAS the lockword and the unlock()
46 // fast-path will store into the lock-byte colocated within the lockword.
47 // We depend on the fact that all our reference platforms have
48 // coherent and atomic byte accesses. More precisely, byte stores
49 // interoperate in a safe, sane, and expected manner with respect to
50 // CAS, ST and LDs to the full-word containing the byte.
51 // If you're porting HotSpot to a platform where that isn't the case
52 // then you'll want change the unlock() fast path from:
53 // STB;MEMBAR #storeload; LDN
54 // to a full-word CAS of the lockword.
57 union SplitWord { // full-word with separately addressable LSB
58 volatile intptr_t FullWord ;
59 volatile void * Address ;
60 volatile jbyte Bytes [sizeof(intptr_t)] ;
61 } ;
63 // Endian-ness ... index of least-significant byte in SplitWord.Bytes[]
64 #ifdef AMD64 // little
65 #define _LSBINDEX 0
66 #else
67 #if IA32 // little
68 #define _LSBINDEX 0
69 #else
70 #ifdef SPARC // big
71 #define _LSBINDEX (sizeof(intptr_t)-1)
72 #else
73 #error "unknown architecture"
74 #endif
75 #endif
76 #endif
78 class ParkEvent ;
80 // See orderAccess.hpp. We assume throughout the VM that mutex lock and
81 // try_lock do fence-lock-acquire, and that unlock does a release-unlock,
82 // *in that order*. If their implementations change such that these
83 // assumptions are violated, a whole lot of code will break.
85 // The default length of monitor name is chosen to be 64 to avoid false sharing.
86 static const int MONITOR_NAME_LEN = 64;
88 class Monitor : public CHeapObj {
90 public:
91 // A special lock: Is a lock where you are guaranteed not to block while you are
92 // holding it, i.e., no vm operation can happen, taking other locks, etc.
93 // NOTE: It is critical that the rank 'special' be the lowest (earliest)
94 // (except for "event"?) for the deadlock dection to work correctly.
95 // The rank native is only for use in Mutex's created by JVM_RawMonitorCreate,
96 // which being external to the VM are not subject to deadlock detection.
97 // The rank safepoint is used only for synchronization in reaching a
98 // safepoint and leaving a safepoint. It is only used for the Safepoint_lock
99 // currently. While at a safepoint no mutexes of rank safepoint are held
100 // by any thread.
101 // The rank named "leaf" is probably historical (and should
102 // be changed) -- mutexes of this rank aren't really leaf mutexes
103 // at all.
104 enum lock_types {
105 event,
106 special,
107 suspend_resume,
108 leaf = suspend_resume + 2,
109 safepoint = leaf + 10,
110 barrier = safepoint + 1,
111 nonleaf = barrier + 1,
112 max_nonleaf = nonleaf + 900,
113 native = max_nonleaf + 1
114 };
116 // The WaitSet and EntryList linked lists are composed of ParkEvents.
117 // I use ParkEvent instead of threads as ParkEvents are immortal and
118 // type-stable, meaning we can safely unpark() a possibly stale
119 // list element in the unlock()-path.
121 protected: // Monitor-Mutex metadata
122 SplitWord _LockWord ; // Contention queue (cxq) colocated with Lock-byte
123 enum LockWordBits { _LBIT=1 } ;
124 Thread * volatile _owner; // The owner of the lock
125 // Consider sequestering _owner on its own $line
126 // to aid future synchronization mechanisms.
127 ParkEvent * volatile _EntryList ; // List of threads waiting for entry
128 ParkEvent * volatile _OnDeck ; // heir-presumptive
129 volatile intptr_t _WaitLock [1] ; // Protects _WaitSet
130 ParkEvent * volatile _WaitSet ; // LL of ParkEvents
131 volatile bool _snuck; // Used for sneaky locking (evil).
132 int NotifyCount ; // diagnostic assist
133 char _name[MONITOR_NAME_LEN]; // Name of mutex
135 // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode)
136 #ifndef PRODUCT
137 bool _allow_vm_block;
138 debug_only(int _rank;) // rank (to avoid/detect potential deadlocks)
139 debug_only(Monitor * _next;) // Used by a Thread to link up owned locks
140 debug_only(Thread* _last_owner;) // the last thread to own the lock
141 debug_only(static bool contains(Monitor * locks, Monitor * lock);)
142 debug_only(static Monitor * get_least_ranked_lock(Monitor * locks);)
143 debug_only(Monitor * get_least_ranked_lock_besides_this(Monitor * locks);)
144 #endif
146 void set_owner_implementation(Thread* owner) PRODUCT_RETURN;
147 void check_prelock_state (Thread* thread) PRODUCT_RETURN;
148 void check_block_state (Thread* thread) PRODUCT_RETURN;
150 // platform-dependent support code can go here (in os_<os_family>.cpp)
151 public:
152 enum {
153 _no_safepoint_check_flag = true,
154 _allow_vm_block_flag = true,
155 _as_suspend_equivalent_flag = true
156 };
158 enum WaitResults {
159 CONDVAR_EVENT, // Wait returned because of condition variable notification
160 INTERRUPT_EVENT, // Wait returned because waiting thread was interrupted
161 NUMBER_WAIT_RESULTS
162 };
164 private:
165 int TrySpin (Thread * Self) ;
166 int TryLock () ;
167 int TryFast () ;
168 int AcquireOrPush (ParkEvent * ev) ;
169 void IUnlock (bool RelaxAssert) ;
170 void ILock (Thread * Self) ;
171 int IWait (Thread * Self, jlong timo);
172 int ILocked () ;
174 protected:
175 static void ClearMonitor (Monitor * m, const char* name = NULL) ;
176 Monitor() ;
178 public:
179 Monitor(int rank, const char *name, bool allow_vm_block=false);
180 ~Monitor();
182 // Wait until monitor is notified (or times out).
183 // Defaults are to make safepoint checks, wait time is forever (i.e.,
184 // zero), and not a suspend-equivalent condition. Returns true if wait
185 // times out; otherwise returns false.
186 bool wait(bool no_safepoint_check = !_no_safepoint_check_flag,
187 long timeout = 0,
188 bool as_suspend_equivalent = !_as_suspend_equivalent_flag);
189 bool notify();
190 bool notify_all();
193 void lock(); // prints out warning if VM thread blocks
194 void lock(Thread *thread); // overloaded with current thread
195 void unlock();
196 bool is_locked() const { return _owner != NULL; }
198 bool try_lock(); // Like lock(), but unblocking. It returns false instead
200 // Lock without safepoint check. Should ONLY be used by safepoint code and other code
201 // that is guaranteed not to block while running inside the VM.
202 void lock_without_safepoint_check();
203 void lock_without_safepoint_check (Thread * Self) ;
205 // Current owner - not not MT-safe. Can only be used to guarantee that
206 // the current running thread owns the lock
207 Thread* owner() const { return _owner; }
208 bool owned_by_self() const;
210 // Support for JVM_RawMonitorEnter & JVM_RawMonitorExit. These can be called by
211 // non-Java thread. (We should really have a RawMonitor abstraction)
212 void jvm_raw_lock();
213 void jvm_raw_unlock();
214 const char *name() const { return _name; }
216 void print_on_error(outputStream* st) const;
218 #ifndef PRODUCT
219 void print_on(outputStream* st) const;
220 void print() const { print_on(tty); }
221 debug_only(int rank() const { return _rank; })
222 bool allow_vm_block() { return _allow_vm_block; }
224 debug_only(Monitor *next() const { return _next; })
225 debug_only(void set_next(Monitor *next) { _next = next; })
226 #endif
228 void set_owner(Thread* owner) {
229 #ifndef PRODUCT
230 set_owner_implementation(owner);
231 debug_only(void verify_Monitor(Thread* thr));
232 #else
233 _owner = owner;
234 #endif
235 }
237 };
239 // Normally we'd expect Monitor to extend Mutex in the sense that a monitor
240 // constructed from pthreads primitives might extend a mutex by adding
241 // a condvar and some extra metadata. In fact this was the case until J2SE7.
242 //
243 // Currently, however, the base object is a monitor. Monitor contains all the
244 // logic for wait(), notify(), etc. Mutex extends monitor and restricts the
245 // visiblity of wait(), notify(), and notify_all().
246 //
247 // Another viable alternative would have been to have Monitor extend Mutex and
248 // implement all the normal mutex and wait()-notify() logic in Mutex base class.
249 // The wait()-notify() facility would be exposed via special protected member functions
250 // (e.g., _Wait() and _Notify()) in Mutex. Monitor would extend Mutex and expose wait()
251 // as a call to _Wait(). That is, the public wait() would be a wrapper for the protected
252 // _Wait().
253 //
254 // An even better alternative is to simply eliminate Mutex:: and use Monitor:: instead.
255 // After all, monitors are sufficient for Java-level synchronization. At one point in time
256 // there may have been some benefit to having distinct mutexes and monitors, but that time
257 // has past.
258 //
259 // The Mutex/Monitor design parallels that of Java-monitors, being based on
260 // thread-specific park-unpark platform-specific primitives.
263 class Mutex : public Monitor { // degenerate Monitor
264 public:
265 Mutex (int rank, const char *name, bool allow_vm_block=false);
266 ~Mutex () ;
267 private:
268 bool notify () { ShouldNotReachHere(); return false; }
269 bool notify_all() { ShouldNotReachHere(); return false; }
270 bool wait (bool no_safepoint_check, long timeout, bool as_suspend_equivalent) {
271 ShouldNotReachHere() ;
272 return false ;
273 }
274 };
276 /*
277 * Per-thread blocking support for JSR166. See the Java-level
278 * Documentation for rationale. Basically, park acts like wait, unpark
279 * like notify.
280 *
281 * 6271289 --
282 * To avoid errors where an os thread expires but the JavaThread still
283 * exists, Parkers are immortal (type-stable) and are recycled across
284 * new threads. This parallels the ParkEvent implementation.
285 * Because park-unpark allow spurious wakeups it is harmless if an
286 * unpark call unparks a new thread using the old Parker reference.
287 *
288 * In the future we'll want to think about eliminating Parker and using
289 * ParkEvent instead. There's considerable duplication between the two
290 * services.
291 *
292 */
294 class Parker : public os::PlatformParker {
295 private:
296 volatile int _counter ;
297 Parker * FreeNext ;
298 JavaThread * AssociatedWith ; // Current association
300 public:
301 Parker() : PlatformParker() {
302 _counter = 0 ;
303 FreeNext = NULL ;
304 AssociatedWith = NULL ;
305 }
306 protected:
307 ~Parker() { ShouldNotReachHere(); }
308 public:
309 // For simplicity of interface with Java, all forms of park (indefinite,
310 // relative, and absolute) are multiplexed into one call.
311 void park(bool isAbsolute, jlong time);
312 void unpark();
314 // Lifecycle operators
315 static Parker * Allocate (JavaThread * t) ;
316 static void Release (Parker * e) ;
317 private:
318 static Parker * volatile FreeList ;
319 static volatile int ListLock ;
320 };