Thu, 07 Feb 2013 16:05:48 -0500
Merge
1 /*
2 * Copyright (c) 1998, 2012, 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.
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 */
25 #ifndef SHARE_VM_RUNTIME_MUTEX_HPP
26 #define SHARE_VM_RUNTIME_MUTEX_HPP
28 #include "memory/allocation.hpp"
29 #include "runtime/os.hpp"
30 #include "utilities/histogram.hpp"
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.
52 // The lock() fast-path will CAS the lockword and the unlock()
53 // fast-path will store into the lock-byte colocated within the lockword.
54 // We depend on the fact that all our reference platforms have
55 // coherent and atomic byte accesses. More precisely, byte stores
56 // interoperate in a safe, sane, and expected manner with respect to
57 // CAS, ST and LDs to the full-word containing the byte.
58 // If you're porting HotSpot to a platform where that isn't the case
59 // then you'll want change the unlock() fast path from:
60 // STB;MEMBAR #storeload; LDN
61 // to a full-word CAS of the lockword.
64 union SplitWord { // full-word with separately addressable LSB
65 volatile intptr_t FullWord ;
66 volatile void * Address ;
67 volatile jbyte Bytes [sizeof(intptr_t)] ;
68 } ;
70 // Endian-ness ... index of least-significant byte in SplitWord.Bytes[]
71 #ifdef VM_LITTLE_ENDIAN
72 #define _LSBINDEX 0
73 #else
74 #define _LSBINDEX (sizeof(intptr_t)-1)
75 #endif
77 class ParkEvent ;
79 // See orderAccess.hpp. We assume throughout the VM that mutex lock and
80 // try_lock do fence-lock-acquire, and that unlock does a release-unlock,
81 // *in that order*. If their implementations change such that these
82 // assumptions are violated, a whole lot of code will break.
84 // The default length of monitor name is chosen to be 64 to avoid false sharing.
85 static const int MONITOR_NAME_LEN = 64;
87 class Monitor : public CHeapObj<mtInternal> {
89 public:
90 // A special lock: Is a lock where you are guaranteed not to block while you are
91 // holding it, i.e., no vm operation can happen, taking other locks, etc.
92 // NOTE: It is critical that the rank 'special' be the lowest (earliest)
93 // (except for "event"?) for the deadlock dection to work correctly.
94 // The rank native is only for use in Mutex's created by JVM_RawMonitorCreate,
95 // which being external to the VM are not subject to deadlock detection.
96 // The rank safepoint is used only for synchronization in reaching a
97 // safepoint and leaving a safepoint. It is only used for the Safepoint_lock
98 // currently. While at a safepoint no mutexes of rank safepoint are held
99 // by any thread.
100 // The rank named "leaf" is probably historical (and should
101 // be changed) -- mutexes of this rank aren't really leaf mutexes
102 // at all.
103 enum lock_types {
104 event,
105 special,
106 suspend_resume,
107 leaf = suspend_resume + 2,
108 safepoint = leaf + 10,
109 barrier = safepoint + 1,
110 nonleaf = barrier + 1,
111 max_nonleaf = nonleaf + 900,
112 native = max_nonleaf + 1
113 };
115 // The WaitSet and EntryList linked lists are composed of ParkEvents.
116 // I use ParkEvent instead of threads as ParkEvents are immortal and
117 // type-stable, meaning we can safely unpark() a possibly stale
118 // list element in the unlock()-path.
120 protected: // Monitor-Mutex metadata
121 SplitWord _LockWord ; // Contention queue (cxq) colocated with Lock-byte
122 enum LockWordBits { _LBIT=1 } ;
123 Thread * volatile _owner; // The owner of the lock
124 // Consider sequestering _owner on its own $line
125 // to aid future synchronization mechanisms.
126 ParkEvent * volatile _EntryList ; // List of threads waiting for entry
127 ParkEvent * volatile _OnDeck ; // heir-presumptive
128 volatile intptr_t _WaitLock [1] ; // Protects _WaitSet
129 ParkEvent * volatile _WaitSet ; // LL of ParkEvents
130 volatile bool _snuck; // Used for sneaky locking (evil).
131 int NotifyCount ; // diagnostic assist
132 char _name[MONITOR_NAME_LEN]; // Name of mutex
134 // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode)
135 #ifndef PRODUCT
136 bool _allow_vm_block;
137 debug_only(int _rank;) // rank (to avoid/detect potential deadlocks)
138 debug_only(Monitor * _next;) // Used by a Thread to link up owned locks
139 debug_only(Thread* _last_owner;) // the last thread to own the lock
140 debug_only(static bool contains(Monitor * locks, Monitor * lock);)
141 debug_only(static Monitor * get_least_ranked_lock(Monitor * locks);)
142 debug_only(Monitor * get_least_ranked_lock_besides_this(Monitor * locks);)
143 #endif
145 void set_owner_implementation(Thread* owner) PRODUCT_RETURN;
146 void check_prelock_state (Thread* thread) PRODUCT_RETURN;
147 void check_block_state (Thread* thread) PRODUCT_RETURN;
149 // platform-dependent support code can go here (in os_<os_family>.cpp)
150 public:
151 enum {
152 _no_safepoint_check_flag = true,
153 _allow_vm_block_flag = true,
154 _as_suspend_equivalent_flag = true
155 };
157 enum WaitResults {
158 CONDVAR_EVENT, // Wait returned because of condition variable notification
159 INTERRUPT_EVENT, // Wait returned because waiting thread was interrupted
160 NUMBER_WAIT_RESULTS
161 };
163 private:
164 int TrySpin (Thread * Self) ;
165 int TryLock () ;
166 int TryFast () ;
167 int AcquireOrPush (ParkEvent * ev) ;
168 void IUnlock (bool RelaxAssert) ;
169 void ILock (Thread * Self) ;
170 int IWait (Thread * Self, jlong timo);
171 int ILocked () ;
173 protected:
174 static void ClearMonitor (Monitor * m, const char* name = NULL) ;
175 Monitor() ;
177 public:
178 Monitor(int rank, const char *name, bool allow_vm_block=false);
179 ~Monitor();
181 // Wait until monitor is notified (or times out).
182 // Defaults are to make safepoint checks, wait time is forever (i.e.,
183 // zero), and not a suspend-equivalent condition. Returns true if wait
184 // times out; otherwise returns false.
185 bool wait(bool no_safepoint_check = !_no_safepoint_check_flag,
186 long timeout = 0,
187 bool as_suspend_equivalent = !_as_suspend_equivalent_flag);
188 bool notify();
189 bool notify_all();
192 void lock(); // prints out warning if VM thread blocks
193 void lock(Thread *thread); // overloaded with current thread
194 void unlock();
195 bool is_locked() const { return _owner != NULL; }
197 bool try_lock(); // Like lock(), but unblocking. It returns false instead
199 // Lock without safepoint check. Should ONLY be used by safepoint code and other code
200 // that is guaranteed not to block while running inside the VM.
201 void lock_without_safepoint_check();
202 void lock_without_safepoint_check (Thread * Self) ;
204 // Current owner - not not MT-safe. Can only be used to guarantee that
205 // the current running thread owns the lock
206 Thread* owner() const { return _owner; }
207 bool owned_by_self() const;
209 // Support for JVM_RawMonitorEnter & JVM_RawMonitorExit. These can be called by
210 // non-Java thread. (We should really have a RawMonitor abstraction)
211 void jvm_raw_lock();
212 void jvm_raw_unlock();
213 const char *name() const { return _name; }
215 void print_on_error(outputStream* st) const;
217 #ifndef PRODUCT
218 void print_on(outputStream* st) const;
219 void print() const { print_on(tty); }
220 debug_only(int rank() const { return _rank; })
221 bool allow_vm_block() { return _allow_vm_block; }
223 debug_only(Monitor *next() const { return _next; })
224 debug_only(void set_next(Monitor *next) { _next = next; })
225 #endif
227 void set_owner(Thread* owner) {
228 #ifndef PRODUCT
229 set_owner_implementation(owner);
230 debug_only(void verify_Monitor(Thread* thr));
231 #else
232 _owner = owner;
233 #endif
234 }
236 };
238 // Normally we'd expect Monitor to extend Mutex in the sense that a monitor
239 // constructed from pthreads primitives might extend a mutex by adding
240 // a condvar and some extra metadata. In fact this was the case until J2SE7.
241 //
242 // Currently, however, the base object is a monitor. Monitor contains all the
243 // logic for wait(), notify(), etc. Mutex extends monitor and restricts the
244 // visiblity of wait(), notify(), and notify_all().
245 //
246 // Another viable alternative would have been to have Monitor extend Mutex and
247 // implement all the normal mutex and wait()-notify() logic in Mutex base class.
248 // The wait()-notify() facility would be exposed via special protected member functions
249 // (e.g., _Wait() and _Notify()) in Mutex. Monitor would extend Mutex and expose wait()
250 // as a call to _Wait(). That is, the public wait() would be a wrapper for the protected
251 // _Wait().
252 //
253 // An even better alternative is to simply eliminate Mutex:: and use Monitor:: instead.
254 // After all, monitors are sufficient for Java-level synchronization. At one point in time
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.
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 };
276 #endif // SHARE_VM_RUNTIME_MUTEX_HPP