Mercurial > hg > graal-compiler
annotate src/share/vm/runtime/mutex.hpp @ 1878:fa83ab460c54
6988353: refactor contended sync subsystem
Summary: reduce complexity by factoring synchronizer.cpp
Reviewed-by: dholmes, never, coleenp
| author | acorn |
|---|---|
| date | Fri, 22 Oct 2010 15:59:34 -0400 |
| parents | c18cbe5936b8 |
| children | f95d63e2154a |
| rev | line source |
|---|---|
| 0 | 1 /* |
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2 * Copyright (c) 1998, 2008, Oracle and/or its affiliates. All rights reserved. |
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| 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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20 * or visit www.oracle.com if you need additional information or have any |
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21 * questions. |
| 0 | 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. | |
| 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. | |
| 55 | |
| 56 | |
| 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 } ; | |
| 62 | |
| 63 // Endian-ness ... index of least-significant byte in SplitWord.Bytes[] | |
| 1010 | 64 #ifdef VM_LITTLE_ENDIAN |
| 0 | 65 #define _LSBINDEX 0 |
| 66 #else | |
| 67 #define _LSBINDEX (sizeof(intptr_t)-1) | |
| 68 #endif | |
| 69 | |
| 70 class ParkEvent ; | |
| 71 | |
| 72 // See orderAccess.hpp. We assume throughout the VM that mutex lock and | |
| 73 // try_lock do fence-lock-acquire, and that unlock does a release-unlock, | |
| 74 // *in that order*. If their implementations change such that these | |
| 75 // assumptions are violated, a whole lot of code will break. | |
| 76 | |
| 605 | 77 // The default length of monitor name is chosen to be 64 to avoid false sharing. |
|
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78 static const int MONITOR_NAME_LEN = 64; |
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79 |
| 0 | 80 class Monitor : public CHeapObj { |
| 81 | |
| 82 public: | |
| 83 // A special lock: Is a lock where you are guaranteed not to block while you are | |
| 84 // holding it, i.e., no vm operation can happen, taking other locks, etc. | |
| 85 // NOTE: It is critical that the rank 'special' be the lowest (earliest) | |
| 86 // (except for "event"?) for the deadlock dection to work correctly. | |
| 87 // The rank native is only for use in Mutex's created by JVM_RawMonitorCreate, | |
| 88 // which being external to the VM are not subject to deadlock detection. | |
| 89 // The rank safepoint is used only for synchronization in reaching a | |
| 90 // safepoint and leaving a safepoint. It is only used for the Safepoint_lock | |
| 91 // currently. While at a safepoint no mutexes of rank safepoint are held | |
| 92 // by any thread. | |
| 93 // The rank named "leaf" is probably historical (and should | |
| 94 // be changed) -- mutexes of this rank aren't really leaf mutexes | |
| 95 // at all. | |
| 96 enum lock_types { | |
| 97 event, | |
| 98 special, | |
| 99 suspend_resume, | |
| 100 leaf = suspend_resume + 2, | |
| 101 safepoint = leaf + 10, | |
| 102 barrier = safepoint + 1, | |
| 103 nonleaf = barrier + 1, | |
| 104 max_nonleaf = nonleaf + 900, | |
| 105 native = max_nonleaf + 1 | |
| 106 }; | |
| 107 | |
| 108 // The WaitSet and EntryList linked lists are composed of ParkEvents. | |
| 109 // I use ParkEvent instead of threads as ParkEvents are immortal and | |
| 110 // type-stable, meaning we can safely unpark() a possibly stale | |
| 111 // list element in the unlock()-path. | |
| 112 | |
| 113 protected: // Monitor-Mutex metadata | |
| 114 SplitWord _LockWord ; // Contention queue (cxq) colocated with Lock-byte | |
| 115 enum LockWordBits { _LBIT=1 } ; | |
| 116 Thread * volatile _owner; // The owner of the lock | |
| 117 // Consider sequestering _owner on its own $line | |
| 118 // to aid future synchronization mechanisms. | |
| 119 ParkEvent * volatile _EntryList ; // List of threads waiting for entry | |
| 120 ParkEvent * volatile _OnDeck ; // heir-presumptive | |
| 121 volatile intptr_t _WaitLock [1] ; // Protects _WaitSet | |
| 122 ParkEvent * volatile _WaitSet ; // LL of ParkEvents | |
| 123 volatile bool _snuck; // Used for sneaky locking (evil). | |
| 124 int NotifyCount ; // diagnostic assist | |
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125 char _name[MONITOR_NAME_LEN]; // Name of mutex |
| 0 | 126 |
| 127 // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode) | |
| 128 #ifndef PRODUCT | |
| 129 bool _allow_vm_block; | |
| 130 debug_only(int _rank;) // rank (to avoid/detect potential deadlocks) | |
| 131 debug_only(Monitor * _next;) // Used by a Thread to link up owned locks | |
| 132 debug_only(Thread* _last_owner;) // the last thread to own the lock | |
| 133 debug_only(static bool contains(Monitor * locks, Monitor * lock);) | |
| 134 debug_only(static Monitor * get_least_ranked_lock(Monitor * locks);) | |
| 135 debug_only(Monitor * get_least_ranked_lock_besides_this(Monitor * locks);) | |
| 136 #endif | |
| 137 | |
| 138 void set_owner_implementation(Thread* owner) PRODUCT_RETURN; | |
| 139 void check_prelock_state (Thread* thread) PRODUCT_RETURN; | |
| 140 void check_block_state (Thread* thread) PRODUCT_RETURN; | |
| 141 | |
| 142 // platform-dependent support code can go here (in os_<os_family>.cpp) | |
| 143 public: | |
| 144 enum { | |
| 145 _no_safepoint_check_flag = true, | |
| 146 _allow_vm_block_flag = true, | |
| 147 _as_suspend_equivalent_flag = true | |
| 148 }; | |
| 149 | |
| 150 enum WaitResults { | |
| 151 CONDVAR_EVENT, // Wait returned because of condition variable notification | |
| 152 INTERRUPT_EVENT, // Wait returned because waiting thread was interrupted | |
| 153 NUMBER_WAIT_RESULTS | |
| 154 }; | |
| 155 | |
| 156 private: | |
| 157 int TrySpin (Thread * Self) ; | |
| 158 int TryLock () ; | |
| 159 int TryFast () ; | |
| 160 int AcquireOrPush (ParkEvent * ev) ; | |
| 161 void IUnlock (bool RelaxAssert) ; | |
| 162 void ILock (Thread * Self) ; | |
| 163 int IWait (Thread * Self, jlong timo); | |
| 164 int ILocked () ; | |
| 165 | |
| 166 protected: | |
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167 static void ClearMonitor (Monitor * m, const char* name = NULL) ; |
| 0 | 168 Monitor() ; |
| 169 | |
| 170 public: | |
| 171 Monitor(int rank, const char *name, bool allow_vm_block=false); | |
| 172 ~Monitor(); | |
| 173 | |
| 174 // Wait until monitor is notified (or times out). | |
| 175 // Defaults are to make safepoint checks, wait time is forever (i.e., | |
| 176 // zero), and not a suspend-equivalent condition. Returns true if wait | |
| 177 // times out; otherwise returns false. | |
| 178 bool wait(bool no_safepoint_check = !_no_safepoint_check_flag, | |
| 179 long timeout = 0, | |
| 180 bool as_suspend_equivalent = !_as_suspend_equivalent_flag); | |
| 181 bool notify(); | |
| 182 bool notify_all(); | |
| 183 | |
| 184 | |
| 185 void lock(); // prints out warning if VM thread blocks | |
| 186 void lock(Thread *thread); // overloaded with current thread | |
| 187 void unlock(); | |
| 188 bool is_locked() const { return _owner != NULL; } | |
| 189 | |
| 190 bool try_lock(); // Like lock(), but unblocking. It returns false instead | |
| 191 | |
| 192 // Lock without safepoint check. Should ONLY be used by safepoint code and other code | |
| 193 // that is guaranteed not to block while running inside the VM. | |
| 194 void lock_without_safepoint_check(); | |
| 195 void lock_without_safepoint_check (Thread * Self) ; | |
| 196 | |
| 197 // Current owner - not not MT-safe. Can only be used to guarantee that | |
| 198 // the current running thread owns the lock | |
| 199 Thread* owner() const { return _owner; } | |
| 200 bool owned_by_self() const; | |
| 201 | |
| 202 // Support for JVM_RawMonitorEnter & JVM_RawMonitorExit. These can be called by | |
| 203 // non-Java thread. (We should really have a RawMonitor abstraction) | |
| 204 void jvm_raw_lock(); | |
| 205 void jvm_raw_unlock(); | |
| 206 const char *name() const { return _name; } | |
| 207 | |
| 208 void print_on_error(outputStream* st) const; | |
| 209 | |
| 210 #ifndef PRODUCT | |
| 211 void print_on(outputStream* st) const; | |
| 212 void print() const { print_on(tty); } | |
| 213 debug_only(int rank() const { return _rank; }) | |
| 214 bool allow_vm_block() { return _allow_vm_block; } | |
| 215 | |
| 216 debug_only(Monitor *next() const { return _next; }) | |
| 217 debug_only(void set_next(Monitor *next) { _next = next; }) | |
| 218 #endif | |
| 219 | |
| 220 void set_owner(Thread* owner) { | |
| 221 #ifndef PRODUCT | |
| 222 set_owner_implementation(owner); | |
| 223 debug_only(void verify_Monitor(Thread* thr)); | |
| 224 #else | |
| 225 _owner = owner; | |
| 226 #endif | |
| 227 } | |
| 228 | |
| 229 }; | |
| 230 | |
| 231 // Normally we'd expect Monitor to extend Mutex in the sense that a monitor | |
| 232 // constructed from pthreads primitives might extend a mutex by adding | |
| 233 // a condvar and some extra metadata. In fact this was the case until J2SE7. | |
| 234 // | |
| 235 // Currently, however, the base object is a monitor. Monitor contains all the | |
| 236 // logic for wait(), notify(), etc. Mutex extends monitor and restricts the | |
| 237 // visiblity of wait(), notify(), and notify_all(). | |
| 238 // | |
| 239 // Another viable alternative would have been to have Monitor extend Mutex and | |
| 240 // implement all the normal mutex and wait()-notify() logic in Mutex base class. | |
| 241 // The wait()-notify() facility would be exposed via special protected member functions | |
| 242 // (e.g., _Wait() and _Notify()) in Mutex. Monitor would extend Mutex and expose wait() | |
| 243 // as a call to _Wait(). That is, the public wait() would be a wrapper for the protected | |
| 244 // _Wait(). | |
| 245 // | |
| 246 // An even better alternative is to simply eliminate Mutex:: and use Monitor:: instead. | |
| 247 // After all, monitors are sufficient for Java-level synchronization. At one point in time | |
| 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 |