5 |
|
*/ |
6 |
|
|
7 |
|
package jsr166e; |
8 |
– |
|
9 |
– |
import java.util.concurrent.ThreadLocalRandom; |
8 |
|
import java.util.concurrent.TimeUnit; |
9 |
|
import java.util.concurrent.locks.Lock; |
10 |
|
import java.util.concurrent.locks.Condition; |
117 |
|
* } |
118 |
|
* } |
119 |
|
* |
120 |
< |
* double distanceFromOriginV1() { // A read-only method |
121 |
< |
* long stamp; |
122 |
< |
* if ((stamp = sl.tryOptimisticRead()) != 0L) { // optimistic |
123 |
< |
* double currentX = x; |
124 |
< |
* double currentY = y; |
125 |
< |
* if (sl.validate(stamp)) |
126 |
< |
* return Math.sqrt(currentX * currentX + currentY * currentY); |
127 |
< |
* } |
128 |
< |
* stamp = sl.readLock(); // fall back to read lock |
129 |
< |
* try { |
130 |
< |
* double currentX = x; |
133 |
< |
* double currentY = y; |
134 |
< |
* return Math.sqrt(currentX * currentX + currentY * currentY); |
135 |
< |
* } finally { |
136 |
< |
* sl.unlockRead(stamp); |
137 |
< |
* } |
138 |
< |
* } |
139 |
< |
* |
140 |
< |
* double distanceFromOriginV2() { // combines code paths |
141 |
< |
* double currentX = 0.0, currentY = 0.0; |
142 |
< |
* for (long stamp = sl.tryOptimisticRead(); ; stamp = sl.readLock()) { |
143 |
< |
* try { |
144 |
< |
* currentX = x; |
145 |
< |
* currentY = y; |
146 |
< |
* } finally { |
147 |
< |
* if (sl.tryConvertToOptimisticRead(stamp) != 0L) // unlock or validate |
148 |
< |
* break; |
149 |
< |
* } |
120 |
> |
* double distanceFromOrigin() { // A read-only method |
121 |
> |
* long stamp = sl.tryOptimisticRead(); |
122 |
> |
* double currentX = x, currentY = y; |
123 |
> |
* if (!sl.validate(stamp)) { |
124 |
> |
* stamp = sl.readLock(); |
125 |
> |
* try { |
126 |
> |
* currentX = x; |
127 |
> |
* currentY = y; |
128 |
> |
* } finally { |
129 |
> |
* sl.unlockRead(stamp); |
130 |
> |
* } |
131 |
|
* } |
132 |
|
* return Math.sqrt(currentX * currentX + currentY * currentY); |
133 |
|
* } |
234 |
|
* motivation to further spread out contended locations, but might |
235 |
|
* be subject to future improvements. |
236 |
|
*/ |
237 |
+ |
|
238 |
|
private static final long serialVersionUID = -6001602636862214147L; |
239 |
|
|
240 |
|
/** Number of processors, for spin control */ |
339 |
|
* Behavior under timeout and interruption matches that specified |
340 |
|
* for method {@link Lock#tryLock(long,TimeUnit)}. |
341 |
|
* |
342 |
+ |
* @param time the maximum time to wait for the lock |
343 |
+ |
* @param unit the time unit of the {@code time} argument |
344 |
|
* @return a stamp that can be used to unlock or convert mode, |
345 |
|
* or zero if the lock is not available |
346 |
|
* @throws InterruptedException if the current thread is interrupted |
420 |
|
* Behavior under timeout and interruption matches that specified |
421 |
|
* for method {@link Lock#tryLock(long,TimeUnit)}. |
422 |
|
* |
423 |
+ |
* @param time the maximum time to wait for the lock |
424 |
+ |
* @param unit the time unit of the {@code time} argument |
425 |
|
* @return a stamp that can be used to unlock or convert mode, |
426 |
|
* or zero if the lock is not available |
427 |
|
* @throws InterruptedException if the current thread is interrupted |
429 |
|
*/ |
430 |
|
public long tryReadLock(long time, TimeUnit unit) |
431 |
|
throws InterruptedException { |
432 |
< |
long next, deadline; |
432 |
> |
long s, m, next, deadline; |
433 |
|
long nanos = unit.toNanos(time); |
434 |
|
if (!Thread.interrupted()) { |
435 |
< |
if ((next = tryReadLock()) != 0L) |
436 |
< |
return next; |
435 |
> |
if ((m = (s = state) & ABITS) != WBIT) { |
436 |
> |
if (m < RFULL) { |
437 |
> |
if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) |
438 |
> |
return next; |
439 |
> |
} |
440 |
> |
else if ((next = tryIncReaderOverflow(s)) != 0L) |
441 |
> |
return next; |
442 |
> |
} |
443 |
|
if (nanos <= 0L) |
444 |
|
return 0L; |
445 |
|
if ((deadline = System.nanoTime() + nanos) == 0L) |
487 |
|
* obtained from {@link #tryOptimisticRead} or a locking method |
488 |
|
* for this lock has no defined effect or result. |
489 |
|
* |
490 |
< |
* @return true if the lock has not been exclusively acquired |
490 |
> |
* @param stamp a stamp |
491 |
> |
* @return {@code true} if the lock has not been exclusively acquired |
492 |
|
* since issuance of the given stamp; else false |
493 |
|
*/ |
494 |
|
public boolean validate(long stamp) { |
701 |
|
* stamp value. This method may be useful for recovery after |
702 |
|
* errors. |
703 |
|
* |
704 |
< |
* @return true if the lock was held, else false |
704 |
> |
* @return {@code true} if the lock was held, else false |
705 |
|
*/ |
706 |
|
public boolean tryUnlockWrite() { |
707 |
|
long s; WNode h; |
719 |
|
* requiring a stamp value. This method may be useful for recovery |
720 |
|
* after errors. |
721 |
|
* |
722 |
< |
* @return true if the read lock was held, else false |
722 |
> |
* @return {@code true} if the read lock was held, else false |
723 |
|
*/ |
724 |
|
public boolean tryUnlockRead() { |
725 |
|
long s, m; WNode h; |
737 |
|
return false; |
738 |
|
} |
739 |
|
|
740 |
+ |
// status monitoring methods |
741 |
+ |
|
742 |
+ |
/** |
743 |
+ |
* Returns combined state-held and overflow read count for given |
744 |
+ |
* state s. |
745 |
+ |
*/ |
746 |
+ |
private int getReadLockCount(long s) { |
747 |
+ |
long readers; |
748 |
+ |
if ((readers = s & RBITS) >= RFULL) |
749 |
+ |
readers = RFULL + readerOverflow; |
750 |
+ |
return (int) readers; |
751 |
+ |
} |
752 |
+ |
|
753 |
|
/** |
754 |
< |
* Returns true if the lock is currently held exclusively. |
754 |
> |
* Returns {@code true} if the lock is currently held exclusively. |
755 |
|
* |
756 |
< |
* @return true if the lock is currently held exclusively |
756 |
> |
* @return {@code true} if the lock is currently held exclusively |
757 |
|
*/ |
758 |
|
public boolean isWriteLocked() { |
759 |
|
return (state & WBIT) != 0L; |
760 |
|
} |
761 |
|
|
762 |
|
/** |
763 |
< |
* Returns true if the lock is currently held non-exclusively. |
763 |
> |
* Returns {@code true} if the lock is currently held non-exclusively. |
764 |
|
* |
765 |
< |
* @return true if the lock is currently held non-exclusively |
765 |
> |
* @return {@code true} if the lock is currently held non-exclusively |
766 |
|
*/ |
767 |
|
public boolean isReadLocked() { |
768 |
|
return (state & RBITS) != 0L; |
769 |
|
} |
770 |
|
|
771 |
< |
private void readObject(java.io.ObjectInputStream s) |
772 |
< |
throws java.io.IOException, ClassNotFoundException { |
773 |
< |
s.defaultReadObject(); |
774 |
< |
state = ORIGIN; // reset to unlocked state |
771 |
> |
/** |
772 |
> |
* Queries the number of read locks held for this lock. This |
773 |
> |
* method is designed for use in monitoring system state, not for |
774 |
> |
* synchronization control. |
775 |
> |
* @return the number of read locks held |
776 |
> |
*/ |
777 |
> |
public int getReadLockCount() { |
778 |
> |
return getReadLockCount(state); |
779 |
|
} |
780 |
|
|
781 |
|
/** |
782 |
+ |
* Returns a string identifying this lock, as well as its lock |
783 |
+ |
* state. The state, in brackets, includes the String {@code |
784 |
+ |
* "Unlocked"} or the String {@code "Write-locked"} or the String |
785 |
+ |
* {@code "Read-locks:"} followed by the current number of |
786 |
+ |
* read-locks held. |
787 |
+ |
* |
788 |
+ |
* @return a string identifying this lock, as well as its lock state |
789 |
+ |
*/ |
790 |
+ |
public String toString() { |
791 |
+ |
long s = state; |
792 |
+ |
return super.toString() + |
793 |
+ |
((s & ABITS) == 0L ? "[Unlocked]" : |
794 |
+ |
(s & WBIT) != 0L ? "[Write-locked]" : |
795 |
+ |
"[Read-locks:" + getReadLockCount(s) + "]"); |
796 |
+ |
} |
797 |
+ |
|
798 |
+ |
// views |
799 |
+ |
|
800 |
+ |
/** |
801 |
|
* Returns a plain {@link Lock} view of this StampedLock in which |
802 |
|
* the {@link Lock#lock} method is mapped to {@link #readLock}, |
803 |
|
* and similarly for other methods. The returned Lock does not |
911 |
|
} |
912 |
|
} |
913 |
|
|
914 |
+ |
private void readObject(java.io.ObjectInputStream s) |
915 |
+ |
throws java.io.IOException, ClassNotFoundException { |
916 |
+ |
s.defaultReadObject(); |
917 |
+ |
state = ORIGIN; // reset to unlocked state |
918 |
+ |
} |
919 |
+ |
|
920 |
|
// internals |
921 |
|
|
922 |
|
/** |
924 |
|
* access bits value to RBITS, indicating hold of spinlock, |
925 |
|
* then updating, then releasing. |
926 |
|
* |
927 |
< |
* @param s, assumed that (s & ABITS) >= RFULL |
927 |
> |
* @param s a reader overflow stamp: (s & ABITS) >= RFULL |
928 |
|
* @return new stamp on success, else zero |
929 |
|
*/ |
930 |
|
private long tryIncReaderOverflow(long s) { |
931 |
+ |
// assert (s & ABITS) >= RFULL; |
932 |
|
if ((s & ABITS) == RFULL) { |
933 |
|
if (U.compareAndSwapLong(this, STATE, s, s | RBITS)) { |
934 |
|
++readerOverflow; |
945 |
|
/** |
946 |
|
* Tries to decrement readerOverflow. |
947 |
|
* |
948 |
< |
* @param s, assumed that (s & ABITS) >= RFULL |
948 |
> |
* @param s a reader overflow stamp: (s & ABITS) >= RFULL |
949 |
|
* @return new stamp on success, else zero |
950 |
|
*/ |
951 |
|
private long tryDecReaderOverflow(long s) { |
952 |
+ |
// assert (s & ABITS) >= RFULL; |
953 |
|
if ((s & ABITS) == RFULL) { |
954 |
|
if (U.compareAndSwapLong(this, STATE, s, s | RBITS)) { |
955 |
|
int r; long next; |
969 |
|
return 0L; |
970 |
|
} |
971 |
|
|
972 |
< |
/* |
972 |
> |
/** |
973 |
|
* Wakes up the successor of h (normally whead). This is normally |
974 |
|
* just h.next, but may require traversal from wtail if next |
975 |
|
* pointers are lagging. This may fail to wake up an acquiring |
1070 |
|
if (deadline == 0L) |
1071 |
|
time = 0L; |
1072 |
|
else if ((time = deadline - System.nanoTime()) <= 0L) |
1073 |
< |
return cancelWaiter(node, null, false); |
1074 |
< |
node.thread = Thread.currentThread(); |
1073 |
> |
return cancelWaiter(node, node, false); |
1074 |
> |
Thread wt = Thread.currentThread(); |
1075 |
> |
U.putObject(wt, PARKBLOCKER, this); // emulate LockSupport.park |
1076 |
> |
node.thread = wt; |
1077 |
|
if (node.prev == p && p.status == WAITING && // recheck |
1078 |
|
(p != whead || (state & ABITS) != 0L)) |
1079 |
|
U.park(false, time); |
1080 |
|
node.thread = null; |
1081 |
+ |
U.putObject(wt, PARKBLOCKER, null); |
1082 |
|
if (interruptible && Thread.interrupted()) |
1083 |
< |
return cancelWaiter(node, null, true); |
1083 |
> |
return cancelWaiter(node, node, true); |
1084 |
|
} |
1085 |
|
} |
1086 |
|
} |
1143 |
|
node.cowait = p.cowait, node)) { |
1144 |
|
node.thread = Thread.currentThread(); |
1145 |
|
for (long time;;) { |
1106 |
– |
if (interruptible && Thread.interrupted()) |
1107 |
– |
return cancelWaiter(node, p, true); |
1146 |
|
if (deadline == 0L) |
1147 |
|
time = 0L; |
1148 |
|
else if ((time = deadline - System.nanoTime()) <= 0L) |
1154 |
|
node.thread = null; |
1155 |
|
break; |
1156 |
|
} |
1157 |
+ |
Thread wt = Thread.currentThread(); |
1158 |
+ |
U.putObject(wt, PARKBLOCKER, this); |
1159 |
|
if (node.thread == null) // must recheck |
1160 |
|
break; |
1161 |
|
U.park(false, time); |
1162 |
+ |
U.putObject(wt, PARKBLOCKER, null); |
1163 |
+ |
if (interruptible && Thread.interrupted()) |
1164 |
+ |
return cancelWaiter(node, p, true); |
1165 |
|
} |
1166 |
|
group = p; |
1167 |
|
} |
1216 |
|
if (deadline == 0L) |
1217 |
|
time = 0L; |
1218 |
|
else if ((time = deadline - System.nanoTime()) <= 0L) |
1219 |
< |
return cancelWaiter(node, null, false); |
1220 |
< |
node.thread = Thread.currentThread(); |
1219 |
> |
return cancelWaiter(node, node, false); |
1220 |
> |
Thread wt = Thread.currentThread(); |
1221 |
> |
U.putObject(wt, PARKBLOCKER, this); |
1222 |
> |
node.thread = wt; |
1223 |
|
if (node.prev == p && p.status == WAITING && |
1224 |
|
(p != whead || (state & ABITS) != WBIT)) |
1225 |
|
U.park(false, time); |
1226 |
|
node.thread = null; |
1227 |
+ |
U.putObject(wt, PARKBLOCKER, null); |
1228 |
|
if (interruptible && Thread.interrupted()) |
1229 |
< |
return cancelWaiter(node, null, true); |
1229 |
> |
return cancelWaiter(node, node, true); |
1230 |
|
} |
1231 |
|
} |
1232 |
|
} |
1233 |
|
|
1234 |
|
/** |
1235 |
|
* If node non-null, forces cancel status and unsplices it from |
1236 |
< |
* queue if possible and wakes up any cowaiters. This is a variant |
1237 |
< |
* of cancellation methods in AbstractQueuedSynchronizer (see its |
1238 |
< |
* detailed explanation in AQS internal documentation) that more |
1239 |
< |
* conservatively wakes up other threads that may have had their |
1240 |
< |
* links changed, so as to preserve liveness in the main |
1241 |
< |
* signalling methods. |
1236 |
> |
* queue if possible and wakes up any cowaiters (of the node, or |
1237 |
> |
* group, as applicable), and in any case helps release current |
1238 |
> |
* first waiter if lock is free. (Calling with null arguments |
1239 |
> |
* serves as a conditional form of release, which is not currently |
1240 |
> |
* needed but may be needed under possible future cancellation |
1241 |
> |
* policies). This is a variant of cancellation methods in |
1242 |
> |
* AbstractQueuedSynchronizer (see its detailed explanation in AQS |
1243 |
> |
* internal documentation). |
1244 |
|
* |
1245 |
|
* @param node if nonnull, the waiter |
1246 |
< |
* @param group, if nonnull, the group current thread is cowaiting with |
1246 |
> |
* @param group either node or the group node is cowaiting with |
1247 |
|
* @param interrupted if already interrupted |
1248 |
|
* @return INTERRUPTED if interrupted or Thread.interrupted, else zero |
1249 |
|
*/ |
1250 |
|
private long cancelWaiter(WNode node, WNode group, boolean interrupted) { |
1251 |
< |
if (node != null) { |
1252 |
< |
node.thread = null; |
1251 |
> |
if (node != null && group != null) { |
1252 |
> |
Thread w; |
1253 |
|
node.status = CANCELLED; |
1254 |
< |
Thread w; // wake up co-waiters; unsplice cancelled ones |
1255 |
< |
for (WNode q, p = (group != null) ? group : node; p != null; ) { |
1256 |
< |
if ((q = p.cowait) == null) |
1209 |
< |
break; |
1210 |
< |
if ((w = q.thread) != null) { |
1211 |
< |
q.thread = null; |
1212 |
< |
U.unpark(w); |
1213 |
< |
} |
1254 |
> |
node.thread = null; |
1255 |
> |
// unsplice cancelled nodes from group |
1256 |
> |
for (WNode p = group, q; (q = p.cowait) != null;) { |
1257 |
|
if (q.status == CANCELLED) |
1258 |
< |
U.compareAndSwapObject(p, WCOWAIT, q, q.cowait); |
1258 |
> |
U.compareAndSwapObject(p, WNEXT, q, q.next); |
1259 |
|
else |
1260 |
|
p = q; |
1261 |
|
} |
1262 |
< |
if (group == null) { // unsplice both prev and next links |
1263 |
< |
for (WNode pred = node.prev; pred != null; ) { |
1264 |
< |
WNode succ, pp; // first unsplice next |
1262 |
> |
if (group == node) { |
1263 |
> |
WNode r; // detach and wake up uncancelled co-waiters |
1264 |
> |
while ((r = node.cowait) != null) { |
1265 |
> |
if (U.compareAndSwapObject(node, WCOWAIT, r, r.cowait) && |
1266 |
> |
(w = r.thread) != null) { |
1267 |
> |
r.thread = null; |
1268 |
> |
U.unpark(w); |
1269 |
> |
} |
1270 |
> |
} |
1271 |
> |
for (WNode pred = node.prev; pred != null; ) { // unsplice |
1272 |
> |
WNode succ, pp; // find valid successor |
1273 |
|
while ((succ = node.next) == null || |
1274 |
|
succ.status == CANCELLED) { |
1275 |
< |
WNode q = null; // find successor the slow way |
1275 |
> |
WNode q = null; // find successor the slow way |
1276 |
|
for (WNode t = wtail; t != null && t != node; t = t.prev) |
1277 |
|
if (t.status != CANCELLED) |
1278 |
< |
q = t; // don't link if succ cancelled |
1279 |
< |
if (succ == q || // ensure accurate successor |
1278 |
> |
q = t; // don't link if succ cancelled |
1279 |
> |
if (succ == q || // ensure accurate successor |
1280 |
|
U.compareAndSwapObject(node, WNEXT, |
1281 |
|
succ, succ = q)) { |
1282 |
|
if (succ == null && node == wtail) |
1288 |
|
U.compareAndSwapObject(pred, WNEXT, node, succ); |
1289 |
|
if (succ != null && (w = succ.thread) != null) { |
1290 |
|
succ.thread = null; |
1291 |
< |
U.unpark(w); // conservatively wake up new succ |
1291 |
> |
U.unpark(w); // wake up succ to observe new pred |
1292 |
|
} |
1293 |
|
if (pred.status != CANCELLED || (pp = pred.prev) == null) |
1294 |
|
break; |
1295 |
< |
node.prev = pp; // repeat in case new pred wrong/cancelled |
1295 |
> |
node.prev = pp; // repeat if new pred wrong/cancelled |
1296 |
|
U.compareAndSwapObject(pp, WNEXT, pred, succ); |
1297 |
|
pred = pp; |
1298 |
|
} |
1299 |
|
} |
1300 |
|
} |
1301 |
< |
release(whead); |
1301 |
> |
WNode h; // Possibly release first waiter |
1302 |
> |
while ((h = whead) != null) { |
1303 |
> |
long s; WNode q; // similar to release() but check eligibility |
1304 |
> |
if ((q = h.next) == null || q.status == CANCELLED) { |
1305 |
> |
for (WNode t = wtail; t != null && t != h; t = t.prev) |
1306 |
> |
if (t.status <= 0) |
1307 |
> |
q = t; |
1308 |
> |
} |
1309 |
> |
if (h == whead) { |
1310 |
> |
if (q != null && h.status == 0 && |
1311 |
> |
((s = state) & ABITS) != WBIT && // waiter is eligible |
1312 |
> |
(s == 0L || q.mode == RMODE)) |
1313 |
> |
release(h); |
1314 |
> |
break; |
1315 |
> |
} |
1316 |
> |
} |
1317 |
|
return (interrupted || Thread.interrupted()) ? INTERRUPTED : 0L; |
1318 |
|
} |
1319 |
|
|
1325 |
|
private static final long WNEXT; |
1326 |
|
private static final long WSTATUS; |
1327 |
|
private static final long WCOWAIT; |
1328 |
+ |
private static final long PARKBLOCKER; |
1329 |
|
|
1330 |
|
static { |
1331 |
|
try { |
1344 |
|
(wk.getDeclaredField("next")); |
1345 |
|
WCOWAIT = U.objectFieldOffset |
1346 |
|
(wk.getDeclaredField("cowait")); |
1347 |
+ |
Class<?> tk = Thread.class; |
1348 |
+ |
PARKBLOCKER = U.objectFieldOffset |
1349 |
+ |
(tk.getDeclaredField("parkBlocker")); |
1350 |
|
|
1351 |
|
} catch (Exception e) { |
1352 |
|
throw new Error(e); |