| 118 |
|
* |
| 119 |
|
*/ |
| 120 |
|
|
| 121 |
< |
public class Semaphore implements java.io.Serializable { |
| 122 |
< |
/* |
| 123 |
< |
* The underlying algorithm here is a simplified adaptation of |
| 124 |
< |
* that used for ReentrantLock. See the internal documentation of |
| 125 |
< |
* lock package classes for detailed explanation. |
| 126 |
< |
*/ |
| 127 |
< |
|
| 121 |
> |
public class Semaphore extends AbstractQueuedSynchronizer implements java.io.Serializable { |
| 122 |
|
private static final long serialVersionUID = -3222578661600680210L; |
| 129 |
– |
|
| 130 |
– |
/** Node status value to indicate thread has cancelled */ |
| 131 |
– |
private static final int CANCELLED = 1; |
| 132 |
– |
/** Node status value to indicate successor needs unparking */ |
| 133 |
– |
private static final int SIGNAL = -1; |
| 134 |
– |
/** Node class for waiting threads */ |
| 135 |
– |
private static class Node { |
| 136 |
– |
volatile int status; |
| 137 |
– |
volatile Node prev; |
| 138 |
– |
volatile Node next; |
| 139 |
– |
Thread thread; |
| 140 |
– |
Node(Thread t) { thread = t; } |
| 141 |
– |
} |
| 142 |
– |
|
| 143 |
– |
/** Number of available permits held in a separate AtomicInteger */ |
| 144 |
– |
private final AtomicInteger perms; |
| 145 |
– |
/** Head of the wait queue, lazily initialized. */ |
| 146 |
– |
private transient volatile Node head; |
| 147 |
– |
/** Tail of the wait queue, lazily initialized. */ |
| 148 |
– |
private transient volatile Node tail; |
| 149 |
– |
/** true if barging disabled */ |
| 123 |
|
private final boolean fair; |
| 124 |
|
|
| 125 |
< |
// Atomic update support |
| 153 |
< |
|
| 154 |
< |
private static final |
| 155 |
< |
AtomicReferenceFieldUpdater<Semaphore, Node> tailUpdater = |
| 156 |
< |
AtomicReferenceFieldUpdater.<Semaphore, Node>newUpdater |
| 157 |
< |
(Semaphore.class, Node.class, "tail"); |
| 158 |
< |
private static final |
| 159 |
< |
AtomicReferenceFieldUpdater<Semaphore, Node> headUpdater = |
| 160 |
< |
AtomicReferenceFieldUpdater.<Semaphore, Node>newUpdater |
| 161 |
< |
(Semaphore.class, Node.class, "head"); |
| 162 |
< |
private static final |
| 163 |
< |
AtomicIntegerFieldUpdater<Node> statusUpdater = |
| 164 |
< |
AtomicIntegerFieldUpdater.<Node>newUpdater |
| 165 |
< |
(Node.class, "status"); |
| 166 |
< |
|
| 167 |
< |
|
| 168 |
< |
/** |
| 169 |
< |
* Insert node into queue, initializing head and tail if necessary. |
| 170 |
< |
* @param node the node to insert |
| 171 |
< |
*/ |
| 172 |
< |
private void enq(Node node) { |
| 173 |
< |
Node t = tail; |
| 174 |
< |
if (t == null) { // Must initialize first |
| 175 |
< |
Node h = new Node(null); |
| 176 |
< |
while ((t = tail) == null) { |
| 177 |
< |
if (headUpdater.compareAndSet(this, null, h)) |
| 178 |
< |
tail = h; |
| 179 |
< |
} |
| 180 |
< |
} |
| 125 |
> |
// Implement abstract methods |
| 126 |
|
|
| 127 |
< |
for (;;) { |
| 128 |
< |
node.prev = t; // Prev field must be valid before/upon CAS |
| 129 |
< |
if (tailUpdater.compareAndSet(this, t, node)) { |
| 130 |
< |
t.next = node; // Next field assignment lags CAS |
| 131 |
< |
return; |
| 187 |
< |
} |
| 188 |
< |
t = tail; |
| 189 |
< |
} |
| 190 |
< |
} |
| 191 |
< |
|
| 192 |
< |
/** |
| 193 |
< |
* Unblock the successor of node |
| 194 |
< |
* @param node the node |
| 195 |
< |
*/ |
| 196 |
< |
private void unparkSuccessor(Node node) { |
| 197 |
< |
statusUpdater.compareAndSet(node, SIGNAL, 0); |
| 198 |
< |
Node s = node.next; |
| 199 |
< |
if (s == null || s.status == CANCELLED) { |
| 200 |
< |
s = tail; |
| 201 |
< |
if (s != null && s != node) { |
| 202 |
< |
Node p = s.prev; |
| 203 |
< |
while (p != null && p != node) { |
| 204 |
< |
if (p.status != CANCELLED) |
| 205 |
< |
s = p; |
| 206 |
< |
p = p.prev; |
| 207 |
< |
} |
| 208 |
< |
} |
| 209 |
< |
} |
| 210 |
< |
if (s != null && s != node) |
| 211 |
< |
LockSupport.unpark(s.thread); |
| 212 |
< |
} |
| 213 |
< |
|
| 214 |
< |
|
| 215 |
< |
/** |
| 216 |
< |
* Internal version of tryAcquire returning number of remaining |
| 217 |
< |
* permits, which is nonnegative only if the acquire succeeded. |
| 218 |
< |
* @param permits requested number of permits |
| 219 |
< |
* @return remaining number of permits |
| 220 |
< |
*/ |
| 221 |
< |
private int doTryAcquire(int permits) { |
| 222 |
< |
final AtomicInteger perms = this.perms; |
| 127 |
> |
protected int acquireSharedState(boolean isQueued, int acquires, |
| 128 |
> |
Thread current) { |
| 129 |
> |
final AtomicInteger perms = getState(); |
| 130 |
> |
if (!isQueued && fair && hasWaiters()) |
| 131 |
> |
return -1; |
| 132 |
|
for (;;) { |
| 133 |
|
int available = perms.get(); |
| 134 |
< |
int remaining = available - permits; |
| 134 |
> |
int remaining = available - acquires; |
| 135 |
|
if (remaining < 0 || |
| 136 |
|
perms.compareAndSet(available, remaining)) |
| 137 |
|
return remaining; |
| 138 |
|
} |
| 139 |
|
} |
| 140 |
< |
|
| 141 |
< |
/** |
| 142 |
< |
* Main code for untimed acquires. |
| 234 |
< |
* @param permits number of permits requested |
| 235 |
< |
* @param interrupts interrupt control: -1 for abort on interrupt, |
| 236 |
< |
* 0 for continue on interrupt |
| 237 |
< |
* @return true if lock acquired (can be false only if interruptible) |
| 238 |
< |
*/ |
| 239 |
< |
private boolean doAcquire(int permits, int interrupts) { |
| 240 |
< |
// Fast path bypasses queue |
| 241 |
< |
if ((!fair || head == tail) && doTryAcquire(permits) >= 0) |
| 242 |
< |
return true; |
| 243 |
< |
Thread current = Thread.currentThread(); |
| 244 |
< |
Node node = new Node(current); |
| 245 |
< |
// Retry fast path before enqueuing |
| 246 |
< |
if (!fair && doTryAcquire(permits) >= 0) |
| 247 |
< |
return true; |
| 248 |
< |
enq(node); |
| 249 |
< |
|
| 140 |
> |
|
| 141 |
> |
protected boolean releaseSharedState(int releases) { |
| 142 |
> |
final AtomicInteger perms = getState(); |
| 143 |
|
for (;;) { |
| 144 |
< |
Node p = node.prev; |
| 145 |
< |
if (p == head) { |
| 146 |
< |
int remaining = doTryAcquire(permits); |
| 254 |
< |
if (remaining >= 0) { |
| 255 |
< |
p.next = null; |
| 256 |
< |
node.thread = null; |
| 257 |
< |
node.prev = null; |
| 258 |
< |
head = node; |
| 259 |
< |
// if still some permits left, wake up successor |
| 260 |
< |
if (remaining > 0 && node.status < 0) |
| 261 |
< |
unparkSuccessor(node); |
| 262 |
< |
if (interrupts > 0) // Re-interrupt on normal exit |
| 263 |
< |
current.interrupt(); |
| 264 |
< |
return true; |
| 265 |
< |
} |
| 266 |
< |
} |
| 267 |
< |
int status = p.status; |
| 268 |
< |
if (status == 0) |
| 269 |
< |
statusUpdater.compareAndSet(p, 0, SIGNAL); |
| 270 |
< |
else if (status == CANCELLED) |
| 271 |
< |
node.prev = p.prev; |
| 272 |
< |
else { |
| 273 |
< |
assert (status == SIGNAL); |
| 274 |
< |
LockSupport.park(); |
| 275 |
< |
if (Thread.interrupted()) { |
| 276 |
< |
if (interrupts < 0) { |
| 277 |
< |
node.thread = null; |
| 278 |
< |
node.status = CANCELLED; |
| 279 |
< |
unparkSuccessor(node); |
| 280 |
< |
return false; |
| 281 |
< |
} |
| 282 |
< |
interrupts = 1; // set to re-interrupt on exit |
| 283 |
< |
} |
| 284 |
< |
} |
| 144 |
> |
int p = perms.get(); |
| 145 |
> |
if (perms.compareAndSet(p, p + releases)) |
| 146 |
> |
return true; |
| 147 |
|
} |
| 148 |
|
} |
| 149 |
|
|
| 150 |
< |
/** |
| 151 |
< |
* Main code for timed acquires. Same as doAcquire but with |
| 152 |
< |
* interspersed time checks. |
| 153 |
< |
* @param permits number of permits requested |
| 292 |
< |
* @param nanos timeout in nanosecs |
| 293 |
< |
* @return true if lock acquired |
| 294 |
< |
*/ |
| 295 |
< |
private boolean doTimedAcquire(int permits, long nanos) throws InterruptedException { |
| 296 |
< |
if ((!fair || head == tail) && doTryAcquire(permits) >= 0) |
| 297 |
< |
return true; |
| 298 |
< |
Thread current = Thread.currentThread(); |
| 299 |
< |
long lastTime = System.nanoTime(); |
| 300 |
< |
Node node = new Node(current); |
| 301 |
< |
// Retry fast path before enqueuing |
| 302 |
< |
if (!fair && doTryAcquire(permits) >= 0) |
| 303 |
< |
return true; |
| 304 |
< |
enq(node); |
| 150 |
> |
protected int acquireExclusiveState(boolean isQueued, int acquires, |
| 151 |
> |
Thread current) { |
| 152 |
> |
throw new UnsupportedOperationException(); |
| 153 |
> |
} |
| 154 |
|
|
| 155 |
< |
for (;;) { |
| 156 |
< |
Node p = node.prev; |
| 308 |
< |
if (p == head) { |
| 309 |
< |
int remaining = doTryAcquire(permits); |
| 310 |
< |
if (remaining >= 0) { |
| 311 |
< |
p.next = null; |
| 312 |
< |
node.thread = null; |
| 313 |
< |
node.prev = null; |
| 314 |
< |
head = node; |
| 315 |
< |
if (remaining > 0 && node.status < 0) |
| 316 |
< |
unparkSuccessor(node); |
| 317 |
< |
return true; |
| 318 |
< |
} |
| 319 |
< |
} |
| 320 |
< |
if (nanos <= 0L) { |
| 321 |
< |
node.thread = null; |
| 322 |
< |
node.status = CANCELLED; |
| 323 |
< |
unparkSuccessor(node); |
| 324 |
< |
return false; |
| 325 |
< |
} |
| 326 |
< |
|
| 327 |
< |
int status = p.status; |
| 328 |
< |
if (status == 0) |
| 329 |
< |
statusUpdater.compareAndSet(p, 0, SIGNAL); |
| 330 |
< |
else if (status == CANCELLED) |
| 331 |
< |
node.prev = p.prev; |
| 332 |
< |
else { |
| 333 |
< |
LockSupport.parkNanos(nanos); |
| 334 |
< |
if (Thread.interrupted()) { |
| 335 |
< |
node.thread = null; |
| 336 |
< |
node.status = CANCELLED; |
| 337 |
< |
unparkSuccessor(node); |
| 338 |
< |
throw new InterruptedException(); |
| 339 |
< |
} |
| 340 |
< |
long now = System.nanoTime(); |
| 341 |
< |
nanos -= now - lastTime; |
| 342 |
< |
lastTime = now; |
| 343 |
< |
} |
| 344 |
< |
} |
| 155 |
> |
protected boolean releaseExclusiveState(int releases) { |
| 156 |
> |
throw new UnsupportedOperationException(); |
| 157 |
|
} |
| 158 |
|
|
| 159 |
< |
/** |
| 160 |
< |
* Internal version of release |
| 349 |
< |
*/ |
| 350 |
< |
private void doRelease(int permits) { |
| 351 |
< |
final AtomicInteger perms = this.perms; |
| 352 |
< |
for (;;) { |
| 353 |
< |
int p = perms.get(); |
| 354 |
< |
if (perms.compareAndSet(p, p + permits)) { |
| 355 |
< |
Node h = head; |
| 356 |
< |
if (h != null && h.status < 0) |
| 357 |
< |
unparkSuccessor(h); |
| 358 |
< |
return; |
| 359 |
< |
} |
| 360 |
< |
} |
| 159 |
> |
protected void checkConditionAccess(Thread thread, boolean waiting) { |
| 160 |
> |
throw new UnsupportedOperationException(); |
| 161 |
|
} |
| 162 |
|
|
| 163 |
|
/** |
| 171 |
|
*/ |
| 172 |
|
public Semaphore(int permits, boolean fair) { |
| 173 |
|
this.fair = fair; |
| 174 |
< |
perms = new AtomicInteger(permits); |
| 174 |
> |
getState().set(permits); |
| 175 |
|
} |
| 176 |
|
|
| 177 |
|
/** |
| 204 |
|
* @see Thread#interrupt |
| 205 |
|
*/ |
| 206 |
|
public void acquire() throws InterruptedException { |
| 207 |
< |
if (Thread.interrupted() || !doAcquire(1, -1)) |
| 408 |
< |
throw new InterruptedException(); |
| 207 |
> |
acquireSharedInterruptibly(1); |
| 208 |
|
} |
| 209 |
|
|
| 210 |
|
/** |
| 227 |
|
* |
| 228 |
|
*/ |
| 229 |
|
public void acquireUninterruptibly() { |
| 230 |
< |
doAcquire(1, 0); |
| 230 |
> |
acquireSharedUninterruptibly(1); |
| 231 |
|
} |
| 232 |
|
|
| 233 |
|
/** |
| 244 |
|
* otherwise. |
| 245 |
|
*/ |
| 246 |
|
public boolean tryAcquire() { |
| 247 |
< |
return doTryAcquire(1) >= 0; |
| 247 |
> |
return acquireSharedState(false, 1, null) >= 0; |
| 248 |
|
} |
| 249 |
|
|
| 250 |
|
/** |
| 290 |
|
*/ |
| 291 |
|
public boolean tryAcquire(long timeout, TimeUnit unit) |
| 292 |
|
throws InterruptedException { |
| 293 |
< |
if (unit == null) |
| 495 |
< |
throw new NullPointerException(); |
| 496 |
< |
if (Thread.interrupted()) |
| 497 |
< |
throw new InterruptedException(); |
| 498 |
< |
return doTimedAcquire(1, unit.toNanos(timeout)); |
| 293 |
> |
return acquireSharedTimed(1, unit.toNanos(timeout)); |
| 294 |
|
} |
| 295 |
|
|
| 296 |
|
/** |
| 306 |
|
* in the application. |
| 307 |
|
*/ |
| 308 |
|
public void release() { |
| 309 |
< |
doRelease(1); |
| 309 |
> |
releaseShared(1); |
| 310 |
|
} |
| 311 |
|
|
| 312 |
|
/** |
| 350 |
|
*/ |
| 351 |
|
public void acquire(int permits) throws InterruptedException { |
| 352 |
|
if (permits < 0) throw new IllegalArgumentException(); |
| 353 |
< |
if (Thread.interrupted() || !doAcquire(permits, -1)) |
| 559 |
< |
throw new InterruptedException(); |
| 353 |
> |
acquireSharedInterruptibly(permits); |
| 354 |
|
} |
| 355 |
|
|
| 356 |
|
/** |
| 379 |
|
*/ |
| 380 |
|
public void acquireUninterruptibly(int permits) { |
| 381 |
|
if (permits < 0) throw new IllegalArgumentException(); |
| 382 |
< |
doAcquire(permits, 0); |
| 382 |
> |
acquireSharedUninterruptibly(permits); |
| 383 |
|
} |
| 384 |
|
|
| 385 |
|
/** |
| 401 |
|
*/ |
| 402 |
|
public boolean tryAcquire(int permits) { |
| 403 |
|
if (permits < 0) throw new IllegalArgumentException(); |
| 404 |
< |
return doTryAcquire(permits) >= 0; |
| 404 |
> |
return acquireSharedState(false, permits, null) >= 0; |
| 405 |
|
} |
| 406 |
|
|
| 407 |
|
/** |
| 458 |
|
public boolean tryAcquire(int permits, long timeout, TimeUnit unit) |
| 459 |
|
throws InterruptedException { |
| 460 |
|
if (permits < 0) throw new IllegalArgumentException(); |
| 461 |
< |
if (unit == null) |
| 668 |
< |
throw new NullPointerException(); |
| 669 |
< |
if (Thread.interrupted()) |
| 670 |
< |
throw new InterruptedException(); |
| 671 |
< |
return doTimedAcquire(permits, unit.toNanos(timeout)); |
| 461 |
> |
return acquireSharedTimed(permits, unit.toNanos(timeout)); |
| 462 |
|
} |
| 463 |
|
|
| 464 |
|
|
| 488 |
|
*/ |
| 489 |
|
public void release(int permits) { |
| 490 |
|
if (permits < 0) throw new IllegalArgumentException(); |
| 491 |
< |
doRelease(permits); |
| 491 |
> |
releaseShared(permits); |
| 492 |
|
} |
| 493 |
|
|
| 494 |
|
/** |
| 497 |
|
* @return the number of permits available in this semaphore. |
| 498 |
|
*/ |
| 499 |
|
public int availablePermits() { |
| 500 |
< |
return perms.get(); |
| 500 |
> |
return getState().get(); |
| 501 |
|
} |
| 502 |
|
|
| 503 |
|
/** |
| 512 |
|
*/ |
| 513 |
|
protected void reducePermits(int reduction) { |
| 514 |
|
if (reduction < 0) throw new IllegalArgumentException(); |
| 515 |
< |
perms.getAndAdd(-reduction); |
| 515 |
> |
getState().getAndAdd(-reduction); |
| 516 |
|
} |
| 517 |
|
|
| 518 |
|
/** |
| 523 |
|
return fair; |
| 524 |
|
} |
| 525 |
|
|
| 736 |
– |
/** |
| 737 |
– |
* Returns an estimate of the number of threads waiting to acquire |
| 738 |
– |
* a permit. The value is only an estimate because the number of |
| 739 |
– |
* threads may change dynamically while this method traverses |
| 740 |
– |
* internal data structures. This method is designed for use in |
| 741 |
– |
* monitoring of the system state, not for synchronization |
| 742 |
– |
* control. |
| 743 |
– |
* @return the estimated number of threads waiting for a permit |
| 744 |
– |
*/ |
| 745 |
– |
public int getQueueLength() { |
| 746 |
– |
int n = 0; |
| 747 |
– |
for (Node p = tail; p != null && p != head; p = p.prev) |
| 748 |
– |
++n; |
| 749 |
– |
return n; |
| 750 |
– |
} |
| 751 |
– |
|
| 752 |
– |
/** |
| 753 |
– |
* Returns a collection containing threads that may be waiting to |
| 754 |
– |
* acquire a permit. Because the actual set of threads may |
| 755 |
– |
* change dynamically while constructing this result, the returned |
| 756 |
– |
* collection is only a best-effort estimate. The elements of the |
| 757 |
– |
* returned collection are in no particular order. This method is |
| 758 |
– |
* designed to facilitate construction of subclasses that provide |
| 759 |
– |
* more extensive monitoring facilities. |
| 760 |
– |
* @return the collection of threads |
| 761 |
– |
*/ |
| 762 |
– |
protected Collection<Thread> getQueuedThreads() { |
| 763 |
– |
ArrayList<Thread> list = new ArrayList<Thread>(); |
| 764 |
– |
for (Node p = tail; p != null; p = p.prev) { |
| 765 |
– |
Thread t = p.thread; |
| 766 |
– |
if (t != null) |
| 767 |
– |
list.add(t); |
| 768 |
– |
} |
| 769 |
– |
return list; |
| 770 |
– |
} |
| 771 |
– |
|
| 526 |
|
} |
