/**
* Equivalent to {@link #tryComplete} but does not invoke {@link #onCompletion(CountedCompleter)}
* along the completion path: If the pending count is nonzero, decrements the count; otherwise,
* similarly tries to complete this task's completer, if one exists, else marks this task as
* complete. This method may be useful in cases where {@code onCompletion} should not, or need
* not, be invoked for each completer in a computation.
*/
public final void propagateCompletion() {
CountedCompleter<?> a = this, s = a;
for (int c; ; ) {
if ((c = a.pending) == 0) {
if ((a = (s = a).completer) == null) {
s.quietlyComplete();
return;
}
} else if (U.compareAndSwapInt(a, PENDING, c, c - 1)) return;
}
}
/**
* Wakes up the successor of h (normally whead). This is normally just h.next, but may require
* traversal from wtail if next pointers are lagging. This may fail to wake up an acquiring thread
* when one or more have been cancelled, but the cancel methods themselves provide extra
* safeguards to ensure liveness.
*/
private void release(WNode h) {
if (h != null) {
WNode q;
Thread w;
U.compareAndSwapInt(h, WSTATUS, WAITING, 0);
if ((q = h.next) == null || q.status == CANCELLED) {
for (WNode t = wtail; t != null && t != h; t = t.prev) if (t.status <= 0) q = t;
}
if (q != null && (w = q.thread) != null) U.unpark(w);
}
}
/**
* If this task's pending count is zero, returns this task; otherwise decrements its pending count
* and returns {@code null}. This method is designed to be used with {@link #nextComplete} in
* completion traversal loops.
*
* @return this task, if pending count was zero, else {@code null}
*/
public final CountedCompleter<?> firstComplete() {
for (int c; ; ) {
if ((c = pending) == 0) return this;
else if (U.compareAndSwapInt(this, PENDING, c, c - 1)) return null;
}
}
/**
* If the pending count is nonzero, (atomically) decrements it.
*
* @return the initial (undecremented) pending count holding on entry to this method
*/
public final int decrementPendingCountUnlessZero() {
int c;
do {} while ((c = pending) != 0 && !U.compareAndSwapInt(this, PENDING, c, c - 1));
return c;
}
/**
* Sets (atomically) the pending count to the given count only if it currently holds the given
* expected value.
*
* @param expected the expected value
* @param count the new value
* @return {@code true} if successful
*/
public final boolean compareAndSetPendingCount(int expected, int count) {
return U.compareAndSwapInt(this, PENDING, expected, count);
}
/**
* See above for explanation.
*
* @param interruptible true if should check interrupts and if so return INTERRUPTED
* @param deadline if nonzero, the System.nanoTime value to timeout at (and return zero)
* @return next state, or INTERRUPTED
*/
private long acquireRead(boolean interruptible, long deadline) {
WNode node = null, p;
boolean interrupted = false;
for (int spins = -1; ; ) {
WNode h;
if ((h = whead) == (p = wtail)) {
for (long m, s, ns; ; ) {
if ((m = (s = state) & ABITS) < RFULL
? U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT)
: (m < WBIT && (ns = tryIncReaderOverflow(s)) != 0L)) {
if (interrupted) Thread.currentThread().interrupt();
return ns;
} else if (m >= WBIT) {
if (spins > 0) {
if (LockSupport.nextSecondarySeed() >= 0) --spins;
} else {
if (spins == 0) {
WNode nh = whead, np = wtail;
if ((nh == h && np == p) || (h = nh) != (p = np)) break;
}
spins = SPINS;
}
}
}
}
if (p == null) { // initialize queue
WNode hd = new WNode(WMODE, null);
if (U.compareAndSwapObject(this, WHEAD, null, hd)) wtail = hd;
} else if (node == null) node = new WNode(RMODE, p);
else if (h == p || p.mode != RMODE) {
if (node.prev != p) node.prev = p;
else if (U.compareAndSwapObject(this, WTAIL, p, node)) {
p.next = node;
break;
}
} else if (!U.compareAndSwapObject(p, WCOWAIT, node.cowait = p.cowait, node))
node.cowait = null;
else {
for (; ; ) {
WNode pp, c;
Thread w;
if ((h = whead) != null
&& (c = h.cowait) != null
&& U.compareAndSwapObject(h, WCOWAIT, c, c.cowait)
&& (w = c.thread) != null) // help release
U.unpark(w);
if (h == (pp = p.prev) || h == p || pp == null) {
long m, s, ns;
do {
if ((m = (s = state) & ABITS) < RFULL
? U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT)
: (m < WBIT && (ns = tryIncReaderOverflow(s)) != 0L)) {
if (interrupted) Thread.currentThread().interrupt();
return ns;
}
} while (m < WBIT);
}
if (whead == h && p.prev == pp) {
long time;
if (pp == null || h == p || p.status > 0) {
node = null; // throw away
break;
}
if (deadline == 0L) time = 0L;
else if ((time = deadline - System.nanoTime()) <= 0L)
return cancelWaiter(node, p, false);
Thread wt = Thread.currentThread();
U.putObject(wt, PARKBLOCKER, this);
node.thread = wt;
if ((h != pp || (state & ABITS) == WBIT) && whead == h && p.prev == pp)
U.park(false, time);
node.thread = null;
U.putObject(wt, PARKBLOCKER, null);
// if (interruptible && Thread.interrupted())
// return cancelWaiter(node, p, true);
if (Thread.interrupted()) {
if (interruptible) return cancelWaiter(node, p, true);
else interrupted = true;
}
}
}
}
}
for (int spins = -1; ; ) {
WNode h, np, pp;
int ps;
if ((h = whead) == p) {
if (spins < 0) spins = HEAD_SPINS;
else if (spins < MAX_HEAD_SPINS) spins <<= 1;
for (int k = spins; ; ) { // spin at head
long m, s, ns;
if ((m = (s = state) & ABITS) < RFULL
? U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT)
: (m < WBIT && (ns = tryIncReaderOverflow(s)) != 0L)) {
WNode c;
Thread w;
whead = node;
node.prev = null;
while ((c = node.cowait) != null) {
if (U.compareAndSwapObject(node, WCOWAIT, c, c.cowait) && (w = c.thread) != null)
U.unpark(w);
}
if (interrupted) Thread.currentThread().interrupt();
return ns;
} else if (m >= WBIT && LockSupport.nextSecondarySeed() >= 0 && --k <= 0) break;
}
} else if (h != null) {
WNode c;
Thread w;
while ((c = h.cowait) != null) {
if (U.compareAndSwapObject(h, WCOWAIT, c, c.cowait) && (w = c.thread) != null)
U.unpark(w);
}
}
if (whead == h) {
if ((np = node.prev) != p) {
if (np != null) (p = np).next = node; // stale
} else if ((ps = p.status) == 0) U.compareAndSwapInt(p, WSTATUS, 0, WAITING);
else if (ps == CANCELLED) {
if ((pp = p.prev) != null) {
node.prev = pp;
pp.next = node;
}
} else {
long time;
if (deadline == 0L) time = 0L;
else if ((time = deadline - System.nanoTime()) <= 0L)
return cancelWaiter(node, node, false);
Thread wt = Thread.currentThread();
U.putObject(wt, PARKBLOCKER, this);
node.thread = wt;
if (p.status < 0 && (p != h || (state & ABITS) == WBIT) && whead == h && node.prev == p)
U.park(false, time);
node.thread = null;
U.putObject(wt, PARKBLOCKER, null);
// if (interruptible && Thread.interrupted())
// return cancelWaiter(node, node, true);
if (Thread.interrupted()) {
if (interruptible) return cancelWaiter(node, p, true);
else interrupted = true;
}
}
}
}
}
/**
* See above for explanation.
*
* @param interruptible true if should check interrupts and if so return INTERRUPTED
* @param deadline if nonzero, the System.nanoTime value to timeout at (and return zero)
* @return next state, or INTERRUPTED
*/
private long acquireWrite(boolean interruptible, long deadline) {
WNode node = null, p;
boolean interrupted = false;
for (int spins = -1; ; ) { // spin while enqueuing
long m, s, ns;
if ((m = (s = state) & ABITS) == 0L) {
if (U.compareAndSwapLong(this, STATE, s, ns = s + WBIT)) {
if (interrupted) Thread.currentThread().interrupt();
return ns;
}
} else if (spins < 0) spins = (m == WBIT && wtail == whead) ? SPINS : 0;
else if (spins > 0) {
if (LockSupport.nextSecondarySeed() >= 0) --spins;
} else if ((p = wtail) == null) { // initialize queue
WNode hd = new WNode(WMODE, null);
if (U.compareAndSwapObject(this, WHEAD, null, hd)) wtail = hd;
} else if (node == null) node = new WNode(WMODE, p);
else if (node.prev != p) node.prev = p;
else if (U.compareAndSwapObject(this, WTAIL, p, node)) {
p.next = node;
break;
}
}
for (int spins = -1; ; ) {
WNode h, np, pp;
int ps;
if ((h = whead) == p) {
if (spins < 0) spins = HEAD_SPINS;
else if (spins < MAX_HEAD_SPINS) spins <<= 1;
for (int k = spins; ; ) { // spin at head
long s, ns;
if (((s = state) & ABITS) == 0L) {
if (U.compareAndSwapLong(this, STATE, s, ns = s + WBIT)) {
whead = node;
node.prev = null;
if (interrupted) Thread.currentThread().interrupt();
return ns;
}
} else if (LockSupport.nextSecondarySeed() >= 0 && --k <= 0) break;
}
} else if (h != null) { // help release stale waiters
WNode c;
Thread w;
while ((c = h.cowait) != null) {
if (U.compareAndSwapObject(h, WCOWAIT, c, c.cowait) && (w = c.thread) != null)
U.unpark(w);
}
}
if (whead == h) {
if ((np = node.prev) != p) {
if (np != null) (p = np).next = node; // stale
} else if ((ps = p.status) == 0) U.compareAndSwapInt(p, WSTATUS, 0, WAITING);
else if (ps == CANCELLED) {
if ((pp = p.prev) != null) {
node.prev = pp;
pp.next = node;
}
} else {
long time; // 0 argument to park means no timeout
if (deadline == 0L) time = 0L;
else if ((time = deadline - System.nanoTime()) <= 0L)
return cancelWaiter(node, node, false);
Thread wt = Thread.currentThread();
U.putObject(wt, PARKBLOCKER, this);
node.thread = wt;
if (p.status < 0 && (p != h || (state & ABITS) != 0L) && whead == h && node.prev == p)
U.park(false, time); // emulate LockSupport.park
node.thread = null;
U.putObject(wt, PARKBLOCKER, null);
// if (interruptible && Thread.interrupted())
// return cancelWaiter(node, node, true);
if (Thread.interrupted()) {
if (interruptible) return cancelWaiter(node, node, true);
else interrupted = true;
}
}
}
}
}
