in java/util/concurrent/locks/StampedLock.java [1141:1315]
private long acquireRead(boolean interruptible, long deadline) {
boolean wasInterrupted = false;
WNode node = null, p;
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 (wasInterrupted)
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 (wasInterrupted)
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) {
if (wasInterrupted)
Thread.currentThread().interrupt();
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 (Thread.interrupted()) {
if (interruptible)
return cancelWaiter(node, p, true);
wasInterrupted = 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 (wasInterrupted)
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 (Thread.interrupted()) {
if (interruptible)
return cancelWaiter(node, node, true);
wasInterrupted = true;
}
}
}
}
}