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8373118: Test java/lang/Thread/virtual/Starvation.java timed out #28797

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96b399a
For testing
DougLea Dec 9, 2025
1fb8970
filter by index
DougLea Dec 10, 2025
094d7d7
signalWork diagnostic
DougLea Dec 11, 2025
496cef3
Address review comments
DougLea Dec 13, 2025
357a3cb
Merge branch 'openjdk:master' into JDK-8373118
DougLea Dec 13, 2025
685a3eb
Revert topLevelExec
DougLea Dec 13, 2025
e3f012f
Reorder signalWork filter
DougLea Dec 14, 2025
76dd5dd
Adjust runworker for previous update
DougLea Dec 14, 2025
61adb1d
Reduce fencing
DougLea Dec 15, 2025
7cc2dd1
Relax orderings in push
DougLea Dec 16, 2025
debaf27
Another diagnostic
DougLea Dec 17, 2025
9b2f082
Merge branch 'openjdk:master' into JDK-8373118
DougLea Dec 17, 2025
45f8a9a
Avoid double-filtering
DougLea Dec 17, 2025
3370c0b
Check diagnosis
DougLea Dec 18, 2025
2d8cff2
Merge branch 'openjdk:master' into JDK-8373118
DougLea Dec 18, 2025
b0b37d3
Merge branch 'openjdk:master' into JDK-8373118
DougLea Dec 18, 2025
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66 changes: 44 additions & 22 deletions src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1254,18 +1254,17 @@ final int queueSize() {
* @throws RejectedExecutionException if array could not be resized
*/
final void push(ForkJoinTask<?> task, ForkJoinPool pool, boolean internal) {
int s = top, b = base, m, cap, room; ForkJoinTask<?>[] a, na;
int s = top, b = base, m, cap, room; ForkJoinTask<?>[] a;
if ((a = array) != null && (cap = a.length) > 0) { // else disabled
int k = (m = cap - 1) & s;
if ((room = m - (s - b)) >= 0) {
if ((room = (m = cap - 1) - (s - b)) >= 0) {
top = s + 1;
long pos = slotOffset(k);
long pos = slotOffset(m & s);
if (!internal)
U.putReference(a, pos, task); // inside lock
else
U.getAndSetReference(a, pos, task); // fully fenced
if (room == 0 && (na = growArray(a, cap, s)) != null)
k = ((a = na).length - 1) & s; // resize
if (room == 0)
growArray(a, cap, s);
}
if (!internal)
unlockPhase();
Expand All @@ -1274,7 +1273,7 @@ final void push(ForkJoinTask<?> task, ForkJoinPool pool, boolean internal) {
if (pool != null &&
(room == 0 ||
U.getReferenceAcquire(a, slotOffset(m & (s - 1))) == null))
pool.signalWork(a, k); // may have appeared empty
pool.signalWork(this, s); // may have appeared empty
}
}

Expand All @@ -1283,9 +1282,8 @@ final void push(ForkJoinTask<?> task, ForkJoinPool pool, boolean internal) {
* @param a old array
* @param cap old array capacity
* @param s current top
* @return new array, or null on failure
*/
private ForkJoinTask<?>[] growArray(ForkJoinTask<?>[] a, int cap, int s) {
private void growArray(ForkJoinTask<?>[] a, int cap, int s) {
int newCap = (cap >= 1 << 16) ? cap << 1 : cap << 2;
ForkJoinTask<?>[] newArray = null;
if (a != null && a.length == cap && cap > 0 && newCap > 0) {
Expand All @@ -1305,7 +1303,6 @@ a, slotOffset(k & mask), null)) == null)
updateArray(newArray); // fully fenced
}
}
return newArray;
}

/**
Expand Down Expand Up @@ -1434,7 +1431,31 @@ else if (U.compareAndSetReference(a, k, t, null)) {
final void topLevelExec(ForkJoinTask<?> task, int fifo) {
while (task != null) {
task.doExec();
task = (fifo != 0) ? localPoll() : localPop();
task = null;
int p = top, cap; ForkJoinTask<?>[] a;
if ((a = array) == null || (cap = a.length) <= 0)
break; // currently impossible
if (fifo == 0) { // specialized localPop
int s = p - 1; long k;
if (U.getReference(
a, k = slotOffset((cap - 1) & s)) != null &&
(task = (ForkJoinTask<?>)
U.getAndSetReference(a, k, null)) != null)
top = s;
} else { // specialized localPoll
for (int b = base; p - b > 0; ) {
int nb = b + 1;
if ((task = (ForkJoinTask<?>)U.getAndSetReference(
a, slotOffset((cap - 1) & b), null)) != null) {
base = nb;
break;
}
if (nb == p)
break;
while (b == (b = U.getIntAcquire(this, BASE)))
Thread.onSpinWait();
}
}
}
}

Expand Down Expand Up @@ -1854,9 +1875,12 @@ final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {

/**
* Releases an idle worker, or creates one if not enough exist,
* giving up if array a is nonnull and task at a[k] already taken.
* giving up q is nonull and signalled slot already taken.
*
* @param q, if nonnull, the WorkQueue containing signalled task
* @param qbase q's base index for the task
*/
final void signalWork(ForkJoinTask<?>[] a, int k) {
final void signalWork(WorkQueue q, int qbase) {
int pc = parallelism;
for (long c = ctl;;) {
WorkQueue[] qs = queues;
Expand All @@ -1878,9 +1902,7 @@ else if ((v = w) == null)
break;
else
nc = (v.stackPred & LMASK) | (c & TC_MASK) | ac;
if (a != null && k < a.length && k >= 0 && a[k] == null)
break;
if (c == (c = ctl) && c == (c = compareAndExchangeCtl(c, nc))) {
if (c == (c = compareAndExchangeCtl(c, nc))) {
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@viktorklang-ora viktorklang-ora Dec 15, 2025

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I think the risk here is that this introduces more cache-coordination contention, esp. on multisocket aarch64.

if (v == null)
createWorker();
else {
Expand All @@ -1890,6 +1912,8 @@ else if ((v = w) == null)
}
break;
}
if (q != null && q.base - qbase > 0)
break;
}
}

Expand Down Expand Up @@ -1976,10 +2000,10 @@ final void runWorker(WorkQueue w) {
if ((q = qs[qid = i & (n - 1)]) != null) {
ForkJoinTask<?>[] a; int cap; // poll queue
while ((a = q.array) != null && (cap = a.length) > 0) {
int b, nb, nk; long bp; ForkJoinTask<?> t;
int b, nb; long bp; ForkJoinTask<?> t;
t = (ForkJoinTask<?>)U.getReferenceAcquire(
a, bp = slotOffset((cap - 1) & (b = q.base)));
long np = slotOffset(nk = (nb = b + 1) & (cap - 1));
long np = slotOffset((nb = b + 1) & (cap - 1));
if (q.base == b) { // else inconsistent
if (t == null) {
if (q.array == a) { // else resized
Expand All @@ -2001,13 +2025,11 @@ else if (inactive != 0) {
}
else if (U.compareAndSetReference(a, bp, t, null)) {
q.base = nb;
Object nt = U.getReferenceAcquire(a, np);
w.source = qid;
rescans = 1;
++taken;
if (nt != null && // confirm a[nk]
U.getReferenceAcquire(a, np) == nt)
signalWork(a, nk); // propagate
if (U.getReferenceAcquire(a, np) != null)
signalWork(q, nb); // propagate
w.topLevelExec(t, fifo);
}
}
Expand Down