From f077eb9eb0c667c767d85fc2e67bd550e1cc077d Mon Sep 17 00:00:00 2001
From: Doug Lea <dl@cs.oswego.edu>
Date: Sat, 3 Jan 2026 10:46:15 -0500
Subject: [PATCH] Strengthen some orderings

---
 .../java/util/concurrent/ForkJoinPool.java    | 51 ++++++++++++-------
 1 file changed, 32 insertions(+), 19 deletions(-)

diff --git a/src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java b/src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java
index 5bd677cac64..94fdd3e0216 100644
--- a/src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java
+++ b/src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java
@@ -1249,16 +1249,16 @@ public class ForkJoinPool extends AbstractExecutorService
          */
         final void push(ForkJoinTask<?> task, ForkJoinPool pool, int unlock) {
             ForkJoinTask<?>[] a = array;
-            int b = base, s = top, m;
+            int b = base, s = top, room, m;
             if (a != null &&
-                (a.length > s + 1 - b || (a = growArray()) != null) &&
+                ((room = a.length - (s + 1 - b)) > 0 || (a = growArray()) != null) &&
                 (m = a.length - 1) >= 0) {    // else rejected or disabled
                 top = s + 1;
                 U.putReferenceVolatile(a, slotOffset(m & s), task);
                 if (unlock != 1)              // release external lock
-                    U.putInt(this, PHASE, unlock);
-                if (U.getReferenceAcquire(a, slotOffset(m & (s - 1))) == null &&
-                    pool != null)
+                    phase = unlock;
+                if ((U.getReferenceAcquire(a, slotOffset(m & (s - 1))) == null ||
+                     room <= 0) && pool != null)
                     pool.signalWork(this, s); // may have appeared empty
             }
         }
@@ -1307,13 +1307,16 @@ public class ForkJoinPool extends AbstractExecutorService
             if (a != null && s - b >= 0 && (cap = a.length) > 0) {
                 if (fifo == 0) {
                     if ((t = (ForkJoinTask<?>)U.getAndSetReference(
-                             a, slotOffset((cap - 1) & s), null)) != null)
+                             a, slotOffset((cap - 1) & s), null)) != null) {
                         top = s;
+                        U.storeFence();
+                    }
                 } else {
                     do {
                         if ((t = (ForkJoinTask<?>)U.getAndSetReference(
                                  a, slotOffset((cap - 1) & b), null)) != null) {
                             base = b + 1;
+                            U.storeFence();
                             break;
                         }
                         if (b == s)
@@ -1330,10 +1333,7 @@ public class ForkJoinPool extends AbstractExecutorService
          * Takes next task, if one exists, using configured mode.
          */
         final ForkJoinTask<?> nextLocalTask() {
-            U.loadFence();  // ensure ordering for external callers
-            ForkJoinTask<?> t= nextLocalTask(config & FIFO);
-            U.storeFence();
-            return t;
+            return nextLocalTask(config & FIFO);
         }
 
         /**
@@ -1350,10 +1350,11 @@ public class ForkJoinPool extends AbstractExecutorService
                 (internal || (lock = tryLockPhase()) != 1)) {
                 if (top == p && U.compareAndSetReference(a, k, task, null)) {
                     taken = true;
-                    U.putIntOpaque(this, TOP, s);
+                    top = s;
+                    U.storeFence();
                 }
                 if (!internal)
-                    U.putIntRelease(this, PHASE, lock + NEXTIDLE);
+                    phase = lock + NEXTIDLE;
             }
             return taken;
         }
@@ -1413,6 +1414,7 @@ public class ForkJoinPool extends AbstractExecutorService
         /**
          * Runs the given task, as well as remaining local tasks
          */
+        //        @jdk.internal.vm.annotation.DontInline
         final void topLevelExec(ForkJoinTask<?> task, int fifo) {
             while (task != null) {
                 task.doExec();
@@ -1452,9 +1454,10 @@ public class ForkJoinPool extends AbstractExecutorService
                                         a, slotOffset(s & m), null));
                                 top = s;
                             }
+                            U.storeFence();
                         }
                         if (!internal)
-                            U.putIntRelease(this, PHASE, lock + NEXTIDLE);
+                            phase = lock + NEXTIDLE;
                         if (taken)
                             task.doExec();
                         break;
@@ -1498,10 +1501,12 @@ public class ForkJoinPool extends AbstractExecutorService
                         break;
                     if (taken =
                         (top == p &&
-                         U.compareAndSetReference(a, k, t, null)))
+                         U.compareAndSetReference(a, k, t, null))) {
                         top = s;
+                        U.storeFence();
+                    }
                     if (!internal)
-                        U.putIntRelease(this, PHASE, lock + NEXTIDLE);
+                        phase = lock + NEXTIDLE;
                     if (!taken)
                         break;
                     t.doExec();
@@ -1537,6 +1542,7 @@ public class ForkJoinPool extends AbstractExecutorService
                 if (base == b && t != null &&
                     U.compareAndSetReference(a, k, t, null)) {
                     base = b + 1;
+                    U.storeFence();
                     t.doExec();
                 }
             }
@@ -2015,16 +2021,23 @@ public class ForkJoinPool extends AbstractExecutorService
             }
             long sp = (phase + NEXTIDLE) & LMASK, pc = ctl;
             U.putInt(w, WorkQueue.PHASE, phase | IDLE);
-            for (long c;;) {                 // try to enqueue
+            for (;;)       {                 // try to enqueue
+                long c, e;
                 w.stackPred = (int)pc;
                 if (pc == (pc = U.compareAndExchangeLong(
                                this, CTL, pc, c = ((pc - RC_UNIT) & UMASK) | sp))) {
                     idle = IDLE;
-                    if ((c & RC_MASK) == 0L)
-                        quiescent();         // check quiescent termination
+                    if (((e = runState) & STOP) == 0L &&
+                        ((e & SHUTDOWN) == 0L || (c & RC_MASK) > 0L ||
+                         quiescent() <= 0)) {  // spin for approx 1 scan cost
+                        int tc = (short)(c >>> TC_SHIFT);
+                        int spins = Math.max((tc << 1) + tc, SPIN_WAITS);
+                        while ((idle = w.phase & IDLE) != 0 && --spins != 0)
+                            Thread.onSpinWait();
+                    }
                     break;
                 }
-                else if ((c & RC_MASK) <= (pc & RC_MASK)) {
+                else if ((c & RC_MASK) < (pc & RC_MASK)) {
                     w.phase = phase;         // back out if lost to signal
                     break;
                 }