Unlink dead nodes in MpscLinkedQueue · ReactiveX/RxJava@4c6c6fa (original) (raw)

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Commit 4c6c6fa

Unlink dead nodes in MpscLinkedQueue

Similar tohttps://github.com/JCTools/JCTools/blob/master/jctools-core/src/main/java/org/jctools/queues/MpscLinkedQueue.java#L120, null out the next pointer in the discarded consumer node when polling from the queue. If not, we leave behind a (potentially long) chain of connected garbage nodes. If we're unlucky (for example one of the early nodes is promoted to old generation, triggering nepotism), this can cause GC issues as now we have a long linked list which must be marked by young collections. Reproducer: ``` import io.reactivex.rxjava3.internal.queue.MpscLinkedQueue; public class MpscLinkedQueueGC { public static void main(String[] args) { MpscLinkedQueue queue = new MpscLinkedQueue<>(); for (int i = 0; i < 10; i++) System.gc(); // tenure consumer node while (true) { queue.offer(123); queue.poll(); } } } ``` ``` Before fix: $ java -Xlog:gc -Xmx1G -cp build/classes/java/main MpscLinkedQueueGC.java ... [1.261s] GC(20) Pause Young (Normal) (G1 Preventive Collection) 115M->115M(204M) 209.335ms [1.385s] GC(23) Pause Young (Normal) (G1 Evacuation Pause) 148M->149M(204M) 31.491ms [1.417s] GC(24) Pause Young (Normal) (G1 Evacuation Pause) 157M->158M(204M) 19.333ms [1.453s] GC(25) Pause Young (Normal) (G1 Evacuation Pause) 166M->167M(599M) 22.678ms [1.966s] GC(26) Pause Young (Normal) (G1 Evacuation Pause) 249M->249M(497M) 305.238ms ... After fix: $ java -Xlog:gc -Xmx1G -cp build/classes/java/main MpscLinkedQueueGC.java ... [1.169s] GC(14) Pause Young (Normal) (G1 Evacuation Pause) 304M->2M(506M) 0.755ms [1.558s] GC(15) Pause Young (Normal) (G1 Evacuation Pause) 304M->2M(506M) 0.689ms [1.948s] GC(16) Pause Young (Normal) (G1 Evacuation Pause) 304M->2M(506M) 0.800ms [2.337s] GC(17) Pause Young (Normal) (G1 Evacuation Pause) 304M->2M(506M) 0.714ms ... ```

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