Tags · ReactiveX/RxJava (original) (raw)
v3.1.10
Toggle v3.1.10's commit message
Fix MpscLinkedQueue GC issues (#7799)
- Refactor MpscLinkedQueue.poll
Handle empty queue first, then share most of the implementation for non-empty scenarios (spin and non-spin).
- Unlink dead nodes in MpscLinkedQueue
Similar to https://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<Integer> 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
...- Revert "Unlink dead nodes in MpscLinkedQueue"
This reverts commit 4c6c6fa.
- Revert "Refactor MpscLinkedQueue.poll"
This reverts commit b8582b9.
- Unlink dead nodes in MpscLinkedQueue
Similar to https://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<Integer> 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
...