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[Bug] notifyMasterOnline aborts the long-polling wake-up with a NullPointerException when an arrival drains a bucket first

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#11,441 1 comentario 0 reacciones 0 asignados Ver en GitHub

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@iloveeyjafjalla ya está trabajando en esto.

Desde el 14/10/2026.

  • #11442 de @iloveeyjafjalla — abierto

Evaluación

Dificultad
2/5
Tiempo estimado
1-3 horas
Aptitud para principiantes
82/100
Tipo de issue
Error
Claridad
Bien especificado
Estado de actividad
Activo
Stack tecnológico
java
Área
backend

Línea de trabajo

Empieza en PullRequestHoldService.notifyMasterOnline, alrededor de la línea 191, donde el bucle sobre pullRequestTable llama a mpr.cloneListAndClear() e itera el resultado directamente. Lee ManyPullRequest.cloneListAndClear(), que devuelve null para un bucket vacío, y compáralo con la comprobación de null en notifyMessageArriving. Está terminado cuando un bucket que se vacía de forma concurrente se omite y el barrido sigue despertando las peticiones de las otras colas.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

Describe the Bug

When the smallest broker of a group changes and this broker becomes the master, BrokerController#onMinBrokerChange ends with pullRequestHoldService.notifyMasterOnline(), whose job is to immediately re-execute every pull request that is currently suspended, so that clients do not have to wait for their own suspend timeout after a master comes online.

That sweep assumes a bucket it has just seen as non-empty still holds requests when it drains it:

for (ManyPullRequest mpr : this.pullRequestTable.values()) {
    if (mpr == null || mpr.isEmpty()) {
        continue;
    }
    for (PullRequest request : mpr.cloneListAndClear()) {

ManyPullRequest#cloneListAndClear() returns null (not an empty list) whenever the bucket is empty at drain time:

public synchronized List<PullRequest> cloneListAndClear() {
    if (!this.pullRequestList.isEmpty()) {
        ...
        return result;
    }
    return null;
}

The buckets are drained by the message-arrival path on the store's dispatch thread (NotifyMessageArrivingListener -> PullRequestHoldService#notifyMessageArriving, which drains the same bucket and replays the requests that did not match). An arrival that wins the race between the isEmpty() check above and the drain makes the loop iterable null, so the enhanced for throws a NullPointerException.

Impact
  1. The NullPointerException escapes notifyMasterOnline() into onMinBrokerChange. The sweep is over, so every bucket that had not yet been visited keeps its requests suspended: those clients sit out their full suspend timeout instead of being woken immediately - exactly the stall this method exists to prevent, and in exactly the failover window it is meant for.
  2. The exception is thrown on the thread that updates the min-broker state (including the UPDATE_MIN_BROKER admin path), so the caller sees a failure for an operation that has otherwise already been applied.

The same class shows what the intended contract is: notifyMessageArriving drains a bucket the same way and guards the result with if (requestList != null) before iterating, so the missing guard in notifyMasterOnline is an oversight rather than a documented behaviour.

How to Reproduce
  • Suspend a pull request on some topic@queueId (long polling enabled, i.e. the client sent the suspend flag and the pull returned PULL_NOT_FOUND longer than the max. offset).
  • Produce a message for that queue from another thread, so the dispatch thread drains the same bucket through notifyMessageArriving in the same instant as notifyMasterOnline().
  • The stricter, deterministic form of the race: the bucket reports itself as non-empty and is drained before notifyMasterOnline() drains it, which is what makes the sweep iterable null.
  • Result with the current code: java.lang.NullPointerException at org.apache.rocketmq.broker.longpolling.PullRequestHoldService.notifyMasterOnline(PullRequestHoldService.java:191), and the remaining buckets are not woken.
Expected Behavior

A bucket that lost that race is skipped; the sweep continues and still wakes the requests held for the other queues.

Proposed Fix

Read the drained list into a local variable and skip the bucket when it answers null, instead of iterating the call result directly:

List<PullRequest> requestList = mpr.cloneListAndClear();
if (requestList == null) {
    continue;
}
for (PullRequest request : requestList) {
Environment
  • 5.5.1-SNAPSHOT (develop, 0dd48c39db), all platforms
Lenguaje dominante
Java
Estrellas
22.6k
Forks
12k
Merge medio
6 d 21 h
PR fusionados (30 d)
17

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