fix(native): Do not discard all tasks in maybeStartNextQueuedTask() (#27548)

[spershin]

Summary:

Skip any tasks that have been aborted or are no longer valid in
maybeStartNextQueuedTask(), but still start the remaining valid tasks. This
avoids a bug where aborting one task (e.g. from a completed fragment) would
silently discard other still-valid tasks from the same query.

Example of the query that got stuck due to this: 20260404_172612_64504_mgsfz

== NO RELEASE NOTE ==

Differential Revision: D100103601

[linux-foundation-easycla]

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[sourcery-ai]

Reviewer's Guide

Adjusts TaskManager's queued task handling so that aborted or invalid tasks are skipped instead of causing all sibling tasks in the same queue entry to be discarded, and adds a regression test to validate the new behavior when one queued task is aborted.

Sequence diagram for updated queued task start behavior in TaskManager

sequenceDiagram
  participant TaskManager
  participant TaskQueue
  participant QueueEntry
  participant TaskA
  participant TaskB

  TaskManager->>TaskQueue: maybeStartNextQueuedTask()
  TaskQueue-->>TaskManager: front() returns QueueEntry
  TaskManager->>TaskQueue: pop_front()

  loop over queuedTasks in QueueEntry
    TaskManager->>QueueEntry: lock(queuedTask A)
    QueueEntry-->>TaskManager: TaskA
    alt TaskA is null or TaskA.task is null
      TaskManager->>TaskManager: log Skipping null task
      Note over TaskManager: continue to next queuedTask
    else TaskA is non-null
      TaskManager->>TaskA: taskState()
      TaskA-->>TaskManager: state != kPlanned
      alt state != kPlanned
        TaskManager->>TaskManager: log Discarding aborted task
        Note over TaskManager: continue to next queuedTask
      end
    end

    TaskManager->>QueueEntry: lock(queuedTask B)
    QueueEntry-->>TaskManager: TaskB
    TaskManager->>TaskB: taskState()
    TaskB-->>TaskManager: state == kPlanned
    TaskManager->>TaskManager: add TaskB to tasksToStart
  end

  alt tasksToStart is not empty
    TaskManager->>TaskManager: proceed to start tasks in tasksToStart
    TaskManager->>TaskB: start()
  else tasksToStart is empty
    TaskManager->>TaskManager: continue checking next QueueEntry
  end

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Class diagram for TaskManager queued task handling changes

classDiagram
  class TaskManager {
    +maybeStartNextQueuedTask() void
    -taskQueue std::deque~std::vector~std::weak_ptr~QueuedTask~~>
  }

  class QueuedTask {
    +task std::shared_ptr~VeloxTaskWrapper~
    +info TaskInfo
    +taskState() PrestoTaskState
  }

  class VeloxTaskWrapper {
    +task void*
  }

  class TaskInfo {
    +taskId std::string
  }

  class PrestoTaskState {
    <<enumeration>>
    kPlanned
    kRunning
    kAborted
    kFinished
    kFailed
  }

  TaskManager "1" --> "*" QueuedTask : manages
  QueuedTask "1" --> "1" VeloxTaskWrapper : has
  QueuedTask "1" --> "1" TaskInfo : has
  QueuedTask "1" --> "1" PrestoTaskState : returns

  note for TaskManager "maybeStartNextQueuedTask now skips aborted or null tasks within a queue entry and starts remaining valid tasks instead of discarding the whole entry"

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File-Level Changes

Change	Details	Files
Change queued task dequeue logic to skip aborted/invalid tasks while still starting remaining planned tasks.	Iterate over queued tasks and continue past null or missing Velox tasks instead of marking the whole queue entry as invalid. For tasks whose state is not planned, log and continue to the next task instead of aborting the entire batch. Only break out of the queue-scanning loop when there is at least one valid task to start, based on a non-empty tasksToStart list, removing the previous queryTasksAreGoodToStart flag and related clearing logic.	presto-native-execution/presto_cpp/main/TaskManager.cpp
Add regression test ensuring that aborting one queued task from a query does not prevent sibling tasks in the same queue entry from starting and completing.	Enable worker overloaded task queuing and construct two plan fragments representing different stages of the same query with partitioned output. Create two queued tasks sharing the same query context but different stage IDs, with no splits and 'no more splits', then verify they are queued and not started. Simulate coordinator abort of one queued task, clear server overload, call maybeStartNextQueuedTask, and assert that the non-aborted sibling task starts and runs to completion.	presto-native-execution/presto_cpp/main/tests/TaskManagerTest.cpp

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[sourcery-ai]

Hey - I've left some high level feedback:

• In queuedTaskAbortDoesNotBlockSiblings, you modify the global SystemConfig::kWorkerOverloadedTaskQueuingEnabled flag but never restore it, which can leak state into other tests; consider saving the previous value and resetting it in a scope guard or test teardown.
• The new maybeStartNextQueuedTask logic now silently skips queue entries where all tasks are invalid; if this is expected, it might be useful to add a single INFO/WARNING log when an entire queue entry is discarded so operators can distinguish this from normal successful dequeues.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In `queuedTaskAbortDoesNotBlockSiblings`, you modify the global `SystemConfig::kWorkerOverloadedTaskQueuingEnabled` flag but never restore it, which can leak state into other tests; consider saving the previous value and resetting it in a scope guard or test teardown.
- The new `maybeStartNextQueuedTask` logic now silently skips queue entries where all tasks are invalid; if this is expected, it might be useful to add a single INFO/WARNING log when an entire queue entry is discarded so operators can distinguish this from normal successful dequeues.

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