fix: Make scheduledFuture thread-safe in HttpNativeExecutionTaskResultFetcher

[xin-zhang2]

Description

As disscussed in #26550 (comment), we will use synchronized methods to fix the potential thread safety issues in HttpNativeExecutionTaskResultFetcher.

Motivation and Context

Impact

Test Plan

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[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

This PR makes scheduledFuture access in HttpNativeExecutionTaskResultFetcher thread-safe by synchronizing core methods, removes the unused completed flag, and cleans up redundant completion logic in result fetching.

Class diagram for updated HttpNativeExecutionTaskResultFetcher thread safety

classDiagram
    class HttpNativeExecutionTaskResultFetcher {
        -Object taskHasResult
        -AtomicReference<Throwable> lastException
        -ScheduledFuture<?> scheduledFuture
        -long token
        +synchronized void start()
        +synchronized void stop(boolean success)
        +boolean hasPage()
        +synchronized void throwIfFailed()
        -void doGetResults()
        +synchronized void onSuccess(PageBufferClient.PagesResponse pagesResponse)
    }
    class ScheduledFuture {
    }
    HttpNativeExecutionTaskResultFetcher --> ScheduledFuture
    class AtomicReference {
    }
    HttpNativeExecutionTaskResultFetcher --> AtomicReference
    class PageBufferClient {
    }
    class PagesResponse {
    }
    HttpNativeExecutionTaskResultFetcher --> PagesResponse
    PageBufferClient --> PagesResponse

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File-Level Changes

Change	Details	Files
Synchronized scheduledFuture management and removed completed flag for thread safety	Annotated scheduledFuture with @GuardedBy("this") Made start(), stop(), throwIfFailed(), and onSuccess() synchronized Removed volatile completed field and its usage/checks Eliminated redundant completion check in doGetResults	presto-spark-base/src/main/java/com/facebook/presto/spark/execution/nativeprocess/HttpNativeExecutionTaskResultFetcher.java

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[sourcery-ai]

Hey there - I've reviewed your changes and they look great!

Prompt for AI Agents

Please address the comments from this code review:

## Individual Comments

### Comment 1
<location> `presto-spark-base/src/main/java/com/facebook/presto/spark/execution/nativeprocess/HttpNativeExecutionTaskResultFetcher.java:133` </location>
<code_context>
     }

-    private void throwIfFailed()
+    private synchronized void throwIfFailed()
     {
         if (scheduledFuture != null && scheduledFuture.isCancelled() && lastException.get() != null) {
</code_context>

<issue_to_address>
**suggestion:** Synchronizing 'throwIfFailed' may be unnecessary if only reading atomic references.

As 'lastException' is an AtomicReference and only reads are performed, you may be able to remove synchronization unless specific ordering is required.

```suggestion
    private void throwIfFailed()
```
</issue_to_address>

### Comment 2
<location> `presto-spark-base/src/main/java/com/facebook/presto/spark/execution/nativeprocess/HttpNativeExecutionTaskResultFetcher.java:158` </location>
<code_context>
     }

-    private void onSuccess(PageBufferClient.PagesResponse pagesResponse)
+    private synchronized void onSuccess(PageBufferClient.PagesResponse pagesResponse)
     {
         List<SerializedPage> pages = pagesResponse.getPages();
</code_context>

<issue_to_address>
**suggestion (performance):** Synchronizing 'onSuccess' may block other operations; review for performance impact.

If 'onSuccess' is invoked often or handles large batches, method-level synchronization may cause delays. Evaluate if finer-grained synchronization is possible.

Suggested implementation:

```java
    private void onSuccess(PageBufferClient.PagesResponse pagesResponse)
    {
        List<SerializedPage> pages = pagesResponse.getPages();
        long bytes = 0;
        // Synchronize only the critical section that modifies shared state
        synchronized (this) {
            token = nextToken;
        }
        if (pagesResponse.isClientComplete()) {
            workerClient.abortResultsAsync(taskId);
            synchronized (this) {
                if (scheduledFuture != null) {
                    scheduledFuture.cancel(false);
                }
            }
        }

```

You should review all shared mutable state accessed in `onSuccess` and ensure only those modifications are synchronized. If other variables (e.g., `token`, `scheduledFuture`) are shared across threads, synchronize their access as shown. If more shared state is present in the full method, wrap only those assignments in `synchronized` blocks. This will minimize blocking and improve performance.
</issue_to_address>

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[tanjialiang]

Thanks @xin-zhang2 for the improvement. Left some comments.

[xin-zhang2]

Left some comments.

Thanks @tanjialiang, but I don’t seem to see the comments. Would you mind checking again?

[hantangwangd]

@xin-zhang2 thanks for this change.

I have a bit of concern about the synchronized(taskHasResult) {...} block in this method. Since taskHasResult is a shared object used beyond this class, we need to ensure this won't cause deadlocks.

For example, if another thread holds the lock on taskHasResult and then attempts to call HttpNativeExecutionTaskResultFetcher.close(), this could lead to a deadlock situation. Any thoughts? PLMK if I have misunderstood anything. @xin-zhang2 @tanjialiang