StreamPollFeeder: declare done and exception as volatile

[elharo]

StreamPollFeeder.done and StreamPollFeeder.exception are accessed from multiple threads without volatile, violating the Java Memory Model.

done (line 40): read in run() outside any synchronized block (line 61), written in waitUntilDone() inside synchronized (lock) (line 107). When the feeder thread is continuously reading data (input.available() > 0), it never enters the synchronized block, so no happens‑before guarantees the write to done is ever seen. The thread loops forever and waitUntilDone()'s join() call hangs.

exception (line 38): written by the run() thread (lines 79, 92) and read from other threads via getException() (line 101). Without volatile, a thread calling getException() may see a stale null. StreamPumper already declares its equivalent field as volatile — StreamPollFeeder should follow the same pattern.

Fixes #385
Fixes #386

[Copilot]

Pull request overview

This PR fixes a Java Memory Model visibility bug in StreamPollFeeder by ensuring cross-thread state (done, exception) is safely published, and adds a regression test that exercises the previously-hanging scenario with continuously-available input.

Changes:

• Declare StreamPollFeeder.done as volatile to guarantee termination visibility when the feeder loop doesn’t enter the synchronized(lock) block.
• Declare StreamPollFeeder.exception as volatile so concurrent readers don’t observe a stale null.
• Add a JUnit regression test that simulates continuously available data and asserts waitUntilDone() completes within a timeout.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/main/java/org/apache/maven/shared/utils/cli/StreamPollFeeder.java	Marks done and exception as volatile to fix cross-thread visibility and prevent hangs/stale reads.
src/test/java/org/apache/maven/shared/utils/cli/StreamPollFeederTest.java	Adds a timeout-based regression test targeting the continuous-data hang scenario.

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