javanna commented on code in PR #12689:
URL: https://github.com/apache/lucene/pull/12689#discussion_r1369190050
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lucene/core/src/java/org/apache/lucene/search/TaskExecutor.java:
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@@ -64,64 +67,124 @@ public final class TaskExecutor {
* @param <T> the return type of the task execution
*/
public <T> List<T> invokeAll(Collection<Callable<T>> callables) throws
IOException {
- List<Task<T>> tasks = new ArrayList<>(callables.size());
- boolean runOnCallerThread = numberOfRunningTasksInCurrentThread.get() > 0;
- for (Callable<T> callable : callables) {
- Task<T> task = new Task<>(callable);
- tasks.add(task);
- if (runOnCallerThread) {
- task.run();
- } else {
- executor.execute(task);
+ TaskGroup<T> taskGroup = new TaskGroup<>(callables);
+ return taskGroup.invokeAll(executor);
+ }
+
+ /**
+ * Holds all the sub-tasks that a certain operation gets split into as it
gets parallelized and
+ * exposes the ability to invoke such tasks and wait for them all to
complete their execution and
+ * provide their results. Ensures that each task does not get parallelized
further: this is
+ * important to avoid a deadlock in situations where one executor thread
waits on other executor
+ * threads to complete before it can progress. This happens in situations
where for instance
+ * {@link Query#createWeight(IndexSearcher, ScoreMode, float)} is called as
part of searching each
+ * slice, like {@link TopFieldCollector#populateScores(ScoreDoc[],
IndexSearcher, Query)} does.
+ * Additionally, if one task throws an exception, all other tasks from the
same group are
+ * cancelled, to avoid needless computation as their results would not be
exposed anyways. Creates
+ * one {@link FutureTask} for each {@link Callable} provided
+ *
+ * @param <T> the return type of all the callables
+ */
+ private static final class TaskGroup<T> {
+ private final Collection<RunnableFuture<T>> futures;
+
+ TaskGroup(Collection<Callable<T>> callables) {
+ List<RunnableFuture<T>> tasks = new ArrayList<>(callables.size());
+ for (Callable<T> callable : callables) {
+ tasks.add(createTask(callable));
}
+ this.futures = Collections.unmodifiableCollection(tasks);
}
- Throwable exc = null;
- final List<T> results = new ArrayList<>();
- for (Future<T> future : tasks) {
- try {
- results.add(future.get());
- } catch (InterruptedException e) {
- var newException = new ThreadInterruptedException(e);
- if (exc == null) {
- exc = newException;
- } else {
- exc.addSuppressed(newException);
+ private FutureTask<T> createTask(Callable<T> callable) {
+ AtomicBoolean started = new AtomicBoolean(false);
+ return new FutureTask<>(callable) {
Review Comment:
I tried wrapping FutureTask, but the methods that I was calling I could only
call from a sub-class, as they are protected. I did update my PR to wrap the
callable, which requires less customization of FutureTask (only cancel and
isCancelled need to be overwritten). I am now wondering if it still makes sense
to have our own RunnableFuture instead of just subclassing FutureTask. the
former seems overkill to me at this point, what do you think?
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