javanna commented on code in PR #12689:
URL: https://github.com/apache/lucene/pull/12689#discussion_r1363626228
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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 am not sure. I guess that overriding run, setException and cancel makes it
a lot. yet RunnableFuture has a lot of methods that I am not keen on
implementing myself :)
I could go for wrapping the callable instead , that would remove the need to
override run and setException. It would be the same logic but integrated into
the callable itself that is provided to FutureTask. Would you be more
comfortable with that approach?
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