GH-49958: [C++][Dataset] DEBUG: log shared_from_this() callsite throwing bad_weak_ptr

[tadeja]

Rationale for this change

Debug #49958

What changes are included in this PR?

Only debug for now.

Are these changes tested?

CI debug

Are there any user-facing changes?

No

• GitHub Issue: [C++][Dataset] std::bad_weak_ptr in multi-threaded writer tests on MinGW gcc-16 #49958

[github-actions]

⚠️ GitHub issue #49958 has been automatically assigned in GitHub to PR creator.

[tadeja]

Both failing tests throw bad_weak_ptr at the same line dataset_writer.cc:212 DatasetWriterFileQueue::ScheduleBatch:

  void ScheduleBatch(std::shared_ptr<RecordBatch> batch) {
    file_tasks_->AddSimpleTask(
        [self = SfwDbg(__LINE__) /* was shared_from_this() */, batch = std::move(batch)]() {
          return self->WriteNext(std::move(batch));
        },
        "DatasetWriter::WriteBatch"sv);
  }

https://github.com/apache/arrow/actions/runs/25690826182/job/75426470835#step:12:614

[ RUN      ] DatasetWriterTestFixture.BatchWriteConcurrent
GH-49958: bad_weak_ptr DatasetWriterFileQueue dataset_writer.cc:212
terminate called after throwing an instance of 'std::bad_weak_ptr'
  what():  bad_weak_ptr

      Start 62: arrow-dataset-dataset-writer-test
    Test #62: arrow-dataset-dataset-writer-test ............Exit code 0xc0000374***Exception:   0.34 sec

https://github.com/apache/arrow/actions/runs/25690826182/job/75426470835#step:12:794

[ RUN      ] TestFileSystemDataset.MultiThreadedWritePersistsOrder
GH-49958: bad_weak_ptr DatasetWriterFileQueue dataset_writer.cc:212
terminate called after throwing an instance of 'std::bad_weak_ptr'
  what():  bad_weak_ptr

      Start 65: arrow-dataset-file-test
    Test #65: arrow-dataset-file-test ......................***Exception: SegFault  0.20 sec

[tadeja]

Diagnosed - The make_shared did not fix this, and the new CI log shows:
https://github.com/apache/arrow/actions/runs/25731999852/job/75559307182?pr=49961#step:12:870

[ RUN      ] DatasetWriterTestFixture.BatchWriteConcurrent
GH-49958: ScheduleBatch this=000002f3e2fda080 EXPIRED use_count=0
GH-49958: bad_weak_ptr DatasetWriterFileQueue dataset_writer.cc:218
terminate called after throwing an instance of 'std::bad_weak_ptr'
  what():  bad_weak_ptr

(dataset_writer.cc:218 is the same as the previous :212 line - because of added diagnostics shifted by 6 lines)

(1) It's not the reset vs make_shared wiring
(2) By the time ScheduleBatch runs, the control block of file queue already reports use_count=0.