Fix BlobIO cleanup deadlock

pygit2/blob.py

@@ -86,10 +86,20 @@ def readinto(self, b, /):
 
     def close(self) -> None:
         try:
-            self._ready.wait()
-            self._writer_closed.wait()
-            while self._queue is not None and not self._queue.empty():
-                self._queue.get()
+            # The writer thread may be blocked in queue.put() because the
+            # queue (maxsize=1) still holds a chunk that was never consumed
+            # (e.g. the reader stopped before reaching EOF). Draining the
+            # queue must happen *before* (not after) waiting for
+            # `_writer_closed`, otherwise the writer can never make progress
+            # to reach its close callback and this would deadlock.
+            while True:
+                self._ready.wait()
+                while self._queue is not None and not self._queue.empty():
+                    self._queue.get()
+                if self._writer_closed.is_set():
+                    # Done
+                    break
+                self._ready.clear()
             self._thread.join()
         except KeyboardInterrupt:
             pass

test/conftest.py

@@ -80,6 +80,12 @@ def testrepo(tmp_path: Path) -> Generator[Repository, None, None]:
         yield pygit2.Repository(path)
 
 
+@pytest.fixture
+def bigrepo(tmp_path: Path) -> Generator[Repository, None, None]:
+    with utils.TemporaryRepository('bigrepo.zip', tmp_path) as path:
+        yield pygit2.Repository(path)
+
+
 @pytest.fixture
 def testrepo_path(tmp_path: Path) -> Generator[tuple[Repository, Path], None, None]:
     with utils.TemporaryRepository('testrepo.zip', tmp_path) as path:

test/test_blob.py

@@ -306,3 +306,16 @@ def test_blob_write_to_queue_invalid_commit_id_str(testrepo: Repository) -> None
             flags=BlobFilter.ATTRIBUTES_FROM_COMMIT,
             commit_id='not-a-valid-oid',  # type: ignore[arg-type]
         )
+
+
+def test_blob_partial_read(bigrepo: Repository) -> None:
+    blob_oid = bigrepo.create_blob_fromworkdir('big.txt')
+    blob = bigrepo[blob_oid]
+    assert isinstance(blob, pygit2.Blob)
+    reader = pygit2.BlobIO(blob)
+    # Read only a few lines then break early
+    for i, line in enumerate(reader):
+        if i >= 3:
+            break
+    reader.close()
+    assert not reader.raw._thread.is_alive()  # type: ignore[attr-defined]