handle a graceful shutdown on request

[BF-1358]

pghoard/compressor.py

@@ -43,7 +43,7 @@ class BaseCompressorEvent:
     file_path: Path
     backup_site_name: str
     source_data: Union[BinaryIO, Path]
-    callback_queue: CallbackQueue
+    callback_queue: Optional[CallbackQueue]
     metadata: Dict[str, str]
 
 

pghoard/pghoard.py

@@ -983,8 +983,50 @@ def _get_all_threads(self):
         all_threads.extend(self.transfer_agents)
         return all_threads
 
+    def _wait_for_queue_to_be_emptied(
+        self,
+        queue: Queue,
+        queue_name: str,
+        timeout: Optional[int] = None,
+    ) -> None:
+        start = time.monotonic()
+        while True:
+            if queue.empty():
+                self.log.info("%r queue has been emptied.", queue_name)
+                break
+
+            if timeout is not None and time.monotonic() - start > timeout:
+                self.log.warning("Exceeded waiting time for %r queue to be emptied", queue_name)
+                break
+
+            time.sleep(0.1)
+
     def handle_exit_signal(self, _signal=None, _frame=None):  # pylint: disable=unused-argument
         self.log.warning("Quitting, signal: %r", _signal)
+        if _signal == signal.SIGTERM:
+            self.graceful_shutdown()
+        else:
+            self.quit()
+
+    def graceful_shutdown(self) -> None:
+        """
+        Makes sure all missing files are compressed, uploaded and deleted before all threads are inactive.
+
+        Steps to follow:
+        - Shutdown receivexlogs and walreceivers threads
+        - Wait for compression, transfer and deletion queues to be empty
+        - Quit (stop remaining threads and write state file)
+        """
+        self.log.info("Gracefully shutting down...")
+        self.running = False
+        for thread in [*self.receivexlogs.values(), *self.walreceivers.values()]:
+            thread.running = False
+
+        # wait for all queues to be emptied
+        self._wait_for_queue_to_be_emptied(self.compression_queue, "compression")
+        self._wait_for_queue_to_be_emptied(self.transfer_queue, "transfer")
+        self._wait_for_queue_to_be_emptied(self.wal_file_deletion_queue, "wal_file_deletion")
+
         self.quit()
 
     def quit(self):

test/test_pghoard.py

@@ -11,14 +11,19 @@
 import time
 from pathlib import Path
 from typing import Any, Dict
-from unittest.mock import Mock, patch
+from unittest.mock import MagicMock, Mock, patch
 
 import pytest
 
 import pghoard.pghoard as pghoard_module
-from pghoard.common import (BaseBackupFormat, FileType, create_alert_file, delete_alert_file, write_json_file)
+from pghoard.common import (
+    BaseBackupFormat, FileType, FileTypePrefixes, create_alert_file, delete_alert_file, write_json_file
+)
+from pghoard.compressor import CompressionEvent
 from pghoard.pghoard import PGHoard
 from pghoard.pgutil import create_connection_string
+from pghoard.receivexlog import PGReceiveXLog
+from pghoard.transfer import TransferAgent
 
 from .base import PGHoardTestCase
 from .util import dict_to_tar_file, switch_wal, wait_for_xlog
@@ -819,6 +824,53 @@ def test_startup_walk_skip_compression_if_already_compressed(
             # uncompressed timeline files are not added to deletion queue, they are immediately unlinked
             assert self.pghoard.wal_file_deletion_queue.qsize() == 0
 
+    @patch("pghoard.compressor.wal.verify_wal", Mock())
+    @patch.object(PGReceiveXLog, "run", Mock())
+    @patch.object(TransferAgent, "get_object_storage")
+    def test_graceful_shutdown(
+        self,
+        mocked_get_object_storage: MagicMock,
+    ) -> None:
+        compressed_wal_path, _ = self.pghoard.create_backup_site_paths(self.test_site)
+        uncompressed_wal_path = compressed_wal_path + "_incoming"
+
+        file_name = "000000010000000000000008"
+        uncompressed_file_path = os.path.join(uncompressed_wal_path, file_name)
+        with open(uncompressed_file_path, "wb") as fp:
+            fp.write(b"foo")
+
+        self.pghoard.compression_queue.put(
+            CompressionEvent(
+                file_type=FileType.Wal,
+                file_path=FileTypePrefixes[FileType.Wal] / file_name,
+                delete_file_after_compression=True,
+                backup_site_name=self.test_site,
+                source_data=Path(uncompressed_file_path),
+                callback_queue=None,
+                metadata={}
+            )
+        )
+
+        # run compressors, transfer_agents and wal_file_deleter
+        for thread in [*self.pghoard.compressors, *self.pghoard.transfer_agents, self.pghoard.wal_file_deleter]:
+            thread.start()
+
+        self.pghoard.graceful_shutdown()
+
+        assert self.pghoard.compression_queue.qsize() == 0
+        assert self.pghoard.transfer_queue.qsize() == 0
+        assert self.pghoard.wal_file_deletion_queue.qsize() == 0
+
+        # called once for uploading renamed partial file
+        assert mocked_get_object_storage.call_count == 1
+
+        # uncompressed file should still exist since WALDeletionThread always keeps last file
+        assert os.path.exists(uncompressed_file_path)
+
+        # verify compressors, transfer_agents and wal_file_deleter are not running
+        for thread in [*self.pghoard.compressors, *self.pghoard.transfer_agents, self.pghoard.wal_file_deleter]:
+            assert thread.is_alive() is False
+
 
 class TestPGHoardWithPG:
     def test_auth_alert_files(self, db, pghoard):