leaked semaphore objects?
aqt 1.2.0b3, macOS 11.4
```
% aqt install --outputdir ~/junkaqt 5.12.11 mac desktop -m qtwebengine

2021-06-11 11:16:07,044 - aqt - INFO - aqtinstall(aqt) vunknown on Python 3.9.4 [CPython Clang 12.0.0 (clang-1200.0.32.29)]
2021-06-11 11:16:07,044 - aqt - WARNING - Specified Qt version is unknown: 5.12.11.
2021-06-11 11:16:56,388 - aqt - INFO - Patching /Users/administrator/junkaqt/5.12.11/clang_64/bin/qmake
2021-06-11 11:16:56,417 - aqt - INFO - Patching /Users/administrator/junkaqt/5.12.11/clang_64/lib/QtCore.framework/Versions/5/QtCore
2021-06-11 11:16:56,429 - aqt - INFO - Patching /Users/administrator/junkaqt/5.12.11/clang_64/lib/QtCore.framework/Versions/5/QtCore_debug
2021-06-11 11:16:56,450 - aqt - INFO - Finished installation
2021-06-11 11:16:56,451 - aqt - INFO - Time elasped: 49.40753163 second
/usr/local/Cellar/python@3.9/3.9.4/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/resource_tracker.py:216: UserWarning: resource_tracker: There appear to be 4 leaked semaphore objects to clean up at shutdown
  warnings.warn('resource_tracker: There appear to be %d '
```
diff --git a/aqt/helper.py b/aqt/helper.py
index 6208a89..2e6dee7 100644
--- a/aqt/helper.py
+++ b/aqt/helper.py
@@ -27,6 +27,7 @@ import os
 import posixpath
 import secrets
 import sys
+import threading
 from logging import Handler, getLogger
 from logging.handlers import QueueListener
 from pathlib import Path
@@ -321,13 +322,30 @@ class SettingsClass:
     """
     Class to hold configuration and settings.
     Actual values are stored in 'settings.ini' file.
-    It also holds a combinations database.
+    It also holds a `combinations` database.
     """
 
+    # this class is Borg
+    _shared_state: Dict[str, Any] = {
+        "config": None,
+        "configfile": None,
+        "loggingconf": None,
+        "_combinations": None,
+        "_lock": threading.Lock(),
+    }
+
+    def __new__(cls, *p, **k):
+        self = object.__new__(cls, *p, **k)
+        self.__dict__ = cls._shared_state
+        return self
+
     def __init__(self):
-        self.config = MyConfigParser()
-        self.configfile = os.path.join(os.path.dirname(__file__), "settings.ini")
-        self.loggingconf = os.path.join(os.path.dirname(__file__), "logging.ini")
+        if self.config is None:
+            with self._lock:
+                if self.config is None:
+                    self.config = MyConfigParser()
+                    self.configfile = os.path.join(os.path.dirname(__file__), "settings.ini")
+                    self.loggingconf = os.path.join(os.path.dirname(__file__), "logging.ini")
 
     def load_settings(self, file: Optional[Union[str, TextIO]] = None) -> None:
         with open(
@@ -478,6 +496,5 @@ Settings = SettingsClass()
 def setup_logging(env_key="LOG_CFG"):
     config = os.getenv(env_key, None)
     if config is not None and os.path.exists(config):
-        logging.config.fileConfig(config)
-    else:
-        logging.config.fileConfig(Settings.loggingconf)
+        Settings.loggingconf = config
+    logging.config.fileConfig(Settings.loggingconf)
diff --git a/aqt/installer.py b/aqt/installer.py
index 33aec9a..1a16cad 100644
--- a/aqt/installer.py
+++ b/aqt/installer.py
@@ -1099,7 +1099,7 @@ def run_installer(archives: List[QtPackage], base_dir: str, sevenzip: Optional[s
     #
     tasks = []
     for arc in archives:
-        tasks.append((arc, base_dir, sevenzip, queue, archive_dest, keep))
+        tasks.append((arc, base_dir, sevenzip, queue, archive_dest, Settings.configfile, keep))
     ctx = multiprocessing.get_context("spawn")
     if is_64bit():
         pool = ctx.Pool(Settings.concurrency, init_worker_sh, (), 4)
@@ -1154,8 +1154,8 @@ def installer(
     command: Optional[str],
     queue: multiprocessing.Queue,
     archive_dest: Path,
-    keep: bool = False,
-    response_timeout: Optional[int] = None,
+    settings_ini: str,
+    keep: bool,
 ):
     """
     Installer function to download archive files and extract it.
@@ -1165,10 +1165,9 @@ def installer(
     base_url = qt_package.base_url
     archive: Path = archive_dest / qt_package.archive
     start_time = time.perf_counter()
-    # set defaults
-    Settings.load_settings()
-    # set logging
-    setup_logging()  # XXX: why need to load again?
+    Settings.load_settings(file=settings_ini)
+    # setup queue logger
+    setup_logging()
     qh = QueueHandler(queue)
     logger = getLogger()
     for handler in logger.handlers:
@@ -1176,10 +1175,7 @@ def installer(
         logger.removeHandler(handler)
     logger.addHandler(qh)
     #
-    if response_timeout is None:
-        timeout = (Settings.connection_timeout, Settings.response_timeout)
-    else:
-        timeout = (Settings.connection_timeout, response_timeout)
+    timeout = (Settings.connection_timeout, Settings.response_timeout)
     hash = get_hash(qt_package.archive_path, algorithm="sha256", timeout=timeout)
 
     def download_bin(_base_url):
diff --git a/ci/settings.ini b/ci/settings.ini
index ae1f837..9aac817 100644
--- a/ci/settings.ini
+++ b/ci/settings.ini
@@ -9,7 +9,10 @@ baseurl: https://download.qt.io
 connection_timeout: 30
 response_timeout: 30
 max_retries: 5
+max_retries_on_connection_error: 5
 retry_backoff: 0.1
+max_retries_on_checksum_error: 5
+max_retries_to_retrieve_hash: 5
 
 [mirrors]
 blacklist:
diff --git a/tests/test_install.py b/tests/test_install.py
index 79945b4..fc373ff 100644
--- a/tests/test_install.py
+++ b/tests/test_install.py
@@ -1215,6 +1215,8 @@ def test_install_installer_archive_extraction_err(monkeypatch):
             command="some_nonexistent_7z_extractor",
             queue=MockMultiprocessingManager.Queue(),
             archive_dest=Path(temp_dir),
+            settings_ini=Settings.configfile,
+            keep=False,
         )
     assert err.type == ArchiveExtractionError
     err_msg = format(err.value).rstrip()
['tests/test_install.py', 'aqt/installer.py', 'ci/settings.ini', 'aqt/helper.py']