From a874235dff32bd77125034cfd9542a91b68efb03 Mon Sep 17 00:00:00 2001
From: K900 <me@0upti.me>
Date: Tue, 19 Oct 2021 15:42:27 +0300
Subject: [PATCH 1/2] nixos/lib/test-driver: clean up threads correctly

The current implementation just forks off a thread to read
QEMU's stdout and lets it exist forever. This, however,
makes the interpreter shutdown racy, as the thread could
still be running and writing out buffered stdout when the
main thread exits (and since it's using the low level API,
the worker thread does not get cleaned up by the atexit hooks
installed by `threading`, either). So, instead of doing that,
let's create a real `threading.Thread` object, and also
explicitly `join` it along with the other stuff when cleaning up.
---
 nixos/lib/test-driver/test-driver.py | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/nixos/lib/test-driver/test-driver.py b/nixos/lib/test-driver/test-driver.py
index e659b0c04f50..f2e7bf3c1d5b 100755
--- a/nixos/lib/test-driver/test-driver.py
+++ b/nixos/lib/test-driver/test-driver.py
@@ -6,7 +6,7 @@ from xml.sax.saxutils import XMLGenerator
 from colorama import Style
 import queue
 import io
-import _thread
+import threading
 import argparse
 import atexit
 import base64
@@ -409,6 +409,7 @@ class Machine:
     pid: Optional[int] = None
     monitor: Optional[socket.socket] = None
     shell: Optional[socket.socket] = None
+    serial_thread: Optional[threading.Thread]
 
     booted: bool = False
     connected: bool = False
@@ -444,6 +445,8 @@ class Machine:
             self.cleanup_statedir()
         self.state_dir.mkdir(mode=0o700, exist_ok=True)
 
+        self.serial_thread = None
+
     @staticmethod
     def create_startcommand(args: Dict[str, str]) -> StartCommand:
         rootlog.warning(
@@ -921,7 +924,8 @@ class Machine:
                 self.last_lines.put(line)
                 self.log_serial(line)
 
-        _thread.start_new_thread(process_serial_output, ())
+        self.serial_thread = threading.Thread(target=process_serial_output)
+        self.serial_thread.start()
 
         self.wait_for_monitor_prompt()
 
@@ -1021,9 +1025,12 @@ class Machine:
         assert self.process
         assert self.shell
         assert self.monitor
+        assert self.serial_thread
+
         self.process.terminate()
         self.shell.close()
         self.monitor.close()
+        self.serial_thread.join()
 
 
 class VLan:

From 9611041ef54b09eb764ed72d95c3111ce52fe984 Mon Sep 17 00:00:00 2001
From: K900 <me@0upti.me>
Date: Tue, 19 Oct 2021 16:29:19 +0300
Subject: [PATCH 2/2] nixos/lib/test-driver: set defaults in __init__ instead
 of class level

Just a minor code style nit to avoid potential footguns
---
 nixos/lib/test-driver/test-driver.py | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/nixos/lib/test-driver/test-driver.py b/nixos/lib/test-driver/test-driver.py
index f2e7bf3c1d5b..3ee8b3227c61 100755
--- a/nixos/lib/test-driver/test-driver.py
+++ b/nixos/lib/test-driver/test-driver.py
@@ -405,14 +405,14 @@ class Machine:
     keep_vm_state: bool
     allow_reboot: bool
 
-    process: Optional[subprocess.Popen] = None
-    pid: Optional[int] = None
-    monitor: Optional[socket.socket] = None
-    shell: Optional[socket.socket] = None
+    process: Optional[subprocess.Popen]
+    pid: Optional[int]
+    monitor: Optional[socket.socket]
+    shell: Optional[socket.socket]
     serial_thread: Optional[threading.Thread]
 
-    booted: bool = False
-    connected: bool = False
+    booted: bool
+    connected: bool
     # Store last serial console lines for use
     # of wait_for_console_text
     last_lines: Queue = Queue()
@@ -445,8 +445,15 @@ class Machine:
             self.cleanup_statedir()
         self.state_dir.mkdir(mode=0o700, exist_ok=True)
 
+        self.process = None
+        self.pid = None
+        self.monitor = None
+        self.shell = None
         self.serial_thread = None
 
+        self.booted = False
+        self.connected = False
+
     @staticmethod
     def create_startcommand(args: Dict[str, str]) -> StartCommand:
         rootlog.warning(