status_checks.py: Properly terminate the process pools (#1795)

* Only spawn a thread pool when strictly needed

For --check-primary-hostname, the pool is not used.
When exiting, the other processes are left alive and will hang.

* Acquire pools with the 'with' statement

management/daemon.py

@@ -437,9 +437,8 @@ def system_status():
 			self.items[-1]["extra"].append({ "text": message, "monospace": monospace })
 	output = WebOutput()
 	# Create a temporary pool of processes for the status checks
-	pool = multiprocessing.pool.Pool(processes=5)
-	run_checks(False, env, output, pool)
-	pool.terminate()
+	with multiprocessing.pool.Pool(processes=5) as pool:
+		run_checks(False, env, output, pool)
 	return json_response(output.items)
 
 @app.route('/system/updates')

management/status_checks.py

@@ -1021,13 +1021,14 @@ if __name__ == "__main__":
 	from utils import load_environment
 
 	env = load_environment()
-	pool = multiprocessing.pool.Pool(processes=10)
 
 	if len(sys.argv) == 1:
-		run_checks(False, env, ConsoleOutput(), pool)
+		with multiprocessing.pool.Pool(processes=10) as pool:
+			run_checks(False, env, ConsoleOutput(), pool)
 
 	elif sys.argv[1] == "--show-changes":
-		run_and_output_changes(env, pool)
+		with multiprocessing.pool.Pool(processes=10) as pool:
+			run_and_output_changes(env, pool)
 
 	elif sys.argv[1] == "--check-primary-hostname":
 		# See if the primary hostname appears resolvable and has a signed certificate.