Fix #198 and #206 - quickjs crash

HISTORY.txt

@@ -3,6 +3,7 @@ v0.9.1 - TBD
 - Fixed issue with environment variables not propagating to all processes in Linux
 - Documented how to install binary version of Px on Windows without running in a
   console window - #203
+- Fixed issue with quickjs crashing in PAC mode with multiple threads - #198 / #206
 
 v0.9.0 - 2024-01-25
 - Added support for domains in noproxy - #2

px/config.py

@@ -8,7 +8,6 @@
 import sys
 import threading
 import time
-import traceback
 import urllib.parse
 
 from .debug import pprint, dprint, Debug

px/pac.py

@@ -2,6 +2,7 @@
 
 import socket
 import sys
+import threading
 
 try:
     import quickjs
@@ -18,31 +19,42 @@
 class Pac:
     "Load and run PAC files using quickjs"
 
-    ctxt = None
+    _ctxt = None
+    _lock = None
 
     def __init__(self, debug_print = None):
         "Initialize a quickjs context with default PAC utility functions"
         global dprint
         if debug_print is not None:
             dprint = debug_print
 
-        self.ctxt = quickjs.Context()
+        self._ctxt = quickjs.Context()
+        self._lock = threading.Lock()
 
         dprint("Loading PAC utils")
 
         # Load Python callables
         for func in [self.alert, self.dnsResolve, self.myIpAddress]:
-            self.ctxt.add_callable(func.__name__, func)
+            self._ctxt.add_callable(func.__name__, func)
 
         # Load PAC js utils
-        self.ctxt.eval(PACUTILS)
+        self._ctxt.eval(PACUTILS)
+
+    def __del__(self):
+        "Release quickjs context"
+        if self._lock is not None:
+            if self._ctxt is not None:
+                with self._lock:
+                    self._ctxt = None
+            self._lock = None
 
     def load(self, pac_data, pac_encoding):
         "Load PAC data in specified encoding into this context"
         pac_encoding = pac_encoding or "utf-8"
         text = pac_data.decode(pac_encoding)
         try:
-            self.ctxt.eval(text)
+            with self._lock:
+                self._ctxt.eval(text)
         except quickjs.JSException as exc:
             dprint(f"PAC file parsing failed - syntax error or file not encoded in {pac_encoding}")
             dprint("Use --pac_encoding or proxy:pac_encoding in px.ini to change")
@@ -71,7 +83,9 @@ def find_proxy_for_url(self, url, host):
         Return comma-separated list of proxy servers to use for this url
             DIRECT can be returned as one of the options in the response
         """
-        proxies = self.ctxt.eval("FindProxyForURL")(url, host)
+        dprint(f"Finding proxy for {url}")
+        with self._lock:
+            proxies = self._ctxt.eval("FindProxyForURL")(url, host)
 
         # Fix #160 - convert PAC return values into CURLOPT_PROXY schemes
         for ptype in ["PROXY", "HTTP"]: