Make thread pools work without multiprocessing semaphores

Author: msimacek

graalpython/lib-python/3/multiprocessing/pool.py

@@ -919,6 +919,30 @@ def _set(self, i, obj):
 #
 #
 
+# GraalPy change: ThreadPool would still have used semaphore-based
+# multiprocessing lock. Use a threading lock to make thread pools work
+# on emulated posix backend
+class _ThreadPoolContext:
+
+    def __init__(self, ctx):
+        self._ctx = ctx
+
+    def __getattr__(self, name):
+        return getattr(self._ctx, name)
+
+    def get_context(self, method=None):
+        if method is None:
+            return self
+        return self._ctx.get_context(method)
+
+    def Lock(self):
+        return threading.Lock()
+
+    def SimpleQueue(self):
+        from .queues import SimpleQueue
+        return SimpleQueue(ctx=self)
+
+
 class ThreadPool(Pool):
     _wrap_exception = False
 
@@ -928,7 +952,8 @@ def Process(ctx, *args, **kwds):
         return Process(*args, **kwds)
 
     def __init__(self, processes=None, initializer=None, initargs=()):
-        Pool.__init__(self, processes, initializer, initargs)
+        # GraalPy change
+        Pool.__init__(self, processes, initializer, initargs, context=_ThreadPoolContext(get_context()))
 
     def _setup_queues(self):
         self._inqueue = queue.SimpleQueue()