Yet another version of the cornless business

cornless-set-progress-handler.py

@@ -0,0 +1,66 @@
+# A super-simple utility to run the WSGI application using the built-in WSGI server. The usefulness of this script is
+# precisely because there is _no_ special handling of SIGINT. This means that SIGINT can be used to get a traceback
+# from the application as it was when interrupted. This is useful to answer the question "why is this application
+# stuck?"
+
+# This version is for SQLite. sqlite3 does not support interrupts (i.e. it does not check with Python's signal handler),
+# so we need to do it ourselves. In this case we attempt that by setting a progress handler that checks for a global
+# variable that is set by the signal handler.
+
+# This solution prints a stack trace, but then hangs for reasons I don't understand.
+# (a version without a signal handler (implicit KeyboardInterrupt) works just as well / just as poorly)
+
+import sys
+import signal
+
+from wsgiref import simple_server
+from bugsink.wsgi import application
+from django.db.backends.sqlite3.base import DatabaseWrapper
+
+
+interrupted = False
+
+
+def handle_sigint(signal, frame):
+    global interrupted
+    interrupted = True
+
+
+signal.signal(signal.SIGINT, handle_sigint)
+
+
+def stop_when_interrupted():
+    global interrupted
+    if interrupted:
+        interrupted = False
+        return -1
+    return 0
+
+
+def get_new_connection_with_check(self, conn_params):
+    conn = original_get_new_connection(self, conn_params)
+    # this is the first thing I tried; it works just fine, but so does any old python code, because any old python code
+    # has PyErr_CheckSignals in its execution path.
+    # conn.set_progress_handler(ctypes.pythonapi.PyErr_CheckSignals, 50)
+    conn.set_progress_handler(stop_when_interrupted, 50)
+    # conn.set_progress_handler(lambda: None, 50)  # the version without the signal handler (assumes signal.siganl is
+    # not done, and the lambda is a moment for the regular Python signal handler, which raises keyboardInterrupt, to
+    # run)
+    return conn
+
+
+original_get_new_connection = DatabaseWrapper.get_new_connection
+DatabaseWrapper.get_new_connection = get_new_connection_with_check
+
+
+if __name__ == "__main__":
+    # the actual server:
+    if len(sys.argv) < 2:
+        host = "127.0.0.1"
+        port = 8000
+    else:
+        host = sys.argv[1].split(":")[0]
+        port = int(sys.argv[1].split(":")[1])
+
+    httpd = simple_server.make_server(host, port, application)
+    httpd.serve_forever()