How can you limit the allowed execution time of specific methods in the python version of Google App Engine?

Question

Since the signal module is not supported in the python version of Google App Engine, what is the simplest way to call a method and throw/catch an exception if the method doe

Answer 1

If you are talking about RPC calls, such as the datastore, you can create an RPC with a deadline (see create_rpc), pass the RPC to your datastore function (db.get, db.put, etc...), then catch DeadlineExceededErrors.

# Set a five-second timeout
rpc = db.create_rpc(deadline=5)

# A query:
query = YourModel.all().fetch(100, rpc=rpc)

The URLFetch fetch function also takes a deadline parameter.

For your own code you could implement checking yourself, see the time module.

Answer 2

In loops, you can store the time the loop started and check how long it's been going on each iteration.

If you're not in a loop, things are a bit trickier. You could add the time-checking bit every few lines of code. This, of course, makes for really ugly code, but without the ability to spawn threads that could run a timer in the background and interrupt the running code, there's not much of a way around it.