Question

How can I test concurrency code of backend instance in development environment ? Here is my backends.xml

<?xml version="1.0" encoding="UTF-8"?>
<backends>
    <backend name="hitsSaver">
        <class>B1</class>
        <instances>4</instances>
        <!-- max-concurrent-requests>20</max-concurrent-requests -->
        <options>
            <dynamic>true</dynamic>
        </options>
    </backend>
</backends>

In Development Console I see only one instance but “/_ah/start” was called 4 times. Are they all handled in the same thread ?

Answer 1

The dev_appserver will not spawn multiple backend instances. With multithreading, though, you can have multiple concurrent requests, which should be sufficient.

Testing with mocks and throwing that exception yourself would be a better idea. Bear in mind that if you’re using datastore transactions, the transaction wrapper will catch that exception and retry.