Good news everyone!
We just wanted to give you a quick update on PDB debugging support in the new dev_appserver. One of the key design goals of the new dev_appserver was to provide a more faithful emulation of how your application performs in production - including servicing each incoming request in a separate thread or process. This not only makes your local development faster, but also means issues (such as race conditions) that may arise from concurrent requests executing in parallel can be more easily identified and corrected. However a development environment with multiple concurrent threads and processes can present a challenge when using a command line debugger such as PDB. We’ve been working on reconciling our design goal of a dev_appserver that supports production-like concurrency while still allowing developers to use tools like PDB to introspect and debug their code in a sensible, serialised way. We’ve made some progress on this front recently, and wanted to share it with you. The latest release 1.8.3 of the Python SDK supports PDB. That is you can add a line such as: import pdb; pdb.set_trace(); into your code, and dev_appserver2 will break at this point, and drop into the PDB REPL, allowing you to debug your code from the command line. However, a note of caution - if you make multiple simultaneous requests that invoke pdb.set_trace(), then two debugging sessions will start concurrently and both will send output to STDOUT. This can lead to unpredictable debugging experiences. To help prevent this, you can also disable some of the dev_appserver’s multi-threading and multi-processing support. - Multi-threading can be disabled by modifying your app.yaml and setting thread_safe to false. - For a given module, you can disable multi-processing using the --max_module_instances=1 flag. Using these techniques you can serialize your requests. Note that, if you are using App Engine modules in your application, the dev_appserver will still serve multiple requests simultaneously for different modules. We hope you enjoy this early support for pdb in dev_appserver2. Please let us know what you think. -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe from this group and stop receiving emails from it, send an email to google-appengine+unsubscr...@googlegroups.com. To post to this group, send email to google-appengine@googlegroups.com. Visit this group at http://groups.google.com/group/google-appengine. For more options, visit https://groups.google.com/groups/opt_out.
