Event loop

Silex is running an event loop in a secondary thread. This event loop is used to run the websocket connection, and the multiple running actions.

Problems you might encounter

• Since the Silex actions and the websocket connection are running in the same event loop, if an action is holding the attention of the event loop for too long, the websocket connection might break. It's actually not a problem since socketio handles disconnection and reconnection automaticaly, but you will get a warning message in the silex UI. To prevent this, make sure to separate your action logic into multiple coroutines.

• Some instructions can take times and are not awaitable (like system calls). To prevent this, silex has the execute_in_thread function. Using execute_in_thread will run the execution in a different thread and return a future with the result.

Interaction with the DCCs

Most DCCs do not handle mutlithreading very well, plus none of them are usable with asyncio. To make all the DCCs function awaitable, we made the class ExecutionInThread a callable class so each DCC can customise it to work with its threading features. (see the Silex Plugins page for more infos)

For example, Maya provides the method executeDefered and executeInMainThreadWithResult wich both takes a callable as a parameter.

• executeDefered is not blocking, it's juste adding the callable to Maya's own event loop without returning the result.
• executeInMainThreadWithResult is blocking, the call will block the event loop until the function is executed and then return the result.

In our case, we don't want to to use executeInMainThreadWithResult, since it is blocking, if the command takes time there is no way for the event loop to do something else while waiting for the result, the websocket connection will break, and if other actions are running at the same time they will all be stuck 😔

That's why we use executeDefered. That way, the call is not blocking, but there is still a problem: how do we get the result ?

The ExecutionInThread class is actually wrapping executeDefered into a function that returns an asyncio future storing the result. The future can then be awaited so the event loop will keep running on other tasks until the result is ready.

info

If you implement a new DCC that does not support asyncio in its API (which is most likely to happen), you will have to reimplement this ExecutionInThread class for the threading API of that DCC. For more details, checkout the implementation done for maya