[BUG] zing-server is not yet able to send WebSocket notifications

[hmeine]

I have started implementing a WebSocket handler, but I have problems with async Rust, and it is not yet able to send notifications.

• async send() does not work while holding the state mutex,
• the sync mpsc::channel()'s Receiver is not Sync and therefore causes problems with tokio::spawn(), and
• blocking_send() causes thread 'tokio-runtime-worker' panicked at 'Cannot block the current thread from within a runtime. This happens because a function attempted to block the current thread while the thread is being used to drive asynchronous tasks.'

[hmeine]

I am trying to get my head back into this fundamental problem and how I tried to approach it. If I remember correctly, the idea was the following:

• The main source of problems is that I was holding a mutex over an .await point.
• The reason I was holding the mutex is that I have been unwrapping the state in main.rs, and then called functions on the mutable state. This was fine as long as all methods were very small and did not have .await points. However, now that we want to do networking inside, I must not hold the mutex which is currently the basis for &mut self.
• Hence, my conclusion was that I must get rid of &mut self in ZingState and instead take the state wrapped in the mutex (or RwLock, as I learned in the meantime). In particular, this allows me to drop the lock before .await'ing.
• I may have to rinse and repeat with the Table struct which is used in ZingState.