Commits on Sep 3, 2023

1. feat(kernel): wake tasks on service registration …

   Depends on #267
   
   Currently, the `Registry::connect_*` methods return an error immediately
   if the requested service is not found in the registry. Most client types
   implement a `from_registry` method which retry in a loop when the
   requested service is not found in the registry. These methods will wait
   for a fixed (short) amount of time and then try again until the registry
   returns the service.
   
   This approach is quite inefficient, as we have to run a bunch of retry
   loops that keep trying to access a service that may not be there. This
   may happen several times before the service actually is registered,
   especially when registering a service requires connecting to another
   service.
   
   This branch improves the efficiency of waiting for a service to be
   registered. Now, rather than retrying with a fixed-duration sleep, we
   instead have the `Registry` own a `WaitCell` which is woken whenever a
   new service is registered. This wakes all takes potentially waiting to
   connect, allowing them to re-check whether the service they want is in
   the registry. This idea was initially proposed by @jamesmunns in a
   [comment] on PR #259
   
   Connections are now established using either `Registry::connect`, which
   retries whenever a new service is registered, or `Registry::try_connect`
   which never retries.
   
   Additionally, we now have the capacity to indicate that a service is not
   found *and* that the registry is full, by closing the `WaitCell`. In
   this case, retrying will never succeed, because the registry is full and
   if the service isn't already there, it will never be added. In this
   case, the retrying methods will also return an error, rather than never
   completing, so we avoid a potential task leak.
   
   In order to make this change, we need to move the `RwLock` from being
   around the entire `Registry` to being inside the registry, around
   `items`. This allows the `WaitCell` to be accessed regardless. It also
   allows us to shorten the duration for which the lock is held. This
   requires changing all methods on `Registry` to take `&self`.
   Therefore, I've removed the wrapper methods on `Kernel` for connecting
   and registering, since they can now just be called on `kernel.registry`
   without a bunch of extra boilerplate for lock management. I've also
   simplified the API surface of the registry a bit by removing the
   `connect` methods that don't take a `Hello`, and just using
   `Registry::connect(())` in those cases. IMO, those methods weren't
   really pulling their weight, and they required us to have a method named
   `Registry::try_connect_userspace_with_hello` if we were going to add a
   non-retrying `connect` variant. Now, we can just have
   `Registry::try_connect_userspace`, `Registry::connect_userspace`,
   `Registry::connect`, and `Registry::try_connect`, which feels much less
   egregious.
   
   [comment]: #258 (comment)

   

   hawkw committed Sep 3, 2023
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2. fix bad eq impl

   

   hawkw committed Sep 3, 2023
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