This adds a new async operation in the message send flow. MessageSender
will now verify that the intended recipients of a message all have UUIDs
before proceeding. If any recipients are missing a UUID, it'll kick off
a CDS lookup for the invalid recipients.
While this code appears to work, this is a first pass. Looking to get
some inital feedback in a pull request. It's unclear to me whether or
not this pattern fits in with the existing error propogation flow in
MessagSender promises. It's also unclear whether or not the error I'm
using is correct.
Some other changes that come along for the ride:
- Add a -perform() method to ContactDiscoveryService to automatically
submit itself and its dependencies to its static operation queue
This commit adds two new synchronization utilities:
- Unfair locks: This adds an Objective-C wrapper around os_unfair_lock
to help bridge it to Swift. (Swift's handling of the underlying C
struct can lead to surprising TSan failures). This will be useful as a
simple, performant lock in cases where fairness is not a concern.
- Shared serial queues: Private serial queues that are untargeted will
target the global concurrent queues. Sometimes this is what we want,
especially for potentially long-running work items. But for cases
where work items are brief private serial queues risk spinning up a
new thread.
For private queues where the individual work items are brief and there
isn't a more appropriate queue to target, the shared serial queues
are a potential candidate.
This change also introduces tests for these new utilities and some QoS
management helper methods.
