[v3] [ios] transaction

[FrankSalad]

@auser I hope this is similar to what you might've done for #78. It's a little bit brittle - it can leak if the beginTransaction call isn't followed up with a tryCommitTransaction. If you had a different implementation strategy in mind I'd like to know 🤸‍♂️

[Ehesp]

cc @Salakar @chrisbianca

[FrankSalad]

Looking at the concurrency again, I don't understand why the 'dispatch_barrier_async' within the 'dispatch_async' call doesn't deadlock every time. Does GCD run the barrier block when it notices the outer block running 'dispatch_semaphore_wait'?

All the docs say barrier blocks do not execute while other blocks on the same queue are executing. Does waiting on a semaphore not count as executing on the queue?

I'm still kind of green when it comes to native code. @auser I'll add info in the docs asap. Thanks.

[auser]

@FrankSalad lmk when you add to the docs. As far as the dispatch async, it does 'queue' it AFAIK, so I think that should work just fine

[FrankSalad]

@auser I was trying to follow https://mikeash.com/pyblog/friday-qa-2011-10-14-whats-new-in-gcd.html

[Salakar]

@FrankSalad nice work, can we get this in on android also if anyone has time to do it?

cc @Ehesp @chrisbianca