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Concurrency From the Ground Up

Greg Heo - @gregheo - from Swift Unboxed

Why?

  • Because we want:
    1. Programs that seem faster to the user.
    2. Programs that are easy to understand for the programmer.

How?

  1. Structuring our programs better
  2. Thinking in terms of tasks
  3. Protecting resources

Concurrency and Structure

  • Concurrency vs Parallelism
    • "Concurrency is the composition of independently executing processes." (- Rob Pike)
    • "Parallelism is the simultaneous execution of computations."
    • "Concurrency is about ** dealing ** with lots of things at once. Parallelism is about ** doing ** lots of things at once."
  • Order? Shared state? Mutable state?

Tasks and Threads

We use threads to model our tasks.

var tProcessData: pthread_t?
pthread_create(&tProcessData, nil, processData, nil)
pthread_join(tProcessData!, nil) //This will block until the work is complete.
  • The concept is:
    1. Create a thread
    2. Run some code
    3. Wait for it to complete

Locks and Resources

We use locks to model our access to resources.

  • Locks are all about protecting access to code.
  • let lock = NSLock()
    • A lock is is like the conch shell that somebody has to be holding to talk. It's a token that means only one thing can access a property at at time.

There are two different uses for locks:

  • Locks as signals (wait until A is done to start B)
  • Locks as mutual exclusion (protect access to shared state from multiple threads)

// Sorry, I got really behind the presenter at this point. Notes end here.