Threads and Processes (Lightning Talk Given at Rails Israel 2015)

Many of us use threads and/or processes in our code, whether explicitly or implicitly. But do we really understand what threads and processes are? Can we clearly evaluate the pros and cons of each? We will attempt to clarify these concepts in a simple, concise fashion.

Transcript

1. Threads and Processes Ariel Caplan
2. Concurrency <= Parallelism
3. Threads && Processes Both provide concurrent execution of code! Neither guarantee execution order! Both add overhead to your code!
4. Threads vs. Processes Process Process Memory Memory Thread Thread Memory
5. Threads vs. Processes @var @var @var = 1 @var = 1 @var @var @var = 1
6. Threads vs. Processes @var @var @var = 1 @var = 1 @var @var @var = 2
7. Threads vs. Processes @var @var @var = 1 @var @var @var = 2 @var = 2
8. Threads vs. Processes @var @var @var = 1 @var @var @var = 2 @var = 2 WARNING:
 OVERSIMPLIFICATION
9. Threads vs. Processes Threads share memory and state! Processes share nothing
10. Threads vs. Processes in MRI Threads share memory and state! Processes share nothing! Threads are concurrent, not parallel, due to the GIL 
 (Global Interpreter Lock)! Processes operate in true parallel
11. Parallelism Concurrency Processes Multi-Core System Single-Core System Threads JRuby, Rubinius, Nonblocking IO Standard Calculations in MRI The Bottom Line
12. Implication: Sidekiq Concurrency For a server running only Sidekiq on MRI:! 1 Sidekiq process per core! Concurrency (number of threads) = 1 / CPU Time! Example: 8-core machine with 75% IO, 25% CPU:! 8 Sidekiq processes! Sidekiq concurrency of 1/(25%) = 4
13. Thank You For Listening! amcaplan.ninja! @amcaplan! ↑! Questions