A question about multi-threading and thread safety

[kostya-sh]

This is not a bug report, just a question that I hope you can answer.

Comparing different versions of the applications I can see the following aproaches to avoid data races:

Go

• Uses a mutex and looks correct

  Node.js

• Doesn't do anything but node.js is single threaded by design

  Reason

• Doesn't do anything but Ocaml is single threaded as far as I know

  Haskell

• Uses MVar for counter however doesn't increment it atomically (https://github.com/spion/hashtable-latencies/blob/master/haskell/app/Main.hs#L32). Could this be a problem?
• Uses Data.HashTable.IO.BasicHashTable without synchronization. Is it thread safe?

  swift-zewo

• No synchronization. Is it single threaded?

Thank you.

[spion]

Swift is single-threaded yes. The language is multi-threaded but the Zewo runtime is based on libmill which is single-threaded.

Haskell is "safe-enough" that it doesn't crash.

MVar is a single-value channel which blocks on the next takeMVar until there is a new value in the channel (putMVar), so the increment is safe. Not sure about BasicHashTable, the mutation should probably be within the MVar lock.

edit: fixed, the hashtable mutation is now done within the lock.

[kostya-sh]

Thank you for the reply