Parallelism

There are a number of ways of achieving parallelism in Nim.

You need to enable threads at compile time, as follows:

$ nim --threads:on c threads.nim

This is needed for all the different ways shown below.

Threads

proc sayHi(num: int) {.thread.} =
  echo "Hi from " & $num

var threads: array[10, Thread[int]]

for i in threads.low..threads.high:
  createThread(threads[i], sayHi, i)
joinThreads(threads)

It is recommended that functions used with threads be marked using the {.thread.} pragma.

Spawn using threadpool

Instead of using threads directly, you can use the higher level abstraction provided by std/threadpool.

import threadpool

proc sayHi(num: int) {.thread.} =
  echo "Hi from " & $num

for i in 0..9:
  spawn sayHi(i)
sync()

Note however, that spawn comes with a number of conditions documented here.

Other options

You can also do the following:

1. The experimental parallel statement.
2. Return data from spawn calls.

Details for both of these can be found in the experimental module’s manual page.