std/typedthreads

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Thread support for Nim. Threads allow multiple functions to execute concurrently.

In Nim, threads are a low-level construct and using a library like malebolgia, taskpools or weave is recommended.

When creating a thread, you can pass arguments to it. As Nim's garbage collector does not use atomic references, sharing ref and other variables managed by the garbage collector between threads is not supported. Use global variables to do so, or pointers.

Memory allocated using `sharedAlloc` can be used and shared between threads.

To communicate between threads, consider using channels

Examples

import std/locks

var
  thr: array[0..4, Thread[tuple[a,b: int]]]
  L: Lock

proc threadFunc(interval: tuple[a,b: int]) {.thread.} =
  for i in interval.a..interval.b:
    acquire(L) # lock stdout
    echo i
    release(L)

initLock(L)

for i in 0..high(thr):
  createThread(thr[i], threadFunc, (i*10, i*10+5))
joinThreads(thr)

deinitLock(L)

When using a memory management strategy that supports shared heaps like arc or boehm, you can pass pointer to threads and share memory between them, but the memory must outlive the thread. The default memory management strategy, orc, supports this. The example below is not valid for memory management strategies that use local heaps like refc!

import locks

var l: Lock

proc threadFunc(obj: ptr seq[int]) {.thread.} =
  withLock l:
    for i in 0..<100:
      obj[].add(obj[].len * obj[].len)

proc threadHandler() =
  var thr: array[0..4, Thread[ptr seq[int]]]
  var s = newSeq[int]()
  
  for i in 0..high(thr):
    createThread(thr[i], threadFunc, s.addr)
  joinThreads(thr)
  echo s

initLock(l)
threadHandler()
deinitLock(l)

Imports

threadtypes, ansi_c

Procs

proc createThread(t: var Thread[void]; tp: proc () {.thread, nimcall.}) {.
    ...raises: [ResourceExhaustedError], tags: [], forbids: [].}

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proc createThread[TArg](t: var Thread[TArg];
                        tp: proc (arg: TArg) {.thread, nimcall.}; param: TArg)

Creates a new thread t and starts its execution.

Entry point is the proc tp. param is passed to tp. TArg can be void if you don't need to pass any data to the thread.

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proc handle[TArg](t: Thread[TArg]): SysThread {.inline.}

Returns the thread handle of t. Source Edit

proc joinThread[TArg](t: Thread[TArg]) {.inline.}

Waits for the thread t to finish. Source Edit

proc joinThreads[TArg](t: varargs[Thread[TArg]])

Waits for every thread in t to finish. Source Edit

proc pinToCpu[Arg](t: var Thread[Arg]; cpu: Natural)

Pins a thread to a CPU.

In other words sets a thread's affinity. If you don't know what this means, you shouldn't use this proc.

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proc running[TArg](t: Thread[TArg]): bool {.inline.}

Returns true if t is running. Source Edit