Mirror of forum.nim-lang.org

3561 :: asyncdispatch.poll() eats cpu

• valex (orginal) [2018-02-19T18:50:16+01:00] view original

  Is this bug fixed yet? https://github.com/nim-lang/Nim/issues/6929 In windows 10 cpu load 50%. How do I use asyncdispatch now? Nim 0.17.2

---

• dom96 (orginal) [2018-02-19T20:19:19+01:00] view original

  It hasn't been fixed yet.

  But that's a pretty extreme case I think? Are you having problems in your application because of it?

---

• valex (orginal) [2018-02-19T23:38:44+01:00] view original

  Thank you, dom96. This is my simple code:

  
  import asyncdispatch, threadpool
  
  var started = false
  
  proc process() {.async.} =
    if started: return
    started = true
    echo "start process"
    while started:
      echo "..."
      await sleepAsync(5000)
    echo "stop process"
  
  proc main() {.async.} =
    var msg = spawn stdin.readLine()
    while true:
      if msg.isReady():
        case ^msg:
        of "stop": started = false
        of "start": asyncCheck process()
        of "bye":
          if started: echo"enter stop before" else: return
        else: echo"invalid command"
        msg = spawn stdin.readLine()
      await sleepAsync(500)
  
  
  waitFor main()
  Run

  After a few seconds cpu load ~50%. What am I doing wrong?

---

• dom96 (orginal) [2018-02-20T11:25:36+01:00] view original

  You're not performing any async IO. As soon as you do this won't be a problem. If you aren't intending to perform async IO then you don't need async.

---

• valex (orginal) [2018-02-20T12:27:31+01:00] view original

  
  import asyncdispatch, threadpool
  
  var started = false
  
  proc process() {.async.} =
    if started: return
    started = true
    echo "start process"
    while started:
      var client = newAsyncHttpClient()
      var resp = await client.getContent("http://google.com")
      echo $len(resp)
      #doSomething
      client.close
      await sleepAsync(5000)
    echo "stop process"
  
  proc main() {.async.} =
    var msg = spawn stdin.readLine()
    while true:
      if msg.isReady():
        case ^msg:
        of "stop": started = false
        of "start": asyncCheck process()
        of "bye":
          if started: echo"enter stop before" else: return
        else: echo"invalid command"
        msg = spawn stdin.readLine()
      await sleepAsync(500)
  
  
  waitFor main()
  Run

  This code has async IO. The result is the same cpu load 50%.

---

• dom96 (orginal) [2018-02-20T15:40:57+01:00] view original

  Hrm, try this as a workaround:

  import asyncdispatch, threadpool, os
  
  var started = false
  
  proc process() {.async.} =
    if started: return
    started = true
    echo "start process"
    while started:
      var client = newAsyncHttpClient()
      var resp = await client.getContent("http://google.com")
      echo $len(resp)
      #doSomething
      client.close
      await sleepAsync(5000)
    echo "stop process"
  
  proc main() =
    var msg = spawn stdin.readLine()
    while true:
      if msg.isReady():
        case ^msg:
        of "stop": started = false
        of "start": asyncCheck process()
        of "bye":
          if started: echo"enter stop before" else: return
        else: echo"invalid command"
        msg = spawn stdin.readLine()
      if hasPendingOperations():
        poll(500)
      else:
        sleep(500)
  
  main()
  Run

---

• valex (orginal) [2018-02-20T18:21:45+01:00] view original

  
  --
      if hasPendingOperations():
        poll(500)
      else:
        sleep(500)
  --
  Run

  This works in part. When I enter start, the load is again 50%. When I enter stop, the load is ok.

  I rewritten in my file the waitFor procedure:

  
  proc waitFor*[T](fut: Future[T]; ms: int = 50): T =
    while not fut.finished:
      poll()
      sleep ms
    
    fut.read
  Run

  It works for me.

---