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2021-07-09

bad practice: busy-waiting

Busy-waiting is one of the easiest ways of exhausting a cpu¹:

package main

func main() {
  for true {
    /* complex logic */
  }
}

What looks like an obvious bad construct one would never do by accident is often introduced on waiting for a resource or state change. One common place where such constructs are used is on reconnecting to a service.

Analyze

Use top:

PID     USER       PR   NI VIRT      RES    SHR S %CPU    %MEM  TIME+   COMMAND
1237306 evilcookie 20   0  702424    936    644 R 100.3   0.0   0:59.39 busywaiting      

The process has a load of one or higher.

Solutions

A general solution for busy-waiting is telling the CPU to do something else for some time using the syscall sleep²:

package main

import "time"

func main() {
  for true {
    /* complex logic */
    time.Sleep(1 * time.Millisecond)
  }
}

Sleeping one millisecond is enough to make the process barely obervable:

PID     USER      PR   NI VIRT      RES    SHR S %CPU  %MEM  TIME+   COMMAND
1242442 rpour     20   0  702476   1340    840 S 8.6   0.0   0:01.05 busywaiting