# Module `posix.sched`

Kernel Thread Scheduling Priority.

Where supported by the underlying system, functions to discover and change the kernel thread scheduling priority. If the module loads successfully, but there is no kernel support, then `posix.sched.version` will be set, but the unsupported APIs will be `nil`.

## Functions

sched_getscheduler ([pid=0]) | get scheduling policy
sched_setscheduler ([pid=0[, policy=`SCHED_OTHER`[, priority=0]]]) | set scheduling policy/priority

## Constants

posix.sched | Scheduler constants.

## Functions

sched_getscheduler ([pid=0])
  get scheduling policy

  ### Parameters:

  - pid int process to act on, or `0` for caller process (default 0)

  ### Returns:

  int scheduling policy `SCHED_FIFO`, `SCHED_RR`, `SCHED_OTHER`, if successful

  ### Or

  1. nil
  2. string error message
  3. int errnum

  ### See also:

  sched_getscheduler(2)
sched_setscheduler ([pid=0[, policy=`SCHED_OTHER`[, priority=0]]])
  set scheduling policy/priority

  ### Parameters:

  - pid int process to act on, or `0` for caller process (default 0)
  - policy int one of `SCHED_FIFO`, `SCHED_RR` or `SCHED_OTHER` (default `SCHED_OTHER`)
  - priority int must be `0` for `SCHED_OTHER`, or else a positive number below 100 for real-time policies (default 0)

  ### Returns:

  int `0`, if successful

  ### Or

  1. nil
  2. string error message
  3. int errnum

  ### See also:

  sched_setscheduler(2)

## Constants

posix.sched
  Scheduler constants. Any constants not available in the underlying system will be `nil` valued.

  ### Fields:

  - SCHED_FIFO int first-in, first-out scheduling policy
  - SCHED_RR int round-robin scheduling policy
  - SCHED_OTHER int another scheduling policy

  ### Usage:

        -- Print scheduler constants supported on this host.
        for name, value in pairs (require "posix.sched") do
          if type (value) == "number" then
            print (name, value)
           end
        end

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