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Cooperative Multitasking

Lua coroutines can be used as concurrent tasks. After creating a coroutine task with async_task, the task will not execute immediately. It only starts running when passed to wait_all or wait_any.

Create Coroutine Task 3.0

Creates a coroutine task. The task will not execute until wait_all or wait_any is called.

  • Function: async_task from the lua module
  • Parameters:
    1. fun: [function] The function to run
    2. args: [any] Arguments passed to function fun, optional
  • Returns: [thread] Coroutine task

Compatibility Note

Equivalent to:

task = coroutine.create(function() return fun(args) end)

Example

task = async_task(function(a, b)
  print(a + b)
end, 1, 2)

Wait for All Tasks 3.0

Waits for all coroutine tasks to complete and returns each task's return value. If any task throws an error, the error is propagated upward.

  • Function: wait_all from the lua module
  • Parameters:
    1. tasks: [thread] Coroutine tasks, multiple can be passed
  • Returns: [any] Return values of each coroutine task, in the order they were passed

Example

function motion(param)
  print(param, 'start running')
  movej({j1=0, j2=0, j3=0, j4=0, j5=0, j6=0}, 0, 0, 1, 0)
  sync() -- Wait for motion to complete
  return "motion complete"
end

function gripper()
  wait(1000)
  set_claw(0, 100)
  return "gripper complete"
end

ret1, ret2 = wait_all(async_task(motion, 'thread 1'), async_task(gripper))
print("motion task return value: ", ret1)
print("gripper task return value: ", ret2)

Wait for Any Task 3.0

Waits for any one coroutine task to complete, returning the first completed task's return value and its index in the parameter list.

  • Function: wait_any from the lua module
  • Parameters:
    1. tasks: [thread] Coroutine tasks, multiple can be passed
  • Returns: ret, index. ret is the return value of the completed task, or nil if no tasks exist; index is the position of the completed task in the parameter list (starting from 1), or -1 if no tasks exist

Example

local task_timeout = async_task(wait, 1000) -- Create a timeout task
ret, index = wait_any(async_task(motion, 'thread 2'), task_timeout)
if index == 2 then -- task_timeout completed first
  print("timeout")
else -- motion completed first
  print("motion task return value: ", ret)
end

Query Coroutine Task Status 3.0

Advances coroutine task execution and returns the task status.

  • Function: async_result from the lua module
  • Parameters:
    1. task: [thread] Coroutine task
  • Returns: status, result. status is the task status: "running": running; "finish": completed, result is the task's return value; "dead": task terminated due to error

Example

task = async_task(function() return "ok" end)
wait_all(task)
status, result = async_result(task)
print(status, result) -- finish ok