VxWorks Multi-tasking function

Http://blog.chinaunix.net/uid-23741326-id-84935.html

VxWorks's task has the priority concept, its task scheduling is also based on the priority consideration, is preemptive, VxWorks's task has 256 levels, 0-255, the smaller the number indicates the higher priority. A high-priority task can break down a low-priority task and be preempted, and a low-priority task can be executed only after a high-priority task has finished executing. There are two kinds of scheduling algorithms: Full preemption and cyclic distribution. The full preemption is that, in addition to the high-priority tasks that can break down the low-priority tasks, they cannot be interrupted between tasks of the same priority, and do not execute concurrently with the priority task, but only after the task has finished executing the tasks with the same priority can be executed; Tasks of the same priority can be performed concurrently, that is, the system time slices are evenly distributed among them, so that tasks of the same priority can be executed concurrently. You can call the kerneltimeslice() function to set the scheduling method, and the parameter is the time slice that the same priority task executes.

The tasks in VxWorks have many states, as shown in the following table:

State	Describe
Ready	This task status is pending execution
PEND	This task status is blocked because some resources are unavailable
DELAY	This task status is dormant for some time
SUSPEND	This task status is pending
Break	This task state is stopped (paused), usually a breakpoint is set in the task.
A combination of various states	See the original documentation for details

To prevent the task from being mistakenly deleted, VxWorks also provides the Tasksafe () function and the taskunsafe () function, the task of calling Tasksafe () cannot be deleted, and the application is invoked elsewhere The taskdelete () function will have an error. The task can only be deleted after the task has been called Taskunsafe () . In addition, VxWorks can change the priority of a task dynamically, that is, you can call the taskpriorityset () function to modify the priority of a task during execution. For task creation, VxWorks also provides a different way for the user to call the taskspawn () function to execute it immediately after the task is created, or to call taskcreate () and taskactivate () The function divides the creation task and the execution task into two steps, that is, after calling Taskcreate () , the task is simply created and not executed, so the user can call taskactivate () when needed. To restore the execution of the task. The following is a list of VxWorks task-related functions:

Name of function	Function
Kerneltimeslice ( )	Controlling the polling scheduler
Tasklock ( )	Canceling a task rescheduling
Taskunlock ( )	Allow tasks to be re-dispatched
Taskspawn ( )	Build (Create and activate) a new task
taskcreate ( )	Creates a new task, but does not activate it.
taskactivate ( )	Activating a task that has already been created
Tasksuspend ( )	Suspend a task
Taskresume ( )	Resuming execution of a pending task
Taskrestart ( )	Restart execution of a task (i.e. from the beginning)
Taskdelay ( )	Delay task, delay unit is time slice
taskidself ( )	Gets the ID of the calling task (running)
taskidverify ( )	Verifies whether a specified task exists
Taskoptionsget ( )	Get user custom Task parameters
Taskoptionsset ( )	Set user custom task parameters
Taskidlistget ( )	Fills the task ID of all active states into a number group
Taskinfoget ( )	Get information on a task
Taskpriorityget ( )	Get the priority of a task
Taskpriorityset ( )	Change task priority
Taskregsset ( )	Set a register for a task (but cannot be used by the current task)
taskissuspended ( )	Check if a task is in the suspended state (suspended.)
Taskisready ( )	Check if a task is ready to run
Exit ( )	End running task, freeing memory *
Taskdelete ( )	End the task you set up and free up memory *
Tasksafe ()	Protect current tasks against deletion
Taskunsafe ( )	Cancels the tasksafe() operation, that is, the ability to delete the current task
Nanosleep ( )	Delay task, delay unit is time slice

Time slices

For a task, only the cyclic assignment under the same priority task has the concept of a time slice: The time slice is the time the system assigns to each task, and if a task is not completed during that time, the CPU is stripped and assigned to another task.

VxWorks Multi-tasking function