When we doing taskSpawn a task is creating in vxworks. What is actually a task. Is there any relation with thread.
In my understanding vxworks is thread based Operating system.
Can some one please help me the real difference between task/thread/process in real scenario.
Somewhere I saw task is the execution of set of instruction. If it is like that then thread also have some set of instruction so can we call thread as task.
Please help
Thread is a concept typically used with an OS supporting process models (Unix/Linux/Windows) where you run a process.
This process could have a single thread of execution (like a simple C program). Or you could create multiple threads to perform certain operations in parallel within the current process memory space.
With older vxWorks, there was no process model. Everything would run in the same memory space. A vxWorks tasks provides the context where the system code would execute. All code (with the exception of interrupt handlers) will execute in the context of a Task.
Tasks are independent execution units. They can share resources, have common memory, etc... but the scheduler executes the tasks based on very specific criteria. Typically, the highest priority task in the system is the task that will be executing at any given time.
Once a task is done/sleeps/blocked waiting for resources, then the next highest priority task in the system will run.
For your purpose, you can probably think of the task as a thread.
A task is abstract concept in OS design. A task is a single context of execution. A task has a memory space it operates in where its data and code is stored. This memory space may or may not be shared with other tasks. A task has a state (e.g. running, stopped, killed...), it (usually) has a stack. A task has a priority over other tasks.
On example of such a task, is a VxWorks task. Another is a Linux thread.
In Linux (and I believe also in latest version of VxWorks btw), there exists a concept of a related group of tasks. Tasks belonging to the same group share memory space and several other resources (e.g. file handlers). A Linux process is such a group of tasks.
By an large, the OS scheduler schedules tasks and not processes. The process is a convective abstraction for the programmer to think about group of related threads together.
I hope that helped.
In vxWorks, tasks is a runnable unit.
Task have TCB (Task Control Block) with a unique task space and specific priority (as you defined in the taskSpawn function).
The vxWorks scheduler can run only task, this is the minimum runnable unit (the scheduler can run the kernel itself and interrupt can run in the system).
The decision which task to run will base on the task state (must be in READY), and the task priority (in vxWorks, the highest priority is the lower number).
Note that several tasks might be in the same priority and then the kernel will run different tasks according the scheme you configured (FIFO or round robin).
In vxWorks, all tasks have the same memory space (including Kernel memory space). This is the reason that WindRiver added the "Process like" mechanism from vxWorks 6.x. Process have its own "virtual memory space" that protected by MMU.
Just to summery it for you:
Tasks have the same memory space over the system.
Threads have the same memory space within their process.
Process memory space protected by MMU.
task and threads are similar to process. but the difference is threads dont have seperate memory space for their own they run under the pcb(stack) of the process itself.but whereas,task has its own stack area and is a light weighted process i.e.,tcb is much smaller when compared to pcb so context switching or task switching can happen faster . since vxworks deals with rtos and switching latency should be very less ,it deals with tasks.
In addition to the existing anwers: If you ever need to create POSIX threads on your VxWorks system (which is possible by including POSIX in the kernel config and calling pthread_create() ), you will notice that those threads will appear as tasks in you task list (type 'i' in C shell).
Hence, tasks and threads are very much alike. VxWorks even wraps POSIX threads as tasks so they can be handled in parallel to existing native tasks.
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