Task Scheduler

Documentation of the Halyde kernel's task scheduler.

Under the hood

Halyde supports multitasking by using coroutines, a feature included in Lua 5.0 and later. Coroutines work differently than threads: when a coroutine gets ran, the code that runs the coroutine gets paused, and the coroutine will run until it runs coroutine.yield(), which will resume the main code afterwards

The task scheduler (/halyde/kernel/tsched.lua) uses these coroutines to simulate multitasking, by storing the coroutines onto a table, and running them one-by-one everytime. This means that the process code will continue executing until it runs coroutine.yield().

OpenComputers (specifically machine.lua) imposes that every coroutine must run coroutine.yield() with an interval of 10 or less seconds, otherwise it will yield the error too long without yielding. This applies to all processes (from the kernel, from an user-installed driver, the shell, or an app).

Public space API

This is for interacting with the task scheduler, for getting, creating, and killing tasks. If the code is a kernel module, the task scheduler is available in _PUBLIC.tsched, otherwise in tsched.

• tsched.addTask(func: function, name: string) Creates a task from a function. This function will run with the environment that it has been created in: these tasks created by the kernel will run in the kernel environment, but tasks created by the shell or an app will run with their user environment.

• tsched.runAsTask(path: string, ...) Creates a task from an executable file in a certain path, with arguments to pass through. The environment of all processes created through this function is confined in their own copy of the public space (stored as _PUBLIC in the kernel). If any process adds anything to its environment, it will not be visible to other processes unless it allows communication through IPC.

• tsched.removeTask(id: number): boolean Removes a task based from a process ID. Returns true if successful, otherwise false.

• tsched.getCurrentTask(): table Returns the current task that is being ran. If this is called from a process, returns table of said process. The table that gets returned contains task, name, and id for the Lua coroutine, process name, and process id respectively.

• tsched.getTasks(): table Returns all the tasks in a list, where every task is in the same format as the table returned by tsched.getCurrentTask.