Add cooperative multitasking support

Author: thomasarmel

src/dos/cooperative_multitasking/mod.rs

@@ -15,22 +15,25 @@ pub struct Tasking{
     current_task_id: u8,
     eflags_register: u32,
     cr3_register: u32,
+    initialized: bool,
 }
 
 impl Tasking {
     const MAX_TASKS: usize = 10;
 
-    pub fn init() -> Self {
+    pub fn init(&mut self) {
+        if self.task_list.is_some() {
+            self.task_list = None;
+        }
         let (eflags, cr3) = Self::get_eflags_and_cr3_registers();
 
         // Create main task
-        let mut tasking: Self = Tasking {
-            task_list: Some(VecDeque::new()),
-            current_task_id: 0,
-            eflags_register: eflags,
-            cr3_register: cr3,
-        };
-        tasking.task_list.as_mut().unwrap().push_back(Task {
+        self.task_list = Some(VecDeque::with_capacity(Self::MAX_TASKS));
+        self.current_task_id = 0;
+        self.eflags_register = eflags;
+        self.cr3_register = cr3;
+        self.initialized = true;
+        self.task_list.as_mut().unwrap().push_back(Task {
             registers: Registers {
                 eax: 0,
                 ebx: 0,
@@ -45,10 +48,12 @@ impl Tasking {
                 cr3,
             },
         });
-        tasking
     }
 
     pub fn add_task(&mut self, main_function: *mut fn()) -> Result<(), &'static str> {
+        if !self.initialized {
+            return Err("Cooperative tasking manager is not initialized");
+        }
         if self.task_list.as_ref().unwrap().len() >= Self::MAX_TASKS {
             return Err("Maximum number of tasks reached");
         }
@@ -58,6 +63,10 @@ impl Tasking {
     }
 
     pub fn yield_task(&mut self) {
+        if !self.initialized {
+            panic!("Cooperative tasking manager is not initialized");
+        }
+
         let task_list = self.task_list.as_mut().unwrap();
 
         let current_task_registers_ptr = &mut task_list[self.current_task_id as usize].registers as *mut Registers;
@@ -92,6 +101,7 @@ pub static mut TASKING: Tasking = Tasking {
     current_task_id: 0,
     eflags_register: 0,
     cr3_register: 0,
+    initialized: false,
 };
 
 #[macro_export]

src/lib.rs

@@ -8,14 +8,14 @@ extern crate rlibc;
 extern crate alloc;
 
 use crate::dos::allocator::GLOBAL_ALLOCATOR;
-use crate::dos::cooperative_multitasking::{Tasking, TASKING};
+use crate::dos::cooperative_multitasking::TASKING;
 
 #[link_section = ".startup"]
 #[no_mangle]
 fn _start() -> ! {
     unsafe {
         GLOBAL_ALLOCATOR.init();
-        TASKING = Tasking::init();
+        TASKING.init(); // Relies on the allocator
     }
     extern "Rust" {
         fn main() -> ();