From f81d1dd2ba44b25fab002811da05e1218ed4a04e Mon Sep 17 00:00:00 2001
From: pjht <pterpstra@pterpstra.com>
Date: Sun, 9 Jun 2024 18:44:12 -0500
Subject: [PATCH] Use a queue instaed of a stack to schedule processes

---
 src/tasking.rs | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/tasking.rs b/src/tasking.rs
index 572fa16..ef4f2b9 100644
--- a/src/tasking.rs
+++ b/src/tasking.rs
@@ -1,7 +1,7 @@
 use crate::{
     dbg, gdt, println, qemu_exit, virtual_memory::{ASpaceMutex, AddressSpace, PagingError, KERNEL_SPACE}
 };
-use alloc::{boxed::Box, vec::Vec};
+use alloc::{boxed::Box, collections::VecDeque, vec::Vec};
 use core::{arch::asm, ptr::addr_of};
 use crossbeam_queue::SegQueue;
 use slab::Slab;
@@ -98,7 +98,7 @@ unsafe impl Send for Process {}
 pub static TASKING: Lazy<Mutex<Tasking>> = Lazy::new(|| {
     Mutex::new(Tasking {
         processes: Slab::new(),
-        ready_to_run: Vec::new(),
+        ready_to_run: VecDeque::new(),
         current_process: None,
         freeable_kstacks: Vec::new(),
     })
@@ -107,7 +107,7 @@ pub static TASKING: Lazy<Mutex<Tasking>> = Lazy::new(|| {
 #[derive(Debug)]
 pub struct Tasking {
     processes: Slab<Process>,
-    ready_to_run: Vec<usize>,
+    ready_to_run: VecDeque<usize>,
     current_process: Option<usize>,
     freeable_kstacks: Vec<Box<[usize], &'static ASpaceMutex>>,
 }
@@ -136,7 +136,7 @@ impl Tasking {
             message_queue: SegQueue::new(),
             sleeping: None,
         });
-        self.ready_to_run.push(pid);
+        self.ready_to_run.push_back(pid);
         Ok(pid)
     }
 
@@ -146,7 +146,7 @@ impl Tasking {
             Some(x) => x,
             None => return,
         };
-        if let Some(next_process_pid) = self.ready_to_run.pop() {
+        if let Some(next_process_pid) = self.ready_to_run.pop_front() {
             let current_address_space = self.processes[next_process_pid]
                 .address_space
                 .take()
@@ -156,7 +156,7 @@ impl Tasking {
             let next_process = &self.processes[next_process_pid];
             gdt::set_tss_stack(next_process.kernel_esp_top);
             if self.processes[current_process].sleeping.is_none() {
-                self.ready_to_run.push(current_process);
+                self.ready_to_run.push_back(current_process);
             }
             let kernel_esp = next_process.kernel_esp;
             let previous_process = self.current_process.replace(next_process_pid).unwrap();
@@ -171,7 +171,7 @@ impl Tasking {
     }
 
     pub fn exit(&mut self) -> ! {
-        if let Some(next_process_pid) = self.ready_to_run.pop() {
+        if let Some(next_process_pid) = self.ready_to_run.pop_front() {
             if let Some(current_process) = self.current_process {
                 self.freeable_kstacks.push(self.processes.remove(current_process).kernel_stack);
             }
@@ -224,7 +224,7 @@ impl Tasking {
     pub fn wake(&mut self, pid: usize) {
         if self.processes[pid].sleeping.is_some() {
             self.processes[pid].sleeping = None;
-            self.ready_to_run.push(pid);
+            self.ready_to_run.push_back(pid);
         }
     }
 }