From db684b8653d93f4a374d8d692bb0afb31db67987 Mon Sep 17 00:00:00 2001
From: Danny Holman <dholman@gymli.org>
Date: Thu, 28 Mar 2024 22:00:16 -0500
Subject: kernel: add a basic thread scheduler

Add a basic thread scheduler. This should allow the kernel to schedule
threads according to the round robin algorithm.

Signed-off-by: Danny Holman <dholman@gymli.org>
---
 kernel/sched.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 kernel/sched.c

(limited to 'kernel')

diff --git a/kernel/sched.c b/kernel/sched.c
new file mode 100644
index 0000000..8aab675
--- /dev/null
+++ b/kernel/sched.c
@@ -0,0 +1,64 @@
+#include <kernel/sched.h>
+#include <kernel/container_of.h>
+#include <kernel/data/list.h>
+#include <kernel/string.h>
+#include <kernel/kmalloc.h>
+#include <stddef.h>
+
+static struct list_head *ready_queue;
+static struct list_head *wait_queue;
+
+static struct task_block *cur = NULL;
+static long int next_id = 1;
+
+static void _enqueue(struct list_head *queue, struct task_block *task) {
+        struct list_head *temp = queue;
+        while (temp->next != NULL)
+                temp = temp->next;
+        list_add(&task->list, temp);
+}
+
+static struct task_block* _dequeue(struct list_head *queue) {
+        if (queue->next == NULL)
+                return NULL;
+        struct list_head *temp = queue->next;
+        list_del(temp);
+        struct task_block *ret = container_of(temp, struct task_block, list);
+        return ret;
+}
+
+void sched_init(void) {
+        ready_queue = kmalloc(sizeof(struct list_head));
+        wait_queue = kmalloc(sizeof(struct list_head));
+        struct task_block *boot_task = init_task(0, 0);
+        boot_task->threads->state = THREAD_RUNNING;
+        cur = boot_task;
+
+        switch_thread(boot_task->threads, boot_task->threads);
+}
+
+void schedule_next(void) {
+        struct task_block *task = _dequeue(ready_queue);
+        if (task == NULL)
+                return;
+        if (cur != NULL)
+                _enqueue(ready_queue, cur);
+        disable_ints();
+        switch_thread(cur->threads, task->threads);
+        enable_ints();
+        task->threads->state = THREAD_RUNNING;
+        cur->threads->state = THREAD_READY;
+        cur = task;
+}
+
+struct task_block* init_task(int nice, unsigned int ppid) {
+        struct task_block *ret = kmalloc(sizeof(struct task_block));
+        ret->pid = next_id++;
+        ret->parent_pid = ppid;
+        ret->nice = nice;
+        ret->num_threads = 1;
+        ret->threads = kmalloc(sizeof(struct thread_block));
+        ret->threads->tid = ret->pid;
+        ret->threads->tgid = ret->pid;
+        return ret;
+}
-- 
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