Why does switching Process is not working properly in this code?

[gamingjam60]

I want to strat process with schedular so I have written following code

Code: Select all

#define STACK_SIZE 16*1024 // 16 KB

process_t *process_list = NULL;
process_t *current_process = NULL;

uint64_t next_pid = 1;

void add_process(process_t *process) {
    process->next = process_list;
    process_list = process;
}


void context_switch(registers_t *old_state, registers_t *new_state) {
    if (old_state) {
        // Save the current process's state
        *old_state = current_process->registers;
    }

    // Switch to the next process
    current_process = current_process->next ? current_process->next : process_list;

    if (new_state) {
        // Restore the next process's state
        *new_state = current_process->registers;
    }
}


void schedule(registers_t *regs) {
    if (current_process != NULL) {
        current_process->registers = *regs;
        print("\nSaved state for PID: ");
        print_dec(current_process->pid);
        print("\n");
    }

    current_process = current_process->next ? current_process->next : process_list;

    if (current_process != NULL) {
        *regs = current_process->registers;
        print("Switched to PID: ");
        print_dec(current_process->pid);
        print("\n");
    }
}



process_t *create_process(void (*entry_point)(void)) {
    process_t *process = (process_t *)kheap_alloc(sizeof(process_t));
    process->pid = next_pid++;
    process->stack = (uint64_t *)kheap_alloc(STACK_SIZE);
    process->state = PROCESS_READY;
    process->next = NULL;

    // Initialize process registers
    memset(&process->registers, 0, sizeof(registers_t));
    process->registers.iret_rip = (uint64_t)entry_point;
    process->registers.iret_cs = 0x08; // Kernel code segment
    process->registers.iret_ss = 0x10; // Kernel stack segment
    process->registers.iret_rsp = (uint64_t)(process->stack + STACK_SIZE / 8);
    process->registers.iret_rflags = 0x202; // Interrupt flag enabled

    add_process(process);
    return process;
}

void terminate_process(process_t *process) {
    process_t *temp = process_list;
    process_t *prev = NULL;

    while (temp) {
        if (temp == process) {
            if (prev) {
                prev->next = temp->next;
            } else {
                process_list = temp->next;
            }

            kheap_free((void *)temp->stack, STACK_SIZE);
            kheap_free((void *)temp, sizeof(process_t));
            return;
        }

        prev = temp;
        temp = temp->next;
    }
   
}


void process_1() {
    while (1) {
        print("Process 1 is running\n");
        delay(1000);
    }
}

void process_2() {
    while (1) {
        print("Process 2 is running\n");
        delay(1000);
    }
}


void init_processes() {
    create_process(process_1);
    create_process(process_2);

    // Debug: Print the process list after initialization
    print_process_list();
    
    // Initialize current_process to the first process in the list
    current_process = process_list; // Set the first process as current
}



void print_process_list() {
    process_t *temp = process_list;
    while (temp) {
        print("Process ID: ");
        print_dec(temp->pid);
        print(" | State: ");
        print_dec(temp->state);
        print("\n");
        temp = temp->next;
    }
}

The schedular present in pit timer handler which fire in each one minute . the output is showing switching from pid one to two is correct but unfortunately "process 2 is running" not printing. I am expecting the below output

Code: Select all

Process ID 2 ! State 0
Process ID 1 ! State 0

Saved State for PID 2
Switch to PID 1
Process 1 is running

Saved State for PID 1
Switch to PID 2

Saved State for PID 2
Switch to PID 1
Process 1 is running

...

I am expecting the following output :

Code: Select all

Process ID 2 ! State 0
Process ID 1 ! State 0

Saved State for PID 2
Switch to PID 1
Process 1 is running

Saved State for PID 1
Switch to PID 2
Process 2 is running

Saved State for PID 2
Switch to PID 1
Process 1 is running

...

Can you tell me what is the problem in here?


Is the switching context not saving the registers in stack or anything else?

Full code link https://github.com/baponkar/KeblaOS

[Octocontrabass]

Relying on interrupts for context switching is usually a bad idea. Before you spend more time debugging this code, you should consider replacing it with something else. For example, like this.