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frabert wrote:@Brendan I'm not sure if this should be addressed here or in the wiki's discussion page, I'll move the post if necessary.
The current issue I'm facing while following your tutorial is this: let's suppose I have a task A, which blocks because it needs to wait for B to finish.

Looking at the code for block_task and unblock_task:

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void block_task(int reason) {
    lock_scheduler();
    current_task_TCB->state = reason;
    schedule();
    unlock_scheduler();
}

void unblock_task(thread_control_block * task) {
    lock_scheduler();
    if(first_ready_to_run_task == NULL) {
        // Only one task was running before, so pre-empt
        switch_to_task(task);
    } else {
        // There's at least one task on the "ready to run" queue already, so don't pre-empt
        last_ready_to_run_task->next = task;
        last_ready_to_run_task = task;
    }
    unlock_scheduler();
}

this happens:

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// A is running, sched_lock_cnt=0:
lock_scheduler(); // sched_lock=1, interrupts disabled
schedule(); // Now B is running
// Something something...
// B ends, unblocks A
lock_scheduler(); // sched_lock_cnt=2
switch_tasks(); // Now A is running
unlock_scheduler(); // sched_lock_cnt=1
// A continues its way, never to be interrupted again...

// A is running, sched_lock_cnt=0:
lock_scheduler(); // sched_lock=1, interrupts disabled
schedule(); // Now B is running
unlock_scheduler(); // B unlocks the scheduler, sched_lock_cnt=0

// Something something...

lock_scheduler(); // B locks the scheduler, sched_lock_cnt=1
switch_tasks(); // Now A is running
unlock_scheduler(); // A unlocks the scheduler, sched_lock_cnt=0

// A continues its way

frabert wrote:That makes sense if B was being resumed from being blocked, so that it was put to sleep by calling schedule, so that when it awakens it returns from schedule and unlocks the scheduler. But what if B was being started for the first time? In that case, B would not start its execution by returning from a schedule call, so no scheduler unlocking would be done, so I presume I need to add a "preamble" to all the tasks to unlock the scheduler when they are first started?