/*
* Cause the current thread to exit.
*
* The parts of the thread structure we don't actually need to run
* should be cleaned up right away. The rest has to wait until
* thread_destroy is called from exorcise().
*
* Note that any dynamically-allocated structures that can vary in size from
* thread to thread should be cleaned up here, not in thread_destroy. This is
* because the last thread left on each core runs the idle loop and does not
* get cleaned up until new threads are created. Differences in the amount of
* memory used by different threads after thread_exit will make it look like
* your kernel in leaking memory and cause some of the test161 checks to fail.
*
* Does not return.
*/
void
thread_exit(void)
{
struct thread *cur;
cur = curthread;
/*
* Detach from our process. You might need to move this action
* around, depending on how your wait/exit works.
*/
proc_remthread(cur);
/* Make sure we *are* detached (move this only if you're sure!) */
KASSERT(cur->t_proc == NULL);
/* Check the stack guard band. */
thread_checkstack(cur);
// Decrement the thread count and notify anyone interested.
if (thread_count) {
spinlock_acquire(&thread_count_lock);
--thread_count;
wchan_wakeall(thread_count_wchan, &thread_count_lock);
spinlock_release(&thread_count_lock);
}
/* Interrupts off on this processor */
splhigh();
thread_switch(S_ZOMBIE, NULL, NULL);
panic("braaaaaaaiiiiiiiiiiinssssss\n");
}
/*
* Cause the current thread to exit.
*
* The parts of the thread structure we don't actually need to run
* should be cleaned up right away. The rest has to wait until
* thread_destroy is called from exorcise().
*
* Does not return.
*/
void
thread_exit(void)
{
struct thread *cur;
cur = curthread;
/*
* Detach from our process. You might need to move this action
* around, depending on how your wait/exit works.
*/
proc_remthread(cur);
/* Make sure we *are* detached (move this only if you're sure!) */
KASSERT(cur->t_proc == NULL);
/* Check the stack guard band. */
thread_checkstack(cur);
/* Interrupts off on this processor */
splhigh();
thread_switch(S_ZOMBIE, NULL, NULL);
panic("braaaaaaaiiiiiiiiiiinssssss\n");
}
/*
* High level, machine-independent context switch code.
*
* The current thread is queued appropriately and its state is changed
* to NEWSTATE; another thread to run is selected and switched to.
*
* If NEWSTATE is S_SLEEP, the thread is queued on the wait channel
* WC, protected by the spinlock LK. Otherwise WC and Lk should be
* NULL.
*/
static
void
thread_switch(threadstate_t newstate, struct wchan *wc, struct spinlock *lk)
{
struct thread *cur, *next;
int spl;
DEBUGASSERT(curcpu->c_curthread == curthread);
DEBUGASSERT(curthread->t_cpu == curcpu->c_self);
/* Explicitly disable interrupts on this processor */
spl = splhigh();
cur = curthread;
/*
* If we're idle, return without doing anything. This happens
* when the timer interrupt interrupts the idle loop.
*/
if (curcpu->c_isidle) {
splx(spl);
return;
}
/* Check the stack guard band. */
thread_checkstack(cur);
/* Lock the run queue. */
spinlock_acquire(&curcpu->c_runqueue_lock);
/* Micro-optimization: if nothing to do, just return */
if (newstate == S_READY && threadlist_isempty(&curcpu->c_runqueue)) {
spinlock_release(&curcpu->c_runqueue_lock);
splx(spl);
return;
}
/* Put the thread in the right place. */
switch (newstate) {
case S_RUN:
panic("Illegal S_RUN in thread_switch\n");
case S_READY:
thread_make_runnable(cur, true /*have lock*/);
break;
case S_SLEEP:
cur->t_wchan_name = wc->wc_name;
/*
* Add the thread to the list in the wait channel, and
* unlock same. To avoid a race with someone else
* calling wchan_wake*, we must keep the wchan's
* associated spinlock locked from the point the
* caller of wchan_sleep locked it until the thread is
* on the list.
*/
threadlist_addtail(&wc->wc_threads, cur);
spinlock_release(lk);
break;
case S_ZOMBIE:
cur->t_wchan_name = "ZOMBIE";
threadlist_addtail(&curcpu->c_zombies, cur);
break;
}
cur->t_state = newstate;
/*
* Get the next thread. While there isn't one, call md_idle().
* curcpu->c_isidle must be true when md_idle is
* called. Unlock the runqueue while idling too, to make sure
* things can be added to it.
*
* Note that we don't need to unlock the runqueue atomically
* with idling; becoming unidle requires receiving an
* interrupt (either a hardware interrupt or an interprocessor
* interrupt from another cpu posting a wakeup) and idling
* *is* atomic with respect to re-enabling interrupts.
*
* Note that c_isidle becomes true briefly even if we don't go
* idle. However, because one is supposed to hold the runqueue
* lock to look at it, this should not be visible or matter.
*/
/* The current cpu is now idle. */
curcpu->c_isidle = true;
do {
next = threadlist_remhead(&curcpu->c_runqueue);
if (next == NULL) {
spinlock_release(&curcpu->c_runqueue_lock);
cpu_idle();
spinlock_acquire(&curcpu->c_runqueue_lock);
}
} while (next == NULL);
curcpu->c_isidle = false;
/*
* Note that curcpu->c_curthread may be the same variable as
* curthread and it may not be, depending on how curthread and
* curcpu are defined by the MD code. We'll assign both and
* assume the compiler will optimize one away if they're the
* same.
*/
curcpu->c_curthread = next;
curthread = next;
/* do the switch (in assembler in switch.S) */
switchframe_switch(&cur->t_context, &next->t_context);
/*
* When we get to this point we are either running in the next
* thread, or have come back to the same thread again,
* depending on how you look at it. That is,
* switchframe_switch returns immediately in another thread
* context, which in general will be executing here with a
* different stack and different values in the local
* variables. (Although new threads go to thread_startup
* instead.) But, later on when the processor, or some
* processor, comes back to the previous thread, it's also
* executing here with the *same* value in the local
* variables.
*
* The upshot, however, is as follows:
*
* - The thread now currently running is "cur", not "next",
* because when we return from switchrame_switch on the
* same stack, we're back to the thread that
* switchframe_switch call switched away from, which is
* "cur".
*
* - "cur" is _not_ the thread that just *called*
* switchframe_switch.
*
* - If newstate is S_ZOMB we never get back here in that
* context at all.
*
* - If the thread just chosen to run ("next") was a new
* thread, we don't get to this code again until
* *another* context switch happens, because when new
* threads return from switchframe_switch they teleport
* to thread_startup.
*
* - At this point the thread whose stack we're now on may
* have been migrated to another cpu since it last ran.
*
* The above is inherently confusing and will probably take a
* while to get used to.
*
* However, the important part is that code placed here, after
* the call to switchframe_switch, does not necessarily run on
* every context switch. Thus any such code must be either
* skippable on some switches or also called from
* thread_startup.
*/
/* Clear the wait channel and set the thread state. */
cur->t_wchan_name = NULL;
cur->t_state = S_RUN;
/* Unlock the run queue. */
spinlock_release(&curcpu->c_runqueue_lock);
/* Activate our address space in the MMU. */
as_activate();
/* Clean up dead threads. */
exorcise();
/* Turn interrupts back on. */
splx(spl);
}
