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#include <minix/mthread.h>
#include "global.h"
#include "proto.h"
#define MAIN_CTX &(mainthread.m_context)
#define MAIN_STATE mainthread.m_state
#define OLD_CTX &(threads[old_thread]->m_context)
#define CURRENT_CTX &(threads[current_thread]->m_context)
#define CURRENT_STATE threads[current_thread]->m_state
static int yield_all;
/*===========================================================================*
* mthread_getcontext *
*===========================================================================*/
int mthread_getcontext(ctx)
ucontext_t *ctx;
{
/* Retrieve this process' current state.*/
/* We're not interested in FPU state nor signals, so ignore them.
* Coincidentally, this significantly speeds up performance.
*/
ctx->uc_flags |= _UC_IGNSIGM | _UC_IGNFPU;
return getcontext(ctx);
}
/*===========================================================================*
* mthread_schedule *
*===========================================================================*/
void mthread_schedule(void)
{
/* Pick a new thread to run and run it. In practice, this involves taking the
* first thread off the (FIFO) run queue and resuming that thread.
*/
mthread_thread_t old_thread;
mthread_tcb_t *new_tcb, *old_tcb;
ucontext_t *new_ctx, *old_ctx;
old_thread = current_thread;
if (mthread_queue_isempty(&run_queue)) {
/* No runnable threads. Let main thread run. */
/* We keep track whether we're running the program's 'main' thread or
* a spawned thread. In case we're already running the main thread and
* there are no runnable threads, we can't jump back to its context.
* Instead, we simply return.
*/
if (running_main_thread) return;
/* We're running the last runnable spawned thread. Return to main
* thread as there is no work left.
*/
current_thread = MAIN_THREAD;
} else {
current_thread = mthread_queue_remove(&run_queue);
}
/* Find thread entries in tcb... */
new_tcb = mthread_find_tcb(current_thread);
old_tcb = mthread_find_tcb(old_thread);
/* ...and subsequently their contexts */
new_ctx = &(new_tcb->m_context);
old_ctx = &(old_tcb->m_context);
/* Are we running the 'main' thread after swap? */
running_main_thread = (current_thread == MAIN_THREAD);
if (swapcontext(old_ctx, new_ctx) == -1)
mthread_panic("Could not swap context");
}
/*===========================================================================*
* mthread_init_scheduler *
*===========================================================================*/
void mthread_init_scheduler(void)
{
/* Initialize the scheduler */
mthread_queue_init(&run_queue);
yield_all = 0;
}
/*===========================================================================*
* mthread_suspend *
*===========================================================================*/
void mthread_suspend(state)
mthread_state_t state;
{
/* Stop the current thread from running. There can be multiple reasons for
* this; the process tries to lock a locked mutex (i.e., has to wait for it to
* become unlocked), the process has to wait for a condition, the thread
* volunteered to let another thread to run (i.e., it called yield and remains
* runnable itself), or the thread is dead.
*/
int continue_thread = 0;
mthread_tcb_t *tcb;
ucontext_t *ctx;
if (state == MS_DEAD) mthread_panic("Shouldn't suspend with MS_DEAD state");
tcb = mthread_find_tcb(current_thread);
tcb->m_state = state;
ctx = &(tcb->m_context);
/* Save current thread's context */
if (mthread_getcontext(ctx) != 0)
mthread_panic("Couldn't save current thread's context");
/* We return execution here with setcontext/swapcontext, but also when we
* simply return from the getcontext call. If continue_thread is non-zero, we
* are continuing the execution of this thread after a call from setcontext
* or swapcontext.
*/
if(!continue_thread) {
continue_thread = 1;
mthread_schedule(); /* Let other thread run. */
}
}
/*===========================================================================*
* mthread_unsuspend *
*===========================================================================*/
void mthread_unsuspend(thread)
mthread_thread_t thread; /* Thread to make runnable */
{
/* Mark the state of a thread runnable and add it to the run queue */
mthread_tcb_t *tcb;
if (!isokthreadid(thread)) mthread_panic("Invalid thread id");
tcb = mthread_find_tcb(thread);
tcb->m_state = MS_RUNNABLE;
mthread_queue_add(&run_queue, thread);
}
/*===========================================================================*
* mthread_yield *
*===========================================================================*/
int mthread_yield(void)
{
/* Defer further execution of the current thread and let another thread run. */
mthread_tcb_t *tcb;
mthread_thread_t t;
/* Detached threads cannot clean themselves up. This is a perfect moment to
* do it */
for (t = (mthread_thread_t) 0; need_reset > 0 && t < no_threads; t++) {
tcb = mthread_find_tcb(t);
if (tcb->m_state == MS_NEEDRESET) {
mthread_thread_reset(t);
used_threads--;
need_reset--;
mthread_queue_add(&free_threads, t);
}
}
if (mthread_queue_isempty(&run_queue)) { /* No point in yielding. */
return(-1);
} else if (current_thread == NO_THREAD) {
/* Can't yield this thread */
return(-1);
}
mthread_queue_add(&run_queue, current_thread);
mthread_suspend(MS_RUNNABLE); /* We're still runnable, but we're just kind
* enough to let someone else run.
*/
return(0);
}
/*===========================================================================*
* mthread_yield_all *
*===========================================================================*/
void mthread_yield_all(void)
{
/* Yield until there are no more runnable threads left. Two threads calling
* this function will lead to a deadlock.
*/
if (yield_all) mthread_panic("Deadlock: two threads trying to yield_all");
yield_all = 1;
/* This works as follows. Thread A is running and threads B, C, and D are
* runnable. As A is running, it is NOT on the run_queue (see
* mthread_schedule). It calls mthread_yield and will be added to the run
* queue, allowing B to run. B runs and suspends eventually, possibly still
* in a runnable state. Then C and D run. Eventually A will run again (and is
* thus not on the list). If B, C, and D are dead, waiting for a condition,
* or waiting for a lock, they are not on the run queue either. At that
* point A is the only runnable thread left.
*/
while (!mthread_queue_isempty(&run_queue)) {
(void) mthread_yield();
}
/* Done yielding all threads. */
yield_all = 0;
}
/* pthread compatibility layer. */
__weak_alias(pthread_yield, mthread_yield)
__weak_alias(sched_yield, mthread_yield)
__weak_alias(pthread_yield_all, mthread_yield_all)
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