76092ddf33
This can be turned back on when the library is compiled with -DMTHREAD_STRICT (which enables more sanity checks). However, always performing this check shows up in system profiling results.
216 lines
6.8 KiB
C
216 lines
6.8 KiB
C
#include <minix/mthread.h>
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#include "global.h"
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#include "proto.h"
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#define MAIN_CTX &(mainthread.m_context)
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#define MAIN_STATE mainthread.m_state
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#define OLD_CTX &(threads[old_thread]->m_context)
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#define CURRENT_CTX &(threads[current_thread]->m_context)
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#define CURRENT_STATE threads[current_thread]->m_state
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static int yield_all;
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/*===========================================================================*
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* mthread_getcontext *
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*===========================================================================*/
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int mthread_getcontext(ctx)
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ucontext_t *ctx;
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{
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/* Retrieve this process' current state.*/
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/* We're not interested in FPU state nor signals, so ignore them.
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* Coincidentally, this significantly speeds up performance.
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*/
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ctx->uc_flags |= (UCF_IGNFPU | UCF_IGNSIGM);
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return getcontext(ctx);
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}
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/*===========================================================================*
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* mthread_schedule *
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*===========================================================================*/
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void mthread_schedule(void)
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{
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/* Pick a new thread to run and run it. In practice, this involves taking the
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* first thread off the (FIFO) run queue and resuming that thread.
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*/
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mthread_thread_t old_thread;
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mthread_tcb_t *new_tcb, *old_tcb;
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ucontext_t *new_ctx, *old_ctx;
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MTHREAD_CHECK_INIT(); /* Make sure libmthread is initialized */
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old_thread = current_thread;
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if (mthread_queue_isempty(&run_queue)) {
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/* No runnable threads. Let main thread run. */
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/* We keep track whether we're running the program's 'main' thread or
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* a spawned thread. In case we're already running the main thread and
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* there are no runnable threads, we can't jump back to its context.
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* Instead, we simply return.
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*/
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if (running_main_thread) return;
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/* We're running the last runnable spawned thread. Return to main
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* thread as there is no work left.
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*/
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current_thread = MAIN_THREAD;
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} else {
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current_thread = mthread_queue_remove(&run_queue);
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}
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/* Find thread entries in tcb... */
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new_tcb = mthread_find_tcb(current_thread);
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old_tcb = mthread_find_tcb(old_thread);
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/* ...and subsequently their contexts */
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new_ctx = &(new_tcb->m_context);
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old_ctx = &(old_tcb->m_context);
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/* Are we running the 'main' thread after swap? */
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running_main_thread = (current_thread == MAIN_THREAD);
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if (swapcontext(old_ctx, new_ctx) == -1)
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mthread_panic("Could not swap context");
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}
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/*===========================================================================*
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* mthread_init_scheduler *
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*===========================================================================*/
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void mthread_init_scheduler(void)
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{
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/* Initialize the scheduler */
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mthread_queue_init(&run_queue);
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yield_all = 0;
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}
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/*===========================================================================*
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* mthread_suspend *
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*===========================================================================*/
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void mthread_suspend(state)
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mthread_state_t state;
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{
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/* Stop the current thread from running. There can be multiple reasons for
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* this; the process tries to lock a locked mutex (i.e., has to wait for it to
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* become unlocked), the process has to wait for a condition, the thread
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* volunteered to let another thread to run (i.e., it called yield and remains
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* runnable itself), or the thread is dead.
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*/
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int continue_thread = 0;
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mthread_tcb_t *tcb;
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ucontext_t *ctx;
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if (state == MS_DEAD) mthread_panic("Shouldn't suspend with MS_DEAD state");
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tcb = mthread_find_tcb(current_thread);
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tcb->m_state = state;
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ctx = &(tcb->m_context);
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/* Save current thread's context */
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if (mthread_getcontext(ctx) != 0)
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mthread_panic("Couldn't save current thread's context");
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/* We return execution here with setcontext/swapcontext, but also when we
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* simply return from the getcontext call. If continue_thread is non-zero, we
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* are continuing the execution of this thread after a call from setcontext
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* or swapcontext.
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*/
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if(!continue_thread) {
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continue_thread = 1;
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mthread_schedule(); /* Let other thread run. */
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}
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}
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/*===========================================================================*
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* mthread_unsuspend *
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*===========================================================================*/
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void mthread_unsuspend(thread)
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mthread_thread_t thread; /* Thread to make runnable */
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{
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/* Mark the state of a thread runnable and add it to the run queue */
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mthread_tcb_t *tcb;
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if (!isokthreadid(thread)) mthread_panic("Invalid thread id");
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tcb = mthread_find_tcb(thread);
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tcb->m_state = MS_RUNNABLE;
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mthread_queue_add(&run_queue, thread);
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}
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/*===========================================================================*
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* mthread_yield *
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*===========================================================================*/
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int mthread_yield(void)
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{
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/* Defer further execution of the current thread and let another thread run. */
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mthread_tcb_t *tcb;
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mthread_thread_t t;
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MTHREAD_CHECK_INIT(); /* Make sure libmthread is initialized */
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/* Detached threads cannot clean themselves up. This is a perfect moment to
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* do it */
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for (t = (mthread_thread_t) 0; need_reset > 0 && t < no_threads; t++) {
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tcb = mthread_find_tcb(t);
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if (tcb->m_state == MS_NEEDRESET) {
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mthread_thread_reset(t);
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used_threads--;
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need_reset--;
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mthread_queue_add(&free_threads, t);
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}
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}
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if (mthread_queue_isempty(&run_queue)) { /* No point in yielding. */
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return(-1);
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} else if (current_thread == NO_THREAD) {
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/* Can't yield this thread */
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return(-1);
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}
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mthread_queue_add(&run_queue, current_thread);
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mthread_suspend(MS_RUNNABLE); /* We're still runnable, but we're just kind
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* enough to let someone else run.
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*/
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return(0);
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}
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/*===========================================================================*
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* mthread_yield_all *
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*===========================================================================*/
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void mthread_yield_all(void)
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{
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/* Yield until there are no more runnable threads left. Two threads calling
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* this function will lead to a deadlock.
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*/
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MTHREAD_CHECK_INIT(); /* Make sure libmthread is initialized */
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if (yield_all) mthread_panic("Deadlock: two threads trying to yield_all");
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yield_all = 1;
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/* This works as follows. Thread A is running and threads B, C, and D are
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* runnable. As A is running, it is NOT on the run_queue (see
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* mthread_schedule). It calls mthread_yield and will be added to the run
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* queue, allowing B to run. B runs and suspends eventually, possibly still
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* in a runnable state. Then C and D run. Eventually A will run again (and is
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* thus not on the list). If B, C, and D are dead, waiting for a condition,
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* or waiting for a lock, they are not on the run queue either. At that
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* point A is the only runnable thread left.
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*/
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while (!mthread_queue_isempty(&run_queue)) {
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(void) mthread_yield();
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}
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/* Done yielding all threads. */
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yield_all = 0;
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}
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