Initial (nonworking) draft of preemptive task switching

[bertos.git] / bertos / kern / preempt.c

diff --git a/bertos/kern/preempt.c b/bertos/kern/preempt.c
index f068a8a82c24d314d159e84a045422de18b55475..0cbaf7c902dd2d65a03015cecf2b15804853f17e 100644 (file)
--- a/bertos/kern/preempt.c
+++ b/bertos/kern/preempt.c
@@ -41,6 +41,10 @@
 #include "proc_p.h"
 #include "proc.h"
 
+#include <cpu/frame.h> // CPU_IDLE
+
+#include <unistd.h> // XXX alarm()
+
 
 /*
  * The time sharing scheduler forces a task switch when the current
@@ -78,3 +82,105 @@ void proc_permit(void)
        /* No need to protect against interrupts here. */
        --CurrentProcess->forbid_cnt;
 }
+
+static void (*irq_handlers[100])(void); // FIXME
+
+
+void proc_preempt(void)
+{
+       TRACE;
+
+       ATOMIC(LIST_ASSERT_VALID(&ProcReadyList));
+
+       IRQ_DISABLE;
+       /* Poll on the ready queue for the first ready process */
+       while (!(CurrentProcess = (struct Process *)list_remHead(&ProcReadyList)))
+       {
+               /*
+                * Make sure we physically reenable interrupts here, no matter what
+                * the current task status is. This is important because if we
+                * are idle-spinning, we must allow interrupts, otherwise no
+                * process will ever wake up.
+                *
+                * During idle-spinning, an interrupt can occur and it may
+                * modify \p ProcReadyList. To ensure that compiler reload this
+                * variable every while cycle we call CPU_MEMORY_BARRIER.
+                * The memory barrier ensure that all variables used in this context
+                * are reloaded.
+                */
+               IRQ_ENABLE;
+               CPU_IDLE;
+               MEMORY_BARRIER;
+               IRQ_DISABLE;
+       }
+       IRQ_ENABLE;
+}
+
+void proc_preempt_timer(void)
+{
+       // TODO: check Quantum
+
+       alarm(1);
+       ATOMIC(SCHED_ENQUEUE(CurrentProcess));
+       proc_schedule();
+}
+
+void proc_schedule(void)
+{
+       kill(0, SIGUSR1);
+}
+
+void proc_yield(void)
+{
+       ATOMIC(SCHED_ENQUEUE(CurrentProcess));
+
+       proc_schedule();
+}
+
+/* signal handler */
+void irq_entry(int signum)
+{
+       Process *old_process;
+
+       TRACEMSG("storing %p:%s", CurrentProcess, CurrentProcess->monitor.name);
+       CurrentProcess->leaving = false;
+       getcontext(&CurrentProcess->context);
+       /* We get here in two ways: directly, and after setcontext() below */
+
+       if (CurrentProcess->leaving)
+       {
+               TRACEMSG("leaving to %p:%s", CurrentProcess, CurrentProcess->monitor.name);
+               return;
+       }
+
+       old_process = CurrentProcess;
+
+       irq_handlers[signum]();
+
+       if (old_process != CurrentProcess)
+       {
+               TRACEMSG("launching %p:%s", CurrentProcess, CurrentProcess->monitor.name);
+               CurrentProcess->leaving = true;
+               setcontext(&CurrentProcess->context);
+               /* not reached */
+       }
+
+       TRACEMSG("keeping %p:%s", CurrentProcess, CurrentProcess->monitor.name);
+}
+
+void preempt_init(void)
+{
+       struct sigaction act;
+       act.sa_handler = irq_entry;
+       sigemptyset(&act.sa_mask);
+       sigaddset(&act.sa_mask, SIGUSR1);
+       sigaddset(&act.sa_mask, SIGALRM);
+       act.sa_flags = SA_RESTART; /* | SA_SIGINFO; */
+
+       irq_handlers[SIGUSR1] = proc_preempt;
+       irq_handlers[SIGALRM] = proc_preempt_timer;
+       sigaction(SIGUSR1, &act, NULL);
+       sigaction(SIGALRM, &act, NULL);
+
+       alarm(1);
+}