Data commit

Task/Active-object/C/active-object.c

@@ -0,0 +1,70 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <math.h>
+#include <sys/time.h>
+#include <pthread.h>
+
+/* no need to lock the object: at worst the readout would be 1 tick off,
+   which is no worse than integrator's inate inaccuracy */
+typedef struct {
+	double (*func)(double);
+	struct timeval start;
+	double v, last_v, last_t;
+	pthread_t id;
+} integ_t, *integ;
+
+void update(integ x)
+{
+	struct timeval tv;
+	double t, v, (*f)(double);
+
+	f = x->func;
+	gettimeofday(&tv, 0);
+	t = ((tv.tv_sec - x->start.tv_sec) * 1000000
+		+ tv.tv_usec - x->start.tv_usec) * 1e-6;
+	v = f ? f(t) : 0;
+	x->v += (x->last_v + v) * (t - x->last_t) / 2;
+	x->last_t = t;
+}
+
+void* tick(void *a)
+{
+	integ x = a;
+	while (1) {
+		usleep(100000); /* update every .1 sec */
+		update(x);
+	}
+}
+
+void set_input(integ x, double (*func)(double))
+{
+	update(x);
+	x->func = func;
+	x->last_t = 0;
+	x->last_v = func ? func(0) : 0;
+}
+
+integ new_integ(double (*func)(double))
+{
+	integ x = malloc(sizeof(integ_t));
+	x->v = x->last_v = 0;
+	x->func = 0;
+	gettimeofday(&x->start, 0);
+	set_input(x, func);
+	pthread_create(&x->id, 0, tick, x);
+	return x;
+}
+
+double sine(double t) { return sin(4 * atan2(1, 1) * t); }
+
+int main()
+{
+	integ x = new_integ(sine);
+	sleep(2);
+	set_input(x, 0);
+	usleep(500000);
+	printf("%g\n", x->v);
+
+	return 0;
+}