#include <inc/assert.h>

#include <kern/env.h>
#include <kern/pmap.h>


// Choose a user environment to run and run it.
void
sched_yield(void)
{
	// Your code here to implement simple round-robin scheduling.
	// Search through envs array for a runnable environment,
	// in circular fashion starting from the previously running env,
	// and switch to the first such environment found.
	// But never choose envs[0], the idle environment,
	// unless NOTHING else is runnable.

        u_long i;
        
        if (curenv != NULL) {
                i = curenv - envs + 1;
        } else {
                i = 1;
        }

        for ( ; i < NENV; i++) {
                if (envs[i].env_status == ENV_RUNNABLE) {
                        env_run(&envs[i]);
                }
        }

        for (i = 1 ; i <= (curenv-envs) && i <NENV; i++) {
                if (envs[i].env_status == ENV_RUNNABLE) {
                        env_run(&envs[i]);
                }
        }
        
	// Run the special idle environment when nothing else is runnable.
	assert(envs[0].env_status == ENV_RUNNABLE);
	env_run(&envs[0]);
}