/*
 * Multithread demo program.
 * Hebrew University OS course.
 *
 * Questions: os@cs.huji.ac.il
 */

#include <stdio.h>
#include <setjmp.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>
#include <sys/time.h>

#define SECOND 1000000
#define JB_SP 4
#define JB_PC 5 
#define STACK_SIZE 4096

char stack1[STACK_SIZE];
char stack2[STACK_SIZE];

sigjmp_buf jbuf[2];

void switchThreads();

void f()
{
    int i=0;
    while(1) {
        ++i;
        printf("in f (%d)\n",i);
        if (i % 3 == 0) {
            printf("f: switching\n");
            switchThreads();
        }
        usleep(SECOND);
    }
}

void g()
{
    int i=0;
    while(1){
        ++i;
        printf("in g (%d)\n",i);
        if (i % 5 == 0) {
            printf("g: switching\n");
            switchThreads();
        }
        usleep(SECOND);
    }
}


//A translation required when using an address of a variable
//Use this as a black box in your code.
unsigned int translate_address(unsigned int addr)
{
    unsigned int ret;
    asm volatile("xor    %%gs:0x18,%0\n"
		"rol    $0x9,%0\n"
                 : "=g" (ret)
                 : "0" (addr));
    
    return ret;
}


void setup()
{
    unsigned int sp, pc;
    
    sp = (unsigned int)stack1 + STACK_SIZE - sizeof(int); 
    pc = (unsigned int)f;
    
    sigsetjmp(jbuf[0],1);
    (jbuf[0]->__jmpbuf)[JB_SP] = translate_address(sp);
    (jbuf[0]->__jmpbuf)[JB_PC] = translate_address(pc);
    sigemptyset(&jbuf[0]->__saved_mask);     


    sp = (unsigned int)stack2 + STACK_SIZE - sizeof(int);
    pc = (unsigned int)g;
    
    sigsetjmp(jbuf[1],1);
    (jbuf[1]->__jmpbuf)[JB_SP] = translate_address(sp);
    (jbuf[1]->__jmpbuf)[JB_PC] = translate_address(pc);
    sigemptyset(&jbuf[1]->__saved_mask);         
}


void switchThreads()
{
    static int currentThread = 0;
    
    int ret_val = sigsetjmp(jbuf[currentThread],1);
    printf("SWITCH: ret_val=%d\n", ret_val); 
    if (ret_val == 1) {
        return;
    }
    
    currentThread = 1 - currentThread;
    siglongjmp(jbuf[currentThread],1);
}


int main()
{
    setup();		
    siglongjmp(jbuf[0],1);
    return 0;
}