CS452 ULT swap_conteext

switch_2threads.c

/*
 * Demonstrate a minimal code to implement thread switching in user
 * space
 **/
#include <ucontext.h>
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <sys/time.h>

ucontext_t c1_ctx, c2_ctx, tmp;
ucontext_t *current;
const int STACK_SIZE = 4 * 1024; // 4K bytes
int whose_turn = 0;

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

// type for a pointer to functions that take zero argument
typedef void (*FuncNoArg)(void);

void one() {
    while(1) {
        printf("In one...\n");
        usleep(100000);
    }
}

void two(const char* text) {
    while(1) {
        printf("In two---%s\n", text);
        usleep(300000);
    }
}

void wakeup() {
    // Flip flop between the two contexts
    whose_turn = 1 - whose_turn;
    switch(whose_turn) {
        case 0:
            swapcontext(&tmp, &c1_ctx);
            break;
        case 1:
            swapcontext(&tmp, &c2_ctx);
    }
}

int main() {
    getcontext(&c1_ctx);
    c1_ctx.uc_stack.ss_sp = stack1;
    c1_ctx.uc_stack.ss_size = STACK_SIZE;
    c1_ctx.uc_link = NULL; // no successor thread
    // Function one takes no arguments
    makecontext(&c1_ctx, one, 0);

    getcontext(&c2_ctx);
    c2_ctx.uc_stack.ss_sp = stack2;
    c2_ctx.uc_stack.ss_size = STACK_SIZE;
    c2_ctx.uc_link = NULL; // no successor thread
    // Function two takes 1 string arg
    makecontext(&c2_ctx, (FuncNoArg) two, 1, "Hello");

    printf("In main\n");

    // Setup periodic timer handler
    struct sigaction alarm_act;
    alarm_act.sa_handler = wakeup;
    sigemptyset(&alarm_act.sa_mask);
    alarm_act.sa_flags = SA_RESTART;
    sigaction(SIGALRM, &alarm_act, NULL);

    struct itimerval freq;

    // Initial 2-sec delay
    freq.it_value.tv_sec = 2;
    freq.it_value.tv_usec = 0;
    // then periodically every 500 millisec
    freq.it_interval.tv_sec = 0;
    freq.it_interval.tv_usec = 500000;
    setitimer(ITIMER_REAL, &freq, NULL);

    while(1) {
        printf("In main thread...\n");
        pause();
    }
    return 0;
}

switch_3threads.c

/*
 * Demonstrate a minimal code to implement thread switching in user
 * space
 **/
#include <ucontext.h>
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <sys/time.h>

ucontext_t c1_ctx, c2_ctx, main_ctx, tmp;
ucontext_t *current;
const int STACK_SIZE = 4 * 1024; // 4K bytes
int whose_turn = 0;

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

// type for a pointer to functions that take zero argument
typedef void (*FuncNoArg)(void);

void one() {
    while(1) {
        printf("In one...\n");
        usleep(100000);
    }
}

void two(const char* text) {
    while(1) {
        printf("In two---%s\n", text);
        usleep(300000);
    }
}

void wakeup() {
    whose_turn++; // Round robun scheduler
    switch(whose_turn) {
        case 0:
            swapcontext(&tmp, &main_ctx);
            break;
        case 1:
            swapcontext(&tmp, &c1_ctx);
            break;
        case 2:
            swapcontext(&tmp, &c2_ctx);
            break;
        case 3:
            whose_turn = -1;
    }
}

int main() {
    getcontext(&main_ctx);
    getcontext(&c1_ctx);
    c1_ctx.uc_stack.ss_sp = stack1;
    c1_ctx.uc_stack.ss_size = STACK_SIZE;
    c1_ctx.uc_link = NULL; // no successor thread
    // Function one takes no arguments
    makecontext(&c1_ctx, one, 0);

    getcontext(&c2_ctx);
    c2_ctx.uc_stack.ss_sp = stack2;
    c2_ctx.uc_stack.ss_size = STACK_SIZE;
    c2_ctx.uc_link = NULL; // no successor thread
    // Function two takes 1 string arg
    makecontext(&c2_ctx, (FuncNoArg) two, 1, "Hello");

    printf("In main\n");

    // Setup periodic timer handler
    struct sigaction alarm_act;
    alarm_act.sa_handler = wakeup;
    sigemptyset(&alarm_act.sa_mask);
    alarm_act.sa_flags = SA_RESTART;
    sigaction(SIGALRM, &alarm_act, NULL);

    struct itimerval freq;

    // Initial 2-sec delay
    freq.it_value.tv_sec = 2;
    freq.it_value.tv_usec = 0;
    // then periodically every 500 millisec
    freq.it_interval.tv_sec = 0;
    freq.it_interval.tv_usec = 500000;
    setitimer(ITIMER_REAL, &freq, NULL);

    while(1) {
        printf("In main thread...\n");
        pause();
    }
    return 0;
}

switch_threads.cpp

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

ucontext_t c1, c2, main_ctx;
ucontext_t *current;
char stack1[4 * 1024];
char stack2[4 * 1024];

void one() {
    while(1) {
        printf("In one...\n");
        usleep(100000);
    }
}

void two() {
    while(1) {
        printf("In two---\n");
        usleep(300000);
    }
}

void wakeup(int _) {
    if (current == NULL || current == &c2) {
        current = &c1;
        swapcontext(&main_ctx, &c1);
    } else {
        current = &c2;
        swapcontext(&main_ctx, &c2);
    }
}

int main() {
    // Prepare context and stack for the first func
    getcontext(&c1);
    c1.uc_stack = {.ss_sp = stack1, .ss_size = 4 * 1024};
    c1.uc_link = NULL;
    makecontext(&c1, one, 0);

    // Prepare context and stack for the second func
    getcontext(&c2);
    c2.uc_stack = {.ss_sp = stack2, .ss_size = 4 * 1024};
    c2.uc_link = NULL;
    makecontext(&c2, two, 0);

    printf("In main\n");

    // Install periodic timer handler
    struct sigaction alarm_act;
    alarm_act.sa_handler = wakeup;
    sigemptyset(&alarm_act.sa_mask);
    alarm_act.sa_flags = SA_RESTART;
    sigaction(SIGALRM, &alarm_act, NULL);

    itimerval freq;

    // Initial 2-sec delay
    // then periodically every 500 millisec
    freq = {
        .it_interval = {.tv_sec = 0, .tv_usec = 500000},
        .it_value = {.tv_sec = 2, .tv_usec = 0}
    };

    // Fire the timer
    setitimer(ITIMER_REAL, &freq, NULL);

    // Main thread does nothing but pause for SIGALRM
    while(1) {
        pause();
    }
    return 0;
}