User:Kr/A Thread's Life/Example Code

//
// gcc -Wall -g example.c -o main.bin -lpthread
// 

#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <string.h>
#include <unistd.h>


void my_pthread_cancel(pthread_t thread) {
    int res;
    if ((res = pthread_cancel(thread))) {
        fprintf(stderr, "%s(%p) => %s\n", __PRETTY_FUNCTION__, (void*)thread, strerror(res));
        // There seems to be an issue on Linux with pthread_cancel,
        // returning an error in case "thread" has already terminated, 
        // though not joined.
//        abort();
    }
}

void my_pthread_join(pthread_t th, void **thread_return) {
    int res;
    if ((res = pthread_join(th, thread_return))) {
        fprintf(stderr, "%s - %s\n", __PRETTY_FUNCTION__, strerror(res));
        abort();
    }
}


typedef struct Daemon  Daemon;

struct Daemon {
    Daemon * previous_;
    Daemon * next_;

    void (*func_)(void);
    pthread_t hd_;
    int       finished_;
};

static pthread_mutex_t daemons_mutex_ = PTHREAD_MUTEX_INITIALIZER;
static Daemon        * firstDaemon_   = NULL;
static unsigned    int daemons_       = 0; 


static void daemons_join_(int finished) {
    pthread_mutex_lock(&daemons_mutex_);
    Daemon * daemon = firstDaemon_;
    while (daemon) {
        Daemon * next = daemon->next_;

        if (!finished || daemon->finished_) {
            -- daemons_;
            
            if (daemon->next_)
                daemon->next_->previous_ = daemon->previous_;
            
            if (daemon->previous_)
                daemon->previous_->next_ = daemon->next_;
            
            if (firstDaemon_ == daemon)
                firstDaemon_ = daemon->next_;

            pthread_mutex_unlock(&daemons_mutex_);
            my_pthread_join(daemon->hd_, NULL);
            pthread_mutex_lock(&daemons_mutex_);

            daemon->hd_ = 0xffffffff;

            free(daemon);

            daemon = firstDaemon_;
        }
        else
            daemon = next;
    }
    pthread_mutex_unlock(&daemons_mutex_);
}

/* Daemon finish function. */
static void daemon_finish(Daemon * daemon) {
    int oldstate;
    pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate);

    daemons_join_(1);

    pthread_mutex_lock(&daemons_mutex_);
    daemon->finished_ = 1;
    pthread_mutex_unlock(&daemons_mutex_);

    pthread_setcancelstate(oldstate, NULL);
}

static void * daemon_func(Daemon * daemon) {
    pthread_cleanup_push((void (*)(void *))daemon_finish, daemon);

    daemon->func_();

    pthread_cleanup_pop(1);

    return NULL;
}

/* Create a "Daemon" struct and register it. 
   Start the "Daemon". */
static void daemon_create_(void (*func)(void)) {
    Daemon * daemon   = malloc(sizeof(Daemon));
    daemon->func_     = func;
    daemon->finished_ = 0;

    pthread_mutex_lock(&daemons_mutex_);

    daemon->previous_ = NULL;
    daemon->next_ = firstDaemon_;

    if (firstDaemon_) 
        firstDaemon_->previous_ = daemon;

    firstDaemon_ = daemon;
    ++ daemons_;

    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, 0);
    pthread_create(&daemon->hd_, NULL, (void *(*)(void *))daemon_func, daemon);
    pthread_attr_destroy(&attr);

    pthread_mutex_unlock(&daemons_mutex_);
}

/* Ask all registered daemons for cancellation and join them. */
static void daemons_cancelAndJoin_(void) {
    fprintf(stderr, "Joining daemons ... ");

    pthread_mutex_lock(&daemons_mutex_);
    Daemon * daemon = firstDaemon_;
    while (daemon) {
        my_pthread_cancel(daemon->hd_);
        // respectively
        //pthread_kill();

        fprintf(stderr, "# ");

        daemon = daemon->next_;
    }
    pthread_mutex_unlock(&daemons_mutex_);

    daemons_join_(0);
    fprintf(stderr, "done\n");
}


static unsigned    int activities_     = 1; // The "main" thread is the first "activity".
static pthread_mutex_t activity_mutex_ = PTHREAD_MUTEX_INITIALIZER;

static void activity_terminate_(void) {
    int use_exit = 0;
    pthread_mutex_lock(&activity_mutex_);
    -- activities_;
    use_exit = activities_ == 0;
    pthread_mutex_unlock(&activity_mutex_);

    // Terminate the process, if this was the last "activity"!
    if (use_exit) 
        exit(0);

    else
        pthread_exit(NULL);
}

static void * activity_func_(void (*func)(void)) {
    func();

    activity_terminate_();

    return NULL;
}

static void activity_create_(void (*func)(void)) {
    pthread_attr_t attr;
    
    /* Activities need to be detached. */
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, 1);
    
    pthread_t bt;
    pthread_create(&bt, &attr, (void *(*)(void *))activity_func_, func);
    pthread_attr_destroy(&attr);
    
    pthread_mutex_lock(&activity_mutex_);
    ++ activities_;
    pthread_mutex_unlock(&activity_mutex_);
}


/* Some daemon functions. */
static void log_threads(void) {
    fprintf(stderr, "activities: %u  daemons: %u\n", activities_, daemons_);
}

static void log_daemon_(void) {
    while (1) {
        log_threads();

        sleep(1); /* This is a cancellation point. */
    }
}

static void some_daemon_(void) {
    int n = 10;
    while (n) {
        sleep(1);
        
        if (rand() < (RAND_MAX / (daemons_ + 1)))
            daemon_create_(some_daemon_);

        -- n;
    }
}

/* Some activity functions. */
static void some_activity_(void) {
    int n = 3;
    while (n) {
        sleep(1);
        
        if (rand() < (RAND_MAX / (activities_ + 1)))
            activity_create_(some_activity_);

        if (rand() < (RAND_MAX / (daemons_ + 1)))
            daemon_create_(some_daemon_);

        -- n;
    }
}

static void main_activity_(void) {
    srand (time (0));

    daemon_create_(log_daemon_);
    daemon_create_(some_daemon_);
    activity_create_(some_activity_);

    sleep(3);
    daemon_create_(some_daemon_);

    sleep(5);
}

int main(void) {
    atexit(log_threads);
    atexit(daemons_cancelAndJoin_);

    main_activity_();

    activity_terminate_();

    return 0;
}