Difference between revisions of "User:Kr/A Thread's Life/Example Code"

1. include <stdlib.h>
2. include <stdio.h>
3. include <pthread.h>
4. include <string.h>

typedef struct Daemon Daemon;

struct Daemon {

   Daemon * previous_;
   Daemon * next_;

   void (*func_)(void);
   pthread_t hd_;

};

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

/* Unregister the given "Daemon" struct

  and terminate this thread.            */

static void daemon_terminate(Daemon * daemon) {

   pthread_mutex_lock(&daemons_mutex_);
   -- 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_);

   free(daemon);

   /* This daemon is not in the list of daemons anymore, 
      and therefor can't be joined. */
   pthread_detach(pthread_self());

}

static void * daemon_func(Daemon * daemon) {

   pthread_cleanup_push((void (*)(void *))daemon_terminate, 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;

   pthread_mutex_lock(&daemons_mutex_);

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

   if (firstDaemon_) 
       firstDaemon_->previous_ = daemon;

   firstDaemon_ = daemon;
   ++ daemons_;

   pthread_mutex_unlock(&daemons_mutex_);

   pthread_create(&daemon->hd_, NULL, (void *(*)(void *))daemon_func, daemon);

}

/* Ask all registered daemons for termination and join them. */ static void daemons_join_(void) {

   fprintf(stderr, "Joining daemons ... ");

   pthread_mutex_lock(&daemons_mutex_);
   while (firstDaemon_) {
       pthread_t hd;
       memcpy(&hd, &firstDaemon_->hd_, sizeof(pthread_t));

       pthread_mutex_unlock(&daemons_mutex_);

       // We may want to cancel a thread actively during termination:
       pthread_cancel(hd);
       // respectively
       //pthread_kill();

       pthread_join(hd, NULL);
       fprintf(stderr, "# ");

       pthread_mutex_lock(&daemons_mutex_);
   }
   pthread_mutex_unlock(&daemons_mutex_);

   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. */
   }

   pthread_exit(NULL);

}

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_join_);

   main_activity_();

   activity_terminate_();

   return 0;