User:Kr/A Thread's Life
From Apache OpenOffice Wiki
Status: draft
Contents
Two types of Threads
- Active threads - activities
- Daemon threads - daemons (see wikipedia:Daemon)
Activity
- Activities keep the process alive.
- The last activity terminating leads to the termination of the entire process.
- Every activity must be detached, as it is not going to be joined.
Examples
- GUI dispatcher thread
Daemon
- Daemons don't keep the process alive.
- Any daemon needs to be joined (terminated / cancelled) when (indirectly) released by an activity.
- Every daemon must be joinable, as an activity is going to join it, latest during termination.
Sleepy Daemons
Short lived Daemons
Examples
- cache flushing threads
Notes
- Threads may dynamically switch from one type to the other and vice versa.
- The "main" thread is an activity.
Example
// // 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; }