/* Simple POSIX threads program. * * Author: Eyal Lebedinsky eyal@eyal.emu.id.au * Written: Sep 1998. * Version Date: 12 Sep 1998 * * Do we need to lock stdout or is it thread safe? * * Used: * pthread_t * pthread_attr_t * pthread_create() * pthread_join() * pthread_mutex_t * PTHREAD_MUTEX_INITIALIZER * pthread_mutex_init() [not used now] * pthread_mutex_destroy() * pthread_mutex_lock() * pthread_mutex_trylock() * pthread_mutex_unlock() * * What this program does is establish a work queue (implemented using * four mutexes for each thread). It then schedules work (by storing * a number in 'todo') and releases the threads. When the work is done * the threads will block. The program then repeats the same thing once * more (just to test the logic) and when the work is done it destroyes * the threads. * * The 'work' we do is simply burning CPU cycles in a loop. * The 'todo' work queue is trivial - each threads pops one element * off it by incrementing it, the poped number is the 'work' to do. * When 'todo' reaches the limit (nwork) the queue is considered * empty. * * The number displayed at the end is the amount of work each thread * did, so we can see if the load was properly distributed. * * The program was written to test a threading setup (not seen here) * rather than to demonstrate correct usage of the pthread facilities. * * Note how each thread is given access to a thread control structure * (TC) which is used for communicating to/from the main program (e.g. * the threads knows its 'id' and also filles in the 'work' done). */ #include "test.h" #include <stdlib.h> #include <math.h> struct thread_control { int id; pthread_t thread; /* thread id */ pthread_mutex_t mutex_start; pthread_mutex_t mutex_started; pthread_mutex_t mutex_end; pthread_mutex_t mutex_ended; long work; /* work done */ int stat; /* pthread_init status */ }; typedef struct thread_control TC; static TC *tcs = NULL; static int nthreads = 10; static int nwork = 100; static int quiet = 0; static int todo = -1; static pthread_mutex_t mutex_todo = PTHREAD_MUTEX_INITIALIZER; static pthread_mutex_t mutex_stdout = PTHREAD_MUTEX_INITIALIZER; static void die (int ret) { if (NULL != tcs) { free (tcs); tcs = NULL; } if (ret) exit (ret); } static double waste_time (int n) { int i; double f; f = rand (); for (i = n*100; i > 0; --i) { f = 2 * f * f / (f * f); } return f; } static int do_work_unit (int who, int n) { int i; static int nchars = 0; double f = 0.0; if (quiet) i = 0; else { /* * get lock on stdout */ assert(pthread_mutex_lock (&mutex_stdout) == 0); /* * do our job */ i = printf ("%c", "0123456789abcdefghijklmnopqrstuvwxyz"[who]); if (!(++nchars % 50)) printf ("\n"); fflush (stdout); /* * release lock on stdout */ assert(pthread_mutex_unlock (&mutex_stdout) == 0); } n = rand () % 10000; /* ignore incoming 'n' */ f = waste_time (n); /* This prevents the statement above from being optimised out */ if (f > 0.0) return(n); return (n); } static int print_server (void *ptr) { int mywork; int n; TC *tc = (TC *)ptr; assert(pthread_mutex_lock (&tc->mutex_started) == 0); for (;;) { assert(pthread_mutex_lock (&tc->mutex_start) == 0); assert(pthread_mutex_unlock (&tc->mutex_start) == 0); assert(pthread_mutex_lock (&tc->mutex_ended) == 0); assert(pthread_mutex_unlock (&tc->mutex_started) == 0); for (;;) { /* * get lock on todo list */ assert(pthread_mutex_lock (&mutex_todo) == 0); mywork = todo; if (todo >= 0) { ++todo; if (todo >= nwork) todo = -1; } assert(pthread_mutex_unlock (&mutex_todo) == 0); if (mywork < 0) break; assert((n = do_work_unit (tc->id, mywork)) >= 0); tc->work += n; } assert(pthread_mutex_lock (&tc->mutex_end) == 0); assert(pthread_mutex_unlock (&tc->mutex_end) == 0); assert(pthread_mutex_lock (&tc->mutex_started) == 0); assert(pthread_mutex_unlock (&tc->mutex_ended) == 0); if (-2 == mywork) break; } assert(pthread_mutex_unlock (&tc->mutex_started) == 0); return (0); } static void dosync (void) { int i; for (i = 0; i < nthreads; ++i) { assert(pthread_mutex_lock (&tcs[i].mutex_end) == 0); assert(pthread_mutex_unlock (&tcs[i].mutex_start) == 0); assert(pthread_mutex_lock (&tcs[i].mutex_started) == 0); assert(pthread_mutex_unlock (&tcs[i].mutex_started) == 0); } /* * Now threads do their work */ for (i = 0; i < nthreads; ++i) { assert(pthread_mutex_lock (&tcs[i].mutex_start) == 0); assert(pthread_mutex_unlock (&tcs[i].mutex_end) == 0); assert(pthread_mutex_lock (&tcs[i].mutex_ended) == 0); assert(pthread_mutex_unlock (&tcs[i].mutex_ended) == 0); } } static void dowork (void) { todo = 0; dosync(); todo = 0; dosync(); } int main (int argc, char *argv[]) { int i; assert(NULL != (tcs = (TC *) calloc (nthreads, sizeof (*tcs)))); /* * Launch threads */ for (i = 0; i < nthreads; ++i) { tcs[i].id = i; assert(pthread_mutex_init (&tcs[i].mutex_start, NULL) == 0); assert(pthread_mutex_init (&tcs[i].mutex_started, NULL) == 0); assert(pthread_mutex_init (&tcs[i].mutex_end, NULL) == 0); assert(pthread_mutex_init (&tcs[i].mutex_ended, NULL) == 0); tcs[i].work = 0; assert(pthread_mutex_lock (&tcs[i].mutex_start) == 0); assert((tcs[i].stat = pthread_create (&tcs[i].thread, NULL, (void *(*)(void *))&print_server, (void *) &tcs[i]) ) == 0); /* * Wait for thread initialisation */ { int trylock = 0; while (trylock == 0) { trylock = pthread_mutex_trylock(&tcs[i].mutex_started); assert(trylock == 0 || trylock == EBUSY); if (trylock == 0) { assert(pthread_mutex_unlock (&tcs[i].mutex_started) == 0); } } } } dowork (); /* * Terminate threads */ todo = -2; /* please terminate */ dosync(); for (i = 0; i < nthreads; ++i) { if (0 == tcs[i].stat) assert(pthread_join (tcs[i].thread, NULL) == 0); } /* * destroy locks */ assert(pthread_mutex_destroy (&mutex_stdout) == 0); assert(pthread_mutex_destroy (&mutex_todo) == 0); /* * Cleanup */ printf ("\n"); /* * Show results */ for (i = 0; i < nthreads; ++i) { printf ("%2d ", i); if (0 == tcs[i].stat) printf ("%10ld\n", tcs[i].work); else printf ("failed %d\n", tcs[i].stat); assert(pthread_mutex_unlock(&tcs[i].mutex_start) == 0); assert(pthread_mutex_destroy (&tcs[i].mutex_start) == 0); assert(pthread_mutex_destroy (&tcs[i].mutex_started) == 0); assert(pthread_mutex_destroy (&tcs[i].mutex_end) == 0); assert(pthread_mutex_destroy (&tcs[i].mutex_ended) == 0); } die (0); return (0); }