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Diffstat (limited to 'linuxthreads/Examples/ex4.c')
-rw-r--r-- | linuxthreads/Examples/ex4.c | 115 |
1 files changed, 0 insertions, 115 deletions
diff --git a/linuxthreads/Examples/ex4.c b/linuxthreads/Examples/ex4.c deleted file mode 100644 index 5c8b929e22..0000000000 --- a/linuxthreads/Examples/ex4.c +++ /dev/null @@ -1,115 +0,0 @@ -/* Making a library function that uses static variables thread-safe. - Illustrates: thread-specific data, pthread_once(). */ - -#include <stddef.h> -#include <stdio.h> -#include <stdlib.h> -#include <string.h> -#include <pthread.h> - -/* This is a typical example of a library function that uses - static variables to accumulate results between calls. - Here, it just returns the concatenation of all string arguments - that were given to it. */ - -#if 0 - -char * -str_accumulate (char *s) -{ - static char accu[1024] = { 0 }; - strcat (accu, s); - return accu; -} - -#endif - -/* Of course, this cannot be used in a multi-threaded program - because all threads store "accu" at the same location. - So, we'll use thread-specific data to have a different "accu" - for each thread. */ - -/* Key identifying the thread-specific data */ -static pthread_key_t str_key; -/* "Once" variable ensuring that the key for str_alloc will be allocated - exactly once. */ -static pthread_once_t str_alloc_key_once = PTHREAD_ONCE_INIT; - -/* Forward functions */ -static void str_alloc_key (void); -static void str_alloc_destroy_accu (void *accu); - -/* Thread-safe version of str_accumulate */ - -static char * -str_accumulate (const char *s) -{ - char *accu; - - /* Make sure the key is allocated */ - pthread_once (&str_alloc_key_once, str_alloc_key); - /* Get the thread-specific data associated with the key */ - accu = (char *) pthread_getspecific (str_key); - /* It's initially NULL, meaning that we must allocate the buffer first. */ - if (accu == NULL) - { - accu = malloc (1024); - if (accu == NULL) - return NULL; - accu[0] = 0; - /* Store the buffer pointer in the thread-specific data. */ - pthread_setspecific (str_key, (void *) accu); - printf ("Thread %lx: allocating buffer at %p\n", pthread_self (), accu); - } - /* Now we can use accu just as in the non thread-safe code. */ - strcat (accu, s); - return accu; -} - -/* Function to allocate the key for str_alloc thread-specific data. */ - -static void -str_alloc_key (void) -{ - pthread_key_create (&str_key, str_alloc_destroy_accu); - printf ("Thread %lx: allocated key %d\n", pthread_self (), str_key); -} - -/* Function to free the buffer when the thread exits. */ -/* Called only when the thread-specific data is not NULL. */ - -static void -str_alloc_destroy_accu (void *accu) -{ - printf ("Thread %lx: freeing buffer at %p\n", pthread_self (), accu); - free (accu); -} - -/* Test program */ - -static void * -process (void *arg) -{ - char *res; - res = str_accumulate ("Result of "); - res = str_accumulate ((char *) arg); - res = str_accumulate (" thread"); - printf ("Thread %lx: \"%s\"\n", pthread_self (), res); - return NULL; -} - -int -main (int argc, char **argv) -{ - char *res; - pthread_t th1, th2; - - res = str_accumulate ("Result of "); - pthread_create (&th1, NULL, process, (void *) "first"); - pthread_create (&th2, NULL, process, (void *) "second"); - res = str_accumulate ("initial thread"); - printf ("Thread %lx: \"%s\"\n", pthread_self (), res); - pthread_join (th1, NULL); - pthread_join (th2, NULL); - return 0; -} |