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-rw-r--r--linuxthreads/Examples/ex4.c115
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diff --git a/linuxthreads/Examples/ex4.c b/linuxthreads/Examples/ex4.c
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-/* 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;
-}