threads/thread_cleanup.c

+/* thread_cleanup.c
+
+   An example of thread cancellation using the POSIX threads API:
+   demonstrate the use of pthread_cancel() and cleanup handlers.
+*/
 #include <pthread.h>
 #include "tlpi_hdr.h"
 
 static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
 static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;
 static int glob = 0;                    /* Predicate variable */
 
 static void     /* Free memory pointed to by 'arg' and unlock mutex */
 cleanupHandler(void *arg)
 {
     int s;
 
     printf("cleanup: freeing block at %p\n", arg);
     free(arg);
 
     printf("cleanup: unlocking mutex\n");
     s = pthread_mutex_unlock(&mtx);
     if (s != 0)
         errExitEN(s, "pthread_mutex_unlock");
 }
 
 static void *
 threadFunc(void *arg)
 {
     int s;
     void *buf = NULL;                   /* Buffer allocated by thread */
 
     buf = malloc(0x10000);              /* Not a cancellation point */
     printf("thread:  allocated memory at %p\n", buf);
 
     s = pthread_mutex_lock(&mtx);       /* Not a cancellation point */
     if (s != 0)
         errExitEN(s, "pthread_mutex_lock");
 
     pthread_cleanup_push(cleanupHandler, buf);
 
     while (glob == 0) {
         s = pthread_cond_wait(&cond, &mtx);     /* A cancellation point */
         if (s != 0)
             errExitEN(s, "pthread_cond_wait");
     }
 
     printf("thread:  condition wait loop completed\n");
     pthread_cleanup_pop(1);             /* Executes cleanup handler */
     return NULL;
 }
 
 int
 main(int argc, char *argv[])
 {
     pthread_t thr;
     void *res;
     int s;
 
     s = pthread_create(&thr, NULL, threadFunc, NULL);
     if (s != 0)
         errExitEN(s, "pthread_create");
 
     sleep(2);                   /* Give thread a chance to get started */
 
     if (argc == 1) {            /* Cancel thread */
         printf("main:    about to cancel thread\n");
         s = pthread_cancel(thr);
         if (s != 0)
             errExitEN(s, "pthread_cancel");
 
     } else {                    /* Signal condition variable */
         printf("main:    about to signal condition variable\n");
+
+        s = pthread_mutex_lock(&mtx);   /* See the TLPI page 679 erratum */
+        if (s != 0)
+            errExitEN(s, "pthread_mutex_lock");
+
         glob = 1;
+
+        s = pthread_mutex_unlock(&mtx); /* See the TLPI page 679 erratum */
+        if (s != 0)
+            errExitEN(s, "pthread_mutex_unlock");
+
         s = pthread_cond_signal(&cond);
         if (s != 0)
             errExitEN(s, "pthread_cond_signal");
     }
 
     s = pthread_join(thr, &res);
     if (s != 0)
         errExitEN(s, "pthread_join");
     if (res == PTHREAD_CANCELED)
         printf("main:    thread was canceled\n");
     else
         printf("main:    thread terminated normally\n");
 
     exit(EXIT_SUCCESS);
 }