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-rw-r--r--linuxthreads/Examples/ex3.c144
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diff --git a/linuxthreads/Examples/ex3.c b/linuxthreads/Examples/ex3.c
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+/* Multi-thread searching.
+ Illustrates: thread cancellation, cleanup handlers. */
+
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <pthread.h>
+
+/* Defines the number of searching threads */
+#define NUM_THREADS 5
+
+/* Function prototypes */
+void *search(void *);
+void print_it(void *);
+
+/* Global variables */
+pthread_t threads[NUM_THREADS];
+pthread_mutex_t lock;
+int tries;
+
+int main(argc, argv)
+ int argc;
+ char ** argv;
+{
+ int i;
+ int pid;
+
+ /* create a number to search for */
+ pid = getpid();
+ printf("Searching for the number = %d...\n", pid);
+
+ /* Initialize the mutex lock */
+ pthread_mutex_init(&lock, NULL);
+
+ /* Create the searching threads */
+ for (i=0; i<NUM_THREADS; i++)
+ pthread_create(&threads[i], NULL, search, (void *)pid);
+
+ /* Wait for (join) all the searching threads */
+ for (i=0; i<NUM_THREADS; i++)
+ pthread_join(threads[i], NULL);
+
+ printf("It took %d tries to find the number.\n", tries);
+
+ /* Exit the program */
+ return 0;
+}
+
+/* This is the cleanup function that is called
+ when the threads are cancelled */
+
+void print_it(void *arg)
+{
+ int *try = (int *) arg;
+ pthread_t tid;
+
+ /* Get the calling thread's ID */
+ tid = pthread_self();
+
+ /* Print where the thread was in its search when it was cancelled */
+ printf("Thread %lx was canceled on its %d try.\n", tid, *try);
+}
+
+/* This is the search routine that is executed in each thread */
+
+void *search(void *arg)
+{
+ int num = (int) arg;
+ int i, j, ntries;
+ pthread_t tid;
+
+ /* get the calling thread ID */
+ tid = pthread_self();
+
+ /* use the thread ID to set the seed for the random number generator */
+ /* Since srand and rand are not thread-safe, serialize with lock */
+ pthread_mutex_lock(&lock);
+ srand((int)tid);
+ i = rand() & 0xFFFFFF;
+ pthread_mutex_unlock(&lock);
+ ntries = 0;
+
+ /* Set the cancellation parameters --
+ - Enable thread cancellation
+ - Defer the action of the cancellation */
+
+ pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
+ pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, NULL);
+
+ /* Push the cleanup routine (print_it) onto the thread
+ cleanup stack. This routine will be called when the
+ thread is cancelled. Also note that the pthread_cleanup_push
+ call must have a matching pthread_cleanup_pop call. The
+ push and pop calls MUST be at the same lexical level
+ within the code */
+
+ /* Pass address of `ntries' since the current value of `ntries' is not
+ the one we want to use in the cleanup function */
+
+ pthread_cleanup_push(print_it, (void *)&ntries);
+
+ /* Loop forever */
+ while (1) {
+ i = (i + 1) & 0xFFFFFF;
+ ntries++;
+
+ /* Does the random number match the target number? */
+ if (num == i) {
+ /* Try to lock the mutex lock --
+ if locked, check to see if the thread has been cancelled
+ if not locked then continue */
+ while (pthread_mutex_trylock(&lock) == EBUSY)
+ pthread_testcancel();
+
+ /* Set the global variable for the number of tries */
+ tries = ntries;
+ printf("Thread %lx found the number!\n", tid);
+
+ /* Cancel all the other threads */
+ for (j=0; j<NUM_THREADS; j++)
+ if (threads[j] != tid) pthread_cancel(threads[j]);
+
+ /* Break out of the while loop */
+ break;
+ }
+
+ /* Every 100 tries check to see if the thread has been cancelled. */
+ if (ntries % 100 == 0) {
+ pthread_testcancel();
+ }
+ }
+
+ /* The only way we can get here is when the thread breaks out
+ of the while loop. In this case the thread that makes it here
+ has found the number we are looking for and does not need to run
+ the thread cleanup function. This is why the pthread_cleanup_pop
+ function is called with a 0 argument; this will pop the cleanup
+ function off the stack without executing it */
+
+ pthread_cleanup_pop(0);
+ return((void *)0);
+}
+