initial import

from
http://www.informit.com/store/programming-with-posix-threads-9780201633924

cond.c

@@ -0,0 +1,95 @@
+/*
+ * cond.c
+ *
+ * Demonstrate a simple condition variable wait.
+ */
+#include <pthread.h>
+#include <time.h>
+#include "errors.h"
+
+typedef struct my_struct_tag {
+    pthread_mutex_t     mutex;  /* Protects access to value */
+    pthread_cond_t      cond;   /* Signals change to value */
+    int                 value;  /* Access protected by mutex */
+} my_struct_t;
+
+my_struct_t data = {
+    PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER, 0};
+
+int hibernation = 1;            /* Default to 1 second */
+
+/*
+ * Thread start routine. It will set the main thread's predicate
+ * and signal the condition variable.
+ */
+void *
+wait_thread (void *arg)
+{
+    int status;
+
+    sleep (hibernation);
+    status = pthread_mutex_lock (&data.mutex);
+    if (status != 0)
+        err_abort (status, "Lock mutex");
+    data.value = 1;             /* Set predicate */
+    status = pthread_cond_signal (&data.cond);
+    if (status != 0)
+        err_abort (status, "Signal condition");
+    status = pthread_mutex_unlock (&data.mutex);
+    if (status != 0)
+        err_abort (status, "Unlock mutex");
+    return NULL;
+}
+
+int main (int argc, char *argv[])
+{
+    int status;
+    pthread_t wait_thread_id;
+    struct timespec timeout;
+
+    /*
+     * If an argument is specified, interpret it as the number
+     * of seconds for wait_thread to sleep before signaling the
+     * condition variable.  You can play with this to see the
+     * condition wait below time out or wake normally.
+     */
+    if (argc > 1)
+        hibernation = atoi (argv[1]);
+
+    /*
+     * Create wait_thread.
+     */
+    status = pthread_create (&wait_thread_id, NULL, wait_thread, NULL);
+    if (status != 0)
+        err_abort (status, "Create wait thread");
+
+    /*
+     * Wait on the condition variable for 2 seconds, or until
+     * signaled by the wait_thread. Normally, wait_thread
+     * should signal. If you raise "hibernation" above 2
+     * seconds, it will time out.
+     */
+    timeout.tv_sec = time (NULL) + 2;
+    timeout.tv_nsec = 0;
+    status = pthread_mutex_lock (&data.mutex);
+    if (status != 0)
+        err_abort (status, "Lock mutex");
+
+    while (data.value == 0) {
+        status = pthread_cond_timedwait (
+            &data.cond, &data.mutex, &timeout);
+        if (status == ETIMEDOUT) {
+            printf ("Condition wait timed out.\n");
+            break;
+        }
+        else if (status != 0)
+            err_abort (status, "Wait on condition");
+    }
+
+    if (data.value != 0)
+        printf ("Condition was signaled.\n");
+    status = pthread_mutex_unlock (&data.mutex);
+    if (status != 0)
+        err_abort (status, "Unlock mutex");
+    return 0;
+}