initial import

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

flock.c

@@ -0,0 +1,84 @@
+/*
+ * flock.c
+ *
+ * Demonstrate use of stdio file locking to generate an "atomic"
+ * prompting sequence. The write to stdout and the read from
+ * stdin cannot be separated.
+ */
+#include <pthread.h>
+#include "errors.h"
+
+/*
+ * This routine writes a prompt to stdout (passed as the thread's
+ * "arg"), and reads a response. All other I/O to stdin and stdout
+ * is prevented by the file locks until both prompt and fgets are
+ * complete.
+ */
+void *prompt_routine (void *arg)
+{
+    char *prompt = (char*)arg;
+    char *string;
+    int len;
+
+    string = (char*)malloc (128);
+    if (string == NULL)
+        errno_abort ("Alloc string");
+    flockfile (stdin);
+    flockfile (stdout);
+    printf (prompt);
+    if (fgets (string, 128, stdin) == NULL)
+        string[0] = '\0';
+    else {
+        len = strlen (string);
+        if (len > 0 && string[len-1] == '\n')
+            string[len-1] = '\0';
+    }
+    funlockfile (stdout);
+    funlockfile (stdin);
+    return (void*)string;
+}
+
+int main (int argc, char *argv[])
+{
+    pthread_t thread1, thread2, thread3;
+    char *string;
+    int status;
+
+#ifdef sun
+    /*
+     * On Solaris 2.5, threads are not timesliced. To ensure
+     * that our threads can run concurrently, we need to
+     * increase the concurrency level.
+     */
+    DPRINTF (("Setting concurrency level to 4\n"));
+    thr_setconcurrency (4);
+#endif
+    status = pthread_create (
+        &thread1, NULL, prompt_routine, "Thread 1> ");
+    if (status != 0)
+        err_abort (status, "Create thread");
+    status = pthread_create (
+        &thread2, NULL, prompt_routine, "Thread 2> ");
+    if (status != 0)
+        err_abort (status, "Create thread");
+    status = pthread_create (
+        &thread3, NULL, prompt_routine, "Thread 3> ");
+    if (status != 0)
+        err_abort (status, "Create thread");
+    status = pthread_join (thread1, (void**)&string);
+    if (status != 0)
+        err_abort (status, "Join thread");
+    printf ("Thread 1: \"%s\"\n", string);
+    free (string);
+    status = pthread_join (thread2, (void**)&string);
+    if (status != 0)
+        err_abort (status, "Join thread");
+    printf ("Thread 1: \"%s\"\n", string);
+    free (string);
+    status = pthread_join (thread3, (void**)&string);
+    if (status != 0)
+        err_abort (status, "Join thread");
+    printf ("Thread 1: \"%s\"\n", string);
+    free (string);
+    return 0;
+}