Esempio di come non fare una sleep. Da un vecchio suggerimento fatto

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diff --git a/sources/sleep-me.c b/sources/sleep-me.c
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+++ b/sources/sleep-me.c
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+/* sleep-me.c
+ * 
+ * Copyright (C) 2012 Simone Piccardi
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or (at
+ * your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+/*****************************************************************************
+ *
+ * File sleep-me.c: An example on how NOT to wait for a time...
+ * thanks to M.E. for suggesting it (for serious) some time ago in the
+ * FLUG (Firenze Linux User Group) mailing list
+ *
+ * Author: S. Piccardi Jan. 2012
+ *
+ *****************************************************************************/
+#include <sys/types.h>   /* primitive system data types */
+#include <sys/stat.h>    /* file characteristics constants and functions */
+#include <unistd.h>      /* unix standard library */
+#include <stdio.h>
+#include <time.h>
+#include <stdlib.h>
+
+/*
+ * Program sleep-me.c
+ *
+ * Wait for N second (burning CPU...)
+ */
+/* Help printing routine */
+void usage(void);
+/* computation function for dir_scan */
+int main(int argc, char *argv[]) 
+{
+    time_t now, end;
+    int i, wait=0;
+    /*
+     * Input section: decode command line parameters 
+     * Use getopt function
+     */
+    opterr = 0;         /* don't want writing to stderr */
+    while ( (i = getopt(argc, argv, "h")) != -1) {
+       switch (i) {
+       /* 
+        * Handling options 
+        */ 
+       case 'h':                                            /* help option */
+           printf("Wrong -h option use\n");
+           usage();
+           return -1;
+           break;
+       case '?':                                    /* unrecognized options */
+           printf("Unrecognized options -%c\n",optopt);
+           usage();
+       default:                                       /* should not reached */
+           usage();
+       }
+    }
+    /* ***********************************************************
+     * 
+     *          Options processing completed
+     *
+     *               Main code beginning
+     * 
+     * ***********************************************************/
+    if ((argc - optind) != 1) {          /* There must be remaing parameters */
+       printf("Wrong number of arguments %d\n", argc - optind);
+        usage();
+    }
+    printf("I will burn CPU for %s seconds\n", argv[1]);
+    wait = atoi(argv[1]);
+    printf("wait %d sec.\n", wait);
+    if (wait != 0) {
+       end = time(NULL)+ wait;
+    } else {
+       usage();
+    }
+    printf("now %d, end %d sec.\n",now, end);
+    now = time(NULL);
+    while (now < end) { 
+       now = time(NULL);
+    }
+    exit(0);
+}
+/*
+ * routine to print usage info and exit
+ */
+void usage(void) {
+    printf("Program sleep-me: wait burning CPU cicles \n");
+    printf("Usage:\n");
+    printf("  sleep-me [-h] -t sec \n");
+    printf("  -t sec      wait sec seconds\n");
+    printf("  -h          print this help\n");
+    exit(1);
+}