Have predict.py fork for itself, and use an alarm to prevent hung processes

predict.py

@@ -70,6 +70,13 @@ def main():
 
     # Set up our command line options
     parser = optparse.OptionParser()
+    parser.add_option('-d', '--cd', dest='directory',
+        help='change to, and run in, directory DIR',
+        metavar='DIR')
+    parser.add_option('--fork', dest='fork', action="store_true",
+            help='detach the process and run in the background')
+    parser.add_option('--alarm', dest='alarm', action="store_true",
+            help='setup an alarm for 10 minutes time to prevent hung processes')
     parser.add_option('-t', '--timestamp', dest='timestamp',
         help='search for dataset covering the POSIX timestamp TIME \t[default: now]', 
         metavar='TIME', type='int',
@@ -133,6 +140,15 @@ def main():
         log.error('Exactly one positional argument should be supplied (uuid).')
         sys.exit(1)
 
+    if options.directory:
+        os.chdir(options.directory)
+
+    if options.fork:
+        detach_process()
+
+    if options.alarm:
+        setup_alarm()
+
     uuid = args[0]
     uuid_path = options.preds_path + "/" + uuid + "/"
 
@@ -518,6 +534,27 @@ def dataset_for_time(time, hd):
     
     raise RuntimeError('Could not find appropriate dataset.')
 
+def detach_process():
+    # Fork
+    if os.fork() > 0:
+        os._exit(0)
+
+    # Detach
+    os.setsid()
+
+    null_fd = os.open(os.devnull, os.O_RDWR)
+    for s in [sys.stdin, sys.stdout, sys.stderr]:
+        os.dup2(null_fd, s.fileno())
+
+    # Fork
+    if os.fork() > 0:
+        os._exit(0)
+
+def setup_alarm():
+    # Prevent hung download:
+    import signal
+    signal.alarm(600)
+
 # If this is being run from the interpreter, run the main function.
 if __name__ == '__main__':
     main()

predict/includes/functions.inc.php

@@ -122,17 +122,13 @@ function runPred($pred_model) {
     $predictor_lat = number_format($pred_model['lat'], 0);
     $predictor_lon = number_format($pred_model['lon'], 0);
 
-    // use `at` to automatically background the task
-    $ph = popen("at now", "w");
-    $sh = "./predict.py -v --latdelta="
+    $sh = ROOT . "/predict.py --cd=" . ROOT . " --fork --alarm -v --latdelta="
         .$pred_model['delta_lat']." --londelta=".$pred_model['delta_lon']
         ." -p1 -f5 -t ".$pred_model['timestamp']
         ." --lat=".$predictor_lat." --lon=".$predictor_lon." " . $use_hd
         . $pred_model['uuid'];
     if (DEBUG) shell_exec("echo " . $sh . " > " . AT_LOG);
-    fwrite($ph, "cd " . ROOT . " && " . $sh );
-    fclose($ph);
-
+    shell_exec($sh);
 }
 
 // Use PHP's mkdir() to create a directory for the prediction data using