FAQ

• How to initialize the DD system?
  One process calling dds_create().
• How to remove the DD system?
  Send a SIGHUP (more precisely $DD_SHUTDOWN_SIGNAL to the garbage demon.
• How to remove one process from the DD system? Send a SIGHUP (more precisely $DD_SHUTDOWN_SIGNAL to this process.
• When does the DD system cease to exist?
  When the garbage demon sees that there are no more processes attached to it. Optional: When a fatal error is detected or the garbage demon receives a SIGHUP signal.
• How to be a DD producer?
  Attach to the INPUT fifo.
• How to be a DD consumer?
  Attach to a fifo of your choice.
• How to attach to the DD system?
  Call ddu_attach().
• How does a process know, whether it is attached to the DD system and the latter still exists?
  Call ddu_attached().
• How to have multiple DDs running on the same host?
  Define the environment variable DD_NAME.
• How to attach to a DD system over the network?
  Define DD_NAME as dd_system@node.
• What happens if a user process dies?
  Under normal conditions an exiting process calls ddu_close upon exit (C routine atexit). However this doesn't work in all cases (e.g. when running a program crashes while running in certain debuggers). In this case the fifo can be filled with empty buffers. The garbage demon will detect this situation and remove the fifo (if the fifo is not protected - see ddu_set_protection.
• Why are the shared memory segments and semaphores still present for a few seconds after the last process detached from the DD system
  The garbage demon typically waits a few seconds before he closes down the DD system to make sure that it is really not in use anymore.
• Which are the most important demonstration programs?
  They are all located in $DD_BIN:
  • dd_test: A simple test program that attaches to the DD system and accepts commands from the standard input.
  • dd_test_p : A simple producer.
  • dd_test_c : A simple consumer.
  • dd_ui : An X11/OSF motif based user interface to the DD system.
  • ddr_ui: A user interface monitoring the fifos.
  • ddp_ui: A user interface monitoring the processes.
• How to get rid any processes that are still alive?
  Call dd_cleanup. Note: you may want to change this script.
• Where to complain and report errors?
  witzig@bnl.gov