Re: Semaphore lifecycle?

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

> The semaphore should exists as long it is not
> deleted or the OS restarts.

semget(2) and semctl(2) mention as explanation text sem_overview(7)
which is mainly about POSIX semaphores.

It promises persistence only for named semaphores:

  Persistence
    POSIX  named  semaphores  have  kernel  persistence:  if not removed by
    sem_unlink(3), a semaphore will exist until the system is shut down.

It fewly talks of sem*(2) calls:

  NOTES
    System V semaphores (semget(2), semop(2), etc.) are an older
    semaphore API.

It might be that the SysV variant has been re-implemented on base of
the POSIX variant and that traditional SysV persistence fell victim.
Or it might be that the usage pattern of IPC namespaces has changed
so that this statement of ipc_namespaces(7) gets into effect:

  When an IPC namespace is destroyed (i.e., when the last process that
  is a member of the namespace terminates), all IPC objects in the
  namespace are automatically destroyed.

The Linux man pages push people towards using POSIX semaphores. In your
use case probably towards named ones.


> Also if I start the program with nohup and & it will stay executed.

By what loop inside ? The program you show will simply end after printing
its "OK" message.


Have a nice day :)

Thomas