From: Phillip Helbig [HELBPHI@sysdev.deutsche-boerse.com]
Sent: Wednesday, April 02, 2003 10:10 AM
To: Info-VAX@Mvb.Saic.Com
Subject: Re: New SPAWN behavior with V7.3-1

> Instead of creating process name sequentially, i.e SYSTEM_1, SYSTEM_2,
> we now generate a random number between 0-255. So your first spawned
> process might be called SYSTEM_57. 

In case anyone doesn't have a 7.3-1 system, below is the exemplary HELP 
on this topic.

First, there is a typo: "one is found that unique" should be "one is
found that is unique".

Wouldn't the following mechanism be even more efficient?  When a new 
subprocess is created, define DCL$SUBPROCESS_NUMBER or whatever in the 
group table to be that number.  Before a process is created, it will 
translate this logical name and increment it by 1.  (One should still 
try again if the process already exists in case two processes were 
simultaneously creating subprocesses, someone created processes with the 
corresponding names by hand etc, but this would happen only occasionally 
and the trial-and-error stuff would only kick in when such a subprocess 
actually already existed.)  I'm not an internals guy, but it seems to me 
that one define and one translation of a logical name with each creation 
would be negligible compared with the full subprocess creation, and 
especially compared to a tried and failed creation, which will still 
happen occasionally even with the new system (unless the random numbers 
aren't truly random, but rather the sequence (preferably of the full 
length of 255) runs once before repeating (perhaps in the same order).

---------8<-------------------------------------------------------------------

SYS_PARAMETERS

  DCL_CTLFLAGS

       DCL_CTLFLAGS is a bitmask used to alter default behavior for
       certain commands on a systemwide basis. At present, only the low
       bit of the bitmask is defined. The low bit controls the default
       process-name assignment for a subprocess created using the SPAWN
       command or LIB$SPAWN routine.

       Prior to OpenVMS Version 7.3-1, if no process name was supplied,
       the system constructed a name by appending _n to the username,
       where n was the next available non-duplicate integer for any
       process currently in the system. For example, the first spawned
       process from user SYSTEM would be called SYSTEM_1, the second,
       SYSTEM_2, and so on. The next available number was chosen, as
       soon as a gap was found.

       A problem with this technique is that determining the next
       available number is very expensive in terms of performance,
       because the mechanism attempts to create the process by
       incrementing names until one is found that unique. When several
       subprocesses already exist, the cost of creating the subprocess
       iteratively becomes even more expensive. When many processes are
       in the same OpenVMS group, the cost multiplies because process
       names must be unique throughout the group.

       Beginning in OpenVMS Version 7.3-1, the default constructed
       process name for subprocesses has changed. Instead of
       incrementally searching for the next unique number, a random
       number is chosen to append to the username. Therefore, the first
       processes that are spawned from user SYSTEM might be SYSTEM_
       154, SYSTEM_42, SYSTEM_87, and so on. This procedure results in
       a very high probability of finding a unique name on the first
       try, because it is unlikely that the same number is already
       in use. This greatly reduces the cost of process creation,
       and applications that rely on spawned subprocesses might see a
       dramatic performance improvement due to this change.

       However, some applications might rely on the previous method
       of assigning subprocess names. The DCL_CTLFLAGS parameter is
       available to allow you to configure the system as necessary.

       Bit 0 of DCL_CTLFLAGS selects the behavior for assigning default
       subprocess names:

       o  If the bit is clear, the new behavior is used. If you do not
          specify a process name, the system assigns the username with a
          random number suffix. This is the default setting.

       o  If the bit is set, the prior behavior is used. If you do not
          specify a process name, the system assigns the username with a
          random number suffix.