🚀 go-pugleaf

    [W]hen I'm debugging some new hardware and software, sometimes a process
    will get into an RWAST state and DCL cannot kill it.  I spoke to the
    DEC folks in Colorado and they confirmed that reboot is the only option
    here (I had been using STOP/ID=nnn, which gives no error message, but
    doesn't do anything either).
    
    Can anyone give me a more favorable second opinion?  Is rebooting the only
    option to getting rid of a process in the RWAST state?  If so, why does
    DEC allow VMS to create processes that it can't delete?

RWAST is a kind of a catch-all wait state:  It means the process needs some
resource that it currently can't get, but it is expected that the delivery of
an AST will make some of that resource available.   A common example occurs
when a process issues a QIO for buffered I/O but already has as many outstand-
ing buffered I/O requests as it is allowed (BIOlm).  A completely different
example occurs when a process that has ACP/XQP work outstanding is deleted;
it will wait in RWAST state until that work completes.

Not all RWAST processes are undeletable.  The example you cite involving the
TK50 is probably undeletable because it is waiting for the mag tape ACP to
finish the operation it requested, which will never happen.  VMS can't delete
the process because it would leave the ACP confused.  (The ACP might possibly
be taught to deal with that, but in the case of XQP operations, which are
really taking place within the process, deleting the process while the XQP is
busy stands a good chance of corrupting a disk.)

There will always be cases in any operating system in which a process hangs
while in a some state - such as holding some important resource like a low-
level disk structure, which it may or may not have modified into some inter-
mediate state - in which it cannot be safely deleted.  Such a "dead" process
often isn't really doing anything harmful - it's just that the OS can't be
SURE, so has to assume the worst.  It costs you very little to just leave
the RWAST (or whatever) process alone; in most cases, you don't HAVE to re-
boot.
							-- Jerry
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