Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Mon, 27 Oct 2008 15:48:00 +0100

Andrew Johnson wrote:
Unfortunately there are major problems with doing this in a running IOC: we
don't have locks in all the database structures that need to be modified when
a new record instance is created, which makes this a precarious activity.
The current dbStaticLib design assumes that all record creation happens while
the IOC is running single-threaded before initialization of any scan or
server threads. For example, the pdbbase->ppvd structure which is a hash
table of all the record instances has no locks, so one or more server threads
could be searching for PV names in the hash bucket linked list that your new
record instance gets added to.
Looking at the code in base/src/dbStatic/dbPvdLib.c I can see several ways
that simultaneous calls to dbPvdFind() and dbPvdAdd() in different threads
could cause a segfault, because this code has not been written with that
possibility in mind.

It might be possible to make this thread-safe by disabling interrupts before
calling dbPvdAdd().
Dirk
--
Dr. Dirk Zimoch
Paul Scherrer Institut, WBGB/006
5232 Villigen PSI, Switzerland
Phone +41 56 310 5182

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System