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: http://www.stsci.edu/~sontag/spicedocs/cspice/swpool_c.html
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Add a name to the list of agents to notify whenever a member of a list of kernel variables is updated.
KERNEL
VARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- agent I The name of an agent to be notified after updates. nnames I The number of variables to associate with agent. lenvals I Length of strings in the names array. names I Variable names whose update causes the notice.
agent is the name of a routine or entry point (agency) that
will want to know when a some variables in the kernel
pool have been updated.
nnames is the number of kernel pool variable names that will
be associated with agent.
lenvals is the length of the strings in the array names,
including the null terminators.
names is an array of names of variables in the kernel pool.
Whenever any of these is updated, a notice will be
posted for agent so that one can quickly check
whether needed data has been modified.
None.
None.
The kernel pool is a convenient place to store a wide variety of
data needed by routines in CSPICE and routines that interface with
CSPICE routines. However, when a single name has a large quantity
of data associated with it, it becomes inefficient to constantly
query the kernel pool for values that are not updated on a frequent
basis.
This entry point allows a routine to instruct the kernel pool to
post a message whenever a particular value gets updated. In this
way, a routine can quickly determine whether or not data it requires
has been updated since the last time the data was accessed. This
makes it reasonable to buffer the data in local storage and update
it only when a variable in the kernel pool that affects this data
has been updated.
Note that swpool_c has a side effect. Whenever a call to swpool_c
is made, the agent specified in the calling sequence is added to the
list of agents that should be notified that an update of its
variables has occurred. In other words the code
swpool_c ( agent, nnames, lenvals, names );
cvpool_c ( agent, &update );
will always return update as SPICETRUE.
This feature allows for a slightly cleaner use of swpool_c and
cvpool_c as shown in the example below. Because swpool_c
automatically loads agent into the list of agents to notify of a
kernel pool update, you do not have to include the code for fetching
the initial values of the kernel variables in the initialization
portion of a subroutine. Instead, the code for the first fetch from
the pool is the same as the code for fetching when the pool is
updated.
Suppose that you have an application subroutine, MYTASK, that
needs to access a large data set in the kernel pool. If this
data could be kept in local storage and kernel pool queries
performed only when the data in the kernel pool has been
updated, the routine can perform much more efficiently.
The code fragment below illustrates how you might make use of this
feature.
#include "SpiceUsr.h"
.
.
.
/.
On the first call to this routine establish those variables
that we will want to read from the kernel pool only when
new values have been assigned.
./
if ( first )
{
first = SPICEFALSE;
swpool_c ( "MYTASK", nnames, lenvals, names );
}
/.
If any of the variables has been updated, fetch them from the
kernel pool.
./
cvpool_c ( "MYTASK", &update );
if ( update )
{
for ( i = 0; i < NVAR; i++ )
{
gdpool_c( MYTASK_VAR[i], 1, NMAX, n[i], val[i], &found[i] );
}
}
None.
1) If sufficient room is not available to hold a name or new agent,
a routine in the call tree for this routine will signal an error.
2) If either of the input string pointers are null, the error
SPICE(NULLPOINTER) will be signaled.
3) If any input string agent has length zero, the error
SPICE(EMPTYSTRING) will be signaled.
4) The caller must pass a value indicating the length of the strings
in the names array. If this value is not at least 2, the error
SPICE(STRINGTOOSHORT) will be signaled.
None.
N.J. Bachman (JPL) W.L. Taber (JPL)
None.
-CSPICE Version 1.3.0, 27-AUG-2002 (NJB)
Call to C2F_CreateStrArr_Sig replaced with call to C2F_MapStrArr.
-CSPICE Version 1.2.0, 28-AUG-2001 (NJB)
Const-qualified input array names.
-CSPICE Version 1.1.0, 14-FEB-2000 (NJB)
Calls to C2F_CreateStrArr replaced with calls to error-signaling
version of this routine: C2F_CreateStrArr_Sig.
-CSPICE Version 1.0.0, 05-JUN-1999 (NJB) (WLT)
Watch for an update to a kernel pool variable Notify a routine of an update to a kernel pool variable