void cvpool_c ( ConstSpiceChar * agent,
SpiceBoolean * update )
Indicate whether or not any watched kernel variables that have a
specified agent on their notification list have been updated.
KERNEL
SYMBOLS
UTILITY
Variable I/O Description
-------- --- --------------------------------------------------
agent I Name of the agent to check for notices.
update O SPICETRUE if variables for `agent' have been updated.
agent is the name of a function or significant portion of code
that needs to access variables in the kernel pool.
Generally this agent will buffer these variables
internally and fetch them from the kernel pool only when
they are updated.
update is a logical flag that will be set to SPICETRUE if the
variables in the kernel pool that are associated with `agent'
have been updated since the last call to cvpool_c.
`update' will be set to SPICETRUE on the first call made for
the specified agent, whether or not the associated
variables have been updated since the agent was placed
on their notification list, as long as the agent is
associated with any watched variables.
See function szpool_c.
1) If the string pointer for agent is null, the error
SPICE(NULLPOINTER) will be signaled.
2) If the input string haslength zero, the error SPICE(EMPTYSTRING)
will be signaled.
None.
This entry point allows the calling program to determine whether or
not variables associated with with agent have been updated. Making
use of this entry point in conjunction with the entry point swpool_c
(set watch on pool variables) modules can buffer kernel pool
variables they need and fetch values from the kernel pool only when
variables have been updated.
Note that the call to cvpool_c has a side effect. Two consecutive
calls to cvpool_c with the same agent will always result in the
update being SPICEFALSE on the second call. In other words, if you
imbed the following two lines of code in a piece of code
cvpool_c ( agent, &update );
cvpool_c ( agent, &update );
and then test update, it will be SPICEFALSE. The idea is that once
a call to cvpool_c has been made, the kernel pool has performed its
duty and notified the calling routine that one of the agent's
variables has been updated. Consequently, on the second call to
cvpool_c above, the kernel pool will not have any updates to report
about any of agent's variables.
If, on the other hand, you have code such as
cvpool_c ( agent, &update );
furnsh_c ( "myfile.dat" );
cvpool_c ( agent, &update );
the value of update will be true if one of the variables associated
with agent was updated by the call to furnsh_c (and that variable
has been specified as one to watch by call a call to swpool_c).
It should also be noted that any call to cvpool_c that occurs
immediately after a call to swpool_c will result in update being
returned as SPICETRUE In other words, code such as shown below,
will always result in the value of UPDATE as being returned
SPICETRUE:
swpool_c ( agent, nnames, namelen, names );
cvpool_c ( agent, &update );
See the header for swpool_c for a full discussion of this
feature.
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, namelen, 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.
None.
N.J. Bachman (JPL)
W.L. Taber (JPL)
E.D. Wright (JPL)
-CSPICE Version 1.0.2, 30-JUN-2014 (NJB)
Description of the output variable `update' now mentions that
the initial value of SPICETRUE will be returned after an agent
is associated with kernel variables.
-CSPICE Version 1.0.1, 14-AUG-2006 (EDW)
Replace mention of ldpool_c with furnsh_c.
-CSPICE Version 1.0.0, 05-JUN-1999 (NJB) (WLT)
Check the kernel pool for updated variables
Link to routine cvpool_c source file cvpool_c.c
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