The XtCallConverter function looks up the specified type converter in the application context associated with the display and, if the converter was not registered or was registered with cache type XtCacheAll or XtCacheByDisplay looks in the conversion cache to see if this conversion procedure has been called with the specified conversion arguments. If so, it checks the success status of the prior call, and if the conversion failed, XtCallConverter returns False immediately; otherwise it checks the size specified in the to argument and, if it is greater than or equal to the size stored in the cache, copies the information stored in the cache into the location specified by to->addr, stores the cache size into to->size, and returns True. If the size specified in the to argument is smaller than the size stored in the cache, XtCallConverter copies the cache size into the to->size and returns False. If the converter was registered with cache type XtCacheNone or no value was found in the conversion cache, XtCallConverter calls the converter and, if it was not registered with cache type XtCacheNone, enters the result into the cache. XtCallConverter then returns what the converter returned.
The cache_ref_return field specifies storage allocated by the caller in which an opaque value will be stored. If the type converter has been registered with the XtCacheRefCount modifier and if the value returned in in cache_ref_return is non-NULL, then the call should store the cache_ref_return value in order to decrement the reference count when the converted value is no longer required. The cache_ref_return argument should be NULL if the caller is unwilling or unable to store the value.