Node:Miscellaneous C API Functions, Previous:Operating System Services, Up:Support

Miscellaneous

A dynamic foreign resource that is used by multiple SICStus run-times in the same process may need to maintain a global state that is kept separate for each SICStus run-time. Each SICStus run-time maintains a location (containing a void*) for each foreign resource. A foreign resource can then access this location to store any data that is specific to the calling SICStus run-time.

void **SP_foreign_stash(void)

You can use SP_foreign_stash() to get access to a location, initially set to NULL, where the foreign resource can store a void*. Typically this would be a pointer to a C struct that holds all information that need to be stored in global variables. This struct can be allocated and initialized by the foreign resource initialization function, it should be deallocated by the foreign resource deinitialization function.

SP_foreign_stash is only available for use in dynamic foreign resources. The value returned by SP_foreign_stash is only valid until the next SICStus API call. The correct way to initialize the location pointed at by SP_foreign_stash is therefore:

struct my_state {...};

init_my_foreign_resource(...)
{
   struct my_state *p = SP_malloc(sizeof(struct my_state));
   (*SP_foreign_stash()) = (void*)p;
}

The following example is incorrect; SP_malloc may be called between the time SP_foreign_stash is called and the time its return value is used:

/* WRONG */
(*SP_foreign_stash()) = SP_malloc(sizeof(struct my_state));

SP_foreign_stash is currently a C macro, not a function. You should not rely on this.