shlib.pl -- Utility library for loading foreign objects (DLLs, shared objects)

This section discusses the functionality of the (autoload) library(shlib), providing an interface to manage shared libraries. We describe the procedure for using a foreign resource (DLL in Windows and shared object in Unix) called mylib.

First, one must assemble the resource and make it compatible to SWI-Prolog. The details for this vary between platforms. The swipl-ld(1) utility can be used to deal with this in a portable manner. The typical commandline is:

swipl-ld -o mylib file.{c,o,cc,C} ...

Make sure that one of the files provides a global function install_mylib() that initialises the module using calls to PL_register_foreign(). Here is a simple example file mylib.c, which creates a Windows MessageBox:

#include <windows.h>
#include <SWI-Prolog.h>

static foreign_t
pl_say_hello(term_t to)
{ char *a;

  if ( PL_get_atom_chars(to, &a) )
  { MessageBox(NULL, a, "DLL test", MB_OK|MB_TASKMODAL);

    PL_succeed;
  }

  PL_fail;
}

install_t
install_mylib()
{ PL_register_foreign("say_hello", 1, pl_say_hello, 0);
}

Now write a file mylib.pl:

:- module(mylib, [ say_hello/1 ]).
:- use_foreign_library(foreign(mylib)).

The file mylib.pl can be loaded as a normal Prolog file and provides the predicate defined in C.

find_library(+LibSpec, -Lib, -Delete) is det[private]

Find a foreign library from LibSpec. If LibSpec is available as a resource, the content of the resource is copied to a temporary file and Delete is unified with true.

load_foreign_library(:FileSpec) is det

load_foreign_library(:FileSpec, +Entry:atom) is det

Load a shared object or DLL. After loading the Entry function is called without arguments. The default entry function is composed from =install_=, followed by the file base-name. E.g., the load-call below calls the function install_mylib(). If the platform prefixes extern functions with =_=, this prefix is added before calling.

      ...
      load_foreign_library(foreign(mylib)),
      ...

Arguments:

FileSpec

- is a specification for absolute_file_name/3. If searching the file fails, the plain name is passed to the OS to try the default method of the OS for locating foreign objects. The default definition of file_search_path/2 searches <prolog home>/lib/<arch> on Unix and <prolog home>/bin on Windows.

See also

- use_foreign_library/1,2 are intended for use in directives.

use_foreign_library(+FileSpec) is det

use_foreign_library(+FileSpec, +Entry:atom) is det

Load and install a foreign library as load_foreign_library/1,2 and register the installation using initialization/2 with the option now. This is similar to using:

:- initialization(load_foreign_library(foreign(mylib))).

but using the initialization/1 wrapper causes the library to be loaded after loading of the file in which it appears is completed, while use_foreign_library/1 loads the library immediately. I.e. the difference is only relevant if the remainder of the file uses functionality of the C-library.

unload_foreign_library(+FileSpec) is det

unload_foreign_library(+FileSpec, +Exit:atom) is det

Unload a shared object or DLL. After calling the Exit function, the shared object is removed from the process. The default exit function is composed from =uninstall_=, followed by the file base-name.

current_foreign_library(?File, ?Public)

Query currently loaded shared libraries.

reload_foreign_libraries

Reload all foreign libraries loaded (after restore of a state created using qsave_program/2.

unload_foreign(+File)[private]

Unload the given foreign file and all `spontaneous' foreign predicates created afterwards. Handling these spontaneous predicates is a bit hard, as we do not know who created them and on which library they depend.