All predicatesShow sourceshlib.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.

Source use_foreign_library(+FileSpec) is det
Source use_foreign_library(+FileSpec, +Options:list) 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.

As of SWI-Prolog 8.1.22, use_foreign_library/1,2 is in provided as a built-in predicate that, if necessary, loads library(shlib). This implies that these directives can be used without explicitly loading library(shlib) or relying on demand loading.

Source 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.
Source lib_to_file(+Lib0, -Lib, -Copy) is det[private]
If Lib0 is not a regular file we need to copy it to a temporary regular file because dlopen() and Windows LoadLibrary() expect a file name. On some systems this can be avoided. Roughly using two approaches (after discussion with Peter Ludemann):
See also
- https://github.com/fancycode/MemoryModule for Windows
Source zipper_members_(+Zipper, -Members) is det[private]
Simplified version of zipper_members/2 from library(zip). We already have a lock on the zipper and by moving this here we avoid dependency on another library.
To be done
- : should we cache this?
Source compatible_architecture_lib(+Entries, +Name, -CompatibleLib) is det[private]
Entries is a list of entries in the zip file, which are already filtered to match the shared library identified by Name. The filtering is done by entries_for_name/3.

CompatibleLib is the name of the entry in the zip file which is compatible with the current architecture. The compatibility is determined according to the description in qsave_program/2 using the qsave:compat_arch/2 hook.

The entries are of the form 'shlib(Arch, Name)'

Source qsave:compat_arch(Arch1, Arch2) is semidet[multifile]
User definable hook to establish if Arch1 is compatible with Arch2 when running a shared object. It is used in saved states produced by qsave_program/2 to determine which shared object to load at runtime.
See also
- foreign option in qsave_program/2 for more information.
Source load_foreign_library(:FileSpec) is det
Source load_foreign_library(:FileSpec, +Options:list) 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. Options provided are below. Other options are passed to open_shared_object/3.
install(+Function)
Installation function to use. Default is default(install), which derives the function from FileSpec.
    ...
    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.
Source unload_foreign_library(+FileSpec) is det
Source 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.
Source current_foreign_library(?File, ?Public)
Query currently loaded shared libraries.
Source reload_foreign_libraries
Reload all foreign libraries loaded (after restore of a state created using qsave_program/2.
Source 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.
Source win_add_dll_directory(+AbsDir) is det[private]
Add AbsDir to the directories where dependent DLLs are searched on Windows systems. This call uses the AddDllDirectory() API when provided. On older Windows systems it extends %PATH%.
Errors
- existence_error(directory, AbsDir) if the target directory does not exist.
- domain_error(absolute_file_name, AbsDir) if AbsDir is not an absolute file name.