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 -shared -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(). Below is a simple example file mylib.c,
which prints a "hello" message. Note that we use SWI-Prolog's Sprintf()
rather than C standard printf() to print the outout through
Prolog's
current_output stream, making the example work in a
windowed environment. The standard C printf() works in a
console environment, but this bypasses Prolog's output redirection. Also
note the use of the standard C bool type, which is
supported in 9.2.x and more actively promoted in the 9.3.x development
series.
#include <SWI-Prolog.h>
#include <SWI-Stream.h>
#include <stdbool.h>
static foreign_t
pl_say_hello(term_t to)
{ char *s;
if ( PL_get_chars(to, &s, CVT_ALL|REP_UTF8) )
{ Sprintf("hello %Us", s);
return true;
}
return false;
}
install_t
install_mylib(void)
{ 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. The generated mylib.so
(or .dll, etc.) must be placed in a directory searched for
using the Prolog search path
foreign (see absolute_file_name/3).
To load this from the current directory, we can use the -p alias=dir
option:
swipl -p foreign=. mylib.pl
?- say_hello(world).
hello world
true.
- [det]use_foreign_library(+FileSpec)
- [det]use_foreign_library(+FileSpec,
+Options:list)
- 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.
- [semidet,multifile]qsave:compat_arch(Arch1,
Arch2)
- 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.
- [det]load_foreign_library(:FileSpec)
- [det]load_foreign_library(:FileSpec,
+Options:list)
- 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)),
...
| 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.
- [det]unload_foreign_library(+FileSpec)
- [det]unload_foreign_library(+FileSpec,
+Exit:atom)
- 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.
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