6.7.3.2 All-in-one Executables

It is possible to embed saved states into an executable (or shared object). Together with static linking, this gives an all-in-one executable, an executable (or shared object) that does not depend on external SICStus files.

In the simplest case, creating an all-in-one executable main.exe from a saved state main.sav can be done with a command like:

% spld --output=main.exe --static main.sav

This will automatically embed the saved state, any foreign resources needed by the saved state as well the SICStus runtime and its runtime saved state.

Creating a shared object is similar, e.g.

% spld --output=main.dll --shared --static main.sav

but the following examples cover the more common case of creating an ordinary executable.

The keys to this feature are:

• Static linking. By linking an application with a static version of the SICStus runtime, you avoid any dependency on e.g. sprt4-9-0.dll (Windows) or libsprt4-9-0.so (UNIX).

  If the application needs foreign resources (predicates written in C code), as used for example by library(random) and library(clpfd), then these foreign resources can be linked statically with the application as well.

  The remaining component is the Prolog code itself; see the next item.

• Data Resources (in-memory files). It is possible to link an application with data resources that can be read directly from memory. In particular, saved states can be embedded in an application and used when restoring the saved state of the application.

  An application needs two saved states:

  1. The SICStus runtime system (sprt.sav).

     This is added automatically when spld is invoked with the --static (or -S) option unless the spld-option --no-embed-rt-sav is specified. It can also be added explicitly with the option --embed-rt-sav.

  2. The user written code of the application as well as any SICStus libraries.

     This saved state is typically created by loading all application code using compile/1 and then creating the saved state with save_program/2.

Data resources are added by specifying their internal name and the path to a file as part of the comma separated list of resources passed with the spld option --resources. Each data resource is specified as file=name where file is the path to the file containing the data (it must exist during the call to spld) and name is the name used to access the content of file during runtime. A typical choice of name would be the base name, i.e. without directories, of file, preceded by a slash (/). name should begin with a slash (/) and look like an ordinary lowercase file path made up of ‘/’-separated, non-empty, names consisting of ‘a’ to ‘z’, underscore (‘_’, period (‘.’), and digits.

Typically, you would use spld --main=restore, which will automatically restore the first ‘.sav’ argument. To manually restore an embedded saved state you should use the syntax URL:x-sicstus-resource:name, e.g. SP_restore("URL:x-sicstus-resource:/main.sav").

An example will make this clearer. Suppose we create a runtime system that consists of a single file main.pl that looks like:

% main.pl

:- use_module(library(random)).
:- use_module(library(clpfd)).

% This will be called when the application starts:
user:runtime_entry(start) :-
   %% You may consider putting some other code here...
   write('hello world'),nl,
   write('Getting a random value:'),nl,
   random(1,10,R),                  % from random
   writeq(R),nl,
   ( all_different([3,9]) ->        % from clpfd
       write('3 != 9'),nl
   ; otherwise ->
       write('3 = 9!?'),nl
   ).

Then create the saved state main.sav, which will contain the compiled code of main.pl as well as the Prolog code of library(random) and library(clpfd) and other Prolog libraries needed by library(clpfd):

% sicstus -i -f
SICStus 4.9.0 …
Licensed to SICS
| ?- compile(main).
% compiling …/main.pl...
% … loading several library modules
| ?- save_program('main.sav').
% …/main.sav created in 201 msec

| ?- halt.

Finally, tell spld to build an executable statically linked with the SICStus runtime and the foreign resources needed by library(random) and library(clpfd). Also, embed the Prolog runtime saved state and the application specific saved state just created.

As noted above, it is possible to build the all-in-one executable with the command line:

% spld --output=main.exe --static main.sav

but for completeness the example below uses all options as if no options were added automatically.

The example is using Cygwin bash (http://www.cygwin.com) under Windows but would look much the same on other platforms. The command should be given on a single line; it is broken up here for better layout:

% spld
  --output=main.exe
  --static
  --embed-rt-sav
  --main=restore
  --resources=main.sav=/main.sav,clpfd,random

The arguments in the example are as follows:

--output=main.exe

This tells spld where to put the resulting executable.

--static

Link statically with the SICStus runtime and foreign resources (clpfd and random, in this case).

--embed-rt-sav

This option embeds the SICStus runtime ‘.sav’ file (sprt.sav). This option is not needed since it is added automatically by --static.

--main=restore

Start the application by restoring the saved state and calling user:runtime_entry(start). This is not strictly needed in the above example since it is the default if any file with extension ‘.sav’ or a data resource with a name where the extension is ‘.sav’ is specified.

--resources=…

This is followed by comma-separated resource specifications:

main.sav=/main.sav

This tells spld to make the content (at the time spld is invoked) of the file main.sav available at runtime in a data resource named /main.sav. That is, the data resource name corresponding to "URL:x-sicstus-resource:/main.sav".

Alternatively, spld can create a default data resource specification when passed a ‘.sav’ file argument and the option --embed-sav-file (which is the default with --static).

clpfd

random

These tell spld to link with the foreign resources (that is, C-code) associated with library(clpfd) and library(random). Since --static was specified the static versions of these foreign resources will be used.

Alternatively, spld can extract the information about the required foreign resources from the saved state (main.sav). This feature is enabled by adding the option --resources-from-sav (which is the default with --static). Using --resources-from-sav instead of an explicit list of foreign resources is preferred since it is hard to know what foreign resources are used by the SICStus libraries.

Since both --embed-sav-file and --resources-from-sav are the default when --static is used the example can be built simply by doing:

% spld --output=main.exe --static main.sav

Finally, we may run this executable on any machine, even if SICStus is not installed:

bash-2.04$ ./main.exe
hello world
Getting a random value:
4
3 != 9
bash-2.04$