1/* Part of SWI-Prolog 2 3 Author: Jan Wielemaker 4 E-mail: J.Wielemaker@vu.nl 5 WWW: http://www.swi-prolog.org 6 Copyright (c) 2008-2024, University of Amsterdam 7 VU University Amsterdam 8 CWI, Amsterdam 9 SWI-Prolog Solutions b.v. 10 All rights reserved. 11 12 Redistribution and use in source and binary forms, with or without 13 modification, are permitted provided that the following conditions 14 are met: 15 16 1. Redistributions of source code must retain the above copyright 17 notice, this list of conditions and the following disclaimer. 18 19 2. Redistributions in binary form must reproduce the above copyright 20 notice, this list of conditions and the following disclaimer in 21 the documentation and/or other materials provided with the 22 distribution. 23 24 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 25 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 26 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 27 FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 28 COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 29 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 30 BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 31 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 32 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 33 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 34 ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 35 POSSIBILITY OF SUCH DAMAGE. 36*/ 37 38:- module(process, 39 [ process_create/3, % +Exe, +Args, +Options 40 process_wait/2, % +PID, -Status 41 process_wait/3, % +PID, -Status, +Options 42 process_id/1, % -PID 43 process_id/2, % +Process, -PID 44 is_process/1, % +PID 45 process_release/1, % +PID 46 process_kill/1, % +PID 47 process_group_kill/1, % +PID 48 process_group_kill/2, % +PID, +Signal 49 process_kill/2, % +PID, +Signal 50 process_which/2, % +Exe, -AbsoluteFile 51 52 process_set_method/1 % +CreateMethod 53 ]). 54:- autoload(library(apply),[maplist/3]). 55:- autoload(library(error),[must_be/2,existence_error/2]). 56:- autoload(library(option),[select_option/3]). 57 58 59:- use_foreign_library(foreign(process)). 60 61:- predicate_options(process_create/3, 3, 62 [ stdin(any), 63 stdout(any), 64 stderr(any), 65 cwd(atom), 66 env(list(any)), 67 environment(list(any)), 68 priority(+integer), 69 process(-integer), 70 detached(+boolean), 71 window(+boolean) 72 ]).
path file alias to
specify an executable file on the current PATH. Args is a list
of arguments that are handed to the new process. On Unix
systems, each element in the list becomes a separate argument in
the new process. In Windows, the arguments are simply
concatenated to form the commandline. Each argument itself is
either a primitive or a list of primitives. A primitive is
either atomic or a term file(Spec). Using file(Spec), the system
inserts a filename using the OS filename conventions which is
properly quoted if needed.
Options:
pipe(Pipe) is used, the Prolog stream is
a stream in text-mode using the encoding of the default
locale. The encoding can be changed using set_stream/2,
or by using the two-argument form of pipe, which accepts an
encoding(Encoding) option.
The options stdout and stderr may use the same stream,
in which case both output streams are connected to the same
Prolog stream.
user_input, etc. are bound to a file handle
but not to 0,1,2 the process I/O is bound to the file
handles of these streams.type(+Type) and encoding(+Encoding) are supported,
which have the same meaning as the stream properties
of the same name (see stream_property/2).
StreamOptions is provided mainly for SICStus compatibility -
the SWI-Prolog predicate set_stream/2 can be used
for the same purpose.file_no).
This option is not provided by the SICStus
implementation.environment(List), but only the specified variables
are passed, i.e., no variables are inherited.Name=Value terms, where Value is expanded
the same way as the Args argument. If neither env nor
environment is passed the environment is inherited from the
Prolog process. At most one env(List) or environment(List) term
may appear in the options. If multiple appear a
permission_error is raised for the second option.true, detach the process from the terminal
Currently mapped to setsid();
Also creates a new process group for the child
In Windows: If true, detach the process from the current
job via the CREATE_BREAKAWAY_FROM_JOB flag. In Vista and beyond,
processes launched from the shell directly have the 'compatibility
assistant' attached to them automatically unless they have a UAC
manifest embedded in them. This means that you will get a
permission denied error if you try and assign the newly-created
PID to a job you create yourself.true, create a window for the process (Windows only)
If the user specifies the process(-PID) option, he must call
process_wait/2 to reclaim the process. Without this option, the
system will wait for completion of the process after the last
pipe stream is closed.
If the process is not waited for, it must succeed with status 0. If not, an process_error is raised.
Windows notes
On Windows this call is an interface to the CreateProcess() API.
The commandline consists of the basename of Exe and the
arguments formed from Args. Arguments are separated by a single
space. If all characters satisfy iswalnum() it is unquoted. If
the argument contains a double-quote it is quoted using single
quotes. If both single and double quotes appear a domain_error
is raised, otherwise double-quote are used.
The CreateProcess() API has many options. Currently only the
CREATE_NO_WINDOW options is supported through the
window(+Bool) option. If omitted, the default is to use this
option if the application has no console. Future versions are
likely to support more window specific options and replace
win_exec/2.
Examples
First, a very simple example that behaves the same as
shell('ls -l'), except for error handling:
?- process_create(path(ls), ['-l'], []).
The following example uses grep to find all matching lines in a file.
grep(File, Pattern, Lines) :-
setup_call_cleanup(
process_create(path(grep), [ Pattern, file(File) ],
[ stdout(pipe(Out))
]),
read_lines(Out, Lines),
close(Out)).
read_lines(Out, Lines) :-
read_line_to_codes(Out, Line1),
read_lines(Line1, Out, Lines).
read_lines(end_of_file, _, []) :- !.
read_lines(Codes, Out, [Line|Lines]) :-
atom_codes(Line, Codes),
read_line_to_codes(Out, Line2),
read_lines(Line2, Out, Lines).
272process_create(Exe, Args, Options) :-
273 ( exe_options(ExeOptions),
274 absolute_file_name(Exe, PlProg, ExeOptions)
275 -> true
276 ),
277 must_be(list, Args),
278 maplist(map_arg, Args, Av),
279 prolog_to_os_filename(PlProg, Prog),
280 Term =.. [Prog|Av],
281 expand_cwd_option(Options, Options1),
282 expand_env_option(env, Options1, Options2),
283 expand_env_option(environment, Options2, Options3),
284 process_create(Term, Options3).
292process_which(Exe, Path) :-
293 exe_options(ExeOptions),
294 absolute_file_name(Exe, Path, [file_errors(fail)|ExeOptions]),
295 !.304exe_options(Options) :- 305 current_prolog_flag(windows, true), 306 !, 307 ( Options = [ extensions(['',exe,com]), access(read), file_errors(fail) ] 308 ; Options = [ extensions(['',exe,com]), access(exist) ] 309 ). 310exe_options(Options) :- 311 Options = [ access(execute) ]. 312 313expand_cwd_option(Options0, Options) :- 314 select_option(cwd(Spec), Options0, Options1), 315 !, 316 ( compound(Spec) 317 -> absolute_file_name(Spec, PlDir, [file_type(directory), access(read)]), 318 prolog_to_os_filename(PlDir, Dir), 319 Options = [cwd(Dir)|Options1] 320 ; exists_directory(Spec) 321 -> Options = Options0 322 ; existence_error(directory, Spec) 323 ). 324expand_cwd_option(Options, Options). 325 326expand_env_option(Name, Options0, Options) :- 327 Term =.. [Name,Value0], 328 select_option(Term, Options0, Options1), 329 !, 330 must_be(list, Value0), 331 maplist(map_env, Value0, Value), 332 NewOption =.. [Name,Value], 333 Options = [NewOption|Options1]. 334expand_env_option(_, Options, Options). 335 336map_env(Name=Value0, Name=Value) :- 337 map_arg(Value0, Value).
file(Spec) or
an atomic value (atom, string, number). If ArgIn is a non-empty
list, all elements are converted and the results are
concatenated.346map_arg([], []) :- !. 347map_arg(List, Arg) :- 348 is_list(List), 349 !, 350 maplist(map_arg_prim, List, Prims), 351 atomic_list_concat(Prims, Arg). 352map_arg(Prim, Arg) :- 353 map_arg_prim(Prim, Arg). 354 355map_arg_prim(file(Spec), File) :- 356 !, 357 ( compound(Spec) 358 -> absolute_file_name(Spec, PlFile) 359 ; PlFile = Spec 360 ), 361 prolog_to_os_filename(PlFile, File). 362map_arg_prim(Arg, Arg).
371process_id(PID) :-
372 current_prolog_flag(pid, PID).
379process_id(PID, PID).
386is_process(PID) :-
387 integer(PID),
388 PID > 0.process_wait(PID, _).
395process_release(PID) :-
396 process_wait(PID, _).infinite. If this option is a number, the
waits for a maximum of Timeout seconds and unifies Status
with timeout if the process does not terminate within
Timeout. In this case PID is not invalidated. On Unix
systems only timeout 0 and infinite are supported. A
0-value can be used to poll the status of the process.release(false) is provided.
421process_wait(PID, Status) :-
422 process_wait(PID, Status, []).term. Signal is an
integer, Unix signal name (e.g. SIGSTOP) or the more Prolog
friendly variation one gets after removing SIG and downcase
the result: stop. On Windows systems, Signal is ignored and
the process is terminated using the TerminateProcess() API. On
Windows systems PID must be obtained from process_create/3,
while any PID is allowed on Unix systems.
438process_kill(PID) :-
439 process_kill(PID, term).term. See process_wait/1 for a description of signal
handling. In Windows, the same restriction on PID applies: it
must have been created from process_create/3, and the the group
is terminated via the TerminateJobObject API.
451process_group_kill(PID) :-
452 process_group_kill(PID, term).spawn (default), fork or vfork. If the method is spawn
but this cannot be used because it is either not supported by the OS
or the cwd(Dir) option is given fork is used.
The problem is to be understood as follows. The official portable
and safe method to create a process is using the fork() system call.
This call however copies the process page tables and get seriously
slow as the (Prolog) process is multiple giga bytes large.
Alternatively, we may use vfork() which avoids copying the process
space. But, the safe usage as guaranteed by the POSIX standard of
vfork() is insufficient for our purposes. On practical systems your
mileage may vary. Modern posix systems also provide posix_spawn(),
which provides a safe and portable alternative for the fork() and
exec() sequence that may be implemented using fork() or may use a
fast but safe alternative. Unfortunately posix_spawn() doesn't
support the option to specify the working directory for the child
and we cannot use working_directory/2 as the working directory is
shared between threads.
Summarizing, the default is safe and tries to be as fast as
possible. On some scenarios and on some OSes it is possible to do
better. It is generally a good idea to avoid using the cwd(Dir)
option of process_create/3 as without we can use posix_spawn().
483 /******************************* 484 * MESSAGES * 485 *******************************/ 486 487:- multifile 488 prolog:error_message/3. 489 490prologerror_message(process_error(File, exit(Status))) --> 491 [ 'Process "~w": exit status: ~w'-[File, Status] ]. 492prologerror_message(process_error(File, killed(Signal))) --> 493 [ 'Process "~w": killed by signal ~w'-[File, Signal] ]. 494prologerror_message(existence_error(source_sink, path(Exe))) --> 495 [ 'Could not find executable file "~p" in '-[Exe] ], 496 path_var. 497 498path_var --> 499 ( { current_prolog_flag(windows, true) } 500 -> [ '%PATH%'-[] ] 501 ; [ '$PATH'-[] ] 502 )
Create processes and redirect I/O
The module library(process) implements interaction with child processes and unifies older interfaces such as shell/[1,2],
open(pipe(command), ...)etc. This library is modelled after SICStus 4.The main interface is formed by process_create/3. If the process id is requested the process must be waited for using process_wait/2. Otherwise the process resources are reclaimed automatically.
In addition to the predicates, this module defines a file search path (see file_search_path/2 and absolute_file_name/3) named
paththat locates files on the system's search path for executables. E.g. the following finds the executable forls:Incompatibilities and current limitations
detached(true)option is supposed to do. Disable signals in the child? Usesetsid()to detach from the session? The current implementation usessetsid()on Unix systems.env([Name=Value, ...])is added to process_create/3. As of version 4.1 SICStus addedenvironment(List)which modifies the environment. A compatible option was added to SWI-Prolog 7.7.23.