/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           https://www.swi-prolog.org
    Copyright (c)  2008-2025, University of Amsterdam
                              VU University Amsterdam
                              CWI, Amsterdam
                              SWI-Prolog Solutions b.v.
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

    1. Redistributions of source code must retain the above copyright
       notice, this list of conditions and the following disclaimer.

    2. Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in
       the documentation and/or other materials provided with the
       distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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*/

:- module(process,
          [ process_create/3,           % +Exe, +Args, +Options
            process_wait/2,             % +PID, -Status
            process_wait/3,             % +PID, -Status, +Options
            process_id/1,               % -PID
            process_id/2,               % +Process, -PID
            is_process/1,               % +PID
            process_release/1,          % +PID
            process_kill/1,             % +PID
            process_group_kill/1,       % +PID
            process_group_kill/2,       % +PID, +Signal
            process_kill/2,             % +PID, +Signal
            process_which/2,            % +Exe, -AbsoluteFile

            process_set_method/1        % +CreateMethod
          ]).
:- multifile prolog:prolog_tool/4.
:- dynamic   prolog:prolog_tool/4.

:- autoload(library(apply),[maplist/3]).
:- autoload(library(error),[must_be/2,existence_error/2]).
:- autoload(library(option),[select_option/3]).

:- use_foreign_library(foreign(process)).

:- predicate_options(process_create/3, 3,
                     [ stdin(any),
                       stdout(any),
                       stderr(any),
                       cwd(atom),
                       env(list(any)),
                       environment(list(any)),
                       priority(+integer),
                       process(-integer),
                       detached(+boolean),
                       window(+boolean)
                     ]).

/** <module> 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 user:file_search_path/2 and absolute_file_name/3) named `path` that
locates files on the system's  search   path  for  executables. E.g. the
following finds the executable for `ls`:

    ?- absolute_file_name(path(ls), Path, [access(execute)]).

__Incompatibilities and current limitations__

  - Where SICStus distinguishes between an internal process id and
    the OS process id, this implementation does not make this
    distinction. This implies that is_process/1 is incomplete and
    unreliable.

  - It is unclear what the detached(true) option is supposed to do.
    Disable signals in the child? Use setsid() to detach from the
    session? The current implementation uses setsid() on Unix systems.

  - An extra option env([Name=Value, ...]) is added to
    process_create/3.  As of version 4.1 SICStus added
    environment(List) which _modifies_ the environment.  A
    compatible option was added to SWI-Prolog 7.7.23.

  - Using prolog(Tool) for `Exe` is a SWI-Prolog extension.

@tbd    Implement detached option in process_create/3
@compat SICStus 4
*/


%!  process_create(+Exe, +Args:list, +Options) is det.
%
%   Create a new process running the file   Exe and using arguments from
%   the  given  list.  Exe  is  a    file  specification  as  handed  to
%   absolute_file_name/3. Typically one use  the   `path`  file alias to
%   specify an executable file on the current PATH. The path `prolog` is
%   reserved. If Exe is prolog(Tool), a   Prolog utility is invoked that
%   belongs to the distribution of the calling Prolog process. `Tool` is
%   one of ``self``,  ``swipl``,  ``swipl-win``   or  ``swipl-ld``.  See
%   prolog:prolog_tool/4 for details.
%
%   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:
%
%       - stdin(Spec)
%       - stdout(Spec)
%       - stderr(Spec)
%         Bind the standard streams of the new   process. Spec is one of
%         the terms below. If 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.
%
%           - std
%             Just share with the Prolog I/O   streams.  On Unix, if the
%             `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.
%           - null
%             Bind to a _null_ stream. Reading from such a stream
%             returns end-of-file, writing produces no output
%           - pipe(-Stream)
%           - pipe(-Stream, +StreamOptions)
%             Attach  input  and/or  output  to  a  Prolog  stream.  The
%             optional StreamOptions argument is a  list of options that
%             affect the stream. Currently only  the options 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.
%           - stream(+Stream)
%             Attach input or output to an  existing Prolog stream. This
%             stream must be associated with  an   OS  file  handle (see
%             stream_property/2, property `file_no`).  This   option  is
%             __not__ provided by the SICStus implementation.
%
%       - cwd(+Directory)
%         Run the new process in Directory.  Directory can be a compound
%         specification, which is converted  using absolute_file_name/3.
%         See also process_set_method/1.
%       - env(+List)
%         As environment(List), but _only_ the specified variables
%         are passed, i.e., no variables are _inherited_.
%       - environment(+List)
%         Specify  _additional_  environment  variables    for  the  new
%         process. List is a list of   `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.
%       - process(-PID)
%         Unify PID with the process id of the created process.
%       - detached(+Bool)
%         In Unix: If `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.
%       - window(+Bool)
%         If `true`, create a window for the process (Windows only)
%       - priority(+Priority)
%         In Unix: specifies the process priority  for the newly created
%         process. Priority must be  an  integer   between  -20  and 19.
%         Positive values are nicer to others,   and negative values are
%         less so. The default is zero. Users   are  free to lower their
%         own priority. Only the super-user may  _raise_ it to less-than
%         zero.
%
%   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).
%   ```
%
%   @error  process_error(Exe, Status) where Status is one of
%           exit(Code) or killed(Signal).  Raised if the process
%           is waited for (i.e., Options does not include
%           process(-PID)), and does not exit with status 0.
%   @bug    On Windows, environment(List) is handled as env(List),
%           i.e., the environment is not inherited.

process_create(prolog(Prolog), Args, Options) =>
    prolog_executable(Prolog, Exe, Args, Args1),
    process_create(Exe, Args1, Options).
process_create(Exe, Args, Options) =>
    (   exe_options(ExeOptions),
        absolute_file_name(Exe, PlProg, ExeOptions)
    ->  true
    ),
    must_be(list, Args),
    maplist(map_arg, Args, Av),
    prolog_to_os_filename(PlProg, Prog),
    Term =.. [Prog|Av],
    expand_cwd_option(Options, Options1),
    expand_env_option(env, Options1, Options2),
    expand_env_option(environment, Options2, Options3),
    process_create(Term, Options3).

%!  prolog_executable(+Tool, -Exe, +ArgvIn, -Argv) is det.
%!  prolog:prolog_tool(+Tool, -Exe, +ArgvIn, -Argv) is semidet.
%
%   Find the executable and commandline arguments for running Tool. This
%   provides    a    hook     for      process_create/3     called    as
%   process_create(prolog(Tool), ...). Tool is currently one of:
%
%     - `self`
%       Run Prolog itself.
%     - `swipl`
%       Run the commandline version, also when called from the
%       ``swipl-win`` _app_.
%     - `swipl-win`
%       Run the ``swipl-win`` _app_, also when called from the
%       commandline version.
%     - `swipl-ld`
%       Run the C/C++ compiler frontend to embed Prolog or build
%       foreign extensions.
%
%    prolog:prolog_tool/4 is defined as multifile and dynamic and can be
%    used for special cases. This hook is  notably intended to provide a
%    portable way of calling Prolog when Prolog is embedded.
%
%    For               example,               when                 using
%    [rswipl](https://cran.r-project.org/web/packages/rolog/vignettes/rswipl.html),
%    we can run Prolog using
%
%        R -s -e 'rswipl::swipl()' --args <Prolog Argv>
%
%    We can make process_create(prolog(swipl), ...) work using
%
%    ```
%    :- multifile prolog:prolog_tool/4.
%    prolog:prolog_tool(swipl, path('R'), Argv,
%                       [ '-s', '-e', 'rswipl::swipl()', '--args'
%                       | Argv
%                       ]).
%    ```

prolog_executable(Prolog, Exe, Args0, Args),
    prolog:prolog_tool(Prolog, Exe, Args0, Args) =>
    true.
prolog_executable(self, Exe, Args0, Args) =>
    current_prolog_flag(executable, Exe),
    add_home_option(Args0, Args).
prolog_executable(Tool, Exe, Args0, Args),
    swipl_tool(Tool) =>
    current_prolog_flag(executable, Me),
    neighbour_exe(Tool, Me, Exe),
    add_home_option(Args0, Args).

swipl_tool(swipl).
swipl_tool('swipl-win').
swipl_tool('swipl-ld').

neighbour_exe(Target, Me, Exe) :-
    file_directory_name(Me, Dir),
    file_name_extension(_, Ext, Me),
    atomic_list_concat([Dir, Target], '/', Base),
    file_name_extension(Base, Ext, Exe).

add_home_option(Args0, [HomeOption|Args0]) :-
    current_prolog_flag(home, Home),
    format(atom(HomeOption), '--home=~w', [Home]).

%!  process_which(+Exe, -Path) is semidet.
%
%   True when Path is an absolute file   name for the specification Exe.
%   This deals with the search path as   well  as extensions used by the
%   OS.

process_which(Exe, Path) :-
    exe_options(ExeOptions),
    absolute_file_name(Exe, Path, [file_errors(fail)|ExeOptions]),
    !.

%!  exe_options(-Options) is multi.
%
%   Get options for absolute_file_name to find   an  executable file. On
%   Windows we first look for a  readable   file,  but  if this does not
%   exist we are happy with a existing file because the file may be a
%   [reparse point](https://docs.microsoft.com/en-us/windows/win32/fileio/reparse-points-and-file-operations)

exe_options(Options) :-
    current_prolog_flag(windows, true),
    !,
    (   Options = [ extensions(['',exe,com]), access(read), file_errors(fail) ]
    ;   Options = [ extensions(['',exe,com]), access(exist) ]
    ).
exe_options(Options) :-
    Options = [ access(execute) ].

expand_cwd_option(Options0, Options) :-
    select_option(cwd(Spec), Options0, Options1),
    !,
    (   compound(Spec)
    ->  absolute_file_name(Spec, PlDir, [file_type(directory), access(read)]),
        prolog_to_os_filename(PlDir, Dir),
        Options = [cwd(Dir)|Options1]
    ;   exists_directory(Spec)
    ->  Options = Options0
    ;   existence_error(directory, Spec)
    ).
expand_cwd_option(Options, Options).

expand_env_option(Name, Options0, Options) :-
    Term =.. [Name,Value0],
    select_option(Term, Options0, Options1),
    !,
    must_be(list, Value0),
    maplist(map_env, Value0, Value),
    NewOption =.. [Name,Value],
    Options = [NewOption|Options1].
expand_env_option(_, Options, Options).

map_env(Name=Value0, Name=Value) :-
    map_arg(Value0, Value).

%!  map_arg(+ArgIn, -Arg) is det.
%
%   Map an individual argument. Primitives  are either 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.

map_arg([], []) :- !.
map_arg(List, Arg) :-
    is_list(List),
    !,
    maplist(map_arg_prim, List, Prims),
    atomic_list_concat(Prims, Arg).
map_arg(Prim, Arg) :-
    map_arg_prim(Prim, Arg).

map_arg_prim(file(Spec), File) :-
    !,
    (   compound(Spec)
    ->  absolute_file_name(Spec, PlFile)
    ;   PlFile = Spec
    ),
    prolog_to_os_filename(PlFile, File).
map_arg_prim(Arg, Arg).


%!  process_id(-PID) is det.
%
%   True if PID is the process id of the running Prolog process.
%
%   @deprecated     Use current_prolog_flag(pid, PID)

process_id(PID) :-
    current_prolog_flag(pid, PID).

%!  process_id(+Process, -PID) is det.
%
%   PID is the process id of Process.  Given that they are united in
%   SWI-Prolog, this is a simple unify.

process_id(PID, PID).

%!  is_process(+PID) is semidet.
%
%   True if PID might  be  a   process.  Succeeds  for  any positive
%   integer.

is_process(PID) :-
    integer(PID),
    PID > 0.

%!  process_release(+PID)
%
%   Release process handle.  In this implementation this is the same
%   as process_wait(PID, _).

process_release(PID) :-
    process_wait(PID, _).

%!  process_wait(+PID, -Status) is det.
%!  process_wait(+PID, -Status, +Options) is det.
%
%   True if PID completed with  Status.   This  call normally blocks
%   until the process is finished.  Options:
%
%       * timeout(+Timeout)
%       Default: `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(+Bool)
%       Do/do not release the process.  We do not support this flag
%       and a domain_error is raised if release(false) is provided.
%
%   @arg  Status is one of exit(Code) or killed(Signal), where
%         Code and Signal are integers.  If the `timeout` option
%         is used Status is unified with `timeout` after the wait
%         timed out.

process_wait(PID, Status) :-
    process_wait(PID, Status, []).

%!  process_kill(+PID) is det.
%!  process_kill(+PID, +Signal) is det.
%
%   Send signal to process PID.  Default   is  `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.
%
%   @compat SICStus does not accept the prolog friendly version.  We
%           choose to do so for compatibility with on_signal/3.

process_kill(PID) :-
    process_kill(PID, term).


%!  process_group_kill(+PID) is det.
%!  process_group_kill(+PID, +Signal) is det.
%
%   Send signal to the group containing process PID.  Default   is
%   `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.

process_group_kill(PID) :-
    process_group_kill(PID, term).


%!  process_set_method(+Method) is det.
%
%   Determine how the process is created on  Unix systems. Method is one
%   of `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().


                 /*******************************
                 *            MESSAGES          *
                 *******************************/

:- multifile
    prolog:error_message/3.

prolog:error_message(process_error(File, exit(Status))) -->
    [ 'Process "~w": exit status: ~w'-[File, Status] ].
prolog:error_message(process_error(File, killed(Signal))) -->
    [ 'Process "~w": killed by signal ~w'-[File, Signal] ].
prolog:error_message(existence_error(source_sink, path(Exe))) -->
    [ 'Could not find executable file "~p" in '-[Exe] ],
    path_var.

path_var -->
    (   { current_prolog_flag(windows, true) }
    ->  [ '%PATH%'-[] ]
    ;   [ '$PATH'-[] ]
    ).
