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) 2000-2017, University of Amsterdam 7 VU University Amsterdam 8 All rights reserved. 9 10 Redistribution and use in source and binary forms, with or without 11 modification, are permitted provided that the following conditions 12 are met: 13 14 1. Redistributions of source code must retain the above copyright 15 notice, this list of conditions and the following disclaimer. 16 17 2. Redistributions in binary form must reproduce the above copyright 18 notice, this list of conditions and the following disclaimer in 19 the documentation and/or other materials provided with the 20 distribution. 21 22 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 23 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 24 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 25 FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 26 COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 27 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 28 BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 29 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 30 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 32 ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 33 POSSIBILITY OF SUCH DAMAGE. 34*/ 35 36:- module(unix, 37 [ fork/1, % -'client'|pid 38 exec/1, % +Command(...Args...) 39 fork_exec/1, % +Command(...Args...) 40 wait/2, % -Pid, -Reason 41 kill/2, % +Pid. +Signal 42 pipe/2, % +Read, +Write 43 dup/2, % +From, +To 44 detach_IO/0, 45 detach_IO/1, % +Stream 46 environ/1 % -[Name=Value] 47 ]). 48:- use_module(library(shlib)). 49 50/** <module> Unix specific operations 51 52The library(unix) library provides the commonly used Unix primitives to 53deal with process management. These primitives are useful for many 54tasks, including server management, parallel computation, exploiting and 55controlling other processes, etc. 56 57The predicates in this library are modelled closely after their native 58Unix counterparts. 59 60@see library(process) provides a portable high level interface to create 61and manage processes. 62*/ 63 64:- use_foreign_library(foreign(unix), install_unix). 65 66%! fork(-Pid) is det. 67% 68% Clone the current process into two branches. In the child, Pid 69% is unified to child. In the original process, Pid is unified to 70% the process identifier of the created child. Both parent and 71% child are fully functional Prolog processes running the same 72% program. The processes share open I/O streams that refer to Unix 73% native streams, such as files, sockets and pipes. Data is not 74% shared, though on most Unix systems data is initially shared and 75% duplicated only if one of the programs attempts to modify the 76% data. 77% 78% Unix fork() is the only way to create new processes and fork/1 79% is a simple direct interface to it. 80% 81% @error permission_error(fork, process, main) is raised if 82% the calling thread is not the only thread in the 83% process. Forking a Prolog process with threads 84% will typically deadlock because only the calling 85% thread is cloned in the fork, while all thread 86% synchronization are cloned. 87 88fork(Pid) :- 89 fork_warn_threads, 90 fork_(Pid). 91 92%! fork_warn_threads 93% 94% See whether we are the only thread. If not, we cannot fork 95 96fork_warn_threads :- 97 findall(T, other_thread(T), Others), 98 ( Others == [] 99 -> true 100 ; Others == [gc] 101 -> thread_signal(gc, abort), 102 thread_join(gc, _) 103 ; throw(error(permission_error(fork, process, main), 104 context(_, running_threads(Others)))) 105 ). 106 107other_thread(T) :- 108 thread_self(Me), 109 thread_property(T, status(Status)), 110 T \== Me, 111 ( Status == running 112 -> true 113 ; print_message(warning, fork(join(T, Status))), 114 thread_join(T, _), 115 fail 116 ). 117 118%! fork_exec(+Command) is det. 119% 120% Fork (as fork/1) and exec (using exec/1) the child immediately. 121% This behaves as the code below, but bypasses the check for the 122% existence of other threads because this is a safe scenario. 123% 124% == 125% fork_exec(Command) :- 126% ( fork(child) 127% -> exec(Command) 128% ; true 129% ). 130% == 131 132fork_exec(Command) :- 133 ( fork_(child) 134 -> exec(Command) 135 ; true 136 ). 137 138%! exec(+Command) 139% 140% Replace the running program by starting Command. Command is a 141% callable term. The functor is the command and the arguments 142% provide the command-line arguments for the command. Each 143% command-line argument must be atomic and is converted to a 144% string before passed to the Unix call execvp(). Here are some 145% examples: 146% 147% - exec(ls('-l')) 148% - exec('/bin/ls'('-l', '/home/jan')) 149% 150% Unix exec() is the only way to start an executable file 151% executing. It is commonly used together with fork/1. For example 152% to start netscape on an URL in the background, do: 153% 154% == 155% run_netscape(URL) :- 156% ( fork(child), 157% exec(netscape(URL)) 158% ; true 159% ). 160% == 161% 162% Using this code, netscape remains part of the process-group of 163% the invoking Prolog process and Prolog does not wait for 164% netscape to terminate. The predicate wait/2 allows waiting for a 165% child, while detach_IO/0 disconnects the child as a deamon 166% process. 167 168%! wait(?Pid, -Status) is det. 169% 170% Wait for a child to change status. Then report the child that 171% changed status as well as the reason. If Pid is bound on entry 172% then the status of the specified child is reported. If not, then 173% the status of any child is reported. Status is unified with 174% exited(ExitCode) if the child with pid Pid was terminated by 175% calling exit() (Prolog halt/1). ExitCode is the return status. 176% Status is unified with signaled(Signal) if the child died due to 177% a software interrupt (see kill/2). Signal contains the signal 178% number. Finally, if the process suspended execution due to a 179% signal, Status is unified with stopped(Signal). 180 181%! kill(+Pid, +Signal) is det. 182% 183% Deliver a software interrupt to the process with identifier Pid 184% using software-interrupt number Signal. See also on_signal/2. 185% Signals can be specified as an integer or signal name, where 186% signal names are derived from the C constant by dropping the 187% =SIG= prefix and mapping to lowercase. E.g. =int= is the same as 188% =SIGINT= in C. The meaning of the signal numbers can be found in 189% the Unix manual. 190 191%! pipe(-InSream, -OutStream) is det. 192% 193% Create a communication-pipe. This is normally used to make a 194% child communicate to its parent. After pipe/2, the process is 195% cloned and, depending on the desired direction, both processes 196% close the end of the pipe they do not use. Then they use the 197% remaining stream to communicate. Here is a simple example: 198% 199% == 200% :- use_module(library(unix)). 201% 202% fork_demo(Result) :- 203% pipe(Read, Write), 204% fork(Pid), 205% ( Pid == child 206% -> close(Read), 207% format(Write, '~q.~n', 208% [hello(world)]), 209% flush_output(Write), 210% halt 211% ; close(Write), 212% read(Read, Result), 213% close(Read) 214% ). 215% == 216 217 218%! dup(+FromStream, +ToStream) is det. 219% 220% Interface to Unix dup2(), copying the underlying filedescriptor 221% and thus making both streams point to the same underlying 222% object. This is normally used together with fork/1 and pipe/2 to 223% talk to an external program that is designed to communicate 224% using standard I/O. 225% 226% Both FromStream and ToStream either refer to a Prolog stream or 227% an integer descriptor number to refer directly to OS 228% descriptors. See also demo/pipe.pl in the source-distribution of 229% this package. 230 231 232%! detach_IO(+Stream) is det. 233% 234% This predicate is intended to create Unix _deamon_ processes. It 235% performs two actions. 236% 237% 1. The I/O streams =user_input=, =user_output= and 238% =user_error= are closed if they are connected to a terminal 239% (see =tty= property in stream_property/2). Input streams are 240% rebound to a dummy stream that returns EOF. Output streams are 241% reboud to forward their output to Stream. 242% 243% 2. The process is detached from the current process-group and 244% its controlling terminal. This is achieved using setsid() if 245% provided or using ioctl() =TIOCNOTTY= on =|/dev/tty|=. 246% 247% To ignore all output, it may be rebound to a null stream. For 248% example: 249% 250% == 251% ..., 252% open_null_stream(Out), 253% detach_IO(Out). 254% == 255% 256% The detach_IO/1 should be called only once per process. 257% Subsequent calls silently succeed without any side effects. 258% 259% @see detach_IO/0 and library(syslog). 260 261%! detach_IO is det. 262% 263% Detach I/O similar to detach_IO/1. The output streams are bound 264% to a file =|/tmp/pl-out.<pid>|=. Output is line buffered (see 265% set_stream/2). 266% 267% @compat Older versions of this predicate only created this file 268% if there was output. 269% @see library(syslog) allows for sending output to the Unix 270% logging service. 271 272detach_IO :- 273 current_prolog_flag(pid, Pid), 274 atom_concat('/tmp/pl-out.', Pid, TmpFile), 275 open(TmpFile, write, Out, [alias(daemon_output)]), 276 set_stream(Out, buffer(line)), 277 detach_IO(Out). 278 279:- if(current_predicate(prctl/1)). 280:- export(prctl/1). 281 282%! prctl(+Option) is det. 283% 284% Access to Linux process control operations. Defines values for 285% Option are: 286% 287% - set_dumpable(+Boolean) 288% Control whether the process is allowed to dump core. This 289% right is dropped under several uid and gid conditions. 290% - get_dumpable(-Boolean) 291% Get the value of the dumpable flag. 292 293:- endif. 294 295:- if(current_predicate(sysconf/1)). 296:- export(sysconf/1). 297 298%! sysconf(+Conf) is semidet. 299% 300% Access system configuration. See sysconf(1) for details. Conf is 301% a term Config(Value), where Value is always an integer. Config 302% is the sysconf() name after removing =_SC_= and conversion to 303% lowercase. Currently support the following configuration info: 304% =arg_max=, =child_max=, =clk_tck=, =open_max=, =pagesize=, 305% =phys_pages=, =avphys_pages=, =nprocessors_conf= and 306% =nprocessors_onln=. Note that not all values may be supported on 307% all operating systems. 308 309:- endif. 310 311 /******************************* 312 * MESSAGES * 313 *******************************/ 314 315:- multifile 316 prolog:message//1. 317 318prologmessage(fork(join(T, Status))) --> 319 [ 'Fork: joining thead ~p (status: ~p)'-[T, Status] ]