1/* Creation of subprocesses, communicating via pipes.
2   Copyright (C) 2001-2003 Free Software Foundation, Inc.
3   Written by Bruno Haible <haible@clisp.cons.org>, 2001.
4
5   This program is free software; you can redistribute it and/or modify
6   it under the terms of the GNU General Public License as published by
7   the Free Software Foundation; either version 2, or (at your option)
8   any later version.
9
10   This program is distributed in the hope that it will be useful,
11   but WITHOUT ANY WARRANTY; without even the implied warranty of
12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13   GNU General Public License for more details.
14
15   You should have received a copy of the GNU General Public License
16   along with this program; if not, write to the Free Software Foundation,
17   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
18
19#ifndef _PIPE_H
20#define _PIPE_H
21
22/* Get pid_t.  */
23#include <stdlib.h>
24#ifdef HAVE_UNISTD_H
25#include <unistd.h>
26#endif
27#include <sys/types.h>
28
29#include <stdbool.h>
30
31
32#ifdef __cplusplus
33extern "C" {
34#endif
35
36
37/* All these functions create a subprocess and don't wait for its termination.
38   They return the process id of the subprocess.  They also return in fd[]
39   one or two file descriptors for communication with the subprocess.
40   If the subprocess creation fails: if exit_on_error is true, the main
41   process exits with an error message; otherwise, an error message is given
42   if null_stderr is false, then -1 is returned and fd[] remain uninitialized.
43
44   After finishing communication, the caller should call wait_subprocess()
45   to get rid of the subprocess in the process table.
46
47   If slave_process is true, the child process will be terminated when its
48   creator receives a catchable fatal signal or exits normally.  If
49   slave_process is false, the child process will continue running in this
50   case, until it is lucky enough to attempt to communicate with its creator
51   and thus get a SIGPIPE signal.
52
53   If exit_on_error is false, a child process id of -1 should be treated the
54   same way as a subprocess which accepts no input, produces no output and
55   terminates with exit code 127.  Why?  Some errors during posix_spawnp()
56   cause the function posix_spawnp() to return an error code; some other
57   errors cause the subprocess to exit with return code 127.  It is
58   implementation dependent which error is reported which way.  The caller
59   must treat both cases as equivalent.
60
61   It is recommended that no signal is blocked or ignored (i.e. have a
62   signal handler with value SIG_IGN) while any of these functions is called.
63   The reason is that child processes inherit the mask of blocked signals
64   from their parent (both through posix_spawn() and fork()/exec());
65   likewise, signals ignored in the parent are also ignored in the child
66   (except possibly for SIGCHLD).  And POSIX:2001 says [in the description
67   of exec()]:
68       "it should be noted that many existing applications wrongly
69        assume that they start with certain signals set to the default
70        action and/or unblocked. In particular, applications written
71        with a simpler signal model that does not include blocking of
72        signals, such as the one in the ISO C standard, may not behave
73        properly if invoked with some signals blocked. Therefore, it is
74        best not to block or ignore signals across execs without explicit
75        reason to do so, and especially not to block signals across execs
76        of arbitrary (not closely co-operating) programs."  */
77
78/* Open a pipe for output to a child process.
79 * The child's stdout goes to a file.
80 *
81 *           write       system                read
82 *    parent  ->   fd[0]   ->   STDIN_FILENO    ->   child
83 *
84 */
85extern pid_t create_pipe_out (const char *progname,
86			      const char *prog_path, char **prog_argv,
87			      const char *prog_stdout, bool null_stderr,
88			      bool slave_process, bool exit_on_error,
89			      int fd[1]);
90
91/* Open a pipe for input from a child process.
92 * The child's stdin comes from a file.
93 *
94 *           read        system                write
95 *    parent  <-   fd[0]   <-   STDOUT_FILENO   <-   child
96 *
97 */
98extern pid_t create_pipe_in (const char *progname,
99			     const char *prog_path, char **prog_argv,
100			     const char *prog_stdin, bool null_stderr,
101			     bool slave_process, bool exit_on_error,
102			     int fd[1]);
103
104/* Open a bidirectional pipe.
105 *
106 *           write       system                read
107 *    parent  ->   fd[1]   ->   STDIN_FILENO    ->   child
108 *    parent  <-   fd[0]   <-   STDOUT_FILENO   <-   child
109 *           read        system                write
110 *
111 */
112extern pid_t create_pipe_bidi (const char *progname,
113			       const char *prog_path, char **prog_argv,
114			       bool null_stderr,
115			       bool slave_process, bool exit_on_error,
116			       int fd[2]);
117
118/* The name of the "always silent" device.  */
119#if defined _MSC_VER || defined __MINGW32__
120/* Native Woe32 API.  */
121# define DEV_NULL "NUL"
122#else
123/* Unix API.  */
124# define DEV_NULL "/dev/null"
125#endif
126
127
128#ifdef __cplusplus
129}
130#endif
131
132
133#endif /* _PIPE_H */
134