gnu/dist/gettext/gettext-tools/lib/pipe.h

   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
  33 extern "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  */
  85 extern 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  */
  98 extern 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  */
 112 extern 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 */