/* Creation of subprocesses, communicating via pipes. Copyright (C) 2001-2003 Free Software Foundation, Inc. Written by Bruno Haible <haible@clisp.cons.org>, 2001. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #ifndef _PIPE_H #define _PIPE_H /* Get pid_t. */ #include <stdlib.h> #ifdef HAVE_UNISTD_H #include <unistd.h> #endif #include <sys/types.h> #include <stdbool.h> #ifdef __cplusplus extern "C" { #endif /* All these functions create a subprocess and don't wait for its termination. They return the process id of the subprocess. They also return in fd[] one or two file descriptors for communication with the subprocess. If the subprocess creation fails: if exit_on_error is true, the main process exits with an error message; otherwise, an error message is given if null_stderr is false, then -1 is returned and fd[] remain uninitialized. After finishing communication, the caller should call wait_subprocess() to get rid of the subprocess in the process table. If slave_process is true, the child process will be terminated when its creator receives a catchable fatal signal or exits normally. If slave_process is false, the child process will continue running in this case, until it is lucky enough to attempt to communicate with its creator and thus get a SIGPIPE signal. If exit_on_error is false, a child process id of -1 should be treated the same way as a subprocess which accepts no input, produces no output and terminates with exit code 127. Why? Some errors during posix_spawnp() cause the function posix_spawnp() to return an error code; some other errors cause the subprocess to exit with return code 127. It is implementation dependent which error is reported which way. The caller must treat both cases as equivalent. It is recommended that no signal is blocked or ignored (i.e. have a signal handler with value SIG_IGN) while any of these functions is called. The reason is that child processes inherit the mask of blocked signals from their parent (both through posix_spawn() and fork()/exec()); likewise, signals ignored in the parent are also ignored in the child (except possibly for SIGCHLD). And POSIX:2001 says [in the description of exec()]: "it should be noted that many existing applications wrongly assume that they start with certain signals set to the default action and/or unblocked. In particular, applications written with a simpler signal model that does not include blocking of signals, such as the one in the ISO C standard, may not behave properly if invoked with some signals blocked. Therefore, it is best not to block or ignore signals across execs without explicit reason to do so, and especially not to block signals across execs of arbitrary (not closely co-operating) programs." */ /* Open a pipe for output to a child process. * The child's stdout goes to a file. * * write system read * parent -> fd[0] -> STDIN_FILENO -> child * */ extern pid_t create_pipe_out (const char *progname, const char *prog_path, char **prog_argv, const char *prog_stdout, bool null_stderr, bool slave_process, bool exit_on_error, int fd[1]); /* Open a pipe for input from a child process. * The child's stdin comes from a file. * * read system write * parent <- fd[0] <- STDOUT_FILENO <- child * */ extern pid_t create_pipe_in (const char *progname, const char *prog_path, char **prog_argv, const char *prog_stdin, bool null_stderr, bool slave_process, bool exit_on_error, int fd[1]); /* Open a bidirectional pipe. * * write system read * parent -> fd[1] -> STDIN_FILENO -> child * parent <- fd[0] <- STDOUT_FILENO <- child * read system write * */ extern pid_t create_pipe_bidi (const char *progname, const char *prog_path, char **prog_argv, bool null_stderr, bool slave_process, bool exit_on_error, int fd[2]); /* The name of the "always silent" device. */ #if defined _MSC_VER || defined __MINGW32__ /* Native Woe32 API. */ # define DEV_NULL "NUL" #else /* Unix API. */ # define DEV_NULL "/dev/null" #endif #ifdef __cplusplus } #endif #endif /* _PIPE_H */