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Diffstat (limited to 'lib/spawn-pipe.h')
| -rw-r--r-- | lib/spawn-pipe.h | 147 |
1 files changed, 147 insertions, 0 deletions
diff --git a/lib/spawn-pipe.h b/lib/spawn-pipe.h new file mode 100644 index 0000000..52576d0 --- /dev/null +++ b/lib/spawn-pipe.h @@ -0,0 +1,147 @@ +/* Creation of subprocesses, communicating via pipes. + Copyright (C) 2001-2003, 2006, 2008-2018 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 3 of the License, 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, see <https://www.gnu.org/licenses/>. */ + +#ifndef _SPAWN_PIPE_H +#define _SPAWN_PIPE_H + +/* Get pid_t. */ +#include <stdlib.h> +#include <unistd.h> +#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, with errno set, 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 + * + * Note: When writing to a child process, it is useful to ignore the SIGPIPE + * signal and the EPIPE error code. + */ +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 + * + * Note: When writing to a child process, it is useful to ignore the SIGPIPE + * signal and the EPIPE error code. + * + * Note: The parent process must be careful to avoid deadlock. + * 1) If you write more than PIPE_MAX bytes or, more generally, if you write + * more bytes than the subprocess can handle at once, the subprocess + * may write its data and wait on you to read it, but you are currently + * busy writing. + * 2) When you don't know ahead of time how many bytes the subprocess + * will produce, the usual technique of calling read (fd, buf, BUFSIZ) + * with a fixed BUFSIZ will, on Linux 2.2.17 and on BSD systems, cause + * the read() call to block until *all* of the buffer has been filled. + * But the subprocess cannot produce more data until you gave it more + * input. But you are currently busy reading from it. + */ +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 _WIN32 && ! defined __CYGWIN__ +/* Native Windows API. */ +# define DEV_NULL "NUL" +#else +/* Unix API. */ +# define DEV_NULL "/dev/null" +#endif + + +#ifdef __cplusplus +} +#endif + + +#endif /* _SPAWN_PIPE_H */ |