1 /* Creation of subprocesses, communicating via pipes. 2 Copyright (C) 2001-2003, 2006 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ 18 19 #ifndef _PIPE_H 20 #define _PIPE_H 21 22 /* Get pid_t. */ 23 #include <stdlib.h> 24 #include <unistd.h> 25 #include <sys/types.h> 26 27 #include <stdbool.h> 28 29 30 #ifdef __cplusplus 31 extern "C" { 32 #endif 33 34 35 /* All these functions create a subprocess and don't wait for its termination. 36 They return the process id of the subprocess. They also return in fd[] 37 one or two file descriptors for communication with the subprocess. 38 If the subprocess creation fails: if exit_on_error is true, the main 39 process exits with an error message; otherwise, an error message is given 40 if null_stderr is false, then -1 is returned and fd[] remain uninitialized. 41 42 After finishing communication, the caller should call wait_subprocess() 43 to get rid of the subprocess in the process table. 44 45 If slave_process is true, the child process will be terminated when its 46 creator receives a catchable fatal signal or exits normally. If 47 slave_process is false, the child process will continue running in this 48 case, until it is lucky enough to attempt to communicate with its creator 49 and thus get a SIGPIPE signal. 50 51 If exit_on_error is false, a child process id of -1 should be treated the 52 same way as a subprocess which accepts no input, produces no output and 53 terminates with exit code 127. Why? Some errors during posix_spawnp() 54 cause the function posix_spawnp() to return an error code; some other 55 errors cause the subprocess to exit with return code 127. It is 56 implementation dependent which error is reported which way. The caller 57 must treat both cases as equivalent. 58 59 It is recommended that no signal is blocked or ignored (i.e. have a 60 signal handler with value SIG_IGN) while any of these functions is called. 61 The reason is that child processes inherit the mask of blocked signals 62 from their parent (both through posix_spawn() and fork()/exec()); 63 likewise, signals ignored in the parent are also ignored in the child 64 (except possibly for SIGCHLD). And POSIX:2001 says [in the description 65 of exec()]: 66 "it should be noted that many existing applications wrongly 67 assume that they start with certain signals set to the default 68 action and/or unblocked. In particular, applications written 69 with a simpler signal model that does not include blocking of 70 signals, such as the one in the ISO C standard, may not behave 71 properly if invoked with some signals blocked. Therefore, it is 72 best not to block or ignore signals across execs without explicit 73 reason to do so, and especially not to block signals across execs 74 of arbitrary (not closely co-operating) programs." */ 75 76 /* Open a pipe for output to a child process. 77 * The child's stdout goes to a file. 78 * 79 * write system read 80 * parent -> fd[0] -> STDIN_FILENO -> child 81 * 82 */ 83 extern pid_t create_pipe_out (const char *progname, 84 const char *prog_path, char **prog_argv, 85 const char *prog_stdout, bool null_stderr, 86 bool slave_process, bool exit_on_error, 87 int fd[1]); 88 89 /* Open a pipe for input from a child process. 90 * The child's stdin comes from a file. 91 * 92 * read system write 93 * parent <- fd[0] <- STDOUT_FILENO <- child 94 * 95 */ 96 extern pid_t create_pipe_in (const char *progname, 97 const char *prog_path, char **prog_argv, 98 const char *prog_stdin, bool null_stderr, 99 bool slave_process, bool exit_on_error, 100 int fd[1]); 101 102 /* Open a bidirectional pipe. 103 * 104 * write system read 105 * parent -> fd[1] -> STDIN_FILENO -> child 106 * parent <- fd[0] <- STDOUT_FILENO <- child 107 * read system write 108 * 109 */ 110 extern pid_t create_pipe_bidi (const char *progname, 111 const char *prog_path, char **prog_argv, 112 bool null_stderr, 113 bool slave_process, bool exit_on_error, 114 int fd[2]); 115 116 /* The name of the "always silent" device. */ 117 #if defined _MSC_VER || defined __MINGW32__ 118 /* Native Woe32 API. */ 119 # define DEV_NULL "NUL" 120 #else 121 /* Unix API. */ 122 # define DEV_NULL "/dev/null" 123 #endif 124 125 126 #ifdef __cplusplus 127 } 128 #endif 129 130 131 #endif /* _PIPE_H */ 132