/* Creation of subprocesses, communicating via pipes.
- Copyright (C) 2001-2003, 2006 Free Software Foundation, Inc.
+ Copyright (C) 2001-2003, 2006, 2008-2010 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
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.
+ 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.
* 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]);
+ 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.
*
*/
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]);
+ 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.
*
* 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]);
+ 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__
+#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
/* Native Woe32 API. */
# define DEV_NULL "NUL"
#else