Convenience functions that encapsulate a sequence of
start_command() followed by finish_command(). The argument argv
specifies the program and its arguments. The argument opt is zero
- or more of the flags `RUN_COMMAND_NO_STDIN`, `RUN_GIT_CMD`, or
- `RUN_COMMAND_STDOUT_TO_STDERR` that correspond to the members
- .no_stdin, .git_cmd, .stdout_to_stderr of `struct child_process`.
+ or more of the flags `RUN_COMMAND_NO_STDIN`, `RUN_GIT_CMD`,
+ `RUN_COMMAND_STDOUT_TO_STDERR`, or `RUN_SILENT_EXEC_FAILURE`
+ that correspond to the members .no_stdin, .git_cmd,
+ .stdout_to_stderr, .silent_exec_failure of `struct child_process`.
The argument dir corresponds the member .dir. The argument env
corresponds to the member .env.
+The functions above do the following:
+
+. If a system call failed, errno is set and -1 is returned. A diagnostic
+ is printed.
+
+. If the program was not found, then -1 is returned and errno is set to
+ ENOENT; a diagnostic is printed only if .silent_exec_failure is 0.
+
+. Otherwise, the program is run. If it terminates regularly, its exit
+ code is returned. No diagnostic is printed, even if the exit code is
+ non-zero.
+
+. If the program terminated due to a signal, then the return value is the
+ signal number - 128, ie. it is negative and so indicates an unusual
+ condition; a diagnostic is printed. This return value can be passed to
+ exit(2), which will report the same code to the parent process that a
+ POSIX shell's $? would report for a program that died from the signal.
+
+
`start_async`::
Run a function asynchronously. Takes a pointer to a `struct
- async` that specifies the details and returns a pipe FD
- from which the caller reads. See below for details.
+ async` that specifies the details and returns a set of pipe FDs
+ for communication with the function. See below for details.
`finish_async`::
.in: The FD must be readable; it becomes child's stdin.
.out: The FD must be writable; it becomes child's stdout.
- .err > 0 is not supported.
+ .err: The FD must be writable; it becomes child's stderr.
The specified FD is closed by start_command(), even if it fails to
run the sub-process!
To specify a new initial working directory for the sub-process,
specify it in the .dir member.
+If the program cannot be found, the functions return -1 and set
+errno to ENOENT. Normally, an error message is printed, but if
+.silent_exec_failure is set to 1, no message is printed for this
+special error condition.
+
* `struct async`
struct async variable;
2. initializes .proc and .data;
3. calls start_async();
-4. processes the data by reading from the fd in .out;
-5. closes .out;
+4. processes communicates with proc through .in and .out;
+5. closes .in and .out;
6. calls finish_async().
+The members .in, .out are used to provide a set of fd's for
+communication between the caller and the callee as follows:
+
+. Specify 0 to have no file descriptor passed. The callee will
+ receive -1 in the corresponding argument.
+
+. Specify < 0 to have a pipe allocated; start_async() replaces
+ with the pipe FD in the following way:
+
+ .in: Returns the writable pipe end into which the caller
+ writes; the readable end of the pipe becomes the function's
+ in argument.
+
+ .out: Returns the readable pipe end from which the caller
+ reads; the writable end of the pipe becomes the function's
+ out argument.
+
+ The caller of start_async() must close the returned FDs after it
+ has completed reading from/writing from them.
+
+. Specify a file descriptor > 0 to be used by the function:
+
+ .in: The FD must be readable; it becomes the function's in.
+ .out: The FD must be writable; it becomes the function's out.
+
+ The specified FD is closed by start_async(), even if it fails to
+ run the function.
+
The function pointer in .proc has the following signature:
- int proc(int fd, void *data);
+ int proc(int in, int out, void *data);
-. fd specifies a writable file descriptor to which the function must
- write the data that it produces. The function *must* close this
- descriptor before it returns.
+. in, out specifies a set of file descriptors to which the function
+ must read/write the data that it needs/produces. The function
+ *must* close these descriptors before it returns. A descriptor
+ may be -1 if the caller did not configure a descriptor for that
+ direction.
. data is the value that the caller has specified in the .data member
of struct async.
There are serious restrictions on what the asynchronous function can do
-because this facility is implemented by a pipe to a forked process on
-UNIX, but by a thread in the same address space on Windows:
+because this facility is implemented by a thread in the same address
+space on most platforms (when pthreads is available), but by a pipe to
+a forked process otherwise:
. It cannot change the program's state (global variables, environment,
- etc.) in a way that the caller notices; in other words, .out is the
- only communication channel to the caller.
+ etc.) in a way that the caller notices; in other words, .in and .out
+ are the only communication channels to the caller.
. It must not change the program's state that the caller of the
facility also uses.