Functions
---------
+`child_process_init`::
+
+ Initialize a struct child_process variable.
+
`start_command`::
Start a sub-process. Takes a pointer to a `struct child_process`
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.
+`child_process_clear`::
+
+ Release the memory associated with the struct child_process.
+ Most users of the run-command API don't need to call this
+ function explicitly because `start_command` invokes it on
+ failure and `finish_command` calls it automatically already.
+
+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. the same value that a POSIX shell's $? would
+ report. A diagnostic is printed.
+
+
`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`::
The first argument is a pathname to an index file, or NULL
if the hook uses the default index file or no index is needed.
The second argument is the name of the hook.
- The further arguments (up to 9) correspond to the hook arguments.
+ The further arguments correspond to the hook arguments.
The last argument has to be NULL to terminate the arguments list.
If the hook does not exist or is not executable, the return
value will be zero.
The caller:
-1. allocates and clears (memset(&chld, 0, sizeof(chld));) a
- struct child_process variable;
+1. allocates and clears (using child_process_init() or
+ CHILD_PROCESS_INIT) a struct child_process variable;
2. initializes the members;
3. calls start_command();
4. processes the data;
without a path). If the command to run is a git command, set argv[0] to
the command name without the 'git-' prefix and set .git_cmd = 1.
+Note that the ownership of the memory pointed to by .argv stays with the
+caller, but it should survive until `finish_command` completes. If the
+.argv member is NULL, `start_command` will point it at the .args
+`argv_array` (so you may use one or the other, but you must use exactly
+one). The memory in .args will be cleaned up automatically during
+`finish_command` (or during `start_command` when it is unsuccessful).
+
The members .in, .out, .err are used to redirect stdin, stdout,
stderr as follows:
.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!
. If the string does not contain '=', it names an environment
variable that will be removed from the child process's environment.
+If the .env member is NULL, `start_command` will point it at the
+.env_array `argv_array` (so you may use one or the other, but not both).
+The memory in .env_array will be cleaned up automatically during
+`finish_command` (or during `start_command` when it is unsuccessful).
+
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.