diff --git a/Documentation/technical/api-run-command.txt b/Documentation/technical/api-run-command.txt
index b26c28133c143b23acf28fc1a3a06d16c10c65f8..f18b4f4817448530a5adbe2c8835bb7791add42a 100644 (file)
ENOENT; a diagnostic is printed only if .silent_exec_failure is 0.
. Otherwise, the program is run. If it terminates regularly, its exit
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 diagnistic is printed, even if the exit code is
+ 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
non-zero.
. If the program terminated due to a signal, then the return value is the
`start_async`::
Run a function asynchronously. Takes a pointer to a `struct
`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`::
`finish_async`::
.in: The FD must be readable; it becomes child's stdin.
.out: The FD must be writable; it becomes child's stdout.
.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!
The specified FD is closed by start_command(), even if it fails to
run the sub-process!
struct async variable;
2. initializes .proc and .data;
3. calls start_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().
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:
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.
. 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
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,
. 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.
. It must not change the program's state that the caller of the
facility also uses.