run-command: allow stdin for run_processes_parallel

While it makes sense not to inherit stdin from the parent process to
avoid deadlocking, it's not necessary to completely ban stdin to
children. An informed user should be able to configure stdin safely. By
setting `some_child.process.no_stdin=1` before calling `get_next_task()`
we provide a reasonable default behavior but enable users to set up
stdin streaming for themselves during the callback.

`some_child.process.stdout_to_stderr`, however, remains unmodifiable by
`get_next_task()` - the rest of the run_processes_parallel() API depends
on child output in stderr.

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/run-command.c b/run-command.c
index b439c7974ca4b71847cb388af0b6cc5d78e63d78..6bd16acb0603b16a71c729978bba812326ca9400 100644 (file)
--- a/run-command.c
+++ b/run-command.c
@@ -1586,6 +1586,14 @@ static int pp_start_one(struct parallel_processes *pp,
        if (i == opts->processes)
                BUG("bookkeeping is hard");
 
+       /*
+        * By default, do not inherit stdin from the parent process - otherwise,
+        * all children would share stdin! Users may overwrite this to provide
+        * something to the child's stdin by having their 'get_next_task'
+        * callback assign 0 to .no_stdin and an appropriate integer to .in.
+        */
+       pp->children[i].process.no_stdin = 1;
+
        code = opts->get_next_task(&pp->children[i].process,
                                   opts->ungroup ? NULL : &pp->children[i].err,
                                   opts->data,
@@ -1601,7 +1609,6 @@ static int pp_start_one(struct parallel_processes *pp,
                pp->children[i].process.err = -1;
                pp->children[i].process.stdout_to_stderr = 1;
        }
-       pp->children[i].process.no_stdin = 1;
 
        if (start_command(&pp->children[i].process)) {
                if (opts->start_failure)