From: Jeff Hostetler <jeffhost@xxxxxxxxxxxxx>
Create a variation of `run_command()` and `start_command()` to launch a command
into the background and optionally wait for it to become "ready" before returning.
Signed-off-by: Jeff Hostetler <jeffhost@xxxxxxxxxxxxx>
---
run-command.c | 123 ++++++++++++++++++++++++++++++++++++++++++++++++++
run-command.h | 48 ++++++++++++++++++++
2 files changed, 171 insertions(+)
diff --git a/run-command.c b/run-command.c
index 3e4e082e94d..fe75fd08f74 100644
--- a/run-command.c
+++ b/run-command.c
@@ -1901,3 +1901,126 @@ void prepare_other_repo_env(struct strvec *env_array, const char *new_git_dir)
}
strvec_pushf(env_array, "%s=%s", GIT_DIR_ENVIRONMENT, new_git_dir);
}
+
+enum start_bg_result start_bg_command(struct child_process *cmd,
+ start_bg_wait_cb *wait_cb,
+ void *cb_data,
+ unsigned int timeout_sec)
+{
+ enum start_bg_result sbgr = SBGR_ERROR;
+ int ret;
+ int wait_status;
+ pid_t pid_seen;
+ time_t time_limit;
+
+ /*
+ * Silently disallow child cleanup -- even if requested.
+ * The child process should persist in the background
+ * and possibly/probably after this process exits. That
+ * is, don't kill the child during our atexit routine.
+ */
+ cmd->clean_on_exit = 0;
+
+ ret = start_command(cmd);
+ if (ret) {
+ /*
+ * We assume that if `start_command()` fails, we
+ * either get a complete `trace2_child_start() /
+ * trace2_child_exit()` pair or it fails before the
+ * `trace2_child_start()` is emitted, so we do not
+ * need to worry about it here.
+ *
+ * We also assume that `start_command()` does not add
+ * us to the cleanup list. And that it calls
+ * calls `child_process_clear()`.
+ */
+ sbgr = SBGR_ERROR;
+ goto done;
+ }
+
+ time(&time_limit);
+ time_limit += timeout_sec;
+
+wait:
+ pid_seen = waitpid(cmd->pid, &wait_status, WNOHANG);
+
+ if (pid_seen == 0) {
+ /*
+ * The child is currently running. Ask the callback
+ * if the child is ready to do work or whether we
+ * should keep waiting for it to boot up.
+ */
+ ret = (*wait_cb)(cb_data, cmd);
+ if (!ret) {
+ /*
+ * The child is running and "ready".
+ *
+ * NEEDSWORK: As we prepare to orphan (release to
+ * the background) this child, it is not appropriate
+ * to emit a `trace2_child_exit()` event. Should we
+ * create a new event for this case?
+ */
+ sbgr = SBGR_READY;
+ goto done;
+ } else if (ret > 0) {
+ time_t now;
+
+ time(&now);
+ if (now < time_limit)
+ goto wait;
+
+ /*
+ * Our timeout has expired. We don't try to
+ * kill the child, but rather let it continue
+ * (hopefully) trying to startup.
+ *
+ * NEEDSWORK: Like the "ready" case, should we
+ * log a custom child-something Trace2 event here?
+ */
+ sbgr = SBGR_TIMEOUT;
+ goto done;
+ } else {
+ /*
+ * The cb gave up on this child.
+ *
+ * NEEDSWORK: Like above, should we log a custom
+ * Trace2 child-something event here?
+ */
+ sbgr = SBGR_CB_ERROR;
+ goto done;
+ }
+ }
+
+ if (pid_seen == cmd->pid) {
+ int child_code = -1;
+
+ /*
+ * The child started, but exited or was terminated
+ * before becoming "ready".
+ *
+ * We try to match the behavior of `wait_or_whine()`
+ * and convert the child's status to a return code for
+ * tracing purposes and emit the `trace2_child_exit()`
+ * event.
+ */
+ if (WIFEXITED(wait_status))
+ child_code = WEXITSTATUS(wait_status);
+ else if (WIFSIGNALED(wait_status))
+ child_code = WTERMSIG(wait_status) + 128;
+ trace2_child_exit(cmd, child_code);
+
+ sbgr = SBGR_DIED;
+ goto done;
+ }
+
+ if (pid_seen < 0 && errno == EINTR)
+ goto wait;
+
+ trace2_child_exit(cmd, -1);
+ sbgr = SBGR_ERROR;
+
+done:
+ child_process_clear(cmd);
+ invalidate_lstat_cache();
+ return sbgr;
+}
diff --git a/run-command.h b/run-command.h
index af1296769f9..58065197d1b 100644
--- a/run-command.h
+++ b/run-command.h
@@ -496,4 +496,52 @@ int run_processes_parallel_tr2(int n, get_next_task_fn, start_failure_fn,
*/
void prepare_other_repo_env(struct strvec *env_array, const char *new_git_dir);
+/**
+ * Possible return values for `start_bg_command()`.
+ */
+enum start_bg_result {
+ /* child process is "ready" */
+ SBGR_READY = 0,
+
+ /* child process could not be started */
+ SBGR_ERROR,
+
+ /* callback error when testing for "ready" */
+ SBGR_CB_ERROR,
+
+ /* timeout expired waiting for child to become "ready" */
+ SBGR_TIMEOUT,
+
+ /* child process exited or was signalled before becomming "ready" */
+ SBGR_DIED,
+};
+
+/**
+ * Callback used by `start_bg_command()` to ask whether the
+ * child process is ready or needs more time to become ready.
+ *
+ * Returns 1 is child needs more time (subject to the requested timeout).
+ * Returns 0 if child is ready.
+ * Returns -1 on any error and cause `start_bg_command()` to also error out.
+ */
+typedef int(start_bg_wait_cb)(void *cb_data,
+ const struct child_process *cmd);
+
+/**
+ * Start a command in the background. Wait long enough for the child to
+ * become "ready". Capture immediate errors (like failure to start) and
+ * any immediate exit status (such as a shutdown/signal before the child
+ * became "ready").
+ *
+ * This is a combination of `start_command()` and `finish_command()`, but
+ * with a custom `wait_or_whine()` that allows the caller to define when
+ * the child is "ready".
+ *
+ * The caller does not need to call `finish_command()`.
+ */
+enum start_bg_result start_bg_command(struct child_process *cmd,
+ start_bg_wait_cb *wait_cb,
+ void *cb_data,
+ unsigned int timeout_sec);
+
#endif
--
gitgitgadget
