[PATCH v10 04/14] run-command: add clean_on_exit_handler

[larsxschneider@gmail.com]

From: Lars Schneider <larsxschneider@gmail.com>

Some processes might want to perform cleanup tasks before Git kills them
due to the 'clean_on_exit' flag. Let's give them an interface for doing
this. The feature is used in a subsequent patch.

Please note, that the cleanup callback is not executed if Git dies of a
signal. The reason is that only "async-signal-safe" functions would be
allowed to be call in that case. Since we cannot control what functions
the callback will use, we will not support the case. See 507d7804 for
more details.

Helped-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
---
 run-command.c | 19 +++++++++++++++----
 run-command.h |  2 ++
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/run-command.c b/run-command.c
index 3269362..e5fd6ff 100644
--- a/run-command.c
+++ b/run-command.c
@@ -21,6 +21,7 @@ void child_process_clear(struct child_process *child)
 
 struct child_to_clean {
 	pid_t pid;
+	struct child_process *process;
 	struct child_to_clean *next;
 };
 static struct child_to_clean *children_to_clean;
@@ -31,6 +32,15 @@ static void cleanup_children(int sig, int in_signal)
 	while (children_to_clean) {
 		struct child_to_clean *p = children_to_clean;
 		children_to_clean = p->next;
+
+		if (p->process && !in_signal) {
+			struct child_process *process = p->process;
+			if (process->clean_on_exit_handler) {
+				trace_printf("trace: run_command: running exit handler for pid %d", p->pid);
+				process->clean_on_exit_handler(process);
+			}
+		}
+
 		kill(p->pid, sig);
 		if (!in_signal)
 			free(p);
@@ -49,10 +59,11 @@ static void cleanup_children_on_exit(void)
 	cleanup_children(SIGTERM, 0);
 }
 
-static void mark_child_for_cleanup(pid_t pid)
+static void mark_child_for_cleanup(pid_t pid, struct child_process *process)
 {
 	struct child_to_clean *p = xmalloc(sizeof(*p));
 	p->pid = pid;
+	p->process = process;
 	p->next = children_to_clean;
 	children_to_clean = p;
 
@@ -422,7 +433,7 @@ int start_command(struct child_process *cmd)
 	if (cmd->pid < 0)
 		error_errno("cannot fork() for %s", cmd->argv[0]);
 	else if (cmd->clean_on_exit)
-		mark_child_for_cleanup(cmd->pid);
+		mark_child_for_cleanup(cmd->pid, cmd);
 
 	/*
 	 * Wait for child's execvp. If the execvp succeeds (or if fork()
@@ -483,7 +494,7 @@ int start_command(struct child_process *cmd)
 	if (cmd->pid < 0 && (!cmd->silent_exec_failure || errno != ENOENT))
 		error_errno("cannot spawn %s", cmd->argv[0]);
 	if (cmd->clean_on_exit && cmd->pid >= 0)
-		mark_child_for_cleanup(cmd->pid);
+		mark_child_for_cleanup(cmd->pid, cmd);
 
 	argv_array_clear(&nargv);
 	cmd->argv = sargv;
@@ -765,7 +776,7 @@ int start_async(struct async *async)
 		exit(!!async->proc(proc_in, proc_out, async->data));
 	}
 
-	mark_child_for_cleanup(async->pid);
+	mark_child_for_cleanup(async->pid, NULL);
 
 	if (need_in)
 		close(fdin[0]);
diff --git a/run-command.h b/run-command.h
index cf29a31..dd1c78c 100644
--- a/run-command.h
+++ b/run-command.h
@@ -43,6 +43,8 @@ struct child_process {
 	unsigned stdout_to_stderr:1;
 	unsigned use_shell:1;
 	unsigned clean_on_exit:1;
+	void (*clean_on_exit_handler)(struct child_process *process);
+	void *clean_on_exit_handler_cbdata;
 };
 
 #define CHILD_PROCESS_INIT { NULL, ARGV_ARRAY_INIT, ARGV_ARRAY_INIT }
-- 
2.10.0