[PATCH v4 07/12] run-command: add clean_on_exit_handler

[larsxschneider@gmail.com]

From: Lars Schneider <larsxschneider@gmail.com>

Some commands might need to perform cleanup tasks on exit. Let's give
them an interface for doing this.

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 | 12 ++++++++----
 run-command.h |  1 +
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/run-command.c b/run-command.c
index 33bc63a..6ca75f3 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;
+	void (*clean_on_exit_handler)(pid_t);
 	struct child_to_clean *next;
 };
 static struct child_to_clean *children_to_clean;
@@ -30,6 +31,8 @@ static void cleanup_children(int sig, int in_signal)
 {
 	while (children_to_clean) {
 		struct child_to_clean *p = children_to_clean;
+		if (!in_signal && p->clean_on_exit_handler)
+			p->clean_on_exit_handler(p->pid);
 		children_to_clean = p->next;
 		kill(p->pid, sig);
 		if (!in_signal)
@@ -49,10 +52,11 @@ 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, void (*clean_on_exit_handler)(pid_t))
 {
 	struct child_to_clean *p = xmalloc(sizeof(*p));
 	p->pid = pid;
+	p->clean_on_exit_handler = clean_on_exit_handler;
 	p->next = children_to_clean;
 	children_to_clean = p;
 
@@ -422,7 +426,7 @@ 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->clean_on_exit_handler);
 
 	/*
 	 * Wait for child's execvp. If the execvp succeeds (or if fork()
@@ -483,7 +487,7 @@ 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->clean_on_exit_handler);
 
 	argv_array_clear(&nargv);
 	cmd->argv = sargv;
@@ -752,7 +756,7 @@ 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 5066649..59d21ea 100644
--- a/run-command.h
+++ b/run-command.h
@@ -43,6 +43,7 @@ struct child_process {
 	unsigned stdout_to_stderr:1;
 	unsigned use_shell:1;
 	unsigned clean_on_exit:1;
+	void (*clean_on_exit_handler)(pid_t);
 };
 
 #define CHILD_PROCESS_INIT { NULL, ARGV_ARRAY_INIT, ARGV_ARRAY_INIT }
-- 
2.9.0