run-command: optionally kill children on exit

When we spawn a helper process, it should generally be done
and finish_command called before we exit. However, if we
exit abnormally due to an early return or a signal, the
helper may continue to run in our absence.

In the best case, this may simply be wasted CPU cycles or a
few stray messages on a terminal. But it could also mean a
process that the user thought was aborted continues to run
to completion (e.g., a push's pack-objects helper will
complete the push, even though you killed the push process).

This patch provides infrastructure for run-command to keep
track of PIDs to be killed, and clean them on signal
reception or input, just as we do with tempfiles. PIDs can
be added in two ways:

  1. If NO_PTHREADS is defined, async helper processes are
     automatically marked. By definition this code must be
     ready to die when the parent dies, since it may be
     implemented as a thread of the parent process.

  2. If the run-command caller specifies the "clean_on_exit"
     option. This is not the default, as there are cases
     where it is OK for the child to outlive us (e.g., when
     spawning a pager).

PIDs are cleared from the kill-list automatically during
wait_or_whine, which is called from finish_command and
finish_async.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Clemens Buchacher <drizzd@aon.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
pull/27/head
Jeff King 11 years ago committed by Junio C Hamano
parent eac2d83247
commit afe19ff7b5
  1. 68
      run-command.c
  2. 1
      run-command.h

@ -1,8 +1,66 @@
#include "cache.h"
#include "run-command.h"
#include "exec_cmd.h"
#include "sigchain.h"
#include "argv-array.h"
struct child_to_clean {
pid_t pid;
struct child_to_clean *next;
};
static struct child_to_clean *children_to_clean;
static int installed_child_cleanup_handler;
static void cleanup_children(int sig)
{
while (children_to_clean) {
struct child_to_clean *p = children_to_clean;
children_to_clean = p->next;
kill(p->pid, sig);
free(p);
}
}
static void cleanup_children_on_signal(int sig)
{
cleanup_children(sig);
sigchain_pop(sig);
raise(sig);
}
static void cleanup_children_on_exit(void)
{
cleanup_children(SIGTERM);
}
static void mark_child_for_cleanup(pid_t pid)
{
struct child_to_clean *p = xmalloc(sizeof(*p));
p->pid = pid;
p->next = children_to_clean;
children_to_clean = p;
if (!installed_child_cleanup_handler) {
atexit(cleanup_children_on_exit);
sigchain_push_common(cleanup_children_on_signal);
installed_child_cleanup_handler = 1;
}
}
static void clear_child_for_cleanup(pid_t pid)
{
struct child_to_clean **last, *p;
last = &children_to_clean;
for (p = children_to_clean; p; p = p->next) {
if (p->pid == pid) {
*last = p->next;
free(p);
return;
}
}
}
static inline void close_pair(int fd[2])
{
close(fd[0]);
@ -130,6 +188,9 @@ static int wait_or_whine(pid_t pid, const char *argv0, int silent_exec_failure)
} else {
error("waitpid is confused (%s)", argv0);
}
clear_child_for_cleanup(pid);
errno = failed_errno;
return code;
}
@ -292,6 +353,8 @@ fail_pipe:
if (cmd->pid < 0)
error("cannot fork() for %s: %s", cmd->argv[0],
strerror(failed_errno = errno));
else if (cmd->clean_on_exit)
mark_child_for_cleanup(cmd->pid);
/*
* Wait for child's execvp. If the execvp succeeds (or if fork()
@ -312,6 +375,7 @@ fail_pipe:
cmd->pid = -1;
}
close(notify_pipe[0]);
}
#else
{
@ -356,6 +420,8 @@ fail_pipe:
failed_errno = errno;
if (cmd->pid < 0 && (!cmd->silent_exec_failure || errno != ENOENT))
error("cannot spawn %s: %s", cmd->argv[0], strerror(errno));
if (cmd->clean_on_exit && cmd->pid >= 0)
mark_child_for_cleanup(cmd->pid);
if (cmd->env)
free_environ(env);
@ -540,6 +606,8 @@ int start_async(struct async *async)
exit(!!async->proc(proc_in, proc_out, async->data));
}
mark_child_for_cleanup(async->pid);
if (need_in)
close(fdin[0]);
else if (async->in)

@ -38,6 +38,7 @@ struct child_process {
unsigned silent_exec_failure:1;
unsigned stdout_to_stderr:1;
unsigned use_shell:1;
unsigned clean_on_exit:1;
void (*preexec_cb)(void);
};

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