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SystemServer: Wait on all waitable children in SIGCHLD handler

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We need to call waitpid until no more waitable children are available.
This is necessary because SIGCHLD signals may coalesce into one when
multiple children terminate almost simultaneously.

This fixes random zombie processes sticking around after e.g. closing
Browser.

Also, switch to EventLoop's asynchronous signal handling mechanism,
which allows more complex operations in the signal handler.
This commit is contained in:
Tom 2020-12-01 20:05:11 -07:00 committed by Andreas Kling
parent ddaab598a7
commit d6174f9c79
1 changed files with 18 additions and 24 deletions
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42
Services/SystemServer/main.cpp
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@ -42,29 +42,28 @@ String g_boot_mode = "graphical";
static void sigchld_handler(int)
{
int status = 0;
pid_t pid = waitpid(-1, &status, WNOHANG);
if (!pid)
return;
for (;;) {
int status = 0;
pid_t pid = waitpid(-1, &status, WNOHANG);
if (pid < 0) {
perror("waitpid");
break;
}
if (pid == 0)
break;
#ifdef SYSTEMSERVER_DEBUG
dbg() << "Reaped child with pid " << pid << ", exit status " << status;
dbg() << "Reaped child with pid " << pid << ", exit status " << status;
#endif
Service* service = Service::find_by_pid(pid);
if (service == nullptr) {
// This can happen for multi-instance services.
return;
}
Service* service = Service::find_by_pid(pid);
if (service == nullptr) {
// This can happen for multi-instance services.
continue;
}
// Call service->did_exit(status) some time soon.
// We wouldn't want to run the complex logic, such
// as possibly spawning the service again, from the
// signal handler, so defer it.
Core::EventLoop::main().post_event(*service, make<Core::DeferredInvocationEvent>([=](auto&) {
service->did_exit(status);
}));
Core::EventLoop::wake();
}
}
static void parse_boot_mode()
@ -112,15 +111,10 @@ int main(int, char**)
mount_all_filesystems();
parse_boot_mode();
struct sigaction sa = {
.sa_handler = sigchld_handler,
.sa_mask = 0,
.sa_flags = SA_RESTART
};
sigaction(SIGCHLD, &sa, nullptr);
Core::EventLoop event_loop;
event_loop.register_signal(SIGCHLD, sigchld_handler);
// Read our config and instantiate services.
// This takes care of setting up sockets.
NonnullRefPtrVector<Service> services;