I have a program which starts a thread (using pthreads) that will do some background task for the remainder of the program. The main program is run in a terminal and a common use-case is to close it before it exits by itself using Ctrl-C. Someone asked me to be vary of the threads I spawn to become zombies. I had not thought about this problem before and I am a novice in multi-threaded programming in general. I created what I am hoping is a small, but complete, and self-contained test program that should mimic the behavior of the real program.
In the code below, is there a risk of the spawned thread to become a zombie? Recall that the program could be killed using Ctrl-C, maybe that is a special scenario, I'm not sure about that.
Right now, the thread keeps running after the MyThread object has been deleted. This is not really a problem, because in the real program, the MyThread object is destroyed just as the program is about to exit anyway. I just want to know that the thread is never in the risk of becoming a zombie in the system after the parent is gone.
I suppose I could have a mutex-protected variable that I check in the thread func each iteration to tell me if I should exit, and I could set this variable to true in the MyThread destructor, but perhaps I don't need to do that? Sorry, got a bit long, thanks for reading and thanks in advance for any help!
#include <iostream>
#include <pthread.h>
#include <unistd.h>
class MyThread
{
public:
MyThread() : is_running(false) {}
void Run()
{
if (!is_running) {
if (pthread_create(&thread, NULL,
(void * (*)(void *))RunThread,
NULL) == 0) {
is_running = true;
}
else {
std::cerr << "pthread_create() failed." << std::endl;
}
}
else {
std::cout << "The thread was already running." << std::endl;
}
}
private:
static void * RunThread(void */*arg*/)
{
while (true) {
sleep(1);
std::cout << "Hello from RunThread" << std::endl;
}
return NULL;
}
pthread_t thread;
bool is_running;
};
int main()
{
MyThread *thread = new MyThread;
thread->Run();
std::cout << "Going to sleep for five seconds." << std::endl;
sleep(5);
std::cout << "No longer asleep, deleting thread object." << std::endl;
delete thread;
std::cout << "Hit enter to exit program." << std::endl;
std::cin.get();
return 0;
}
