how to save a thread stack before it exits?

Question

I'm working on a multi-threading project and I need to make a copy of a thread's stack at some point in code (I need a pointer to that). because I'm going to need that pointer after this thread is exited (and it's stack is freed). It would also do the job if I could somehow tell pthread_exit() not to free the stack of thread!

PS: The reason behind this is that I want to use setcontext(ucontext_t*) later when this thread is actually dead.

Answer 1

As was mentioned, this may be a case of the XY problem. However, the solution is to use a pthread_mutex_t in each thread.

The function creating the thread would create the pthread_mutext_t and pass it to the thread.

pthread_t tid;
pthread_mutext_t mutex;

pthread_mutex_init(&mutex, NULL);
pthread_mutex_lock(&mutex);

pthread_create(&tid, NULL, fun, &mutex);

// do stuff

pthread_mutex_unlock(&mutex);

The thread function would be as follows...

void fun(void* arg) {

  pthread_mutex_t* mutex = (pthread_mutex_t*) arg;
  pthread_mutex_lock(mutex);

  // do stuff
}

If you need to do this asynchronously, you can register a signal handler for SIGUSR1 and SIGUSR2 and use pause to unschedule the thread.

signal(SIGUSR1, on_usr1);
signal(SIGUSR2, on_usr2);

void on_usr1(int sig) {

  pause();
}

void on_usr2(int sig) {
}

Then use pthread_kill to raise the signal to the thread...

pthread_kill(tid, SIGUSR1);