NSTimer in command line tool

Question

I'm getting to know the NS/Objective-C model of concurrency. Say I have a command line tool that does something like this:

#include "myLibrary.h"

void callback(void* parameter){
  cout<<"callback called.\n";
  //some logic...
}

int main(int argc, char* argv[]){
  myLibraryInit(callback);
  std::string s;
  while(true){
    cin>>s;
    myLibrarysResponseTo(s);
  }
}

In my library, I'd like to be able to have two responses. One which starts a repeating timer and one which stops it. The timer should call the callback supplied to the library by myLibraryInit.

I've used NSTimers before in iPhone/iPad apps, and I think the problem stems from the different paradigm command line tools have. The main thread goes into main and never finishes it until the program is finished. This means it's not free to run the main run loop, which is what gets the timer going. I think. So how do I make an NSTimer work in this context?

The other thing is that Apple NSTimer documentation says I need to invalidate an NSTimer on the same thread it was installed. I don't know how to figure out what thread I was on when I installed the timer, and then keep track of it (and ensure it stays alive) until I want to invalidate the timer. I'm not sure if I'm just missing an obvious mapping between threads and dispatch queues, run loops, or something else. I am using core bluetooth and I initialize a central manager like so:

_centralManager=[[CBCentralManager alloc]
  initWithDelegate: self
  queue: dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
];

so a callback may be triggered from here. If the callback includes some logic to call the library function that stops the timer, I can't guarantee from which thread came the invalidate. So how do I properly invalidate the timer?

I found this question but it doesn't allow a main to happen at the same time as the run loop that that the timer is on.

I hope I gave enough context. Thanks in advance for your replies.

Answer 1

You must call dispatch_main() or run an NSRunLoop in the main thread if any of the system frameworks [that use GCD or asynchronous operations] are to work correctly.

This can be as simple as calling [[NSRunLoop currentRunLoop] run]; at the end of your main() function (just make sure you schedule the kickoff work first as that method never returns).