//
// Very simple program demonstrating the use of threads.
//
// Command-line argument is P (number of threads).
//
// Each thread creates a string containing "hello" message and writes
//   it to standard output.  No attempt is made to synchronize, but
//   by having each thread output its message in the form of a single
//   stream, we hope to avoid garbled output.  
//
#include <iostream.h>
#include <stdlib.h>		// has exit(), etc.
#include <pthread.h>		// has pthread_ routines
#include <string>
#include <strstream.h>		// has ostrstream class

// ---- Code to be executed by each thread ---------------------------

void * printHello(void * threadArg) {
  int * myID = (int *) threadArg;
  ostrstream messageStream;
  messageStream << "Hello from thread " << *myID << endl;
  string message = messageStream.str();
  cout << message;
  return NULL;
}

// ---- Main program -------------------------------------------------

int main(int argc, char* argv[]) {

  if (argc < 2) {
    cerr << "Usage:  " << argv[0] << " numThreads\n";
    exit(EXIT_FAILURE);
  }
  int P = atoi(argv[1]);

  // Set up IDs for threads.
  int * threadIDs = new int[P];
  for (int i = 0; i < P; ++i)
    threadIDs[i] = i;

  // Start P new threads.
  pthread_t * threads = new pthread_t[P];
  for (int i = 0; i < P; ++i) {
    if (pthread_create(&threads[i], NULL, printHello, 
		       (void *) &threadIDs[i]) != 0)
      cerr << "Unable to create thread " << i << endl;
  }

  // Wait for all threads to complete.
  for (int i = 0; i < P; ++i) {
    if (pthread_join(threads[i], NULL) != 0)
      cerr << "Unable to perform join on thread " << i << endl;
  }

  cout << "That's all, folks!\n";
  return EXIT_SUCCESS;
}