//
// Simple program demonstrating the use of threads.  Each thread executes
//  a loop similar to what is described in the mutual-exclusion problem.
//
// Command-line arguments are P (number of threads) and N (number of times
//   each should execute its loop).
//
#include <iostream>
#include <string>
#include <strstream>
#include <cstdlib>		// has exit(), etc.
#include <unistd.h>		// has usleep()
#include <pthread.h>		// has pthread_ routines
using namespace std;            // C++ "standard" namespace

// declaration for function to be executed by each thread
void * threadFcn(void * threadArg);

// ---- Shared variables ----

int N; // trips through loop
const int CR_DELAY = 10; // maximum delay in critical region
const int NON_CR_DELAY = 100; // maximum delay in non-critical region

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

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

    if (argc < 3) {
        cerr << "Usage:  " << argv[0] << " numThreads tripsThroughLoop\n";
        exit(EXIT_FAILURE);
    }
    int P = atoi(argv[1]);
    N = atoi(argv[2]);

    // Set up IDs for threads (need a separate variable for each since they're
    //   shared among threads).
    int * threadIDs = new int[P];
    for (int i = 0; i < P; ++i)
        threadIDs[i] = i;

    // Start P new threads, each with different ID.
    pthread_t * threads = new pthread_t[P];
    for (int i = 0; i < P; ++i) 
        pthread_create(&threads[i], NULL, threadFcn, (void *) &threadIDs[i]);

    // Wait for all threads to complete.
    for (int i = 0; i < P; ++i) 
        pthread_join(threads[i], NULL);

    // Clean up and exit.
    delete [] threadIDs;
    delete [] threads;
    cout << "That's all, folks!\n";
    return EXIT_SUCCESS;
}

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

void * threadFcn(void * threadArg) {
    int myID = * (int *) threadArg;

    // Make strings containing messages to print to improve the odds that
    //   they'll print atomically.  (This works most of the time, but not
    //   always.  Probably the printing should be done as part of the critical 
    //   region.)
    ostrstream startMsgStream;
    startMsgStream << "thread " << myID << " starting critical region\n";
    ostrstream endMsgStream;
    endMsgStream << "thread " << myID << " ending critical region\n";
    string startMsg = startMsgStream.str();
    string endMsg = endMsgStream.str();

    for (int i = 0; i < N; ++i) {
        cout << startMsg;
        usleep(rand() % CR_DELAY);
        cout << endMsg;
        usleep(rand() % NON_CR_DELAY);
    }
    pthread_exit((void* ) NULL);
}