// The program illustrates the creation
// of threads and the usage of a mutex.
// It creates 2 threads with the same starting function.
// The first thread prints 10 times the word "Heads",
// the second thread prints 10 times the word "Tails".
// Between prints each thread sleeps a random
// time up to 2 sec. The last printed word
// (Heads or Tails) is the result of the draw.
//
// The mutex is used to exclude simultaneous
// prints by different threads.

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>

// Thread body function
DWORD WINAPI run(void* arg);

static HANDLE hMutex = NULL;

int main() {
    HANDLE hThread1, hThread2;
    DWORD threadID1, threadID2;
    const char *heads = "Heads";
    const char *tails = "Tails";

    int curtime = (int) GetTickCount();
    srand(curtime);     // Set the random generator

    // Create the mutex
    hMutex = CreateMutex(
        NULL,           // default security attributes
        FALSE,          // initially not owned
        NULL            // unnamed mutex
    );
    if (hMutex == NULL) {
        printf("Cannot create a mutex: error %d\n", GetLastError());
        exit(-1);
    }

    // Create the first thread
    hThread1 = CreateThread(
        NULL,           // lpThreadAttributes
        0,              // dwStackSize - default
        &run,            // thread starting function
        (void *) heads, // parameter of thread starting function
        0,              // dwCreationFlags
        &threadID1
    );

    if (hThread1 == NULL) {
        printf("Cannot create thread 1: error %d\n", GetLastError());
        exit(-1);
    }

    WaitForSingleObject(hMutex, INFINITE);
    printf("Thread 1 is created.\n");
    ReleaseMutex(hMutex);

    // Create the second thread
    hThread2 = CreateThread(
        NULL,           // lpThreadAttributes
        0,              // dwStackSize - default
        &run,           // thread starting function
        (void *) tails, // parameter of thread starting function
        0,              // dwCreationFlags
        &threadID2
    );

    if (hThread2 == NULL) {
        printf("Cannot create thread 2: error %d\n", GetLastError());
        exit(-1);
    }
    WaitForSingleObject(hMutex, INFINITE);
    printf("Thread 2 is created.\n");
    ReleaseMutex(hMutex);

    // Wait until threads terminate
    WaitForSingleObject(hThread1, INFINITE);
    WaitForSingleObject(hThread2, INFINITE);

    CloseHandle(hThread1);
    CloseHandle(hThread2);
    CloseHandle(hMutex);

    return 0;
}

DWORD WINAPI run(void* arg) {
    int i;
    const char *txt = (const char *) arg;

    for (i = 0; i < 10; i++) {
        WaitForSingleObject(hMutex, INFINITE);
        printf("%s\n", txt);
        ReleaseMutex(hMutex);

        int t = rand()%2000 + 1; // Random time in millisec
        Sleep(t);
    }
    return 0;
}