Sample Multithread C Program

Bounce.c is a sample multithread program that creates a new thread each time the letter a or A is typed. Each thread bounces a letter of a different color around the screen. Up to 32 threads can be created. The program's normal termination occurs when q or Q is typed.

Compile and link a multithread program

Programs are compiled as multithreaded by default.

To compile and link the multithread program Bounce.c from within the development environment

1. On the File menu, choose New > Project.

2. In the Create a new project dialog, select the Console App template that has C++, Windows, and Console tags. Choose Next to continue.

3. In the Configure your new project dialog, enter a name for your project, such as "Bounce". Choose Create to continue.

4. In the Solution Explorer window, open the Source Files folder under your project, and change the name of your source file to have a .c extension.

5. In the edit window, delete the existing source code and replace it with the sample code.

6. On the Build menu, choose Build Solution.

7. Press F5 to start the program in the debugger.

To compile and link the multithread program Bounce.c from the command line

1. Open a Visual Studio tools command prompt. This ensures the path is set to include the compiler.

2. Compile and link the program:

   cl bounce.c
   

Example

To build on the command line, copy and save this sample in a source file with a .c extension. In the IDE, replace any source code created by the template with this sample:

// sample_multithread_c_program.c
// compile with: /c
//
//  Bounce - Creates a new thread each time the letter 'a' is typed.
//  Each thread bounces a character of a different color around
//  the screen. All threads are terminated when the letter 'Q' is
//  entered.
//

#include <windows.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <conio.h>
#include <process.h>

#define MAX_THREADS  32

// The function getrandom returns a random number between
// min and max, which must be in integer range.
#define getrandom( min, max ) (SHORT)((rand() % (int)(((max) + 1) - \
                               (min))) + (min))

int main(void);                    // Thread 1: main
void KbdFunc(void);                // Keyboard input, thread dispatch
void BounceProc(void* pMyID);      // Threads 2 to n: display
void ClearScreen(void);            // Screen clear
void ShutDown(void);               // Program shutdown
void WriteTitle(int ThreadNum);    // Display title bar information

HANDLE  hConsoleOut;                 // Handle to the console
HANDLE  hRunMutex;                   // "Keep Running" mutex
HANDLE  hScreenMutex;                // "Screen update" mutex
int     ThreadNr = 0;                // Number of threads started
CONSOLE_SCREEN_BUFFER_INFO csbiInfo; // Console information
COORD   consoleSize;
BOOL    bTrails = FALSE;

HANDLE  hThreads[MAX_THREADS] = { NULL }; // Handles for created threads

int main(void) // Thread One
{
    // Get display screen information & clear the screen.
    hConsoleOut = GetStdHandle(STD_OUTPUT_HANDLE);
    GetConsoleScreenBufferInfo(hConsoleOut, &csbiInfo);
    consoleSize.X = csbiInfo.srWindow.Right;
    consoleSize.Y = csbiInfo.srWindow.Bottom;
    ClearScreen();
    WriteTitle(0);

    // Create the mutexes and reset thread count.
    hScreenMutex = CreateMutexW(NULL, FALSE, NULL);  // Cleared
    hRunMutex = CreateMutexW(NULL, TRUE, NULL);      // Set

    // Start waiting for keyboard input to dispatch threads or exit.
    KbdFunc();

    // All threads done. Clean up handles.
    if (hScreenMutex) CloseHandle(hScreenMutex);
    if (hRunMutex) CloseHandle(hRunMutex);
    if (hConsoleOut) CloseHandle(hConsoleOut);
}

void ShutDown(void) // Shut down threads
{
    // Tell all threads to die
    ReleaseMutex(hRunMutex);

    while (ThreadNr > 0)
    {
        // Wait for each thread to complete
        WaitForSingleObject(hThreads[--ThreadNr], INFINITE);
    }

    // Clean up display when done
    WaitForSingleObject(hScreenMutex, INFINITE);
    ClearScreen();
}

void KbdFunc(void) // Dispatch and count threads.
{
    int         KeyInfo;

    do
    {
        KeyInfo = _getch();
        if (tolower(KeyInfo) == 'a' &&
            ThreadNr < MAX_THREADS)
        {
            ++ThreadNr;
            hThreads[ThreadNr] = 
                (HANDLE)_beginthread(BounceProc, 0, (void*)(uintptr_t)ThreadNr);
            WriteTitle(ThreadNr);
        }

        if (tolower(KeyInfo) == 't')
        {
            bTrails = !bTrails;
        }
    } while (tolower(KeyInfo) != 'q');

    ShutDown();
}

void BounceProc(void* pMyID)
{
    wchar_t MyCell, OldCell;
    WORD    MyAttrib, OldAttrib = 0;
    wchar_t BlankCell = 0x20;
    COORD   Coords, Delta;
    COORD   Old = { 0,0 };
    DWORD   Dummy;
    int MyID = (int)(uintptr_t)pMyID;

    // Generate update increments and initial
    // display coordinates.
    srand(MyID * 3);

    Coords.X = getrandom(0, consoleSize.X - 1);
    Coords.Y = getrandom(0, consoleSize.Y - 1);
    Delta.X = getrandom(-3, 3);
    Delta.Y = getrandom(-3, 3);

    // Set up character & generate color
    // attribute from thread number.
    if (MyID > 16)
        MyCell = (wchar_t)(0x60 + MyID - 16); // lower case
    else
        MyCell = (wchar_t)(0x40 + MyID);      // upper case
    MyAttrib = MyID & 0x0f;   // force black background

    do
    {
        // Wait for display to be available, then lock it.
        WaitForSingleObject(hScreenMutex, INFINITE);

        if (!bTrails)
        {
            // If we still occupy the old screen position, blank it out.
            ReadConsoleOutputCharacterW(hConsoleOut, &OldCell, 1,
                Old, &Dummy);
            ReadConsoleOutputAttribute(hConsoleOut, &OldAttrib, 1,
                Old, &Dummy);
            if ((OldCell == MyCell) && (OldAttrib == MyAttrib))
                WriteConsoleOutputCharacterW(hConsoleOut, &BlankCell, 1,
                    Old, &Dummy);
        }

        // Draw new character, then clear screen lock
        WriteConsoleOutputCharacterW(hConsoleOut, &MyCell, 1,
            Coords, &Dummy);
        WriteConsoleOutputAttribute(hConsoleOut, &MyAttrib, 1,
            Coords, &Dummy);
        ReleaseMutex(hScreenMutex);

        // Increment the coordinates for next placement of the block.
        Old.X = Coords.X;
        Old.Y = Coords.Y;
        Coords.X += Delta.X;
        Coords.Y += Delta.Y;

        // If we are about to go off the screen, reverse direction
        if (Coords.X < 0 || Coords.X >= consoleSize.X)
        {
            Delta.X = -Delta.X;
            Beep(400, 50);
        }
        if (Coords.Y < 0 || Coords.Y > consoleSize.Y)
        {
            Delta.Y = -Delta.Y;
            Beep(600, 50);
        }
    }
    // Repeat while RunMutex is still taken.
    while (WaitForSingleObject(hRunMutex, 75L) == WAIT_TIMEOUT);
}

void WriteTitle(int ThreadNum)
{
    enum
    {
        sizeOfNThreadMsg = 120
    };
    wchar_t    NThreadMsg[sizeOfNThreadMsg] = { L"" };

    swprintf_s(NThreadMsg, sizeOfNThreadMsg,
        L"Threads running: %02d.  Press 'A' "
        L"to start a thread, 'T' to toggle "
        L"trails, 'Q' to quit.", ThreadNum);
    SetConsoleTitleW(NThreadMsg);
}

void ClearScreen(void)
{
    DWORD    dummy = 0;
    COORD    Home = { 0, 0 };
    FillConsoleOutputCharacterW(hConsoleOut, L' ',
        consoleSize.X * consoleSize.Y,
        Home, &dummy);
}

See also

Multithreading with C and Win32