Infinite loop inside a thread not working

Question

Was going through some tutorials on multi-threading and wrote some code to create an infinite thread. However, the infinite loop doesn't seem to work. The print routine inside the loop just runs once. Find the code below for reference. Cant understand what I am doing wrong. I am using the MSVC compiler.

#include <Windows.h>
#include <iostream>


DWORD __stdcall ThreadProc(LPVOID lpParameter) {

    const char* StringToPrint = (const char*)lpParameter;

    //expected this block to run infinitely.
    while (1) {
        std::cout << StringToPrint << "\n";
        Sleep(1000);
    }

    return 0;
}


int main() {

    DWORD ThreadId = 0;
    const char *Param = "Inside Thread";
    LPVOID Param1 = (LPVOID)Param;


    HANDLE Threadhandle = CreateThread(0, 0, ThreadProc, Param1, 0, &ThreadId);
    std::cout << "Thread ID " << ThreadId << " started" << "\n";
    CloseHandle(Threadhandle);
    return 0;

}

Your program exits without any chance for thread to start and continue working. — 273K, Mar 08 '20 at 17:20
Are you sure it only "runs once"? Did you confirm it with your debugger? Or are you relying solely on that console output? Because you haven't flushed it y'know... — Asteroids With Wings, Mar 08 '20 at 17:20
@AsteroidsWithWings Microsoft (R) C/C++ Optimizing Compiler Version 19.24.28316 for x86. — user1720897, Mar 08 '20 at 17:24
@user7860670 The answer to my specific issue isnt covered in the question you linked to. Kindly reconsider if this is a duplicate. — user1720897, Mar 08 '20 at 17:31
What is specific about this issue? There is a detached thread and `main` exits. — user7860670, Mar 08 '20 at 17:32
The solution is specific. Namely, `WaitForSingleObject` API. — user1720897, Mar 08 '20 at 17:34

score 2 · Accepted Answer · answered Mar 08 '20 at 17:21

The loop appears to run once because your program terminates just after you've started the thread.

If you want the thread to run forever, wait for it to finish in the main function:

    HANDLE Threadhandle = CreateThread(0, 0, ThreadProc, Param1, 0, &ThreadId);
    std::cout << "Thread ID " << ThreadId << " started" << "\n";
    WaitForSingleObject(Threadhandle, INFINITE);
    CloseHandle(Threadhandle);                    // it will never reach this

Infinite loop inside a thread not working

1 Answers1