On Windows the Perl getppid is not implemented. I have used the following C code in some of my XS modules:

#include <windows.h>
#include <tlhelp32.h>

static int getppid(void) {

    HANDLE hToolSnapshot;
    PROCESSENTRY32 Pe32 = {0};
    BOOL bResult;
    DWORD PID;
    DWORD PPID = 0;
    
    PID = GetCurrentProcessId ();

    hToolSnapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
    if (hToolSnapshot == INVALID_HANDLE_VALUE) {
        return 0;
    }

    Pe32.dwSize = sizeof(PROCESSENTRY32); 

    bResult = Process32First(hToolSnapshot, &Pe32); 

    if (!bResult) 
        return 0;
    
    while ( Process32Next(hToolSnapshot, &Pe32) ) {
        if (Pe32.th32ProcessID == PID) {
            PPID = Pe32.th32ParentProcessID;
            break;
        }
    }

    /* Expected */
    if (GetLastError() == ERROR_NO_MORE_FILES) {
        SetLastError(ERROR_SUCCESS);
    }

    return PPID;
}
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Ah, I see you have upgraded to Linux, maybe it might be useful to some poor Windows coder.