uses
  TlHelp32
...
var
  aSnapProcHandle: THandle;
  aThreadEntry: TThreadEntry32;
  aCurrentProcessID : Cardinal;
  aThreadHandle : Cardinal;
  aNext: Boolean;
begin
  aSnapProcHandle := CreateToolhelp32Snapshot(TH32CS_SNAPTHREAD, 0);
  if aSnapProcHandle <> THandle(-1) then
  try
    aCurrentProcessID  := GetCurrentProcessId;
    aThreadEntry.dwSize := Sizeof(aThreadEntry);
    aNext := Thread32First(aSnapProcHandle, aThreadEntry);
    while aNext do begin
      if aThreadEntry.th32OwnerProcessID = aCurrentProcessID then begin
        { наши потоки }
      end;
      aNext := Thread32Next(aSnapProcHandle, aThreadEntry);
    end;
  finally
    CloseHandle(aSnapProcHandle);
  end;
end;

function CheckThreadIsAlive(Thread: TThread): Boolean;
begin
    Result := WaitForSingleObject(Thread.Handle, 0) = WAIT_OBJECT_0;
end;

S>проверил — супер

Parameters
hHandle
[in] Handle to the object. For a list of the object types whose handles can be specified, see the following Remarks section.
If this handle is closed while the wait is still pending, the function's behavior is undefined.

The handle must have the SYNCHRONIZE access right. For more information, see Standard Access Rights.

dwMilliseconds
[in] Time-out interval, in milliseconds. The function returns if the interval elapses, even if the object's state is nonsignaled. If dwMilliseconds is zero, the function tests the object's state and returns immediately. If dwMilliseconds is INFINITE, the function's time-out interval never elapses.

E>function CheckThreadIsAlive(Thread: TThread): Boolean;
E>begin
E>    Result := WaitForSingleObject(Thread.Handle, 0) = WAIT_OBJECT_0;
E>end;
E>

if (WAIT_TIMEOUT != WaitForSingleObject((HANDLE)(sec_thread->Handle), 1)) {
    /* thread "killed" */
};

if (sec_thread->Suspended) { 
    /* сюда никогда не попадаем */ 
};

    sec_thread->Resume();

    BOOL IsThreadRunning(HANDLE  hThread) 
    { 
    DWORD dwCount; 


    // temporarily suspend thread to get 
    // previous suspend count 


    dwCount = SuspendThread(hThread); 


    // if no error, decrease the new suspend count 
    // by resuming the thread.  You must call 
    // ResumeThread if the above SuspendThread 
    // succeeded. 


    if (dwCount != 0xFFFFFFFF) ResumeThread(hThread); 


    // thread is running if suspend count was zero 


    return(dwCount==0); 
    }

D>WAIT_OBJECT_0 — значит поток активный? Я всегда считал что это значит что поток закончился Чесно не пробовал

WaitForSingleObject

...
dwMilliseconds
[in] Time-out interval, in milliseconds. The function returns if the interval elapses, even if the object's state is nonsignaled. If dwMilliseconds is zero, the function tests the object's state and returns immediately. If dwMilliseconds is INFINITE, the function's time-out interval never elapses.