Spot the Defect!

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At
Microsoft we have an internal email list called "Spot the Defect" -- people mail around
buggy code they've discovered and we compete to see who can find the most problems
with it. It's fun, and you learn a lot
about what other people consider bugs -- everything from security holes to lying comments!

I
love playing Spot the Defect. Here is the code for the WScript.Sleep method
with the comments removed and some serious
bugs added. You'll note that this
code has all the required features I mentioned in my previous post. We
go to sleep in one-second (or less) intervals, and tell the operating system to wake
us up if COM posts a message to the message queue, because there might be an event
handler to dispatch. We also check to
see if the host recorded a script error (either due to an event handler or due to
the script timeout firing) so that we can abort the sleep. This
way we never keep the script alive more than a second after it was shut down due to
error.

What
bug did I add?

HRESULT
CWScript::Sleep(long Time)

{

    const
DWORD TimerGranularity = 1000;

    if
(Time < 0)

        return
E_INVALIDARG;

    DWORD
StartTickCount = ::GetTickCount();

    DWORD
EndTickCount = StartTickCount + Time;

    DWORD
CurTickCount = StartTickCount;

    while(CurTickCount
< EndTickCount)

    {

    MSG
msg;

        DWORD
CurWaitTime = (DWORD)(EndTickCount - CurTickCount);

        if
(CurWaitTime > TimerGranularity)

            CurWaitTime
= TimerGranularity;

        ::MsgWaitForMultipleObjects(0,
NULL, TRUE, CurWaitTime, QS_ALLINPUT | QS_ALLPOSTMESSAGE);

        if
(0 != ::PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))

            ::DispatchMessage(&msg);

        if
(m_pHost->FErrorPending())

            return
S_OK;

        CurTickCount
= ::GetTickCount();

    }

    return
S_OK;

}