Re: MT Design Question

From:

Joshua Maurice <joshuamaurice@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sun, 29 Aug 2010 12:04:15 -0700 (PDT)

Message-ID:

<de94aea5-d84b-4291-b209-f866484cbcf8@m17g2000prl.googlegroups.com>

On Aug 29, 12:02 pm, Joshua Maurice <joshuamaur...@gmail.com> wrote:

On Aug 29, 10:02 am, "Chris M. Thomasson" <cris...@charter.net> wrote:

"Joshua Maurice" <joshuamaur...@gmail.com> wrote in message

news:c56c7bf9-86d4-44dc-a4fa-04ea55227325@s17g2000prh.googlegroups.com..=

On Aug 28, 9:32 pm, "joe" <jc1...@att.net> wrote:

Joshua Maurice wrote:

On Aug 26, 1:35 pm, "joe" <jc1...@att.net> wrote:

See the Windows API WaitForMultipleObjects. This kind of stuff i=

trivial in Windows.

This is sort of a pet peeve of mine, but please don't suggest to
anyone to actually directly use the windows threading API if at a=

possible. It's borked, at least for windows XP and earlier, as it
lacks condition variables.

Well, ya see, me a programmer on Wintel has no need for UNIX/pthrea=

ds. I

am not a computer scientist like you are.

Do you have any nontrivial
examples where windows event classes result in simpler and more
efficient code than the condition variable alternative?

An event can make some code simpler. Take a slow path for, say a simple
mutex algorithm:

<event version - pseudo-code sketch>
_________________________________________________________
struct mutex
{
    LONG m_state; // = 0
    HANDLE m_waitset; // auto reset event; set to false

    void lock()
    {
        if (InterlockedExchange(&m_state, 1))
        {
            while (InterlockedExchange(&m_state, 2))
            {
                WaitForSingleObject(m_waitset, INFINITE=

);

            }
        }
    }

    void unlock()
    {
        if (InterlockedExchange(&m_state, 0) == 2)
        {
            SetEvent(m_waitset);
        }
    }};

Surely you mean:
  void lock()
  {
    //while, not if
    while (InterlockedExchange(&m_state, 1))
    {
      while (InterlockedExchange(&m_state, 2))
      {
        WaitForSingleObject(m_waitset, INFINITE);
      }
    }
  }
You need to set the m_state to locked aka 1 after a wakeup. Right?

Err, that's not quite right. Sorry. (I really need to review more
before submitting. I'm in a rush atm.) But yeah, you should get the
idea.