QThread and reading memory.

Question

Dear All:

I have faced such a problem. I have a library which allows through UDP inter-process communication. It is very straight forward. The library creates shared memory available for other processes to write and read from. When process wants to read a interested memory it passes a string value which uniquely points to corresponding shared memory and passes pointer to container (char array) where he expects to receive result of reading. Library supplies safe multi-threading.

I have a exception when thread has left a run() routine.

Exception: is access violation and it is raised in

void __cdecl _freeptd (
        _ptiddata ptd
        )
{
        /*
         * Do nothing unless per-thread data has been allocated for this module!
         */

        if ( __flsindex != 0xFFFFFFFF ) {

            /*
             * if parameter "ptd" is NULL, get the per-thread data pointer
             * Must NOT call _getptd because it will allocate one if none exists!
             * If FLS_GETVALUE is NULL then ptd could not have been set
             */

            if ( ptd == NULL
#ifndef _M_AMD64
                 && (FLS_GETVALUE != NULL)
#endif  /* _M_AMD64 */
                )
                ptd = FLS_GETVALUE(__flsindex);

            /*
             * Zero out the one pointer to the per-thread data block
             */

            FLS_SETVALUE(__flsindex, (LPVOID)0);

            _freefls(ptd);
        }

        if ( __getvalueindex != 0xFFFFFFFF ) {
            /*
             * Zero out the FlsGetValue pointer
             */
            TlsSetValue(__getvalueindex, (LPVOID)0);
        }
} 

code:

char* memory = new char(2000);
string struct_name = "struct";
bool m_running = false;
void Reader::run()
{
    initalizeLibrary();
    m_running = true;
    //loop
    while(true)
    {
              if ( ! m_running ) break;
              library->readFromSharedMemory(struct_name, memory);
    }

    finalize();
}

void Reader::stop()
{
     m_running = false;
}

Exception is raised only when we allow to library->readFromSharedMemory(struct_name, memory);. _freeptd cannot access memory which cause access violation.

I need a hand. Thx in advance.

Answer 1

I have found a solution:

if you allocate memory: char* memory = new char(2000); it will fail, if you will use char* memory = (char*) malloc(2000); and then free up accordingly, it will work. I suppose it has something with new and different way of allocation a memory by compiler.

Lukasz.