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std string value mysteriously changes.

Posted on 2004-09-15
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Last Modified: 2013-11-20
Hi experts,
I have a list of CString file paths and would like to
process them one by one. But when I start the thread
the value mysteriously changes to nothing.
Some code:
      if(pidl){
            ::SHGetPathFromIDList(pidl, szDir);
            dir = CString(szDir);
            SetFolderList(GetFolderList(dir));
            for(list<CString>::iterator i=databaseList.begin(); i!=databaseList.end(); i++) {
                  options.PATHTODATABASE = (*i).GetString();
               //at this point  options.PATHTODATABASE contains for example "c:\database\chlre2.fasta"
                  AfxBeginThread(BatchThread,this,THREAD_PRIORITY_BELOW_NORMAL,0);
            }
      }
      UpdateAllViews(NULL);


UINT CMainDoc::BatchThread(LPVOID pParam)
{
      CString path;
      size_t pos1,pos2;
      string temp,file;
      CMainDoc *pDoc = (CMainDoc*)pParam;
     //At this point the value of options.PATHTODATABASE is empty.
      pDoc->options.PATHTODATABASE = CString("c:\\database\\chlre2.fasta").GetString();
      CFileFind finder;
      string dir;
      if(pDoc->dir.GetLength() > 1) {
            dir = pDoc->dir.GetString();
            pDoc->dir += "\\*.*";
            BOOL bWorking = finder.FindFile(pDoc->dir);
            while(bWorking) {      

I am really lost at this point.
Any ideas?
Cheers,
Jens
0
Comment
Question by:allmer
  • 4
  • 4
8 Comments
 
LVL 86

Expert Comment

by:jkr
ID: 12069283
It seems that your path variable gets overwritten (remember, you are starting multiple threads and are using the same doc). Try

// somewhere in a header file
struct ThreadOptions {

    CString strPathToDatabase;
    CString strDir;

    // basically everything you need in the threads
};


     if(pidl){
         ::SHGetPathFromIDList(pidl, szDir);
         dir = CString(szDir);
         SetFolderList(GetFolderList(dir));
         for(list<CString>::iterator i=databaseList.begin(); i!=databaseList.end(); i++) {

              ThreadOptions* pOpt = new ThreadOptions;

              pOpt->strPathToDatabase = (*i).GetString();

              // etc.

              AfxBeginThread(BatchThread,pOpt,THREAD_PRIORITY_BELOW_NORMAL,0);
         }
    }
    UpdateAllViews(NULL);


UINT CMainDoc::BatchThread(LPVOID pParam)
{
    CString path;
    size_t pos1,pos2;
    string temp,file;
    ThreadOptions *pOpt = (ThreadOptions*)pParam;
 
    //... at the end of the thread, use 'delete pOpt;'
0
 
LVL 5

Author Comment

by:allmer
ID: 12069423
Sounds good jkr
that could be the problem.
I'll try first thing tomorrow morning.
Thanks,
Jens
0
 
LVL 5

Author Comment

by:allmer
ID: 12075303
I am passing the this pointer to the thread
and I guess I also need it (progress bars, data display, ..). Instead of rewriting
the whole thing would it be ok to make the
COptions options //in maindoc.h
a pointer so I can new the options for each thread?
Best,
Jens
0
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LVL 86

Expert Comment

by:jkr
ID: 12075514
As long as you don't use the same storage space for all threads (as above), that's OK.
0
 
LVL 5

Author Comment

by:allmer
ID: 12086012
Can I Only start one thread at a time and wait for it to finish?
I don't really want them to execute in parallel.
That would probably also solve the problem.
Cheers,
Jens
0
 
LVL 86

Accepted Solution

by:
jkr earned 600 total points
ID: 12086107
Sure you can. All you need to do is using the thread handle:

CWinThread* p = AfxBeginThread(BatchThread,pOpt,THREAD_PRIORITY_BELOW_NORMAL,0);

   while   (   WAIT_OBJECT_0   !=  MsgWaitForMultipleObjects   (   1,
                                                                   &p->m_hThread,
                                                                   FALSE,
                                                                   INFINITE,
                                                                   QS_ALLINPUT
                                                               )
           )
           {
               while   (   PeekMessage (   &msg,   NULL,   0,  0,  PM_REMOVE))
                       {
                           DispatchMessage     (   &msg);
                       }
           }
0
 
LVL 5

Author Comment

by:allmer
ID: 12231038
Sorry jkr
that I get back to you this late :(
can I simply call
SleepEx(3000,false);
instead of the second while loop?
I don't have any msg var. And I don't control my own messages.
Too much work for a little biologist ;)
Thanks for your help,
Jens
0
 
LVL 86

Expert Comment

by:jkr
ID: 12244436
>>can I simply call
>>SleepEx(3000,false);

No, that won't fix the problem unless you *can* ensure that the job is *really* done within these 3kms...
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