My idea of stress testing the algorithm is removing the sleep from while not done loop in the sample script, and replacing the sleep with usleep(1);.

I've added mutexes guarding the getting of the callback status from the global PM hash, and the calling of the Perl method that sets the status into the global PM hash from XS.

I consider stability, FOR NOW, to be 10 runs without crashes or perl panics or strange errors on the console.

void WINAPI CALLBACK
PerlCallback(HINTERNET h, 
       DWORD context, 
       DWORD mystatus, 
       LPVOID mystatusinfo, 
       DWORD mystatuslength) {

    DWORD myret;
    HINTERNET myhandle;

    // Let's try with perl_call_method
    // ...to clarify:
    // a C routine 
    // called from Perl
    // callbacks this C routine 
    // that callbacks a Perl routine.
    // ;)

    // if(mystatus!=status) {
        SV **sp;
          HANDLE hMutex;
          char mutexname [sizeof("Win32InternetPerlMutex") + sizeof(DW
+ORD)*8];
          DWORD waitres;
          //char [23 + sizeof(DWORD)*8] mutexname;
        //void * myptr;
        //printf("PerlCallback: entering\n");
        printf("PerlCallback: got handle=%d context=%d mystatus=%d\n",
+h,context,mystatus);
        //printf("PerlCallback: myWin32InternetPerlInterpreterPtr=%p\n
+",myWin32InternetPerlInterpreterPtr);
        
        //comment below out to trigger original crash/bug in Win32::In
+ternet and recompile
        PERL_SET_CONTEXT(myWin32InternetPerlInterpreterPtr);
        
        //printf("PerlCallback: ThreadId=%d\n",GetCurrentThreadId());
        //printf("PerlCallback: GetLastError() =%d\n",GetLastError());
        //myptr = PERL_GET_CONTEXT;
        //printf("PerlCallback: GetLastError() =%d\n",GetLastError());
        //printf("PerlCallback: pointer from Perl_get_context() =%p\n"
+,myptr);
        //can't use dSP because we are after variable declarations
        sp = PL_stack_sp;
        ENTER;
        SAVETMPS;
        PUSHMARK(sp);
        // XPUSHs(sv_2mortal(newSVpv("Win32::Internet\0",0)));
        XPUSHs(sv_2mortal(newSViv(context)));
        XPUSHs(sv_2mortal(newSViv(mystatus)));
        switch(mystatus) {
        case INTERNET_STATUS_HANDLE_CREATED:
            myhandle=(HINTERNET) *(LPHINTERNET)mystatusinfo;
            XPUSHs(sv_2mortal(newSViv((DWORD) myhandle)));
            break;
        case INTERNET_STATUS_RESPONSE_RECEIVED:
        case INTERNET_STATUS_REQUEST_SENT:
            myret=(DWORD) *(LPDWORD)mystatusinfo;
            // printf("PerlCallback: received/sent(%d) %d bytes\n",mys
+tatus,myret);
            XPUSHs(sv_2mortal(newSViv(myret)));
            break;
        default:
            XPUSHs(sv_2mortal(newSViv(0)));
            break;
        }
        PUTBACK;
        // printf("PerlCallback: calling callback with context=%d, sta
+tus=%d\n",context,mystatus);
          sprintf(mutexname ,"Win32InternetPerlMutex%u", GetCurrentPro
+cessId());
          //printf("PerlCallback: mutexname=%s\n",mutexname);
          hMutex = OpenMutex(MUTEX_ALL_ACCESS, FALSE, mutexname);
          if (hMutex == NULL) printf("PerlCallback: OpenMutex error: %
+d\n", GetLastError() );
          else printf("PerlCallback: OpenMutex successfully opened the
+ mutex.\n");
          waitres = WaitForSingleObject(hMutex,500000);
          printf("PerlCallback: wait result =%d\n",waitres);



        perl_call_pv("Win32::Internet::callback", G_DISCARD);

          printf("PerlCallback: release mutex res=%d\n",ReleaseMutex(h
+Mutex));
          CloseHandle(hMutex);
          
        FREETMPS;
        LEAVE;

    // }
    // status=mystatus;
    // return;
}
[download]

was never stable until usleep(100000);

void WINAPI CALLBACK
PerlCallback(HINTERNET h, 
       DWORD context, 
       DWORD mystatus, 
       LPVOID mystatusinfo, 
       DWORD mystatuslength) {

    DWORD myret;
    HINTERNET myhandle;



    // Let's try with perl_call_method
    // ...to clarify:
    // a C routine 
    // called from Perl
    // callbacks this C routine 
    // that callbacks a Perl routine.
    // ;)

    // if(mystatus!=status) {
        SV **sp;
          HANDLE hMutex;
          char mutexname [sizeof("Win32InternetPerlMutex") + sizeof(DW
+ORD)*8];
          DWORD waitres;
          //char [23 + sizeof(DWORD)*8] mutexname;
        //void * myptr;
        //printf("PerlCallback: entering\n");
          sprintf(mutexname ,"Win32InternetPerlMutex%u", GetCurrentPro
+cessId());
          //printf("PerlCallback: mutexname=%s\n",mutexname);
          hMutex = OpenMutex(MUTEX_ALL_ACCESS, FALSE, mutexname);
          if (hMutex == NULL) printf("PerlCallback: OpenMutex error: %
+d\n", GetLastError() );
          else printf("PerlCallback: OpenMutex successfully opened the
+ mutex.\n");
          waitres = WaitForSingleObject(hMutex,500000);
          printf("PerlCallback: wait result =%d\n",waitres);
        printf("PerlCallback: got handle=%d context=%d mystatus=%d\n",
+h,context,mystatus);
        //printf("PerlCallback: myWin32InternetPerlInterpreterPtr=%p\n
+",myWin32InternetPerlInterpreterPtr);
        
        //comment below out to trigger original crash/bug in Win32::In
+ternet and recompile
        PERL_SET_CONTEXT(myWin32InternetPerlInterpreterPtr);
        
        //printf("PerlCallback: ThreadId=%d\n",GetCurrentThreadId());
        //printf("PerlCallback: GetLastError() =%d\n",GetLastError());
        //myptr = PERL_GET_CONTEXT;
        //printf("PerlCallback: GetLastError() =%d\n",GetLastError());
        //printf("PerlCallback: pointer from Perl_get_context() =%p\n"
+,myptr);
        //can't use dSP because we are after variable declarations
        sp = PL_stack_sp;
        ENTER;
        SAVETMPS;
        PUSHMARK(sp);
        // XPUSHs(sv_2mortal(newSVpv("Win32::Internet\0",0)));
        XPUSHs(sv_2mortal(newSViv(context)));
        XPUSHs(sv_2mortal(newSViv(mystatus)));
        switch(mystatus) {
        case INTERNET_STATUS_HANDLE_CREATED:
            myhandle=(HINTERNET) *(LPHINTERNET)mystatusinfo;
            XPUSHs(sv_2mortal(newSViv((DWORD) myhandle)));
            break;
        case INTERNET_STATUS_RESPONSE_RECEIVED:
        case INTERNET_STATUS_REQUEST_SENT:
            myret=(DWORD) *(LPDWORD)mystatusinfo;
            // printf("PerlCallback: received/sent(%d) %d bytes\n",mys
+tatus,myret);
            XPUSHs(sv_2mortal(newSViv(myret)));
            break;
        default:
            XPUSHs(sv_2mortal(newSViv(0)));
            break;
        }
        PUTBACK;
        // printf("PerlCallback: calling callback with context=%d, sta
+tus=%d\n",context,mystatus);



        perl_call_pv("Win32::Internet::callback", G_DISCARD);

        FREETMPS;
        LEAVE;
          printf("PerlCallback: release mutex res=%d\n",ReleaseMutex(h
+Mutex));
          CloseHandle(hMutex);
    // }
    // status=mystatus;
    // return;
}
[download]

Only 1 out of 5 runs weren't stable at usleep(10000); in the getstatus loop in the test script.

I'm guessing that some of what BrowserUk said in Win32::Internet crash, XS, callbacks, perl stack & context, windows api, interpreter thread safety, 1 perl, many C threads by windows, in suggesting starting a new perl instance every time the C callback was fired by Windows, rather than using the main perl instance, is the "safe" way to do it.

I'm guessing a single perl instance isn't thread safe. From my amateur looking at the XS of [threads-shared], the "shared" variables have their own perl instance that lives with them, and the "context" is switched around before using perl functions. Neither the parent/main thread or child thread perl interpreters ever get to operate on the shared variables, I think. Mutexes guard the shared interpreter from being commanded by 2 or more threads at the same time I think.

Saving a copy of the perl instance pointer to use from another thread would only work if I can put the other, main thread to sleep, without question. I wonder if http://msdn.microsoft.com/en-us/library/ms686345%28VS.85%29.aspx would work? or is it completely unacceptable to use that in anything remotely approaching production code?

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