Please ignore that email, I didn't mean to send it yet and since figured out my question.
However there is 1 small point, in the function Capture_lstAddItem we have the line: if (Capture_lstGetListItem(item->list_element_id)) return NULL; I think that should be changed to: if (item->list_element_id && Capture_lstGetListItem(item->list_element_id)) return NULL; Because we only call that function with a (valid) pointer to null data. Lio. ----- Original Message From: "Arieh Schneier" ----- > I was looking at the list code in capture.c just to see if I could find the > bug (harder if I can't run it, but thought Id take a quick look). The code > to add items to the list is:Capture_lstAddItem(item) > > > > ----- Original Message From: "Youness Alaoui" ----- > On Sat, 26 Nov 2005 18:57:03 -0500, Harry Vennik <[EMAIL PROTECTED]> > wrote: > > > Op zaterdag 26 november 2005 20:03, schreef Youness Alaoui: > >> Hi, > >> that's nice! > >> the thing is "why does it only happen with pwc" ? > > I think I understand. The list contains the attributes we can set. And > > there > > are some attributes that cannot be set with the pwc driver, so those > > attributes won't appear in the list. All other drivers we know support > > these > > attributes. So only with the pwc driver it happens that we have to loop > > through all the list, to know that the attribute is not available, so > > only > > with the pwc driver we get far enough to reach the bad pointer! > > humm.. probably, now I get it... I don't know what causes this to be like > that, but what if we initialize (memset(0, list)) the list to NULL and > each time we add something, we set to NULL the next pointer... I guess > that's what it should be... I'm too tired to look at the code now, but > MAYBE tomorrow, I"ll have a peek > > >> > >> anyways, what you found confirms what someone else told me a few weeks > >> ago, I just never had time to look into it... here's more info about the > >> linked list problem and maybe a fix for it : > >> original post (see the comments) : > >> > https://sourceforge.net/tracker/?group_id=54091&atid=472655&func=detail&aid > >> =1281369 > >> > >> and here's a transcipt of the discussion with him on the pwc forum > >> thread : > >> > >> By: Willem Monsuwe - monsuwe > >> RE: segfault when trying to start webcam > >> 2005-10-02 15:20 > >> To be more exact, the driver doesn't support changing all the properties > >> that the program wants to. > >> For example, on a LT Quickcam 4000, you can set brightness and contrast > >> just fine, it just doesn't happen to have a hue setting. > >> IMHO, the webcam plugin should check what properties the driver supports > >> and be able to change those, but that's a lot of work to do, so that's > >> for > >> later. > > No, let's just have a set of attributes to set, and check if those are > > available, and disable them if not. (That's what we are trying to do > > now, but > > it fails because of the dangling pointer bug. Please also note that > > doing it > > the way proposed here - detect features and use those - will always fail, > > with every driver (!), because of the same bug.) > > > > I didn't really get it but do you mean initialize the list with all > possible value and add a boolean enable == TRUE | FALSE ? so if we find an > attribute, instead of adding it to the list, we just set the enabled to > TRUE? I'm not sure that's what you meant, but in any case, I'd prefer > libng stays clean and portable... > maybe someone could go check xawtv's cvs and see if libng was in any way > updated.. > I remind those who don't know that libng is the library used by xawtv, it > is not available anywhere besides in xawtv's source code (no separate > individual download for it), it's internal to xawtv and may have been > updated... > > >> In any case, the reason for the crash is a fault in the way linked lists > >> are handled in libng(*). If that is remedied, the webcam works better, > >> although not okay, because then the function returns an error, which the > >> tcl code doesn't handle. > > Hmm, have to look at it better to know if this is true. But even if it > > is, it > > probably won't hurt anyway. > >> > >> *) Linked lists in libng are built by linking to a root pointer, that is > >> allocated by the caller. This means that if you have a linked list as > >> member of a struct, the first item in the list will actually be that > >> member. Furthermore, it's a doubly linked, circular list. This is all > >> fine, as long as you use the original root pointer. As soon as you copy > >> it, for example by assigning the struct, the root pointer will be at a > >> different address. However, inside the linked list there are two > >> pointers > >> pointing to the old address, so as soon as a function traverses the > >> entire > >> list, you will have a dangling pointer bug. > > This is how things may go, but I think the dangling pointer problem has a > > different cause in this case. I think so because of the unlikely value > > of the > > pointer in an otherwise correctly filled structure for the 'Gain Level' > > attribute. I think there is just some buggy code in libng that happens to > > overwrite the pointer with something else. > > > > Harry > > > > > > > > > > ------------------------------------------------------- > This SF.net email is sponsored by: Splunk Inc. Do you grep through log files > for problems? Stop! Download the new AJAX search engine that makes > searching your log files as easy as surfing the web. DOWNLOAD SPLUNK! > http://ads.osdn.com/?ad_id=7637&alloc_id=16865&op=click > _______________________________________________ > Amsn-devel mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/amsn-devel > ------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Do you grep through log files for problems? Stop! Download the new AJAX search engine that makes searching your log files as easy as surfing the web. 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