[PyQt] Threading crashes

[andre hotz]

Mark Summerfield schrieb:
> On 2010-04-20, andre hotz wrote:
>   
>> Hey,
>>
>> I have a problem with my QThreads (running on windows). It is the first
>> time I use multithreading, so I am probably doing something wrong ;)
>>
>> The situation is as follows: I have a QTreeWidget which works like a
>> filebrowser, listing a few thousand files. Creating
>> the treeitems from the files is pretty fast, but I also want the
>> treeWidget to display more information about the files.
>> This is taking some time depending on the quantity of the files. So what
>> I did is to first fill the treeView with all the filenames.
>> After that, I start an update-threat, which loops through all the items
>> in the treeWidget, gathers its data and fills the additional
>> columns in the treeView with the data. While the thread is updating the
>> treeWidget, the user can already work with the files and does not need
>> to wait for the update to finish.
>>
>> This all works pretty well.
>>     
>
> I think you've been pretty lucky to have it work at all!
>
>   
hehe, yeah, I was pretty happy when I got it working the first time ;)

> Qt does not provide any means of locking items or views. As a
> consequence, Qt does _not_ support updating models, scenes, or items in
> models, or items in widgets such as QTreeWidgetItems or
> QTableWidgetItems, etc. outside the main (GUI) thread. So any such
> update is potentially the source of a crash.
>
>   
hm, yes, this might explain the crashes..

> One technique that could be used is to hold the data in a thread-safe
> data structure and read data from that into the GUI as needed (locking
> the data structure or each item read from it as needed), and updating
> the data from one or more secondary threads (locking as needed).
>
>
>   
That sounds like it could work. Would it be possible to hold the data as 
you said, but when the update thread is finished, let it emit a signal 
to the treeWidget which then updates itself with the given data 
structure? Or does emitting signals from another thread also not work?