[Qt-interest] thread safety of Qt containers

[Thiago Macieira]

Em Segunda-feira 26 Abril 2010, às 11:26:17, Andre Somers escreveu:
> Hi,
> 
> I was wondering:
> Qt's documentation states that the methods in QList, QVector and QHash
> (and maybe QMap, I did not check) are reentrant. That means that they
> can be used in a thread, as long as the instance that is used is not the
> same, right?

Correct.

> So... how does QtConcurrent work? QtConcurrent::map() and the likes have
> multiple threads operating on data in the same container. How save is
> that? The docs say that only the non-in place operations make a copy of
> the container, so that would mean that multiple threads at the same time
> can write to a QList? They can't be using a QMutableListIterator though,
> as only one of those can be savely operating on a list at the same time...

There's a mutex. That ensures that there's only one thread accessing the 
container at a time.

> I am looking into QtConcurrent to speed up some heavy calculation work
> that I need to do. However, the amount of data is such that copying
> around data is really not an option. It is simply too much (datasets may
> range into the GB range).

-- 
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
  Senior Product Manager - Nokia, Qt Development Frameworks
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