[Qt-interest] Overhead considerations: QObject::startTimer(), QTimer, QBasicTimer

[Thiago Macieira]

On Tuesday, 13 de September de 2011 17:24:04 Pritam Ghanghas wrote:
> Hi All,
> 
> I need to use a lot of timers in my application. There are three
> approaches to timer in qt. I looked at documentation and couldn't
> anything that compares their performance or overhead figures.

All three are the same. The difference is the actual object that you're 
creating.

QObject::startTimer operates on your existing QObject. There's no extra 
overhead.

QBasicTimer also operates on your existing QObject, but it's an extra class 
that you have to keep around.

QTimer is a QObject of its own and therefore it operates on itself. It also 
communicates via signals, which have a small overhead too.

> QObject::startTimer(), QBasicTimer look very similar in functionality.
> QTimer is easy and neat to use but comes with QObject overhead. I was
> wondering "how much is this overhead? and are there other overheads to
> using QTimer instead of the other two?"

One QObject costs approximately 100 bytes of memory. The overhead of a signal-
slot delivery is around 3 function calls. So unless you're using hundreds of 
those or you're in a time-critical section, QTimer is very much acceptable.

-- 
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
   Software Architect - Intel Open Source Technology Center
      PGP/GPG: 0x6EF45358; fingerprint:
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