[Development] Announcing moc_combine

Joerg Bornemann joerg.bornemann at qt.io
Tue May 31 18:13:18 CEST 2016

On 29/05/2016 18:05, Thiago Macieira wrote:

> I've just pushed a feature[1] to moc that makes it process multiple headers at
> the same time, producing only one output file, and a second feature[2] that
> "precompiles" a header. Since moc is single-threaded, this often means more
> wall-clock time than the previous case, but it's always less CPU time:

While this feature reduces the build time for full builds within a 
measurable range, it drastically increases build time for incremental 
builds. Changing just one Q_OBJECT header file results in full 
regeneration of combined_moc.cpp.

Take for example:
touch src/widgets/dialogs/qprogressdialog.h

moc time without moc_combine:  0.8s
moc time with moc_combine:    15.6s

This feature is nice for source distributions but isn't suitable for 
code being developed.



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