how to modify the number of parallel compilation with Xcode

Question

How to change the number of parallel compilations when building a C++ project with XCode ?

I am not talking about distributed builds, but on simultaneous compilations of

Answer 1

For Xcode 4 you must set the IDEBuildOperationMaxNumberOfConcurrentCompileTasks user default, for example:

defaults write com.apple.dt.Xcode IDEBuildOperationMaxNumberOfConcurrentCompileTasks 4

Note the "dt". This won't affect xcodebuild on the command line. To do that, use something like

xcodebuild -IDEBuildOperationMaxNumberOfConcurrentCompileTasks=4 ...

(See http://lists.apple.com/archives/xcode-users/2011/Apr/msg00403.html and http://lists.apple.com/archives/xcode-users/2011/Jul//msg00377.html )