How to change the amount of building threads in Xcode?

The number of threads Xcode is using to perform tasks is controlled by PBXNumberOfParallelBuildSubtasks option. You can change it with the following command: - defaults write com.apple.Xcode <key> <value>. For example:

defaults write com.apple.Xcode PBXNumberOfParallelBuildSubtasks 8

See Xcode User Defaults for more details.

There are also many other ways to speed up a compilation, from precompiled headers to distributed builds. Read Reducing Build Times for more information on this.

Good luck!

With XCode 5, you can use -parallelizeTargets and -jobs NUMBER with xcodebuild. According to xcodebuild --help:

-parallelizeTargets     build independent targets in parallel-jobs NUMBER            specify the maximum number of concurrent build operations

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 )