Section 22.3.  Distributed Builds

22.3. Distributed Builds If you have a large project and more than one Macintosh at your disposal, you can see dramatically shorter build times with distributed builds. A Macintosh can volunteer idle time for distributed builds by opening the Distributed Builds panel of the Preferences window (Figure 22.1) and checking the first checkbox in the panel. Xcode processes on other computers or even the same computer can then send portions of their builds to the volunteer for compilation. The volunteer can choose to give the distributed-build background process low, medium, or high priority. Figure 22.1. The Distributed Builds panel of the Xcode Preferences window. The upper checkbox makes this machine available to others for compiling modules. The lower checkbox makes this machine a host for distributed builds, either on every machine that advertises itself on the local Bonjour net as a distcc node or on only those listed machines you mark as trusted. [View full size image] If you want to take advantage of distributed builds, check the second checkbox in the Distributed Builds panel of the Preferences window. The list below the checkbox will then fill with the names of all the local net's computers that are advertising via Bonjour (formerly Rendezvous) that they can take distributed builds. You can choose to distribute work to all comers or only to the machines you indicate in the list are trusted. Each machine participating in a distributed build must be running the same architecture and the same versions of Mac OS X, gcc, and Xcode. Xcode need not be running on the distributed machines. No matter what your Distributed Builds settings, some tasks are always done on the home machine of the build. In particular, the home machine builds precompiled headers and does preprocessing before sending out compilation units. Because the home machine has work to do that no other machine can, it is wisest not to enable the local machine as sharable for distributed builds. Distributed compilation can't benefit from more than about six remotes; beyond that point, the local machine is spending all its time assembling preprocessed compilands for the remotes and becomes the limiting factor. Remember that distributing the source and getting the compiled objects back takes time. Distributed builds may be a net loss in productivity if you use it on a network of less than 100Mb/second capacity. This rules out wireless and 10Base-T networks. If you are dealing with a firewall, be sure that it passes the distributed-build ports of 3632 and 7264.