On Fri, Feb 20, 2009 at 3:09 AM, nicolas de loof <nicolas.del...@gmail.com>wrote:
> I may be wrong, but doesn't the ProcessBuilder use the OS interpreter to > parse the forked process command line & arguments ? (This may be JRE > dependenant) > Not sure, but it's worth pointing out that CompilePermsServer doesn't actually need a really long classpath... it is designed to work with only gwt-dev on the classpath. > For my personnal info, why do you fork a JVM and not just use multiple > threads using java.util.concurrent ? > You can manually raise the number of local threads by setting the System property "gwt.jjs.maxThreads". If you don't set it, it defaults to 1. The reason we prefer processes to threads has to do with heap usage. The compiler is extremely memory intensive-- the amount of memory required to compile is nearly linear with the number of permutations you run at the same time. This causes several problems. - The user has to start up the VM with a much higher memory ceiling or they risk running out of memory. - If you get anywhere near the hard memory ceiling, you'll start thrashing GC badly and everything will grind to a standstill. This is far less likely to happen with multiple processes each with their own heap. - Even when you don't get anywhere near the memory ceiling, we've seen that empirically, GC appears to be super-linear with respect to the amount of heap being used. By sharding across processes instead of threads, we tend to find that GC overhead is reduced overall. - Finally, some operating systems (particularly Linux) will simply devote more processing time to a set of processes than it will to a single process with a lot of threads. We tend to get much higher CPU utilization with multi-process Bob, I went searching for the design doc for multi-process/threaded compiles but couldn't find it. Does one exist already? If not, could this email be a start for one? Thanks, Scott --~--~---------~--~----~------------~-------~--~----~ http://groups.google.com/group/Google-Web-Toolkit-Contributors -~----------~----~----~----~------~----~------~--~---
