Hi David, > > please review an enhancement which I've identified when working with > > Processhelper for JDK-8230850. > > > > I noticed that ProcessHelper is an interface in common code with a > > static method that would lookup the actual platform implementation via > > reflection. This seems a little cumbersome since we can have a common > > dummy for ProcessHelper and override it with the platform specific > > implementation, leveraging the build system. > > I don't see you leveraging the build system. You have two source files > that compile to the same destination class file. What is ensuring the > platform specific version is compiled after the generic one? > > Service-provider patterns use reflection to instantiate the service > implementation. I don't see any problem here that needs solving.
TL;DR: There are two source files, one in share/classes and one in linux/classes. The build system overrides the share/classes implementation with the linux/classes implementation in the linux build. This is not by coincidence and only one class is contained in the generated jdk.jcmd module. Then there won't be a need for having a service interface and a service implementation that is looked up via reflection (which is not a bad pattern by itself). I agree that it's not a big problem to be solved but still not "no problem". Here is some longer elaboration how the build system prefers specific implementations of classes and filters generic duplicates: The SetupJavaCompilation function from JavaCompilation.gmk [0] is used to compile the java sources for JDK modules. In its documentation, for argument SRC [1], it claims: "one or more directories to search for sources. The order of the source roots is significant. The first found file of a certain name has priority". In its implementation the found files are first ordered [3] and duplicates filtered out [4]. The potential source files are handed to SetupJavaCompilation in CompileJavaModules.gmk [5] and were collected by a call to FindModuleSrcDirs [6]. FindModuleSrcDirs iterates over all potential source dirs for Java classes in the module [7]. The evaluated subdirs are (in that order) $(OPENJDK_TARGET_OS)/classes, $(OPENJDK_TARGET_OS_TYPE)/classes and share/classes, as per [8]. Hope that explains what I'm trying to leverage here. I've uploaded an updated webrev which contains some cleanup to the Test changes: http://cr.openjdk.java.net/~clanger/webrevs/8230857.1/ Thanks Christoph [0] http://hg.openjdk.java.net/jdk/jdk/file/ea93d6a9f720/make/common/JavaCompilation.gmk#l185 [1] http://hg.openjdk.java.net/jdk/jdk/file/ea93d6a9f720/make/common/JavaCompilation.gmk#l157 [3] http://hg.openjdk.java.net/jdk/jdk/file/ea93d6a9f720/make/common/JavaCompilation.gmk#l225 [4] http://hg.openjdk.java.net/jdk/jdk/file/ea93d6a9f720/make/common/JavaCompilation.gmk#l257 [5] http://hg.openjdk.java.net/jdk/jdk/file/ea93d6a9f720/make/CompileJavaModules.gmk#l603 [6] http://hg.openjdk.java.net/jdk/jdk/file/ea93d6a9f720/make/CompileJavaModules.gmk#l555 [7] http://hg.openjdk.java.net/jdk/jdk/file/ea93d6a9f720/make/common/Modules.gmk#l300 [8] http://hg.openjdk.java.net/jdk/jdk/file/ea93d6a9f720/make/common/Modules.gmk#l243
