Support JRuby on Java >= 9

.travis.yml

@@ -24,6 +24,9 @@ before_install:
   - ruby -e "system('gem update --system') if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new('2.3')"
   - gem install bundler --version '~> 1.17'
 
+before_script:
+  - 'export JAVA_OPTS="${JAVA_OPTS_FOR_SPECS}"'
+
 env:
   global:
   matrix:
@@ -36,6 +39,10 @@ matrix:
     - rvm: jruby-9.1.9.0
     - rvm: ruby-head
     - env: "CHILDPROCESS_POSIX_SPAWN=true"
+  include:
+  - rvm: jruby-9.2.5.0
+    jdk: openjdk11
+    env: "JAVA_OPTS_FOR_SPECS='--add-opens java.base/java.io=org.jruby.dist --add-opens java.base/sun.nio.ch=org.jruby.dist'"
   exclude:
     # Travis does not provide 1.9.3 on OSX
   - rvm: 1.9.3

README.md

@@ -173,6 +173,8 @@ ChildProcess.logger = logger
 ## Caveats
 
 * With JRuby on Unix, modifying `ENV["PATH"]` before using childprocess could lead to 'Command not found' errors, since JRuby is unable to modify the environment used for PATH searches in `java.lang.ProcessBuilder`. This can be avoided by setting `ChildProcess.posix_spawn = true`.
+* With JRuby on Java >= 9, the JVM may need to be configured to allow JRuby to access neccessary implementations; this can be done by adding `--add-opens java.base/java.io=org.jruby.dist` and `--add-opens java.base/sun.nio.ch=org.jruby.dist` to the `JAVA_OPTS` environment variable that is used by JRuby when launching the JVM.
+
 
 # Implementation
 

lib/childprocess/jruby/process.rb

@@ -46,24 +46,49 @@ def wait
         end
       end
 
-      #
-      # Only supported in JRuby on a Unix operating system, thanks to limitations
-      # in Java's classes
-      #
-      # @return [Integer] the pid of the process after it has started
-      # @raise [NotImplementedError] when trying to access pid on non-Unix platform
-      #
-      def pid
-        if @process.getClass.getName != "java.lang.UNIXProcess"
-          raise NotImplementedError, "pid is only supported by JRuby child processes on Unix"
+      # Implementation of ChildProcess::JRuby::Process#pid depends heavily on
+      # what Java SDK is being used; here, we look it up once at load, then
+      # define the method once to avoid runtime overhead.
+      normalised_java_version_major = java.lang.System.get_property("java.version")
+                                                      .slice(/^(1\.)?([0-9]+)/, 2)
+                                                      .to_i
+      if normalised_java_version_major >= 9
+
+        # On modern Javas, we can simply delegate through to `Process#pid`,
+        # which was introduced in Java 9.
+        #
+        # @return [Integer] the pid of the process after it has started
+        # @raise [NotImplementedError] when trying to access pid on platform for
+        #                              which it is unsupported in Java
+        def pid
+          @process.pid
+        rescue java.lang.UnsupportedOperationException => e
+          raise NotImplementedError, "pid is not supported on this platform: #{e.message}"
+        end
+
+      else
+
+        # On Legacy Javas, fall back to reflection.
+        #
+        # Only supported in JRuby on a Unix operating system, thanks to limitations
+        # in Java's classes
+        #
+        # @return [Integer] the pid of the process after it has started
+        # @raise [NotImplementedError] when trying to access pid on non-Unix platform
+        #
+        def pid
+          if @process.getClass.getName != "java.lang.UNIXProcess"
+            raise NotImplementedError, "pid is only supported by JRuby child processes on Unix"
+          end
+
+          # About the best way we can do this is with a nasty reflection-based impl
+          # Thanks to Martijn Courteaux
+          # http://stackoverflow.com/questions/2950338/how-can-i-kill-a-linux-process-in-java-with-sigkill-process-destroy-does-sigter/2951193#2951193
+          field = @process.getClass.getDeclaredField("pid")
+          field.accessible = true
+          field.get(@process)
         end
 
-        # About the best way we can do this is with a nasty reflection-based impl
-        # Thanks to Martijn Courteaux
-        # http://stackoverflow.com/questions/2950338/how-can-i-kill-a-linux-process-in-java-with-sigkill-process-destroy-does-sigter/2951193#2951193
-        field = @process.getClass.getDeclaredField("pid")
-        field.accessible = true
-        field.get(@process)
       end
 
       private