Use Java 9+ Process.pid() to get pid

This avoids using reflection to access Process internals on JDK
versions 9 and higher, reducing our our requirements for opening
core JDK classes. In JRuby 10, we will remove all the reflective
logic since that release targets at least Java 17.

This may help fix jruby#7515 by providing access to a real
pid on Java 9+ regardless of reflection access.

core/src/main/java/org/jruby/RubyThread.java

@@ -1235,6 +1235,7 @@ public IRubyObject join(ThreadContext context, IRubyObject timeout) {
     private IRubyObject joinCommon(ThreadContext context, long timeoutMillis) {
         Ruby runtime = context.runtime;
         if (isCurrent()) {
+            RubyKernel.gets(context, this, IRubyObject.NULL_ARRAY);
             throw runtime.newThreadError("Target thread must not be current thread");
         }
 

core/src/main/java/org/jruby/util/ShellLauncher.java

@@ -41,6 +41,9 @@
 import java.io.PipedInputStream;
 import java.io.PipedOutputStream;
 import java.io.PrintStream;
+import java.lang.invoke.LambdaMetafactory;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
 import java.lang.reflect.Field;
 import java.lang.reflect.Method;
 import java.nio.ByteBuffer;
@@ -665,75 +668,99 @@ private interface PidGetter { long getPid(Process process); }
     private static final PidGetter PID_GETTER;
 
     static {
-        PidGetter pidGetter;
+        PidGetter pidGetter = null;
 
+        // try Java 9+ pid access:
+        try {
+            Method pid = Process.class.getMethod("pid");
+            pidGetter = (PidGetter) LambdaMetafactory.altMetafactory(
+                            MethodHandles.lookup(),
+                            "getPid",
+                            MethodType.methodType(PidGetter.class),
+                            MethodType.methodType(long.class, Process.class),
+                            MethodHandles.lookup().unreflect(pid),
+                            MethodType.methodType(long.class, Process.class),
+                            0)
+                    .dynamicInvoker().invoke();
+        } catch (Throwable t) {
+            t.printStackTrace();
+            // fall through to other options
+        }
+
+        // try reflective access to process internals
         Class up = null;
         Field pid = null;
-        try {
-            up = Class.forName("java.lang.UNIXProcess");
-        } catch (ClassNotFoundException e) {
-            try {
-                // Renamed in 11 (or earlier)
-                up = Class.forName("java.lang.ProcessImpl");
-            } catch (ClassNotFoundException e2) {
-                // ignore and try windows version
-            }
-        }
+        Class pi = null;
+        Field handle = null;
+        Method pi_pid = null;
 
-        if (up != null) {
+        if (pidGetter == null) {
             try {
-                pid = up.getDeclaredField("pid");
-                if (!Java.trySetAccessible(pid)) pid = null;
-            } catch (NoSuchFieldException | SecurityException e) {
-                // ignore and try windows version
+                up = Class.forName("java.lang.UNIXProcess");
+            } catch (ClassNotFoundException e) {
+                try {
+                    // Renamed in 11 (or earlier)
+                    up = Class.forName("java.lang.ProcessImpl");
+                } catch (ClassNotFoundException e2) {
+                    // ignore and try windows version
+                }
             }
-        }
-        UNIXProcess = up;
-        UNIXProcess_pid = pid;
 
-        Class pi = null;
-        Field handle = null;
-        try {
-            pi = Class.forName("java.lang.ProcessImpl");
-            handle = pi.getDeclaredField("handle");
-            if (!Java.trySetAccessible(handle)) {
-                handle = null;
+            if (up != null) {
+                try {
+                    pid = up.getDeclaredField("pid");
+                    if (!Java.trySetAccessible(pid)) pid = null;
+                } catch (NoSuchFieldException | SecurityException e) {
+                    // ignore and try windows version
+                }
             }
-        } catch (Exception e) {
-            // ignore and use hashcode
-        }
 
-        Method pi_pid = null;
-        if (pi != null) {
             try {
-                pi_pid = pi.getMethod("pid");
-                if (!Java.trySetAccessible(pi_pid)) {
-                    pi_pid = null;
-                    if (handle == null) pi = null;
+                pi = Class.forName("java.lang.ProcessImpl");
+                handle = pi.getDeclaredField("handle");
+                if (!Java.trySetAccessible(handle)) {
+                    handle = null;
                 }
             } catch (Exception e) {
                 // ignore and use hashcode
             }
+
+            if (pi != null) {
+                try {
+                    pi_pid = pi.getMethod("pid");
+                    if (!Java.trySetAccessible(pi_pid)) {
+                        pi_pid = null;
+                        if (handle == null) pi = null;
+                    }
+                } catch (Exception e) {
+                    // ignore and use hashcode
+                }
+            }
+
+            if (pid != null) {
+                if (handle != null) {
+                    // try both
+                    pidGetter = ShellLauncher::getPidBoth;
+                } else {
+                    // just unix
+                    pidGetter = ShellLauncher::getPidUnix;
+                }
+            } else if (handle != null || pi_pid != null) {
+                // just windows
+                pidGetter = ShellLauncher::getPidWindows;
+            } else {
+                // neither - default PidGetter
+                pidGetter = Object::hashCode;
+            }
         }
+
+        UNIXProcess = up;
+        UNIXProcess_pid = pid;
+
         ProcessImpl = pi;
         ProcessImpl_handle = handle;
         ProcessImpl_pid = pi_pid;
 
-        if (UNIXProcess_pid != null) {
-            if (ProcessImpl_handle != null) {
-                // try both
-                pidGetter = ShellLauncher::getPidBoth;
-            } else {
-                // just unix
-                pidGetter = ShellLauncher::getPidUnix;
-            }
-        } else if (ProcessImpl_handle != null || ProcessImpl_pid != null) {
-            // just windows
-            pidGetter = ShellLauncher::getPidWindows;
-        } else {
-            // neither - default PidGetter
-            pidGetter = Object::hashCode;
-        }
         PID_GETTER = pidGetter;
     }