Avoid calling "ps" from GraalVM native images (#8)

We can trivially call 'kill' (system call) there.

Author: alexarchambault

library/src/libdaemonjvm/internal/IsRunning.java

@@ -0,0 +1,7 @@
+package libdaemonjvm.internal;
+
+public class IsRunning {
+  public Boolean isRunning(int pid) {
+    return null;
+  }
+}

library/src/libdaemonjvm/internal/IsRunningSubst.java

@@ -0,0 +1,18 @@
+package libdaemonjvm.internal;
+
+import com.oracle.svm.core.annotate.Substitute;
+import com.oracle.svm.core.annotate.TargetClass;
+import com.oracle.svm.core.posix.headers.Signal;
+import org.graalvm.nativeimage.Platform;
+import org.graalvm.nativeimage.Platforms;
+
+import java.nio.file.Path;
+
+@TargetClass(className = "libdaemonjvm.internal.IsRunning")
+@Platforms({Platform.LINUX.class, Platform.DARWIN.class})
+final class IsRunningSubst {
+  @Substitute
+  Boolean isRunning(int pid) {
+      return Signal.kill(pid, 0) == 0;
+  }
+}

library/src/libdaemonjvm/internal/LockProcess.scala

@@ -12,7 +12,9 @@ object LockProcess {
         sys.error("Cannot get PID")
       }
     def isRunning(pid: Int): Boolean =
-      Processes.isRunning(pid)
+      Option((new IsRunning).isRunning(pid)).map(b => (b: Boolean)).getOrElse {
+        Processes.isRunning(pid)
+      }
   }
 
   def default: LockProcess =

library/src/libdaemonjvm/internal/PidSubst.java

@@ -2,7 +2,6 @@
 
 import com.oracle.svm.core.annotate.Substitute;
 import com.oracle.svm.core.annotate.TargetClass;
-import com.oracle.svm.core.posix.headers.Signal;
 import com.oracle.svm.core.posix.headers.Unistd;
 import org.graalvm.nativeimage.Platform;
 import org.graalvm.nativeimage.Platforms;