8301627: System.exit and Runtime.exit debug logging

Reviewed-by: alanb, chegar

src/java.base/share/classes/java/lang/Runtime.java

@@ -156,6 +156,11 @@ public class Runtime {
      * <p> The {@link System#exit(int) System.exit} method is the
      * conventional and convenient means of invoking this method.
      *
+     * @implNote
+     * If the {@linkplain System#getLogger(String) system logger} for {@code java.lang.Runtime}
+     * is enabled with logging level {@link System.Logger.Level#DEBUG Level.DEBUG} the stack trace
+     * of the call to {@code Runtime.exit()} is logged.
+     *
      * @param  status
      *         Termination status.  By convention, a nonzero status code
      *         indicates abnormal termination.

src/java.base/share/classes/java/lang/Shutdown.java

@@ -157,16 +157,36 @@ class Shutdown {
      * which should pass a nonzero status code.
      */
     static void exit(int status) {
+        System.Logger log = getRuntimeExitLogger(); // Locate the logger without holding the lock;
         synchronized (Shutdown.class) {
             /* Synchronize on the class object, causing any other thread
              * that attempts to initiate shutdown to stall indefinitely
              */
+            if (log != null) {
+                Throwable throwable = new Throwable("Runtime.exit(" + status + ")");
+                log.log(System.Logger.Level.DEBUG, "Runtime.exit() called with status: " + status,
+                        throwable);
+            }
             beforeHalt();
             runHooks();
             halt(status);
         }
     }
 
+    /* Locate and return the logger for Shutdown.exit, if it is functional and DEBUG enabled.
+     * Exceptions should not prevent System.exit; the exception is printed and otherwise ignored.
+     */
+    private static System.Logger getRuntimeExitLogger() {
+        try {
+            System.Logger log = System.getLogger("java.lang.Runtime");
+            return (log.isLoggable(System.Logger.Level.DEBUG)) ? log : null;
+        } catch (Throwable throwable) {
+            // Exceptions from locating the Logger are printed but do not prevent exit
+            System.err.println("Runtime.exit() log finder failed with: " + throwable.getMessage());
+        }
+        return null;
+    }
+
 
     /* Invoked by the JNI DestroyJavaVM procedure when the last non-daemon
      * thread has finished.  Unlike the exit method, this method does not

src/java.base/share/classes/java/lang/System.java

@@ -1902,6 +1902,9 @@ public final class System {
      * Runtime.getRuntime().exit(n)
      * </pre></blockquote>
      *
+     * @implNote
+     * The initiation of the shutdown sequence is logged by {@link Runtime#exit(int)}.
+     *
      * @param  status exit status.
      * @throws SecurityException
      *         if a security manager exists and its {@code checkExit} method