Recurring callback fixes.

Author: christianhaeubl

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/RecurringCallbackSupport.java

@@ -353,6 +353,10 @@ private void maybeExecuteCallback() {
                     /*
                      * Before executing the callback, reset the safepoint requested counter as we
                      * don't want to trigger another callback execution in the near future.
+                     *
+                     * Recurring callbacks typically execute VM-internal code that performs hardly
+                     * any safepoint checks. We explicitly don't update the recurring callback
+                     * statistics anywhere in this method as this could skew the numbers.
                      */
                     setCounter(SafepointCheckCounter.MAX_VALUE);
                     try {
@@ -364,7 +368,6 @@ private void maybeExecuteCallback() {
                          */
                     } finally {
                         lastCallbackExecution = System.nanoTime();
-                        updateStatistics();
                     }
                 }
             } finally {

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/SafepointCheckCounter.java

@@ -62,8 +62,11 @@
  */
 public class SafepointCheckCounter {
     private static final FastThreadLocalInt valueTL = FastThreadLocalFactory.createInt("SafepointCheckCounter.value").setMaxOffset(FastThreadLocal.FIRST_CACHE_LINE);
-    /** Can be used to reset the thread-local value after a safepoint. */
-    static final int MAX_VALUE = Integer.MAX_VALUE;
+    /**
+     * Can be used to reset the thread-local value after a safepoint. We explicitly keep some
+     * distance to {@link Integer#MAX_VALUE} to avoid corner cases.
+     */
+    static final int MAX_VALUE = Integer.MAX_VALUE >>> 1;
 
     @Uninterruptible(reason = CALLED_FROM_UNINTERRUPTIBLE_CODE, mayBeInlined = true)
     static boolean compareAndSet(IsolateThread thread, int oldValue, int newValue) {