Fixes for -XX:MaxRAM and -XX:MaxDirectMemorySize at runtime

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/Target_jdk_internal_misc_VM.java

@@ -78,6 +78,12 @@ public static ClassLoader latestUserDefinedLoader0() {
     public static void initLevel(int newVal) {
         throw VMError.shouldNotReachHere("This is an alias to the method in the target class, so this code is unreachable");
     }
+
+    @Alias //
+    @SuppressWarnings("unused")
+    public static int initLevel() {
+        return -1; // Aliased code. Should not reach here
+    }
 }
 
 final class DirectMemoryAccessors {
@@ -134,14 +140,28 @@ private static synchronized void initialize() {
                 newDirectMemory = STATIC_DIRECT_MEMORY_AMOUNT; // Static value during initialization
                 INIT_COUNT.incrementAndGet();
             } else {
-                VMError.guarantee(INIT_COUNT.get() == 1, "Second cycle needs to have init count 1");
+                VMError.guarantee(INIT_COUNT.get() <= 1, "Runtime.maxMemory() invariant");
                 /*
                  * Once we know PhysicalMemory has been properly initialized we can use
-                 * Runtime.maxMemory()
+                 * Runtime.maxMemory(). Note that we might end up in this branch for code explicitly
+                 * using the JDK cgroups code. At that point PhysicalMemory has likely been
+                 * initialized.
                  */
                 INIT_COUNT.incrementAndGet();
                 newDirectMemory = Runtime.getRuntime().maxMemory();
             }
+        } else {
+            /*
+             * For explicitly set direct memory we are done
+             */
+            Unsafe.getUnsafe().storeFence();
+            directMemory = newDirectMemory;
+            isInitialized = true;
+            if (Target_jdk_internal_misc_VM.initLevel() < 1) {
+                // only the first accessor needs to set this
+                Target_jdk_internal_misc_VM.initLevel(1);
+            }
+            return;
         }
         VMError.guarantee(newDirectMemory > 0, "New direct memory should be initialized");
 
@@ -154,7 +174,10 @@ private static synchronized void initialize() {
              * MAX_MEMORY field.
              */
             isInitialized = true;
-            Target_jdk_internal_misc_VM.initLevel(1);
+            if (Target_jdk_internal_misc_VM.initLevel() < 1) {
+                // only the first accessor needs to set this
+                Target_jdk_internal_misc_VM.initLevel(1);
+            }
         }
     }
 }