Only use manual safepoint polling in PlatformDependent0.copyMemory(..…

….) when using java <= 8 (netty#8124)

Motivation:

Java9 and later does the safepoint polling by itself so there is not need for us to do it.

Modifications:

Check for java version before doing manual safepoint polling.

Result:

Less custom code and less overhead when using java9 and later. Fixes netty#8122.

common/src/main/java/io/netty/util/internal/PlatformDependent0.java

@@ -550,7 +550,16 @@ static void putLong(byte[] data, int index, long value) {
     }
 
     static void copyMemory(long srcAddr, long dstAddr, long length) {
-        //UNSAFE.copyMemory(srcAddr, dstAddr, length);
+        // Manual safe-point polling is only needed prior Java9:
+        // See https://bugs.openjdk.java.net/browse/JDK-8149596
+        if (javaVersion() <= 8) {
+            copyMemoryWithSafePointPolling(srcAddr, dstAddr, length);
+        } else {
+            UNSAFE.copyMemory(srcAddr, dstAddr, length);
+        }
+    }
+
+    private static void copyMemoryWithSafePointPolling(long srcAddr, long dstAddr, long length) {
         while (length > 0) {
             long size = Math.min(length, UNSAFE_COPY_THRESHOLD);
             UNSAFE.copyMemory(srcAddr, dstAddr, size);
@@ -561,7 +570,17 @@ static void copyMemory(long srcAddr, long dstAddr, long length) {
     }
 
     static void copyMemory(Object src, long srcOffset, Object dst, long dstOffset, long length) {
-        //UNSAFE.copyMemory(src, srcOffset, dst, dstOffset, length);
+        // Manual safe-point polling is only needed prior Java9:
+        // See https://bugs.openjdk.java.net/browse/JDK-8149596
+        if (javaVersion() <= 8) {
+            copyMemoryWithSafePointPolling(src, srcOffset, dst, dstOffset, length);
+        } else {
+            UNSAFE.copyMemory(src, srcOffset, dst, dstOffset, length);
+        }
+    }
+
+    private static void copyMemoryWithSafePointPolling(
+            Object src, long srcOffset, Object dst, long dstOffset, long length) {
         while (length > 0) {
             long size = Math.min(length, UNSAFE_COPY_THRESHOLD);
             UNSAFE.copyMemory(src, srcOffset, dst, dstOffset, size);