Page cache cursor unclaimed check made explicit

Previously this check was an assertion and thus was not executed in many cases.
This commit makes it explicit so we would catch more incorrect usages or page
cache cursors at runtime.
Check is guarded by a static final boolean flag obtained from system property.
So if `ThreadLocal#get()` appears to be very heavy, this additional check could
be turned off.

community/io/src/main/java/org/neo4j/io/pagecache/impl/muninn/CursorPool.java

@@ -23,6 +23,8 @@ final class CursorPool
 {
     private static boolean disableCursorPooling = Boolean.getBoolean(
             "org.neo4j.io.pagecache.impl.muninn.CursorPool.disableCursorPooling" );
+    private static boolean disableClaimedCheck = Boolean.getBoolean(
+            "org.neo4j.io.pagecache.impl.muninn.CursorPool.disableClaimedCheck" );
 
     private final ThreadLocal<MuninnReadPageCursor> readCursorCache = new MuninnReadPageCursorThreadLocal();
     private final ThreadLocal<MuninnWritePageCursor> writeCursorCache = new MuninnWritePageCursorThreadLocal();
@@ -36,7 +38,7 @@ public MuninnReadPageCursor takeReadCursor()
 
         MuninnReadPageCursor cursor = readCursorCache.get();
 
-        assert unclaimed( cursor, writeCursorCache );
+        assertUnclaimed( cursor, writeCursorCache );
 
         cursor.markAsClaimed();
         return cursor;
@@ -51,20 +53,19 @@ public MuninnWritePageCursor takeWriteCursor()
 
         MuninnWritePageCursor cursor = writeCursorCache.get();
 
-        assert unclaimed( cursor, readCursorCache );
+        assertUnclaimed( cursor, readCursorCache );
 
         cursor.markAsClaimed();
         return cursor;
     }
 
-    private static boolean unclaimed( MuninnPageCursor first, ThreadLocal<? extends MuninnPageCursor> second )
+    private static void assertUnclaimed( MuninnPageCursor first, ThreadLocal<? extends MuninnPageCursor> second )
     {
-        // This has been pulled out into a static method and guarded behind
-        // `assert`s to reduce the overhead put upon the inlining budget
-        // by something that should never happen.
-        first.assertUnclaimed();
-        second.get().assertUnclaimed();
-        return true;
+        if ( !disableClaimedCheck )
+        {
+            first.assertUnclaimed();
+            second.get().assertUnclaimed();
+        }
     }
 
     private static class MuninnReadPageCursorThreadLocal extends ThreadLocal<MuninnReadPageCursor>

community/io/src/main/java/org/neo4j/io/pagecache/impl/muninn/MuninnReadPageCursor.java

@@ -62,12 +62,14 @@ public boolean next() throws IOException
         return true;
     }
 
+    @Override
     protected void lockPage( MuninnPage page )
     {
         lockStamp = page.tryOptimisticRead();
         optimisticLock = true;
     }
 
+    @Override
     protected void unlockPage( MuninnPage page )
     {
     }

community/io/src/main/java/org/neo4j/io/pagecache/impl/muninn/MuninnWritePageCursor.java

@@ -61,11 +61,13 @@ public boolean next() throws IOException
         return true;
     }
 
+    @Override
     protected void lockPage( MuninnPage page )
     {
         lockStamp = page.writeLock();
     }
 
+    @Override
     protected void unlockPage( MuninnPage page )
     {
         page.unlockWrite( lockStamp );