8202788: Explicitly reclaim cached thread-local direct buffers at thread exit

Add internal TerminatingThreadLocal and use it to free cached thread-local direct buffers and nio-fs native buffers

Reviewed-by: tonyp, alanb

src/java.base/share/classes/sun/nio/ch/Util.java

@@ -26,6 +26,7 @@
 package sun.nio.ch;
 
 import java.io.FileDescriptor;
+import java.io.IOException;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
 import java.nio.ByteBuffer;
@@ -35,9 +36,10 @@ import java.security.PrivilegedAction;
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.Set;
+
+import jdk.internal.misc.TerminatingThreadLocal;
 import jdk.internal.misc.Unsafe;
 import sun.security.action.GetPropertyAction;
-import java.io.IOException;
 
 public class Util {
 
@@ -50,13 +52,18 @@ public class Util {
     private static final long MAX_CACHED_BUFFER_SIZE = getMaxCachedBufferSize();
 
     // Per-thread cache of temporary direct buffers
-    private static ThreadLocal<BufferCache> bufferCache =
-        new ThreadLocal<BufferCache>()
-    {
+    private static ThreadLocal<BufferCache> bufferCache = new TerminatingThreadLocal<>() {
         @Override
         protected BufferCache initialValue() {
             return new BufferCache();
         }
+        @Override
+        protected void threadTerminated(BufferCache cache) { // will never be null
+            while (!cache.isEmpty()) {
+                ByteBuffer bb = cache.removeFirst();
+                free(bb);
+            }
+        }
     };
 
     /**

src/java.base/share/classes/sun/nio/fs/NativeBuffers.java

@@ -25,6 +25,7 @@
 
 package sun.nio.fs;
 
+import jdk.internal.misc.TerminatingThreadLocal;
 import jdk.internal.misc.Unsafe;
 
 /**
@@ -37,8 +38,21 @@ class NativeBuffers {
     private static final Unsafe unsafe = Unsafe.getUnsafe();
 
     private static final int TEMP_BUF_POOL_SIZE = 3;
-    private static ThreadLocal<NativeBuffer[]> threadLocal =
-        new ThreadLocal<NativeBuffer[]>();
+    private static ThreadLocal<NativeBuffer[]> threadLocal = new TerminatingThreadLocal<>() {
+        @Override
+        protected void threadTerminated(NativeBuffer[] buffers) {
+            // threadLocal may be initialized but with initialValue of null
+            if (buffers != null) {
+                for (int i = 0; i < TEMP_BUF_POOL_SIZE; i++) {
+                    NativeBuffer buffer = buffers[i];
+                    if (buffer != null) {
+                        buffer.free();
+                        buffers[i] = null;
+                    }
+                }
+            }
+        }
+    };
 
     /**
      * Allocates a native buffer, of at least the given size, from the heap.