xintongsong commented on a change in pull request #9747: [FLINK-13985] Use
unsafe memory for managed memory
URL: https://github.com/apache/flink/pull/9747#discussion_r335273631
##########
File path:
flink-core/src/main/java/org/apache/flink/core/memory/MemoryUtils.java
##########
@@ -57,4 +64,79 @@
/** Should not be instantiated. */
private MemoryUtils() {}
+
+ private static Constructor<? extends ByteBuffer>
getDirectBufferPrivateConstructor() {
+ //noinspection OverlyBroadCatchBlock
+ try {
+ Constructor<? extends ByteBuffer> constructor =
+
ByteBuffer.allocateDirect(1).getClass().getDeclaredConstructor(long.class,
int.class);
+ constructor.setAccessible(true);
+ return constructor;
+ } catch (NoSuchMethodException e) {
+ ExceptionUtils.rethrow(
+ e,
+ "The private constructor
java.nio.DirectByteBuffer.<init>(long, int) is not available.");
+ } catch (SecurityException e) {
+ ExceptionUtils.rethrow(
+ e,
+ "The private constructor
java.nio.DirectByteBuffer.<init>(long, int) is not available, " +
+ "permission denied by security
manager");
+ } catch (Throwable t) {
+ ExceptionUtils.rethrow(
+ t,
+ "Unclassified error while trying to access
private constructor " +
+ "java.nio.DirectByteBuffer.<init>(long,
int).");
+ }
+ throw new RuntimeException("unexpected to avoid returning
null");
+ }
+
+ /**
+ * Allocates unsafe native memory.
+ *
+ * @param size size of the unsafe memory to allocate.
+ * @return address of the allocated unsafe memory
+ */
+ static long allocateUnsafe(long size) {
+ return UNSAFE.allocateMemory(Math.max(1L, size));
+ }
+
+ /**
+ * Creates a cleaner to release the unsafe memory by VM GC.
+ *
+ * <p>When memory owner becomes <a
href="package-summary.html#reachability">phantom reachable</a>,
+ * GC will release the underlying unsafe memory if not released yet.
+ *
+ * @param owner memory owner which phantom reaching is to monitor by GC
and release the unsafe memory
+ * @param address address of the unsafe memory to release
+ * @return action to run to release the unsafe memory manually
+ */
+ static Runnable createMemoryGcCleaner(@Nullable Object owner, long
address) {
+ return createGcCleaner(owner, () -> releaseUnsafe(address));
+ }
+
+ @SuppressWarnings("UseOfSunClasses")
+ private static Runnable createGcCleaner(@Nullable Object owner,
Runnable toClean) {
+ return owner == null ? toClean : sun.misc.Cleaner.create(owner,
toClean)::clean;
Review comment:
Agree with removing null case.
I get the idea that we use `Cleaner#clean` to guarantee that
`Unsafe#freeMemory` will be called only once. And I think it's a elegant
design. My point is we should add test cases to protect this. E.g., first call
`HybridMemorySegment#free` then explicitly trigger a GC, and verify that there
should be no failures due to multiple calls of `Unsafe#freeMemory`.
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