java - Java中如何释放内存？

Question

为了减少 GC 压力，我需要分配一定量的堆外内存，如下所示:

long sz;
//...
long pointer = sun.misc.Unsafe.getUnsafe().allocateMemory(sz);

但是由于它无法用于 GC，因此我需要稍后手动释放它。如何？可以吗？

Answer 1

如果你真的读过它的javadoc你不会到达那里:

/**
 * Allocates a new block of native memory, of the given size in bytes.  The
 * contents of the memory are uninitialized; they will generally be
 * garbage.  The resulting native pointer will never be zero, and will be
 * aligned for all value types.  Dispose of this memory by calling {@link
 * #freeMemory}, or resize it with {@link #reallocateMemory}.
 *
 * @throws IllegalArgumentException if the size is negative or too large
 *         for the native size_t type
 *
 * @throws OutOfMemoryError if the allocation is refused by the system
 *
 * @see #getByte(long)
 * @see #putByte(long, byte)
 */
public native long allocateMemory(long bytes);

因此，您需要 unsafe.freeMemory(pointer) 来解除分配，或 unsafe.reallocateMemory(pointer) 来重新分配。请记住，您始终可以通过访问 openjdk's mercury repository 来访问 sun.* 类的源代码。