前言

最近看到一篇文章, 然后基于改文章的代码, 做了一些调整, 然后发现了一些奇怪的事情, 并稍微整理了一下原因

该文章地址 : https://hllvm-group.iteye.com/group/topic/34934

测试代码如下 :

package com.hx.test02;import java.lang.ref.PhantomReference;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.reflect.Field;/*** Test02WeakReferenceAfterGc** @author Jerry.X.He <970655147@qq.com>* @version 1.0* @date 2019-10-14 11:23*/
public class Test02WeakReferenceAfterGc {// Test02WeakReferenceAfterGc// refer : https://hllvm-group.iteye.com/group/topic/34934public static void main(String[] args) throws Exception {ReferenceQueue<Obj> referenceQueue = new ReferenceQueue<>();for (int i = 0; i < 1; i++) {Obj o = new Obj("object_" + i);
//      SoftReference<Obj> ref = new SoftReference<>(o, referenceQueue);
//      WeakReference<Obj> ref = new WeakReference<>(o, referenceQueue);PhantomReference<Obj> ref = new PhantomReference<>(o, referenceQueue);o = null;System.gc();Field field = Reference.class.getDeclaredField("referent");field.setAccessible(true);System.out.println(field.get(ref));}// 这个现象, 有 finalize 和 没有 finalize 是两个不同的情况, 按照理论上来说[常规的思考], 有 finalize 的情况下, 应该会有两个 Reference 分别进入 两个队列, 但是没有Thread.sleep(3000);System.gc();// consumernew Thread() {public void run() {while (true) {Object o = referenceQueue.poll();if (o != null) {try {Field rereferent = Reference.class.getDeclaredField("referent");rereferent.setAccessible(true);Object result = rereferent.get(o);System.out.println("gc will collect : " + o.getClass() + "@" + o.hashCode() + ", referent : " + result);} catch (Exception e) {e.printStackTrace();}}}}}.start();}/*** Obj** @author Jerry.X.He <970655147@qq.com>* @version 1.0* @date 2019-10-14 11:24*/static class Obj {private final String name;Obj(String name) {this.name=name;}// test for FinalReference
//    @Override
//    protected void finalize() throws Throwable {
//      System.out.println("执行finalize方法：" + name);
//      super.finalize();
//    }@Overridepublic String toString() {return name;}}}

然后我们这里需要关注的主要的问题在于, Test02WeakReferenceAfterGc$Obj 在没有重写 finalize 方法的时候, 输出如下

object_0
gc will collect : class java.lang.ref.PhantomReference@1964850888, referent : object_0

在 Test02WeakReferenceAfterGc$Obj 重写了 finalize 方法之后输出如下

object_0
执行finalize方法：object_0

这里直观感觉就很奇怪了呀, 为什么是否重写 finalize 方法, 会影响到 PhantomReference 进入对应的引用队列呢 ?

针对重写 finalize 方法的情况讨论

最开始我以为是第一个 System.gc 之后, Obj 的实例 o 对应的 FinalReferece 会引用该对象, 所以该对象在gc的时候没有被清理, 所以该 PhantomReference 没有被整理, 然后上面的这段代码, 是我为了这个猜想增加的

        Thread.sleep(3000);System.gc();

但是, 发现给定的 PhantomReference 还是没有进入对应的引用队列

这个就很令人疑惑了

测试代码均在jdk8下面编译, 以上测试代码结果, 运行于 jdk8, 一下部分代码, 截图基于 openjdk9

在 openjdk9 下面运行该测试方法, ref.get() 均为 null, 后面会提及到这一点的原因

以下描述仅仅会描述一些和我们这里相关的部分, 整体的其他逻辑不会做过多描述

以下调试的参数为

-da -dsa -Xint -XX:+UseSerialGC com.hx.test02.Test02WeakReferenceAfterGc

以下调试的基于 openjdk9, 并且有一部分个人方便调试的调整, 调整的部分为

jvm.cpp

JVM_ENTRY_NO_ENV(void, JVM_GC(void))JVMWrapper("JVM_GC");if (!DisableExplicitGC) {
-    Universe::heap()->collect(GCCause::_java_lang_system_gc);
+    VM_GenCollectForAllocation op(100, true, Universe::heap()->total_collections());
+    VMThread::execute(&op);}
JVM_END

System.gc 调整成为 ygc, 所以可能和我们直接使用 jdk 运行的运行时情况稍有不一致的地方, 所以本文的调试可能会存在一些局限

另外由于本人水平有限, 理解能力有限有限, 可能也会导致一些问题的存在

问题的细节

1. 相关代码片段

首先先贴一下一部分关键代码, 在gc处理的过程中会进行引用处理, 这里的 _discoveredXXRefs 来自于复制算法遍历活跃对象的时候额外的针对 Reference 对象做了一些 Discover[参见instanceRefKlass.inline.oop_oop_iterate]

ReferenceProcessor::process_discovered_references

ReferenceProcessorStats ReferenceProcessor::process_discovered_references(BoolObjectClosure*           is_alive,OopClosure*                  keep_alive,VoidClosure*                 complete_gc,AbstractRefProcTaskExecutor* task_executor,GCTimer*                     gc_timer) {assert(!enqueuing_is_done(), "If here enqueuing should not be complete");// Stop treating discovered references specially.disable_discovery();// If discovery was concurrent, someone could have modified// the value of the static field in the j.l.r.SoftReference// class that holds the soft reference timestamp clock using// reflection or Unsafe between when discovery was enabled and// now. Unconditionally update the static field in ReferenceProcessor// here so that we use the new value during processing of the// discovered soft refs._soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();ReferenceProcessorStats stats(total_count(_discoveredSoftRefs),total_count(_discoveredWeakRefs),total_count(_discoveredFinalRefs),total_count(_discoveredPhantomRefs));// Soft references{GCTraceTime(Debug, gc, ref) tt("SoftReference", gc_timer);process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,is_alive, keep_alive, complete_gc, task_executor);}update_soft_ref_master_clock();// Weak references{GCTraceTime(Debug, gc, ref) tt("WeakReference", gc_timer);process_discovered_reflist(_discoveredWeakRefs, NULL, true,is_alive, keep_alive, complete_gc, task_executor);}// Final references{GCTraceTime(Debug, gc, ref) tt("FinalReference", gc_timer);process_discovered_reflist(_discoveredFinalRefs, NULL, false,is_alive, keep_alive, complete_gc, task_executor);}// Phantom references{GCTraceTime(Debug, gc, ref) tt("PhantomReference", gc_timer);process_discovered_reflist(_discoveredPhantomRefs, NULL, true,is_alive, keep_alive, complete_gc, task_executor);}// Weak global JNI references. It would make more sense (semantically) to// traverse these simultaneously with the regular weak references above, but// that is not how the JDK1.2 specification is. See #4126360. Native code can// thus use JNI weak references to circumvent the phantom references and// resurrect a "post-mortem" object.{GCTraceTime(Debug, gc, ref) tt("JNI Weak Reference", gc_timer);if (task_executor != NULL) {task_executor->set_single_threaded_mode();}process_phaseJNI(is_alive, keep_alive, complete_gc);}log_debug(gc, ref)("Ref Counts: Soft: " SIZE_FORMAT " Weak: " SIZE_FORMAT " Final: " SIZE_FORMAT " Phantom: " SIZE_FORMAT,stats.soft_count(), stats.weak_count(), stats.final_count(), stats.phantom_count());log_develop_trace(gc, ref)("JNI Weak Reference count: " SIZE_FORMAT, count_jni_refs());return stats;
}

ReferenceProcessor::process_discovered_reflist

void ReferenceProcessor::process_discovered_reflist(DiscoveredList               refs_lists[],ReferencePolicy*             policy,bool                         clear_referent,BoolObjectClosure*           is_alive,OopClosure*                  keep_alive,VoidClosure*                 complete_gc,AbstractRefProcTaskExecutor* task_executor)
{bool mt_processing = task_executor != NULL && _processing_is_mt;// If discovery used MT and a dynamic number of GC threads, then// the queues must be balanced for correctness if fewer than the// maximum number of queues were used.  The number of queue used// during discovery may be different than the number to be used// for processing so don't depend of _num_q < _max_num_q as part// of the test.bool must_balance = _discovery_is_mt;if ((mt_processing && ParallelRefProcBalancingEnabled) ||must_balance) {balance_queues(refs_lists);}// Phase 1 (soft refs only):// . Traverse the list and remove any SoftReferences whose//   referents are not alive, but that should be kept alive for//   policy reasons. Keep alive the transitive closure of all//   such referents.if (policy != NULL) {if (mt_processing) {RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);task_executor->execute(phase1);} else {for (uint i = 0; i < _max_num_q; i++) {process_phase1(refs_lists[i], policy,is_alive, keep_alive, complete_gc);}}} else { // policy == NULLassert(refs_lists != _discoveredSoftRefs,"Policy must be specified for soft references.");}// Phase 2:// . Traverse the list and remove any refs whose referents are alive.if (mt_processing) {RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);task_executor->execute(phase2);} else {for (uint i = 0; i < _max_num_q; i++) {process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);}}// Phase 3:// . Traverse the list and process referents as appropriate.if (mt_processing) {RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);task_executor->execute(phase3);} else {for (uint i = 0; i < _max_num_q; i++) {process_phase3(refs_lists[i], clear_referent,is_alive, keep_alive, complete_gc);}}
}

process_phase1 : 主要是 SoftReference 的处理[只有SoftReference传入了 policy], 根据 referencePolicy 来校验当前 Reference 是否应该移出 discoverList

process_phase2 : 如果 referent 经过了 ygc 还存活着, 那么将当前 Reference 移出 discoverList

process_phase3 : 如果需要 clear_referent, 则清理掉 Reference.referent, 否则将Reference.referent移动到存活对象区域 [仅仅FinalReference传入为false, FinalReference业务处理的时候还需要referent]

ReferenceProcessor::process_phase3

// Traverse the list and process the referents, by either
// clearing them or keeping them (and their reachable
// closure) alive.
void
ReferenceProcessor::process_phase3(DiscoveredList&    refs_list,bool               clear_referent,BoolObjectClosure* is_alive,OopClosure*        keep_alive,VoidClosure*       complete_gc) {ResourceMark rm;DiscoveredListIterator iter(refs_list, keep_alive, is_alive);while (iter.has_next()) {iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));if (clear_referent) {// NULL out referent pointeriter.clear_referent();} else {// keep the referent arounditer.make_referent_alive();}log_develop_trace(gc, ref)("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",clear_referent ? "cleared " : "", p2i(iter.obj()), iter.obj()->klass()->internal_name());assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");iter.next();}// Close the reachable setcomplete_gc->do_void();
}

经过 ReferenceProcessor::process_discovered_references 处理之后, 最后还存在于 discoverList 的 Reference 与 Reference.pending 关联 [gc处理之后, genCollectedHeap.collect_generation里面 rp->enqueue_discovered_references]

然后 ReferenceHandler 线程会进行下一个阶段的处理, 将 Reference.pending 关联的列表的所有的 Reference 关联到 Reference 对应的队列[参见 Reference$ReferenceHandler]

2. Test02WeakReferenceAfterGc$Obj 没有重写 finalize

首先我们来看一下 Test02WeakReferenceAfterGc$Obj 没有重写 finalize 方法的场景

三个断点, thread.create_vm 方法末尾一个, defNewGeneration.collect 里面 ref_processor.process_discovered_references 一个, referenceProcessor.process_discovered_references 里面 process_discovered_reflist(_discoveredPhantomRefs 一个

当断点停留在 "referenceProcessor.process_discovered_references" 里面的时候

2.1 确定当前位置

找到 main 线程, 打印 main 线程的 stackTrace, 从这里可以知道目前是在第一个 System.gc 方法的执行期间

$jerry : thread->print()
"main" #1 prio=5 os_prio=31 tid=0x00007fa786803800 nid=0x2403 waiting on condition [0x0000700007756000]java.lang.Thread.State: RUNNABLEJavaThread state: _thread_blocked
Thread: 0x00007fa786803800  [0x2403] State: _at_safepoint _has_called_back 0 _at_poll_safepoint 0$jerry : thread->print_stack()JavaThread state: _thread_blockedat java.lang.Runtime.gc(java.base/Native Method)at java.lang.System.gc(java.base/System.java:1726)at com.hx.test02.Test02WeakReferenceAfterGc.main(Test02WeakReferenceAfterGc.java:27)

2.2 process_discovered_reflist(_discoveredPhantomRefs 处理之前

然后我们回到 gc 线程, 在断点处执行如下脚本, 打印探测到的 PhantomReference 列表

oop current = ((_discoveredPhantomRefs)->head());
for(int i=0; i<_discoveredPhantomRefs->length(); i++) {// tty->print_cr(current->klass()->external_name());current.print();current = java_lang_ref_Reference::discovered(current);
}

得到结果如下

jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x000000074275dcd0} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x00000007404034b0} (e8080696 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84ebb91)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074275dc88} (e84ebb91 e84eaf9e)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742757cf0} (e84eaf9e e84ebb91)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074275dc88} (e84ebb91 e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84ec6c6)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x0000000742763630} (e84ec6c6 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x000000074275dc88} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x000000074036f6a0} (e806ded4 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84eaf9e)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742757cf0} (e84eaf9e e84ebb9a)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074275dcd0} (e84ebb9a e84eaf95)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742757ca8} (e84eaf95 e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84ec6c3)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x0000000742763618} (e84ec6c3 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x0000000742757cf0} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x0000000740409798} (e80812f3 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84eaf95)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742757ca8} (e84eaf95 e84ea6b5)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007427535a8} (e84ea6b5 e84ebb9a)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074275dcd0} (e84ebb9a e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84ebba0)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x000000074275dd00} (e84ebba0 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x0000000742757ca8} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x000000074036d7f8} (e806daff e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84ea6b5)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007427535a8} (e84ea6b5 e84ebb91)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074275dc88} (e84ebb91 e84ea6ac)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742753560} (e84ea6ac e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84ebb97)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x000000074275dcb8} (e84ebb97 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x00000007427535a8} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x0000000740410730} (e80820e6 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84ea6ac)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742753560} (e84ea6ac e84e9c27)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074274e138} (e84e9c27 e84eaf9e)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742757cf0} (e84eaf9e e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84eafa4)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x0000000742757d20} (e84eafa4 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x0000000742753560} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x000000074036a828} (e806d505 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84e9c27)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074274e138} (e84e9c27 e84eaf95)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742757ca8} (e84eaf95 e84e9c1e)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074274e0f0} (e84e9c1e e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84eaf9b)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x0000000742757cd8} (e84eaf9b 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x000000074274e138} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x00000007404242d0} (e808485a e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84e9c1e)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074274e0f0} (e84e9c1e e84e8c52)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742746290} (e84e8c52 e84ea6b5)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007427535a8} (e84ea6b5 e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84ea6bb)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x00000007427535d8} (e84ea6bb 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x000000074274e0f0} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x0000000740359488} (e806b291 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84e8c52)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742746290} (e84e8c52 e84ea6ac)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742753560} (e84ea6ac e84e8c49)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742746248} (e84e8c49 e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84ea6b2)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x0000000742753590} (e84ea6b2 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x0000000742746290} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x0000000740431a28} (e8086345 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84e8c49)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742746248} (e84e8c49 e84e77b7)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074273bdb8} (e84e77b7 e84e9c27)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074274e138} (e84e9c27 e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84e9c2d)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x000000074274e168} (e84e9c2d 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x0000000742746248} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x0000000740351e60} (e806a3cc e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84e77b7)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074273bdb8} (e84e77b7 e84e9c1e)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074274e0f0} (e84e9c1e e84e77ae)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074273bd70} (e84e77ae e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84e9c24)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x000000074274e120} (e84e9c24 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x000000074273bdb8} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x0000000740438e00} (e80871c0 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84e77ae)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074273bd70} (e84e77ae e84e571d)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074272b8e8} (e84e571d e84e8c52)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742746290} (e84e8c52 e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84e8c58)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x00000007427462c0} (e84e8c58 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x000000074273bd70} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x000000074019cef8} (e80339df e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84e571d)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074272b8e8} (e84e571d e84e8c49)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742746248} (e84e8c49 e84e5714)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074272b8a0} (e84e5714 e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84e8c4f)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x0000000742746278} (e84e8c4f 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x000000074272b8e8} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x0000000740445580} (e8088ab0 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84e5714)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074272b8a0} (e84e5714 e84e2db8)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742716dc0} (e84e2db8 e84e77b7)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074273bdb8} (e84e77b7 e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84e77bd)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x000000074273bde8} (e84e77bd 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x000000074272b8a0} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x0000000740193d48} (e80327a9 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84e2db8)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742716dc0} (e84e2db8 e84e77ae)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074273bd70} (e84e77ae e84e2daf)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742716d78} (e84e2daf e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84e77b4)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x000000074273bda0} (e84e77b4 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x0000000742716dc0} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x0000000740449470} (e808928e e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84e2daf)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742716d78} (e84e2daf e84de643)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007426f3218} (e84de643 e84e571d)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074272b8e8} (e84e571d e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84e5723)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x000000074272b918} (e84e5723 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x0000000742716d78} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x0000000740188140} (e8031028 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84de643)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007426f3218} (e84de643 e84e5714)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x000000074272b8a0} (e84e5714 e84de63a)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007426f31d0} (e84de63a e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84e571a)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x000000074272b8d0} (e84e571a 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x00000007426f3218} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x000000074044c550} (e80898aa e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84de63a)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007426f31d0} (e84de63a e84da7f7)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007426d3fb8} (e84da7f7 e84e2db8)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742716dc0} (e84e2db8 e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84e2dbe)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x0000000742716df0} (e84e2dbe 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x00000007426f31d0} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x0000000740172188} (e802e431 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84da7f7)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007426d3fb8} (e84da7f7 e84e2daf)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742716d78} (e84e2daf e84da7f1)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007426d3f88} (e84da7f1 e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84e2db5)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x0000000742716da8} (e84e2db5 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x00000007426d3fb8} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x000000074044ed28} (e8089da5 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84da7f1)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007426d3f88} (e84da7f1 e84d6a6d)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007426b5368} (e84d6a6d e84de643)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007426f3218} (e84de643 e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84de649)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x00000007426f3248} (e84de649 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x00000007426d3f88} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'sun/nio/fs/NativeBuffer'{0x0000000740036f20} (e8006de4 e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84d6a6d)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007426b5368} (e84d6a6d e84de63a)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007426f31d0} (e84de63a e84d6a68)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$CleanerCleanable'{0x00000007426b5340} (e84d6a68 e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84de640)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'sun/nio/fs/NativeBuffer$Deallocator'{0x00000007426f3200} (e84de640 0)
jdk.internal.ref.CleanerImpl$PhantomCleanableRef
{0x00000007426b5368} - klass: 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'- ---- fields (total size 6 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/invoke/ConstantCallSite'{0x000000074045dfe8} (e808bbfd e84d06ce)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683670} (e84d06ce 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84d2df2)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'jdk/internal/ref/Cleaner'{0x0000000742696f90} (e84d2df2 e84d2fe6)- strict 'prev' 'Ljdk/internal/ref/PhantomCleanable;' @28  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84da7f7)- strict 'next' 'Ljdk/internal/ref/PhantomCleanable;' @32  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x00000007426d3fb8} (e84da7f7 e84d2fe6)- private final strict 'list' 'Ljdk/internal/ref/PhantomCleanable;' @36  a 'jdk/internal/ref/CleanerImpl$PhantomCleanableRef'{0x0000000742697f30} (e84d2fe6 e84da7fd)- private final 'action' 'Ljava/lang/Runnable;' @40  a 'java/lang/invoke/MethodHandleNatives$CallSiteContext'{0x00000007426d3fe8} (e84da7fd 0)
jdk.internal.ref.Cleaner
{0x0000000742696f90} - klass: 'jdk/internal/ref/Cleaner'- ---- fields (total size 5 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/nio/DirectByteBuffer'{0x0000000740189c90} (e8031392 e84d2dee)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742696f70} (e84d2dee 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84d0774)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'java/lang/ref/PhantomReference'{0x0000000742683ba0} (e84d0774 0)- private 'next' 'Ljdk/internal/ref/Cleaner;' @28  NULL (0 0)- private 'prev' 'Ljdk/internal/ref/Cleaner;' @32  NULL (0 e84d60c1)- private final 'thunk' 'Ljava/lang/Runnable;' @36  a 'java/nio/DirectByteBuffer$Deallocator'{0x00000007426b0608} (e84d60c1 9)
java.lang.ref.PhantomReference
{0x0000000742683ba0} - klass: 'java/lang/ref/PhantomReference'- ---- fields (total size 4 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'com/hx/test02/Test02WeakReferenceAfterGc$Obj'{0x00000007404e1df0} (e809c3be e84d0770)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683b80} (e84d0770 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84d0774)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'java/lang/ref/PhantomReference'{0x0000000742683ba0} (e84d0774 0)

这里面的内容很多, 但是实际上我们只用关心最后一个 "private strict 'referent' 'Ljava/lang/Object;' @12 a 'com/hx/test02/Test02WeakReferenceAfterGc$Obj'{0x00000007404e1df0} (e809c3be e84d0770)"

在之后的截图, 可能我这边会去掉部分与本主题无关的的引用的信息, 方便查看 , 并且都会加上备注

可以发现 gc 的时候找到了我们的这个 “ref” 引用, 然后这里是待处理的状态, 那么会怎么处理呢 ?

1.3 process_discovered_reflist(_discoveredPhantomRefs 处理之后

然后断点下走一步, 我们再来看一下 _discoveredPhantomRefs 列表的数据

同样执行上面查看 _discoveredPhantomRefs 列表的代码片, 得到如下结果

## 省略掉部分无关的 CleanerImpl$PhantomCleanableRef, Cleaner
java.lang.ref.PhantomReference
{0x0000000742683ba0} - klass: 'java/lang/ref/PhantomReference'- ---- fields (total size 4 words):- private strict 'referent' 'Ljava/lang/Object;' @12  NULL (0 e84d0770)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683b80} (e84d0770 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84d0774)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'java/lang/ref/PhantomReference'{0x0000000742683ba0} (e84d0774 0)

根据上面的 oop 的地址 0x0000000742683ba0 可以定位到上面的 PhantomReference 就是 "process_discovered_reflist(_discoveredPhantomRefs" 处理之后的数据了

可以发现变化在于 referent 被置为 NULL 了

tips : 但是在openjdk8对于 PhantomReference 的 process_phase3的处理是不会将 referent 置为 NULL 的, 参见 : http://hg.openjdk.java.net/jdk8/jdk8/hotspot/file/87ee5ee27509/src/share/vm/memory/referenceProcessor.cpp 249-252行

这个是由于 process_phase3 的过程中发现 referent 已经 gg 了, 然后就清理掉了 ref.referent 然后并且把它留在了 discoverList, 等待后续的步骤进行处理

然后后续 vm 将还存在的 discoverList 的引用关联到 Reference.pending 的列表上面

ReferenceHandler 将 Reference.pending 列表上的 Reference 放到该Reference注册的 ReferenceQueue, 对应于我们这里 ref 会被放到 referenceQueue

然后我们这里的消费线程, 从队列里面取引用, 拿到数据, 打印日志 "gc will collect ... "

这就是一个相对比较常规的流程

3. Test02WeakReferenceAfterGc$Obj 重写 finalize

增加一个 referenceProcessor.process_discovered_references 里面 process_discovered_reflist(_discoveredFinalRefs 断点

3.1 process_discovered_reflist(_discoveredFinalRefs 处理之前

打印 _discoveredFinalRefs 列表的数据如下

java.lang.ref.Finalizer
{0x00000007426cf9e8} - klass: 'java/lang/ref/Finalizer'- ---- fields (total size 5 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/io/FileInputStream'{0x00000007404dbdb0} (e809b7b6 e84d073a)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x00000007426839d0} (e84d073a 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84d6618)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'java/lang/ref/Finalizer'{0x00000007426b30c0} (e84d6618 e84de472)- private 'next' 'Ljava/lang/ref/Finalizer;' @28  a 'java/lang/ref/Finalizer'{0x00000007426f2390} (e84de472 e84d6618)- private 'prev' 'Ljava/lang/ref/Finalizer;' @32  a 'java/lang/ref/Finalizer'{0x00000007426b30c0} (e84d6618 0)
java.lang.ref.Finalizer
{0x00000007426b30c0} - klass: 'java/lang/ref/Finalizer'- ---- fields (total size 5 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/io/FileInputStream'{0x00000007404e14d8} (e809c29b e84d073a)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x00000007426839d0} (e84d073a 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84d2f87)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'java/lang/ref/Finalizer'{0x0000000742697c38} (e84d2f87 e84d9f3d)- private 'next' 'Ljava/lang/ref/Finalizer;' @28  a 'java/lang/ref/Finalizer'{0x00000007426cf9e8} (e84d9f3d e84d2f87)- private 'prev' 'Ljava/lang/ref/Finalizer;' @32  a 'java/lang/ref/Finalizer'{0x0000000742697c38} (e84d2f87 0)
java.lang.ref.Finalizer
{0x0000000742697c38} - klass: 'java/lang/ref/Finalizer'- ---- fields (total size 5 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'com/hx/test02/Test02WeakReferenceAfterGc$Obj'{0x00000007404e1fa0} (e809c3f4 e84d073a)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x00000007426839d0} (e84d073a 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84d2f87)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'java/lang/ref/Finalizer'{0x0000000742697c38} (e84d2f87 e84d6618)- private 'next' 'Ljava/lang/ref/Finalizer;' @28  a 'java/lang/ref/Finalizer'{0x00000007426b30c0} (e84d6618 0)- private 'prev' 'Ljava/lang/ref/Finalizer;' @32  NULL (0 0)

第三个 FinalReference 为 vm为我们创建的 Obj 实例 o 创建的 Finalzer

3.2 process_discovered_reflist(_discoveredFinalRefs 处理之后

打印 _discoveredFinalRefs 列表的数据如下

java.lang.ref.Finalizer
{0x00000007426cf9e8} - klass: 'java/lang/ref/Finalizer'- ---- fields (total size 5 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/io/FileInputStream'{0x0000000742770968} (e84ee12d e84d073a)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x00000007426839d0} (e84d073a 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84d6618)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'java/lang/ref/Finalizer'{0x00000007426b30c0} (e84d6618 e84de472)- private 'next' 'Ljava/lang/ref/Finalizer;' @28  a 'java/lang/ref/Finalizer'{0x00000007426f2390} (e84de472 e84d6618)- private 'prev' 'Ljava/lang/ref/Finalizer;' @32  a 'java/lang/ref/Finalizer'{0x00000007426b30c0} (e84d6618 0)
java.lang.ref.Finalizer
{0x00000007426b30c0} - klass: 'java/lang/ref/Finalizer'- ---- fields (total size 5 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/io/FileInputStream'{0x0000000742770988} (e84ee131 e84d073a)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x00000007426839d0} (e84d073a 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84d2f87)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'java/lang/ref/Finalizer'{0x0000000742697c38} (e84d2f87 e84d9f3d)- private 'next' 'Ljava/lang/ref/Finalizer;' @28  a 'java/lang/ref/Finalizer'{0x00000007426cf9e8} (e84d9f3d e84d2f87)- private 'prev' 'Ljava/lang/ref/Finalizer;' @32  a 'java/lang/ref/Finalizer'{0x0000000742697c38} (e84d2f87 0)
java.lang.ref.Finalizer
{0x0000000742697c38} - klass: 'java/lang/ref/Finalizer'- ---- fields (total size 5 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'com/hx/test02/Test02WeakReferenceAfterGc$Obj'{0x00000007427709a8} (e84ee135 e84d073a)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x00000007426839d0} (e84d073a 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84d2f87)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'java/lang/ref/Finalizer'{0x0000000742697c38} (e84d2f87 e84d6618)- private 'next' 'Ljava/lang/ref/Finalizer;' @28  a 'java/lang/ref/Finalizer'{0x00000007426b30c0} (e84d6618 0)- private 'prev' 'Ljava/lang/ref/Finalizer;' @32  NULL (0 0)

可以看到这个我们创建的 Obj 实例 o 对应的 FinalReference 依然存在于 discoverList, 这就意味着之后这个 FinalReference 之后会被添加到它对应的 ReferenceQueue, 然后 FinalizerThread 线程进行 finalize 的相关业务处理

注意, 这个处理的过程的 process_phase3 这里传递的 clear_referent 为 false, 表示需要将 Obj 实例 o, 复制到存活区, FinalReference 依赖这个对象

3.3 process_discovered_reflist(_discoveredPhantomRefs 处理之前

打印 _discoveredPhantomRefs 列表的数据如下

## 省略掉部分无关的 CleanerImpl$PhantomCleanableRef, Cleaner
java.lang.ref.PhantomReference
{0x0000000742683bb8} - klass: 'java/lang/ref/PhantomReference'- ---- fields (total size 4 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'com/hx/test02/Test02WeakReferenceAfterGc$Obj'{0x00000007404e1fa0} (e809c3f4 e84d0773)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742683b98} (e84d0773 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e84d0777)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'java/lang/ref/PhantomReference'{0x0000000742683bb8} (e84d0777 0)

这里的 PhantomReference 为我们为我们创建的 Obj 实例 o 创建的 PhantomReference

3.4 process_discovered_reflist(_discoveredPhantomRefs 处理之后

打印 _discoveredPhantomRefs 列表的数据如下

## 省略掉部分无关的 CleanerImpl$PhantomCleanableRef, Cleaner
# 找不到 0x0000000742683bb8 对应的 PhantomReference 了

这里我们发现 Obj 的实例 o 对应的 PhantomReference ref 被从 discoverList 里面移除了

这个是因为上面处理 o 对应的 FinalReference 的时候, 将 o 复制到了存活区, 因此这里在 o 对应的 PhantomReference 处理 process_phase2 的时候, 因为 PhantomReference 还存活, 所以将 PhantomReference ref 移出了 discoverList

所以在第一个 System.gc 的时候 Obj 的实例 o 对应的 FinalReference 进入了 Finalizer.queue

但是 Obj 的实例 o 对应的 PhantomReference ref 没有进入其对应的 referenceQueue

3.5 第二次 System.gc process_discovered_reflist(_discoveredFinalRefs 处理之前

打印 _discoveredFinalRefs 列表的数据如下

java.lang.ref.Finalizer
{0x00000007422741d8} - klass: 'java/lang/ref/Finalizer'- ---- fields (total size 5 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/ClassLoader$NativeLibrary'{0x00000007426d3dd8} (e84da7bb e84487a3)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742243d18} (e84487a3 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e844b086)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'java/lang/ref/Finalizer'{0x0000000742258430} (e844b086 e84521bd)- private 'next' 'Ljava/lang/ref/Finalizer;' @28  a 'java/lang/ref/Finalizer'{0x0000000742290de8} (e84521bd e844b086)- private 'prev' 'Ljava/lang/ref/Finalizer;' @32  a 'java/lang/ref/Finalizer'{0x0000000742258430} (e844b086 0)
java.lang.ref.Finalizer
{0x0000000742258430} - klass: 'java/lang/ref/Finalizer'- ---- fields (total size 5 words):- private strict 'referent' 'Ljava/lang/Object;' @12  a 'java/lang/ClassLoader$NativeLibrary'{0x00000007426d3e00} (e84da7c0 e84487a3)- volatile strict 'queue' 'Ljava/lang/ref/ReferenceQueue;' @16  a 'java/lang/ref/ReferenceQueue'{0x0000000742243d18} (e84487a3 0)- volatile 'next' 'Ljava/lang/ref/Reference;' @20  NULL (0 e844b086)- private transient strict 'discovered' 'Ljava/lang/ref/Reference;' @24  a 'java/lang/ref/Finalizer'{0x0000000742258430} (e844b086 e844e83b)- private 'next' 'Ljava/lang/ref/Finalizer;' @28  a 'java/lang/ref/Finalizer'{0x00000007422741d8} (e844e83b 0)- private 'prev' 'Ljava/lang/ref/Finalizer;' @32  NULL (0 0)

没有了 Obj 实例对应的 o 的 FinalReference, 没有强引用引用关联该 FinalReference 了, 复制算法 Discover 不到该 FinalReference

3.6 第二次 System.gc process_discovered_reflist(_discoveredPhantomRefs 处理之前

打印 _discoveredPhantomRefs 列表的数据如下

## 省略掉部分无关的 CleanerImpl$PhantomCleanableRef, Cleaner
# 找不到 0x0000000742683bb8 对应的 PhantomReference 了

没有了 Obj 实例对应的 o 的 PhantomReference, 没有强引用引用关联该 PhantomReference了, 复制算法 Discover 不到该 PhantomReference

所以第二次 gc 的时候, Obj 的实例 o 对应的 PhantomReference ref 没有进入其对应的 referenceQueue

经过这一次 gc, 一般情况下 Obj 实例 o, 对应的 FinalReference 已经处理了 finalize 的相关业务[sleep 3s], 并且 FinalizerThread 处理了该 FinalReference的后续流程, Obj 的实例 o, o 对应的 FinalReference, o 对应的 PhantomReference 都会被处理掉

4. 如何确保 o 对应的 PhantomReference 入队

相信看完了上面的这一系列, 你应该有办法了吧

参考

https://hllvm-group.iteye.com/group/topic/34934

https://blog.csdn.net/KevinMite/article/details/83745080

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01 PhantomReference没有进入ReferenceQueue

前言

问题的细节

1. 相关代码片段

2. Test02WeakReferenceAfterGc$Obj 没有重写 finalize

3. Test02WeakReferenceAfterGc$Obj 重写 finalize

4. 如何确保 o 对应的 PhantomReference 入队

参考

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