Java弱引用寿命长

我终于可以检查Hotspot JVM源代码，并找到以下代码。

在referenceProcessor.cpp中：

void ReferenceProcessor::process_discovered_references(  BoolObjectClosure*is_alive,  OopClosure*       keep_alive,  VoidClosure*      complete_gc,  AbstractRefProcTaskExecutor* task_executor) {  NOT_PRODUCT(verify_ok_to_handle_reflists());  assert(!enqueuing_is_done(), "If here enqueuing should not be complete");  // Stop treating discovered references specially.  disable_discovery();  bool trace_time = PrintGCDetails && PrintReferenceGC;  // Soft references  {    TraceTime tt("SoftReference", trace_time, false, gclog_or_tty);    process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,         is_alive, keep_alive, complete_gc, task_executor);  }  update_soft_ref_master_clock();  // Weak references  {    TraceTime tt("WeakReference", trace_time, false, gclog_or_tty);    process_discovered_reflist(_discoveredWeakRefs, NULL, true,         is_alive, keep_alive, complete_gc, task_executor);  }

函数process_discovered_reflist具有以下签名：

voidReferenceProcessor::process_discovered_reflist(  DiscoveredList    refs_lists[],  ReferencePolicy*  policy,  bool   clear_referent,  BoolObjectClosure*is_alive,  OopClosure*       keep_alive,  VoidClosure*      complete_gc,  AbstractRefProcTaskExecutor* task_executor)

这表明WeakRefs被ReferenceProcessor :: process_discovered_references无条件清除。

在Hotspot代码中搜索process_discovered_reference会显示CMS收集器（这是我正在使用的）从以下调用堆栈中调用此方法。

CMSCollector::refProcessingWorkCMSCollector::checkpointRootsFinalWorkCMSCollector::checkpointRootsFinal

每次运行CMS集合时，都将调用此调用堆栈。

假设这是真的，那么对长期存在的弱引用对象的唯一解释将是微妙的JVM错误或GC是否尚未运行。