Java程序陷入时间裂缝：探索代码深处的神秘停顿｜得物技术

一

初探

-XX:+UnlockDiagnosticVMOptions-XX:+PrintGCApplicationStoppedTime-XX:+PrintGCApplicationConcurrentTime-XX:+PrintSafepointStatistics-XX:PrintSafepointStatisticsCount=1-XX:-DisplayVMOutput-XX:+LogVMOutput-XX:LogFile=/logs/vm.log-Xloggc:/logs/gc.log

2024-03-07T20:43:34.027+0800: 549.045: Total time for which application threads were stopped: 0.0021832 seconds, Stopping threads took: 0.0003043 seconds2024-03-07T20:43:34.078+0800: 549.096: Total time for which application threads were stopped: 0.0022472 seconds, Stopping threads took: 0.0002551 seconds2024-03-07T20:43:34.081+0800: 549.099: Total time for which application threads were stopped: 0.0020218 seconds, Stopping threads took: 0.0002485 seconds2024-03-07T20:43:34.082+0800: 549.101: Total time for which application threads were stopped: 0.0015735 seconds, Stopping threads took: 0.0001436 second

二

安全点

三

停顿细节分析

四

停顿类型一览

ThreadStop,ThreadDump,PrintThreads,FindDeadlocks,ForceSafepoint,ForceAsyncSafepoint,Deoptimize,DeoptimizeFrame,DeoptimizeAll,ZombieAll,UnlinkSymbols,Verify,PrintJNI,HeapDumper,DeoptimizeTheWorld,CollectForMetadataAllocation,GC_HeapInspection,GenCollectFull,GenCollectFullConcurrent,GenCollectForAllocation,ParallelGCFailedAllocation,ParallelGCSystemGC,CGC_Operation,CMS_Initial_Mark,CMS_Final_Remark,G1CollectFull,G1CollectForAllocation,G1IncCollectionPause,EnableBiasedLocking,RevokeBias,BulkRevokeBias,PopulateDumpSharedSpace,JNIFunctionTableCopier,RedefineClasses,GetOwnedMonitorInfo,GetObjectMonitorUsage,GetCurrentContendedMonitor,GetStackTrace,GetMultipleStackTraces,GetAllStackTraces,GetThreadListStackTraces,GetFrameCount,GetFrameLocation,ChangeBreakpoints,GetOrSetLocal,GetCurrentLocation,EnterInterpOnlyMode,ChangeSingleStep,HeapWalkOperation,HeapIterateOperation,ReportJavaOutOfMemory,JFRCheckpoint,Exit,LinuxDllLoad,Terminating

GC

System.gc()的显式调用

Metasapce区域的危机

偏向锁的问题

探测工具

虚拟机内部运行时

RedefineClassesForceSafepoint(safepoint, vm)ForceAsyncSafepoint(safepoint, vm)PopulateDumpSharedSpace(jvm)ExitLinuxDllLoad ReportJavaOutOfMemory 

RedefineClasses

[arthas@84852]$ trace java.util.Set clear

逆优化

sh configure--with-debug-level=slowdebug--disable-warnings-as-errors--with-freetype-include=/usr/local/Cellar/freetype/2.9.1/include/freetype2--with-freetype-lib=/usr/local/Cellar/freetype/2.9.1/lib--with-boot-jdk=/Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home--with-target-bits=64

#ifndef PRODUCTvoid JavaThread::record_jump(address target, address instr, const char* file,                             int line) {
...}#endif // PRODUCT

废弃类型-ThreadStop

六

No vm operation

从输出入手

void SafepointSynchronize::print_statistics() {  SafepointStats* sstats = _safepoint_stats;
  for (int index = 0; index <= _cur_stat_index; index++) {    if (index % 30 == 0) {      print_header();    }    sstats = &_safepoint_stats[index];    tty->print("%.3f: ", sstats->_time_stamp);    tty->print("%-26s       ["               INT32_FORMAT_W(8) INT32_FORMAT_W(11) INT32_FORMAT_W(15)               "    ]    ",               sstats->_vmop_type == -1 ? "no vm operation" :               VM_Operation::name(sstats->_vmop_type),               sstats->_nof_total_threads,               sstats->_nof_initial_running_threads,               sstats->_nof_threads_wait_to_block);    ...} 

匿名的停顿类型 

SafepointSynchronize::begin();op->evaluate();SafepointSynchronize::end();

虚拟机的方案

while (!should_terminate() && _cur_vm_operation == NULL) {  bool timedout =    VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,                                GuaranteedSafepointInterval);  if (timedout && (SafepointALot ||                   SafepointSynchronize::is_cleanup_needed())) {    MutexUnlockerEx mul(VMOperationQueue_lock,                        Mutex::_no_safepoint_check_flag);     SafepointSynchronize::begin();     SafepointSynchronize::end();  }   ...}

七

非counted loop的循环

for (int i = 0; i < reps; i++) {     ... }*SAFEPOINT*

八

总结