OpenJDK 17 JIT编译器堆栈分析

##堆栈

(gdb) bt
#0  PhaseOutput::safepoint_poll_table (this=0x7fffd0bfb950) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/output.hpp:173
#1  0x00007ffff689634e in PhaseOutput::fill_buffer (this=0x7fffd0bfb950, cb=0x7fffd0bfb970, blk_starts=0x7fffb0042e40)at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/output.cpp:1824
#2  0x00007ffff6890444 in PhaseOutput::Output (this=0x7fffd0bfb950) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/output.cpp:432
#3  0x00007ffff602fe6b in Compile::Code_Gen (this=0x7fffd0bfde90) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/compile.cpp:2775
#4  0x00007ffff6027214 in Compile::Compile (this=0x7fffd0bfde90, ci_env=0x7fffd0bfeac0, generator=0x7ffff695a52a <OptoRuntime::monitor_notify_Type()>,stub_function=0x7ffff6959db8 <OptoRuntime::monitor_notify_C(oopDesc*, JavaThread*)> "\363\017\036\372UH\211\345SH\203\354hH\211}\230H\211u\220H\213U\220H\215E\300H\211\326H\211\307\350\346rN\377\350\030ړ\377\203\360\001\204\300t&H\213M\220H\213E\230\272", stub_name=0x7ffff72816b7 "_monitor_notify_Java", is_fancy_jump=0, pass_tls=false, return_pc=false, directive=0x7ffff01b1f90)at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/compile.cpp:925
#5  0x00007ffff6958b70 in OptoRuntime::generate_stub (env=0x7fffd0bfeac0, gen=0x7ffff695a52a <OptoRuntime::monitor_notify_Type()>,C_function=0x7ffff6959db8 <OptoRuntime::monitor_notify_C(oopDesc*, JavaThread*)> "\363\017\036\372UH\211\345SH\203\354hH\211}\230H\211u\220H\213U\220H\215E\300H\211\326H\211\307\350\346rN\377\350\030ړ\377\203\360\001\204\300t&H\213M\220H\213E\230\272", name=0x7ffff72816b7 "_monitor_notify_Java", is_fancy_jump=0, pass_tls=false, return_pc=false)at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/runtime.cpp:171
#6  0x00007ffff6958934 in OptoRuntime::generate (env=0x7fffd0bfeac0) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/runtime.cpp:148
#7  0x00007ffff5f07753 in C2Compiler::init_c2_runtime () at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/c2compiler.cpp:78
#8  0x00007ffff5f077d7 in C2Compiler::initialize (this=0x7ffff02c01f0) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/c2compiler.cpp:91
#9  0x00007ffff6043287 in CompileBroker::init_compiler_runtime () at /home/yym/openjdk17/jdk17-master/src/hotspot/share/compiler/compileBroker.cpp:1801
#10 0x00007ffff6043806 in CompileBroker::compiler_thread_loop () at /home/yym/openjdk17/jdk17-master/src/hotspot/share/compiler/compileBroker.cpp:1938
#11 0x00007ffff6065c02 in CompilerThread::thread_entry (thread=0x7ffff02c08c0, __the_thread__=0x7ffff02c08c0)at /home/yym/openjdk17/jdk17-master/src/hotspot/share/compiler/compilerThread.cpp:59
#12 0x00007ffff6b5e498 in JavaThread::thread_main_inner (this=0x7ffff02c08c0) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/runtime/thread.cpp:1305
#13 0x00007ffff6b5e32e in JavaThread::run (this=0x7ffff02c08c0) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/runtime/thread.cpp:1288
#14 0x00007ffff6b5ba31 in Thread::call_run (this=0x7ffff02c08c0) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/runtime/thread.cpp:394
#15 0x00007ffff68752bb in thread_native_entry (thread=0x7ffff02c08c0) at /home/yym/openjdk17/jdk17-master/src/hotspot/os/linux/os_linux.cpp:720
#16 0x00007ffff7c94ac3 in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:442
#17 0x00007ffff7d26850 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81Thread 14 "C2 CompilerThre" hit Breakpoint 5, PhaseOutput::safepoint_poll_table (this=0x7fffd0bfb950) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/output.hpp:173
173       C2SafepointPollStubTable* safepoint_poll_table() { return &_safepoint_poll_table; }
(gdb) bt
#0  PhaseOutput::safepoint_poll_table (this=0x7fffd0bfb950) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/output.hpp:173
#1  0x00007ffff689634e in PhaseOutput::fill_buffer (this=0x7fffd0bfb950, cb=0x7fffd0bfb970, blk_starts=0x7fffb0033610)at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/output.cpp:1824
#2  0x00007ffff6890444 in PhaseOutput::Output (this=0x7fffd0bfb950) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/output.cpp:432
#3  0x00007ffff602fe6b in Compile::Code_Gen (this=0x7fffd0bfde90) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/compile.cpp:2775
#4  0x00007ffff6027214 in Compile::Compile (this=0x7fffd0bfde90, ci_env=0x7fffd0bfeac0, generator=0x7ffff695a0fe <OptoRuntime::new_array_Type()>,stub_function=0x7ffff6959052 <OptoRuntime::new_array_nozero_C(Klass*, int, JavaThread*)> "\363\017\036\372UH\211\345H\201", <incomplete sequence \354\220>,stub_name=0x7ffff728160d "_new_array_nozero_Java", is_fancy_jump=0, pass_tls=true, return_pc=false, directive=0x7ffff01b1f90)at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/compile.cpp:925
#5  0x00007ffff6958b70 in OptoRuntime::generate_stub (env=0x7fffd0bfeac0, gen=0x7ffff695a0fe <OptoRuntime::new_array_Type()>,C_function=0x7ffff6959052 <OptoRuntime::new_array_nozero_C(Klass*, int, JavaThread*)> "\363\017\036\372UH\211\345H\201", <incomplete sequence \354\220>,name=0x7ffff728160d "_new_array_nozero_Java", is_fancy_jump=0, pass_tls=true, return_pc=false) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/runtime.cpp:171
#6  0x00007ffff69586d3 in OptoRuntime::generate (env=0x7fffd0bfeac0) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/runtime.cpp:141
#7  0x00007ffff5f07753 in C2Compiler::init_c2_runtime () at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/c2compiler.cpp:78
#8  0x00007ffff5f077d7 in C2Compiler::initialize (this=0x7ffff02c01f0) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/opto/c2compiler.cpp:91
#9  0x00007ffff6043287 in CompileBroker::init_compiler_runtime () at /home/yym/openjdk17/jdk17-master/src/hotspot/share/compiler/compileBroker.cpp:1801
#10 0x00007ffff6043806 in CompileBroker::compiler_thread_loop () at /home/yym/openjdk17/jdk17-master/src/hotspot/share/compiler/compileBroker.cpp:1938
#11 0x00007ffff6065c02 in CompilerThread::thread_entry (thread=0x7ffff02c08c0, __the_thread__=0x7ffff02c08c0)at /home/yym/openjdk17/jdk17-master/src/hotspot/share/compiler/compilerThread.cpp:59
#12 0x00007ffff6b5e498 in JavaThread::thread_main_inner (this=0x7ffff02c08c0) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/runtime/thread.cpp:1305
#13 0x00007ffff6b5e32e in JavaThread::run (this=0x7ffff02c08c0) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/runtime/thread.cpp:1288
#14 0x00007ffff6b5ba31 in Thread::call_run (this=0x7ffff02c08c0) at /home/yym/openjdk17/jdk17-master/src/hotspot/share/runtime/thread.cpp:394
#15 0x00007ffff68752bb in thread_native_entry (thread=0x7ffff02c08c0) at /home/yym/openjdk17/jdk17-master/src/hotspot/os/linux/os_linux.cpp:720
#16 0x00007ffff7c94ac3 in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:442
#17 0x00007ffff7d26850 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81

OpenJDK 17堆栈信息，分析如下：

核心结论

线程正在执行C2编译器初始化工作：线程名为"C2 CompilerThre"，说明这是C2编译器线程（JIT编译线程）。
处于运行时存根（Runtime Stub）生成阶段：正在为JVM关键操作（如monitor_notify和new_array_nozero）生成本地代码存根。
核心操作是代码生成与安全点轮询表处理：在PhaseOutput::fill_buffer()阶段，正在处理安全点轮询表（Safepoint Poll Table），用于JVM安全点检查。

堆栈关键点解析

首次堆栈（生成`monitor_notify`存根）

plaintext

#4  Compile::Compile(... stub_function=OptoRuntime::monitor_notify_C ...)
#5  OptoRuntime::generate_stub(... name="_monitor_notify_Java" ...)
#7  C2Compiler::init_c2_runtime()

目标存根：为Object.notify()方法生成本地代码存根（_monitor_notify_Java）。
作用：实现Java对象监视器（锁）的唤醒操作。

第二次堆栈（生成`new_array_nozero`存根）

plaintext

#4  Compile::Compile(... stub_function=OptoRuntime::new_array_nozero_C ...)
#5  OptoRuntime::generate_stub(... name="_new_array_nozero_Java" ...)
#6  OptoRuntime::generate()

目标存根：为数组分配生成本地代码存根（_new_array_nozero_Java）。
作用：优化new T[size]操作（跳过数组初始化为零的步骤）。

执行流程说明

初始化C2运行时
C2Compiler::init_c2_runtime() → 触发生成JVM关键操作的本地代码存根。
存根生成
- OptoRuntime::generate()：选择需要生成的存根类型。
- OptoRuntime::generate_stub()：具体存根生成入口。
- 创建Compile对象，传入存根函数指针（如monitor_notify_C或new_array_nozero_C）。
代码生成（JIT编译）
- Compile::Code_Gen()：调用代码生成模块。
- PhaseOutput::Output()：进入代码输出阶段。
- PhaseOutput::fill_buffer()：填充代码缓冲区，处理安全点轮询表。
安全点轮询表处理
- PhaseOutput::safepoint_poll_table()：访问安全点轮询表。
- 作用：在生成的本地代码中插入安全点检查点，确保JVM能在GC等操作时挂起线程。

关键组件作用

组件	作用
C2编译器线程	后台线程，负责将热点Java方法编译为本地代码。
OptoRuntime	运行时存根生成器，为JVM关键操作（如锁、数组分配）提供优化后的本地代码。
PhaseOutput	代码输出模块，负责将中间表示（IR）转换为机器码，并处理元数据（如安全点）。
安全点轮询表	存储代码中的安全点检查位置，确保线程能响应JVM暂停请求（如GC）。

总结

当前操作：C2编译器线程正在为monitor_notify和new_array_nozero等JVM核心操作生成本地代码存根。
核心任务：在代码生成阶段（PhaseOutput::fill_buffer）处理安全点轮询表，确保生成的本地代码能正确响应JVM安全点请求。
背景目的：这些存根是JVM运行时的重要组成部分，用于优化高频操作（如锁、内存分配），提升Java程序性能。