我正在调查应用程序中futex系统调用的频繁调用，该应用程序正在将数据从文件传输到perf record显示的套接字。
我尝试使用gdb附加到jvm并在futex syscall上设置捕获点，然后打印backtrace来了解它的来源。问题是bt失败并出现一些内部错误：
gdb -p <jvm_pid>
(gdb) catch syscall futex
Catchpoint 1 (syscall 'futex' [202])
(gdb) continue
Continuing.
Thread 2 "java" received signal SIGSTOP, Stopped (signal).
[Switching to Thread 0x7fa60385c700 (LWP 27739)]
0x00007fa602a0e9f3 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/x86_64-linux-gnu/libpthread.so.0
(gdb) backtrace
/build/gdb-GT4MLW/gdb-8.1/gdb/frame.c:534: internal-error: frame_id get_frame_id(frame_info*): Assertion `fi->level == 0' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
所以最终我得到了以下内容：
Python Exception <class 'KeyboardInterrupt'> Quit:
#0 0x00007fa602a0e9f3 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/x86_64-linux-gnu/libpthread.so.0
#1 0x00007fa60236e9bb in os::PlatformEvent::park (this=0x7fa5fc018200) at ./src/hotspot/src/os/linux/vm/os_linux.cpp:5987
，它看起来不完整。 gdb是否抱怨动态代码生成，因此可能无法使用它来跟踪这些东西？
我尝试在附加后立即打印回溯，但效果很好：
gdp -p <jvm pid>
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
0x00007fa602a09d2d in __pthread_timedjoin_ex () from /lib/x86_64-linux-gnu/libpthread.so.0
Installing openjdk unwinder
(gdb) bt
#0 0x00007fa602a09d2d in __pthread_timedjoin_ex () at /lib/x86_64-linux-gnu/libpthread.so.0
#1 0x00007fa60343a91d in ContinueInNewThread0 (continuation=continuation@entry=0x7fa603434c50 <JavaMain>, stack_size=1048576, args=args@entry=0x7ffd45c7ec50) at ./src/jdk/src/solaris/bin/java_md_solinux.c:1056
#2 0x00007fa603436b1a in ContinueInNewThread (ifn=ifn@entry=0x7ffd45c7ed70, threadStackSize=<optimized out>, argc=<optimized out>, argv=0x556124e8f600, mode=mode@entry=0, what=what@entry=0x0, ret=0)
at ./src/jdk/src/share/bin/java.c:2037
#3 0x00007fa60343a9eb in JVMInit (ifn=ifn@entry=0x7ffd45c7ed70, threadStackSize=<optimized out>, argc=<optimized out>, argv=<optimized out>, mode=0, mode@entry=1, what=0x0,
what@entry=0x7ffd45c83c8c "xxx.xxx.xxx.xxx.Main", ret=<optimized out>) at ./src/jdk/src/solaris/bin/java_md_solinux.c:1103
#4 0x00007fa603437267 in JLI_Launch (argc=<optimized out>, argv=<optimized out>, jargc=<optimized out>, jargv=<optimized out>, appclassc=1, appclassv=0x0, fullversion=0x55612461e848 "1.8.0_191-8u191-b12-0ubuntu0.18.04.1-b12", dotversion=0x55612461e841 "1.8", pname=0x55612461e83c "java", lname=0x55612461e834 "openjdk", javaargs=0 '\000', cpwildcard=1 '\001', javaw=0 '\000', ergo=0)
at ./src/jdk/src/share/bin/java.c:304
#5 0x000055612461e691 in main (argc=<optimized out>, argv=<optimized out>) at ./src/jdk/src/share/bin/main.c:125
动态代码生成有问题吗？也许有解决方法？