作者:破砂锅 开源的GDB被广泛使用在Linux、OSX、Unix和各种嵌入式系统(例如手机),这次它又带给我们一个惊喜。 多线程调试之痛 调试器(如VS2008和老版GDB)往往只支持all-stop模式,调试多线程程序时,如果某个线程断在一个断点上,你的调试器会让整个程序 freeze,直到你continue这个线程,程序中的其他线程才会继续运行。这个限制使得被调试的程序不能够像真实环境中那样运行--当某个线程断在 一个断点上,让其他线程并行运行。 GDBv7.0引入的non-stop模式使得这个问题迎刃而解。在这个模式下, - 当某个或多个线程断在一个断点上,其他线程仍会并行运行
- 你可以选择某个被断的线程,并让它继续运行
让我们想象一下,有了这个功能后 - 当其他线程断在断点上时,程序里的定时器线程可以正常的运行了,从而避免不必要得超时
- 当其他线程断在断点上时,程序里的watchdog线程可以正常的运行了,从而避免嵌入式硬件以为系统崩溃而重启
- 可以控制多个线程运行的顺序,从而重现deadlock场景了。由于GDB可以用python脚本驱动调试,理论上可以对程序在不同的线程运行顺序下进行自动化测试。
因此,non-stop模式理所当然成为多线程调试“必杀技”。这2009年下半年之后发布的Linux版本里都带有GDBv7.0之后的版本。很好奇,不知道VS2010里是不是也支持类似的调试模式了。 演示GDB的non-stop模式 让破砂锅用一个C++小程序在Ubuntu Linux 09.10下demo这个必杀技。虽然我的demo使用命令行版gdb,如果你喜欢图形化的调试器,Eclipse2009年5月之后的版本可以轻松的调 用这个功能,详情参见Eclipse参见http://live.eclipse.org/node/723 1. 编译以下程序nonstop -
-
-
- #include <iostream>
- #include <boost/thread/thread.hpp>
-
- struct op
- {
- op(int id): m_id(id) {}
-
- void operator()()
- {
- std::cout << m_id << " begin" << std::endl;
- std::cout << m_id << " end" << std::endl;
- }
-
- int m_id;
- };
-
- int main(int argc, char ** argv)
- {
- boost::thread t1(op(1)), t2(op(2)), t3(op(3));
- t1.join(); t2.join(); t3.join();
- return 0;
- }
2. 把一下3行添加到~/.gdbinit来打开non-stop模式 set target-async 1 set pagination off set non-stop on 3. 启动gdb,设断点,运行.可以看到主线程1是running,3个子线程都断在断点上,而不是只有一个子线程断在断点上. - ~/devroot/nonstop$ gdb ./nonstop
- GNU gdb (GDB) 7.0-ubuntu
- Reading symbols from /home/frankwu/devroot/nonstop/nonstop...done.
- (gdb) break 14
- Breakpoint 1 at 0x402058: file nonstop.cpp, line 14.
- (gdb) break 24
- Breakpoint 3 at 0x401805: file nonstop.cpp, line 24.
- (gdb) run
- Starting program: /home/frankwu/devroot/nonstop/nonstop
- [Thread debugging using libthread_db enabled]
- [New Thread 0x7ffff6c89910 (LWP 2762)]
- [New Thread 0x7ffff6488910 (LWP 2763)]
- begin
- Breakpoint 1, op::operator() (this=0x605118) at nonstop.cpp:14
- std::cout << m_id << " end" << std::endl;
- begin
- Breakpoint 1, op::operator() (this=0x605388) at nonstop.cpp:14
- std::cout << m_id << " end" << std::endl;
- [New Thread 0x7ffff5c87910 (LWP 2764)]
- begin
- Breakpoint 1, op::operator() (this=0x605618) at nonstop.cpp:14
- std::cout << m_id << " end" << std::endl;
- (gdb) info threads
- Thread 0x7ffff5c87910 (LWP 2764) op::operator() (this=0x605618) at nonstop.cpp:14
- Thread 0x7ffff6488910 (LWP 2763) op::operator() (this=0x605388) at nonstop.cpp:14
- Thread 0x7ffff6c89910 (LWP 2762) op::operator() (this=0x605118) at nonstop.cpp:14
- * 1 Thread 0x7ffff7fe3710 (LWP 2759) (running)
4. 让线程3继续运行,注意我顾意把主线程1也continue,这是我发现的workaround,否则gdb不能切回thread 1. -
-
- Thread 3 (Thread 0x7ffff6488910 (LWP 2763)):
- Continuing.
-
- Thread 1 (Thread 0x7ffff7fe3710 (LWP 2759)):
- Continuing.
- Cannot execute this command while the selected thread is running.
- end
- [Thread 0x7ffff6488910 (LWP 2763) exited]
-
- warning: Unknown thread 3.
-
- Thread 1 (Thread 0x7ffff7fe3710 (LWP 2759)):
- Continuing.
- Cannot execute this command while the selected thread is running.
- (gdb) info threads
- Thread 0x7ffff5c87910 (LWP 2764) op::operator() (this=0x605618) at nonstop.cpp:14
- Thread 0x7ffff6c89910 (LWP 2762) op::operator() (this=0x605118) at nonstop.cpp:14
- * 1 Thread 0x7ffff7fe3710 (LWP 2759) (running)
5. 让另外两个线程继续运行而结束,主线程断在第24行,最后结束. - (gdb) thread apply 4 2 1 continue
-
- Thread 4 (Thread 0x7ffff5c87910 (LWP 2764)):
- Continuing.
-
- Thread 2 (Thread 0x7ffff6c89910 (LWP 2762)):
- Continuing.
-
- Thread 1 (Thread 0x7ffff7fe3710 (LWP 2759)):
- Continuing.
- Cannot execute this command while the selected thread is running.
- end
- end
- [Thread 0x7ffff5c87910 (LWP 2764) exited]
- [Thread 0x7ffff6c89910 (LWP 2762) exited]
-
- Breakpoint 3, main (argc=1, argv=0x7fffffffe348) at nonstop.cpp:24
- return 0;
-
- (gdb) continue
- Thread 1 (Thread 0x7ffff7fe3710 (LWP 2759)):
- Continuing.
-
- Program exited normally.
参考资料 Debugging with GDB Reverse Debugging, Multi-Process and Non-Stop Debugging Come to the CDT (破砂锅 ) |