转载地址： http://blog.csdn.net/kangroger/article/details/47986197
gdb与多线程
在多线程编程时，当我们需要调试时，有时需要控制某些线程停在断点，有些线程继续执行。有时需要控制线程的运行顺序。有时需要中断某个线程，切换到其他线程。这些都可以通过gdb实现。
先来看一下gdb调试多线程常用命令：
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info threads：显示可以调试的所有线程。gdb会为每个线程分配一个ID（和tid不同），编号一般从1开始。后面的ID是指这个ID。
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thread ID:切换当前调试的线程为指定ID的线程。
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break FileName.cpp:LinuNum thread all:所有线程都在文件FileName.cpp的第LineNum行有断点。
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thread apply ID1 ID2 IDN command:多个线程执行gdb命令command。
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thread apply all command：所有线程都执行command命令。
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set scheduler-locking off|on|step：在调式某一个线程时，其他线程是否执行。off，不锁定任何线程，默认值。on，锁定其他线程，只有当前线程执行。step，在step（单步）时，只有被调试线程运行。
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set non-stop on/off:当调式一个线程时，其他线程是否运行。
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set pagination on/off:在使用backtrace时，在分页时是否停止。
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set target-async on/ff:同步和异步。同步，gdb在输出提示符之前等待程序报告一些线程已经终止的信息。而异步的则是直接返回。
来看一个例子：
gdbTest.cpp。程序很简单，只是让两个线程执行函数ThreadFun，在函数中打印传入的参数。
#include <iostream>
#include <pthread.h>
void* ThreadFun(void* arg)
{
int *value=static_cast<int*> (arg);
std::cout<<"This is thread"<<*value<<std::endl;
pthread_exit(0);
}
int main()
{
int ret=0;
pthread_t thread_id1,thread_id2;
int* v1=new int(1);
int* v2=new int(2);
ret = pthread_create(&thread_id1, NULL, ThreadFun, static_cast<void*>(v1));
if (ret)
{
std::cout<<"Create pthread error!"<<std::endl;
return 1;
}
ret = pthread_create(&thread_id2, NULL, ThreadFun, static_cast<void*>(v2));
if (ret)
{
std::cout<<"Create pthread error!"<<std::endl;
return 1;
}
pthread_join(thread_id1, NULL);
pthread_join(thread_id2, NULL);
return 0;
}[root@SpinfoServer src]# gdb -tui ./gdbthreadtest //调试程序
设置断点：
(gdb) break 7 Breakpoint 1 at 0x400a19: file kangThread.cpp, line 7. (gdb) break 35 Breakpoint 2 at 0x400b35: file kangThread.cpp, line 35. (gdb) info break Num Type Disp Enb Address What 1 breakpoint keep y 0x0000000000400a19 in ThreadFun(void*) at kangThread.cpp:7 2 breakpoint keep y 0x0000000000400b35 in main() at kangThread.cpp:35开始运行：
(gdb) r
Starting program: /home/kang/src/mulThread/kangThread
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Traceback (most recent call last):
File "/usr/share/gdb/auto-load/usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.19-gdb.py", line 63, in <module>
from libstdcxx.v6.printers import register_libstdcxx_printers
ImportError: No module named 'libstdcxx'
[New Thread 0x7ffff6fd5700 (LWP 2773)]
[Switching to Thread 0x7ffff6fd5700 (LWP 2773)]
Breakpoint 1, ThreadFun (arg=0x602010) at kangThread.cpp:7
warning: Source file is more recent than executable.
7 int *value=static_cast<int*> (arg);
查看线程信息：
(gdb) info thread [New Thread 0x7ffff67d4700 (LWP 2774)] Id Target Id Frame 3 Thread 0x7ffff67d4700 (LWP 2774) "kangThread" clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:81 * 2 Thread 0x7ffff6fd5700 (LWP 2773) "kangThread" ThreadFun (arg=0x602010) at kangThread.cpp:7 1 Thread 0x7ffff7fda780 (LWP 2769) "kangThread" clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:81可以看到ID为2的线程执行到了断点Breakpoint 1。可以看一下value的值
(gdb) n 8 std::cout<<"This is thread"<<*value<<std::endl; (gdb) p *value $2 = 1切换到线程3：
(gdb) c
Continuing.
1
[Switching to Thread 0x7ffff67d4700 (LWP 2774)]
Breakpoint 1, ThreadFun (arg=0x602030) at kangThread.cpp:7
7 int *value=static_cast<int*> (arg);
(gdb) info thread
Id Target Id Frame
* 3 Thread 0x7ffff67d4700 (LWP 2774) "kangThread" ThreadFun (arg=0x602030) at kangThread.cpp:7
2 Thread 0x7ffff6fd5700 (LWP 2773) "kangThread" __GI__dl_debug_state () at dl-debug.c:74
1 Thread 0x7ffff7fda780 (LWP 2769) "kangThread" 0x00007ffff7bc566b in pthread_join (threadid=140737337186048,
thread_return=0x0) at pthread_join.c:92
(gdb) thread 3
[Switching to thread 3 (Thread 0x7ffff67d4700 (LWP 2774))]
#0 ThreadFun (arg=0x602030) at kangThread.cpp:7
7 int *value=static_cast<int*> (arg);
(gdb) n
8 std::cout<<"This is thread"<<*value<<std::endl;
(gdb) p *value
$3 = 2
可以看出线程3的value为2。
还有其他许多命令和方法，要在实践中慢慢熟悉。