gdb调试多线程

gdb使用

gdb是非常强大的调试工具，在文本模式下使用。使用方法可以参考陈皓的两篇文章 
用GDB调试程序（一） 
用GDB调试程序（二）
gdb常用命令在下表列出：

命令	描述
backtrace（或bt）	查看各级函数调用及参数
finish	连续运行到当前函数返回为止，然后停下来等待命令
frame（或f）	帧编号 选择栈帧
info（或i）	locals 查看当前栈帧局部变量的值
list（或l）	列出源代码，接着上次的位置往下列，每次列10行
list 行号	列出从第几行开始的源代码
list 函数名	列出某个函数的源代码
next（或n）	执行下一行语句
print（或p）	打印表达式的值，通过表达式可以修改变量的值或者调用函数
quit（或q）	退出gdb调试环境
set var	修改变量的值
start	开始执行程序，停在main函数第一行语句前面等待命令
step（或s）	执行下一行语句，如果有函数调用则进入到函数中

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：

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。

thread ID:切换当前调试的线程为指定ID的线程。

break FileName.cpp:LinuNum thread all:所有线程都在文件FileName.cpp的第LineNum行有断点。

thread apply ID1 ID2 IDN command:多个线程执行gdb命令command。

thread apply all command：所有线程都执行command命令。

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。

set non-stop on/off:当调式一个线程时，其他线程是否运行。

set pagination on/off:在使用backtrace时，在分页时是否停止。

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。

<code class="hljs cpp has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <iostream></span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <pthread.h></span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>* ThreadFun(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>* arg)
{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> *value=<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>*> (arg);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">cout</span><<<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"This is thread"</span><<*value<<<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::endl;
pthread_exit(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);
}

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> main()
{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>  ret=<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
pthread_t thread_id1,thread_id2;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>* v1=<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>* v2=<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>);
ret = pthread_create(&thread_id1, NULL, ThreadFun, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>*>(v1));
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (ret)
{
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">cout</span><<<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Create pthread error!"</span><<<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::endl;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
}

ret = pthread_create(&thread_id2, NULL, ThreadFun, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>*>(v2));
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (ret)
{
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">cout</span><<<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Create pthread error!"</span><<<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::endl;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
}

pthread_join(thread_id1, NULL);
pthread_join(thread_id2, NULL);

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li></ul>

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">$ gdb gdbThreadTest<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//调试gdbThreadTest</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

加断点

<code class="hljs livecodeserver has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">(gdb) break <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>
Breakpoint <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">at</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x400a19</span>: <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">file</span> kangThread.cpp, <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">line</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7.</span>
(gdb) break <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">35</span>
Breakpoint <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">at</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x400b35</span>: <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">file</span> kangThread.cpp, <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">line</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">35.</span>
(gdb) info break
Num     Type           Disp Enb Address            What
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>       <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">breakpoint</span>     keep y   <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x0000000000400a19</span> <span class="hljs-operator" style="box-sizing: border-box;">in</span> ThreadFun(void*) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">at</span> kangThread.cpp:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>       <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">breakpoint</span>     keep y   <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x0000000000400b35</span> <span class="hljs-operator" style="box-sizing: border-box;">in</span> main() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">at</span> kangThread.cpp:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">35</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

开始运行

<code class="hljs sql has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">(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 <span class="hljs-operator" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">call</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">last</span>):
File <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"/usr/share/gdb/auto-load/usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.19-gdb.py"</span>, line <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">63</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> <<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">module</span>>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">from</span> libstdcxx.v6.printers import register_libstdcxx_printers
ImportError: <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">No</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">module</span> named <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'libstdcxx'</span>
[New Thread <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x7ffff6fd5700</span> (LWP <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2773</span>)]
[Switching <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> Thread <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x7ffff6fd5700</span> (LWP <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2773</span>)]

Breakpoint <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>, ThreadFun (arg=<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x602010</span>) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">at</span> kangThread.cpp:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>
warning: Source file <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> more recent than executable.
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>       <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> *<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">value</span>=static_cast<<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>*> (arg);</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li></ul>

查看线程信息

<code class="hljs mathematica has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">(gdb) info thread
[New <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Thread</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x7ffff67d4700</span> (LWP <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2774</span>)]
Id   Target Id         <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Frame</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Thread</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x7ffff67d4700</span> (LWP <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2774</span>) <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"kangThread"</span> clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">81</span>
* <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Thread</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x7ffff6fd5700</span> (LWP <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2773</span>) <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"kangThread"</span> ThreadFun (arg=<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x602010</span>) at kangThread.cpp:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Thread</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x7ffff7fda780</span> (LWP <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2769</span>) <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"kangThread"</span> clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">81</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

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

<code class="hljs ruby has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">(gdb) n
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>       <span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">std:</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:cout<<<span class="hljs-string" style="box-sizing: border-box;">"This is thread"</span><<*value<<std</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:endl</span>;
(gdb) p *value
<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">$2</span> = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

切换到线程3,看一下线程3执行到了哪里

<code class="hljs cpp has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">(gdb) c
Continuing.
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>
[Switching to Thread <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x7ffff67d4700</span> (LWP <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2774</span>)]

Breakpoint <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>, ThreadFun (arg=<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x602030</span>) at kangThread.cpp:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>       <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> *value=<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>*> (arg);
(gdb) info thread
Id   Target Id         Frame
* <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>    Thread <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x7ffff67d4700</span> (LWP <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2774</span>) <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"kangThread"</span> ThreadFun (arg=<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x602030</span>) at kangThread.cpp:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>    Thread <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x7ffff6fd5700</span> (LWP <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2773</span>) <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"kangThread"</span> __GI__dl_debug_state () at dl-debug.c:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">74</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>    Thread <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x7ffff7fda780</span> (LWP <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2769</span>) <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"kangThread"</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x00007ffff7bc566b</span> in pthread_join (threadid=<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">140737337186048</span>,
thread_return=<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x0</span>) at pthread_join.c:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">92</span>
(gdb) thread <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>
[Switching to thread <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span> (Thread <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x7ffff67d4700</span> (LWP <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2774</span>))]
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#0  ThreadFun (arg=0x602030) at kangThread.cpp:7</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>       <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> *value=<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static_cast</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>*> (arg);
(gdb) n
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>       <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">cout</span><<<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"This is thread"</span><<*value<<<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">std</span>::endl;
(gdb) p *value
$<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span> = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li></ul>

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。



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