如何使用gdb来解决死锁

博主： peter
发布时间：2025 年 02 月 01 日
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分类：多线程高并发调试手段

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# 一、死锁demo

```cpp
#include <iostream>   // 用于输入输出
#include <thread>     // 用于线程创建和管理
#include <mutex>      // 用于互斥锁
#include <chrono>     // 用于时间操作

using std::cout;      // 简化cout的调用
using std::endl;      // 简化endl的调用

// 定义三个互斥锁
std::mutex mutex1;
std::mutex mutex2;
std::mutex mutex3;

// 线程A：先锁mutex1，再锁mutex2（可能导致死锁）
void FuncA() {
		std::cout << "FuncA Begin." << endl;
    std::lock_guard<std::mutex> guard1(mutex1);
    std::this_thread::sleep_for(std::chrono::seconds(1));  // 模拟耗时操作
    std::lock_guard<std::mutex> guard2(mutex2);
    std::cout << "FuncA completed." << endl;
}

// 线程B：先锁mutex2，再锁mutex3（可能导致死锁）
void FuncB() {
    std::cout << "FuncB Begin." << endl;
    std::lock_guard<std::mutex> guard2(mutex2);
    std::this_thread::sleep_for(std::chrono::seconds(1));
    std::lock_guard<std::mutex> guard3(mutex3);
    std::cout << "FuncB completed." << endl;
}

// 线程C：先锁mutex3，再锁mutex1（可能导致死锁）
void FuncC() {
    std::cout << "FuncC Begin." << endl;
    std::lock_guard<std::mutex> guard3(mutex3);
    std::this_thread::sleep_for(std::chrono::seconds(1));
    std::lock_guard<std::mutex> guard1(mutex1);
    std::cout << "FuncC completed." << endl;
}

int main() {
    // 创建三个线程
    std::thread t1(FuncA);
    std::thread t2(FuncB);
    std::thread t3(FuncC);

// 等待所有线程完成（实际可能因死锁卡死）
    t1.join();
    t2.join();
    t3.join();

cout << "All threads finished." << endl;
    return 0;
}
```

g++ --std=c++11 -g -O0 deadlock.cpp -o deadlock -lpthread

查看运行状态并生成coredump文件：

```cpp
root@iZbp1est4y0mdt6ask7pgpZ:~# ps -aux | grep dead
peter     329370  0.0  0.0  96148  1552 pts/2    Sl+  13:55   0:00 ./deadlock
root      329375  0.0  0.0   8872   656 pts/3    S+   13:55   0:00 grep --color=auto dead
root@iZbp1est4y0mdt6ask7pgpZ:~# kill -3 329370
root@iZbp1est4y0mdt6ask7pgpZ:~#

**S：进程处于 休眠状态**（Interruptible Sleep），等待资源或事件触发。
**l：进程是 多线程的**（使用 clone() 系统调用创建线程）。
**+：进程是 前台进程组** 的成员（可通过 Ctrl+C 终止）。

触发产生coredump文件：
peter@iZbp1est4y0mdt6ask7pgpZ:~/deadlock$ ./deadlock
FuncA Begin.
FuncB Begin.
FuncC Begin.
Quit (core dumped)

```

# 二、使用gdb来检测死锁

```cpp

```

## 1、info threads查看当前进程中所有线程的信息，也可以查看到部分堆栈信息

```cpp
(gdb) info thread
  Id   Target Id                          Frame
* 1    Thread 0x7f74738e0740 (LWP 329370) __pthread_clockjoin_ex (threadid=140138131617536, thread_return=0x0, clockid=<optimized out>, abstime=<optimized out>, block=<optimized out>)
    at pthread_join_common.c:145
  2    Thread 0x7f74730de700 (LWP 329372) __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1e0 <mutex3>, private=0) at lowlevellock.c:52
  3    Thread 0x7f74728dd700 (LWP 329373) __lll_lock_wait (futex=futex@entry=0x55f8c2bbb160 <mutex1>, private=0) at lowlevellock.c:52
  4    Thread 0x7f74738df700 (LWP 329371) __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1a0 <mutex2>, private=0) at lowlevellock.c:52

```

1 是主线程， 2-3是其他线程，而且都是加锁的过程，如果在生产环境中可能有很多线程在等锁，等什么锁

## 2、查看每个线程在等什么锁

```cpp
(gdb) thread 2
[Switching to thread 2 (Thread 0x7f74730de700 (LWP 329372))]
#0  **__lll_lock_wait** (futex=futex@entry=0x55f8c2bbb1e0 <**mutex3**>, private=0) at lowlevellock.c:52
52      lowlevellock.c: No such file or directory.
(gdb) bt
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1e0 <mutex3>, private=0) at lowlevellock.c:52
#1  0x00007f7473e2d0a3 in __GI___pthread_mutex_lock (mutex=0x55f8c2bbb1e0 <mutex3>) at ../nptl/pthread_mutex_lock.c:80
#2  0x000055f8c2bb6888 in __gthread_mutex_lock (__mutex=0x55f8c2bbb1e0 <mutex3>) at /usr/include/x86_64-linux-gnu/c++/9/bits/gthr-default.h:749
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb1e0 <mutex3>) at /usr/include/c++/9/bits/std_mutex.h:100
#4  0x000055f8c2bb6a78 in std::lock_guard<std::mutex>::lock_guard (this=0x7f74730dddf0, __m=...) at /usr/include/c++/9/bits/std_mutex.h:159
#5  0x000055f8c2bb6519 in FuncB () at deadlock.cpp:28
#6  0x000055f8c2bb7658 in std::__invoke_impl<void, void (*)()> (__f=@0x55f8c4797008: 0x55f8c2bb6489 <**FuncB()**>) at /usr/include/c++/9/bits/invoke.h:60
#7  0x000055f8c2bb75f0 in std::__invoke<void (*)()> (__fn=@0x55f8c4797008: 0x55f8c2bb6489 <**FuncB()**>) at /usr/include/c++/9/bits/invoke.h:95
#8  0x000055f8c2bb7582 in std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul> (this=0x55f8c4797008) at /usr/include/c++/9/thread:244
#9  0x000055f8c2bb753f in std::thread::_Invoker<std::tuple<void (*)()> >::operator() (this=0x55f8c4797008) at /usr/include/c++/9/thread:251
#10 0x000055f8c2bb7510 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run (this=0x55f8c4797000) at /usr/include/c++/9/thread:195
#11 0x00007f7473d17cb4 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f7473e2a609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#13 0x00007f7473b53353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

```

线程2【B】在给mutex3加锁，在等mutex3

```cpp
(gdb) thread 3
[Switching to thread 3 (Thread 0x7f74728dd700 (LWP 329373))]
#0  **__lll_lock_wait** (futex=futex@entry=0x55f8c2bbb160 <**mutex1**>, private=0) at lowlevellock.c:52
52      in lowlevellock.c
(gdb) bt
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb160 <mutex1>, private=0) at lowlevellock.c:52
#1  0x00007f7473e2d0a3 in __GI___pthread_mutex_lock (mutex=0x55f8c2bbb160 <mutex1>) at ../nptl/pthread_mutex_lock.c:80
#2  0x000055f8c2bb6888 in __gthread_mutex_lock (__mutex=0x55f8c2bbb160 <mutex1>) at /usr/include/x86_64-linux-gnu/c++/9/bits/gthr-default.h:749
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb160 <mutex1>) at /usr/include/c++/9/bits/std_mutex.h:100
#4  0x000055f8c2bb6a78 in std::lock_guard<std::mutex>::lock_guard (this=0x7f74728dcdf0, __m=...) at /usr/include/c++/9/bits/std_mutex.h:159
#5  0x000055f8c2bb663a in FuncC () at deadlock.cpp:37
#6  0x000055f8c2bb7658 in std::__invoke_impl<void, void (*)()> (__f=@0x55f8c4797158: 0x55f8c2bb65aa <FuncC()>) at /usr/include/c++/9/bits/invoke.h:60
#7  0x000055f8c2bb75f0 in std::__invoke<void (*)()> (__fn=@0x55f8c4797158: 0x55f8c2bb65aa <**FuncC()**>) at /usr/include/c++/9/bits/invoke.h:95
#8  0x000055f8c2bb7582 in std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul> (this=0x55f8c4797158) at /usr/include/c++/9/thread:244
#9  0x000055f8c2bb753f in std::thread::_Invoker<std::tuple<void (*)()> >::operator() (this=0x55f8c4797158) at /usr/include/c++/9/thread:251
#10 0x000055f8c2bb7510 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run (this=0x55f8c4797150) at /usr/include/c++/9/thread:195
#11 0x00007f7473d17cb4 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f7473e2a609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#13 0x00007f7473b53353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

```

线程3【\*\*C】\*\*在给mutex1加锁，在等mutex1

```cpp
(gdb) thread 4
[Switching to thread 4 (Thread 0x7f74738df700 (LWP 329371))]
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1a0 <mutex2>, private=0) at lowlevellock.c:52
52      lowlevellock.c: No such file or directory.
(gdb) bt
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1a0 <mutex2>, private=0) at lowlevellock.c:52
#1  0x00007f7473e2d0a3 in __GI___pthread_mutex_lock (mutex=0x55f8c2bbb1a0 <mutex2>) at ../nptl/pthread_mutex_lock.c:80
#2  0x000055f8c2bb6888 in __gthread_mutex_lock (__mutex=0x55f8c2bbb1a0 <mutex2>) at /usr/include/x86_64-linux-gnu/c++/9/bits/gthr-default.h:749
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb1a0 <mutex2>) at /usr/include/c++/9/bits/std_mutex.h:100
#4  0x000055f8c2bb6a78 in std::lock_guard<std::mutex>::lock_guard (this=0x7f74738dedf0, __m=...) at /usr/include/c++/9/bits/std_mutex.h:159
#5  0x000055f8c2bb63f8 in FuncA () at deadlock.cpp:19
#6  0x000055f8c2bb7658 in std::__invoke_impl<void, void (*)()> (__f=@0x55f8c4796eb8: 0x55f8c2bb6368 <FuncA()>) at /usr/include/c++/9/bits/invoke.h:60
#7  0x000055f8c2bb75f0 in std::__invoke<void (*)()> (__fn=@0x55f8c4796eb8: 0x55f8c2bb6368 <**FuncA()**>) at /usr/include/c++/9/bits/invoke.h:95
#8  0x000055f8c2bb7582 in std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul> (this=0x55f8c4796eb8) at /usr/include/c++/9/thread:244
#9  0x000055f8c2bb753f in std::thread::_Invoker<std::tuple<void (*)()> >::operator() (this=0x55f8c4796eb8) at /usr/include/c++/9/thread:251
#10 0x000055f8c2bb7510 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run (this=0x55f8c4796eb0) at /usr/include/c++/9/thread:195
#11 0x00007f7473d17cb4 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f7473e2a609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#13 0x00007f7473b53353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

```

线程4【A】在给mutex2加锁，在等mutex2

## 3、查看这些在等的锁是谁拥有的

```cpp
(gdb) thread 2
[Switching to thread 2 (Thread 0x7f74730de700 (LWP 329372))]
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1e0 <mutex3>, private=0) at lowlevellock.c:52
52      in lowlevellock.c
(gdb) bt
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1e0 <mutex3>, private=0) at lowlevellock.c:52
#1  0x00007f7473e2d0a3 in __GI___pthread_mutex_lock (mutex=0x55f8c2bbb1e0 <mutex3>) at ../nptl/pthread_mutex_lock.c:80
#2  0x000055f8c2bb6888 in __gthread_mutex_lock (__mutex=0x55f8c2bbb1e0 <mutex3>) at /usr/include/x86_64-linux-gnu/c++/9/bits/gthr-default.h:749
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb1e0 <mutex3>) at /usr/include/c++/9/bits/std_mutex.h:100
#4  0x000055f8c2bb6a78 in std::lock_guard<std::mutex>::lock_guard (this=0x7f74730dddf0, __m=...) at /usr/include/c++/9/bits/std_mutex.h:159
#5  0x000055f8c2bb6519 in FuncB () at deadlock.cpp:28
#6  0x000055f8c2bb7658 in std::__invoke_impl<void, void (*)()> (__f=@0x55f8c4797008: 0x55f8c2bb6489 <FuncB()>) at /usr/include/c++/9/bits/invoke.h:60
#7  0x000055f8c2bb75f0 in std::__invoke<void (*)()> (__fn=@0x55f8c4797008: 0x55f8c2bb6489 <FuncB()>) at /usr/include/c++/9/bits/invoke.h:95
#8  0x000055f8c2bb7582 in std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul> (this=0x55f8c4797008) at /usr/include/c++/9/thread:244
#9  0x000055f8c2bb753f in std::thread::_Invoker<std::tuple<void (*)()> >::operator() (this=0x55f8c4797008) at /usr/include/c++/9/thread:251
#10 0x000055f8c2bb7510 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run (this=0x55f8c4797000) at /usr/include/c++/9/thread:195
#11 0x00007f7473d17cb4 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f7473e2a609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#13 0x00007f7473b53353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
(gdb) f 3
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb1e0 <mutex3>) at /usr/include/c++/9/bits/std_mutex.h:100
100           int __e = __gthread_mutex_lock(&_M_mutex);
(gdb) p mutex3
$1 = {
  <std::__mutex_base> = {
    _M_mutex = {
      __data = {
        __lock = 2,
        __count = 0,
        __owner = 329373,
        __nusers = 1,
        __kind = 0,
        __spins = 0,
        __elision = 0,
        __list = {
          __prev = 0x0,
          __next = 0x0
        }
      },
      __size = "\\002\\000\\000\\000\\000\\000\\000\\000\\235\\006\\005\\000\\001", '\\000' <repeats 26 times>,
      __align = 2
    }
  }, <No data fields>}

```

进入到std::mutex::lock 这行代码所在的栈帧， 查看锁是被谁占有的，\_\_owner = **329373**, 后面如果非零，就代表这个锁被这个线程占有着。

```cpp
(gdb) info thread
  Id   Target Id                          Frame
  1    Thread 0x7f74738e0740 (LWP 329370) __pthread_clockjoin_ex (threadid=140138131617536, thread_return=0x0, clockid=<optimized out>, abstime=<optimized out>, block=<optimized out>)
    at pthread_join_common.c:145
* 2    Thread 0x7f74730de700 (LWP 329372) __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1e0 <mutex3>, private=0) at lowlevellock.c:52
  3    Thread 0x7f74728dd700 (LWP **329373**) __lll_lock_wait (futex=futex@entry=0x55f8c2bbb160 <mutex1>, private=0) at lowlevellock.c:52
  4    Thread 0x7f74738df700 (LWP 329371) __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1a0 <mutex2>, private=0) at lowlevellock.c:52

```

查看线程号，发现这把锁是被线程3  **329373**拿到的

这个线程2在等mutex3，而mutex3是被329373拿到的，也就是线程3

下一步干嘛？ 应该去排查**329373**这个线程在干嘛

### 3.1、线程**329373的状态**

```cpp
(gdb) thread 3
[Switching to thread 3 (Thread 0x7f74728dd700 (LWP 329373))]
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb160 <mutex1>, private=0) at lowlevellock.c:52
52      lowlevellock.c: No such file or directory.
(gdb) bt
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb160 <mutex1>, private=0) at lowlevellock.c:52
#1  0x00007f7473e2d0a3 in __GI___pthread_mutex_lock (mutex=0x55f8c2bbb160 <mutex1>) at ../nptl/pthread_mutex_lock.c:80
#2  0x000055f8c2bb6888 in __gthread_mutex_lock (__mutex=0x55f8c2bbb160 <mutex1>) at /usr/include/x86_64-linux-gnu/c++/9/bits/gthr-default.h:749
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb160 <mutex1>) at /usr/include/c++/9/bits/std_mutex.h:100
#4  0x000055f8c2bb6a78 in std::lock_guard<std::mutex>::lock_guard (this=0x7f74728dcdf0, __m=...) at /usr/include/c++/9/bits/std_mutex.h:159
#5  0x000055f8c2bb663a in FuncC () at deadlock.cpp:37
#6  0x000055f8c2bb7658 in std::__invoke_impl<void, void (*)()> (__f=@0x55f8c4797158: 0x55f8c2bb65aa <FuncC()>) at /usr/include/c++/9/bits/invoke.h:60
#7  0x000055f8c2bb75f0 in std::__invoke<void (*)()> (__fn=@0x55f8c4797158: 0x55f8c2bb65aa <FuncC()>) at /usr/include/c++/9/bits/invoke.h:95
#8  0x000055f8c2bb7582 in std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul> (this=0x55f8c4797158) at /usr/include/c++/9/thread:244
#9  0x000055f8c2bb753f in std::thread::_Invoker<std::tuple<void (*)()> >::operator() (this=0x55f8c4797158) at /usr/include/c++/9/thread:251
#10 0x000055f8c2bb7510 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run (this=0x55f8c4797150) at /usr/include/c++/9/thread:195
#11 0x00007f7473d17cb4 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f7473e2a609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#13 0x00007f7473b53353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
(gdb) f 3
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb160 <mutex1>) at /usr/include/c++/9/bits/std_mutex.h:100
100           int __e = __gthread_mutex_lock(&_M_mutex);
(gdb) p mutex1
$2 = {
  <std::__mutex_base> = {
    _M_mutex = {
      __data = {
        __lock = 2,
        __count = 0,
        __owner = 329371,
        __nusers = 1,
        __kind = 0,
        __spins = 0,
        __elision = 0,
        __list = {
          __prev = 0x0,
          __next = 0x0
        }
      },
      __size = "\\002\\000\\000\\000\\000\\000\\000\\000\\233\\006\\005\\000\\001", '\\000' <repeats 26 times>,
      __align = 2
    }
  }, <No data fields>}

```

这个线程3在等mutex1，而mutex1是被329371拿到的，也就是线程4

### 3.2、线程**329371的状态**

```cpp
(gdb) thread 4
[Switching to thread 4 (Thread 0x7f74738df700 (LWP 329371))]
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1a0 <mutex2>, private=0) at lowlevellock.c:52
52      lowlevellock.c: No such file or directory.
(gdb) bt
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1a0 <mutex2>, private=0) at lowlevellock.c:52
#1  0x00007f7473e2d0a3 in __GI___pthread_mutex_lock (mutex=0x55f8c2bbb1a0 <mutex2>) at ../nptl/pthread_mutex_lock.c:80
#2  0x000055f8c2bb6888 in __gthread_mutex_lock (__mutex=0x55f8c2bbb1a0 <mutex2>) at /usr/include/x86_64-linux-gnu/c++/9/bits/gthr-default.h:749
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb1a0 <mutex2>) at /usr/include/c++/9/bits/std_mutex.h:100
#4  0x000055f8c2bb6a78 in std::lock_guard<std::mutex>::lock_guard (this=0x7f74738dedf0, __m=...) at /usr/include/c++/9/bits/std_mutex.h:159
#5  0x000055f8c2bb63f8 in FuncA () at deadlock.cpp:19
#6  0x000055f8c2bb7658 in std::__invoke_impl<void, void (*)()> (__f=@0x55f8c4796eb8: 0x55f8c2bb6368 <FuncA()>) at /usr/include/c++/9/bits/invoke.h:60
#7  0x000055f8c2bb75f0 in std::__invoke<void (*)()> (__fn=@0x55f8c4796eb8: 0x55f8c2bb6368 <**FuncA()**>) at /usr/include/c++/9/bits/invoke.h:95
#8  0x000055f8c2bb7582 in std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul> (this=0x55f8c4796eb8) at /usr/include/c++/9/thread:244
#9  0x000055f8c2bb753f in std::thread::_Invoker<std::tuple<void (*)()> >::operator() (this=0x55f8c4796eb8) at /usr/include/c++/9/thread:251
#10 0x000055f8c2bb7510 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run (this=0x55f8c4796eb0) at /usr/include/c++/9/thread:195
#11 0x00007f7473d17cb4 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f7473e2a609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#13 0x00007f7473b53353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
(gdb) f 3
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb1a0 <mutex2>) at /usr/include/c++/9/bits/std_mutex.h:100
100           int __e = __gthread_mutex_lock(&_M_mutex);
(gdb) p mutex2
$3 = {
  <std::__mutex_base> = {
    _M_mutex = {
      __data = {
        __lock = 2,
        __count = 0,
        __owner = 329372,
        __nusers = 1,
        __kind = 0,
        __spins = 0,
        __elision = 0,
        __list = {
          __prev = 0x0,
          __next = 0x0
        }
      },
      __size = "\\002\\000\\000\\000\\000\\000\\000\\000\\234\\006\\005\\000\\001", '\\000' <repeats 26 times>,
      __align = 2
    }
  }, <No data fields>}

```

这个线程4在等mutex2，而mutex2是被329372拿到的，也就是线程2

### 3.3、综上所述

```cpp
这个线程2在等mutex3，而mutex3是被329373拿到的，也就是线程3
这个线程3在等mutex1，而mutex1是被329371拿到的，也就是线程4
这个线程4在等mutex2，而mutex2是被329372拿到的，也就是线程2

其中线程2 3 4分别对应thread B C A
```

由此得出结论，出现了环形死锁的情况：

![image.png](http://121.40.244.168/usr/uploads/2025/07/2906227173.png)

还是拿上面图举例：

* 线程A已经持有mutex1，想要申请mutex2，拿到mutex2后才可以释放mutex1和mutex2，而此时mutex2被线程B占用。
* 线程B已经持有mutex2，想要申请mutex3，拿到mutex3后才可以释放mutex2和mutex3，而此时mutex3被线程C占用。
* 线程C已经持有mutex3，想要申请mutex1，拿到mutex1后才可以释放mutex3和mutex1，而此时mutex1被线程A占用。

![image.png](http://121.40.244.168/usr/uploads/2025/07/376142519.png)

如图，三个线程形成了一个环，死锁检测就是检查线程之间是否有环的存在。A->B, B->C, C->A

最后修改：2025 年 07 月 13 日

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如何使用gdb来解决死锁

peter • 2025 年 02 月 01 日

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# 一、死锁demo

```cpp
#include <iostream>   // 用于输入输出
#include <thread>     // 用于线程创建和管理
#include <mutex>      // 用于互斥锁
#include <chrono>     // 用于时间操作

using std::cout;      // 简化cout的调用
using std::endl;      // 简化endl的调用

// 定义三个互斥锁
std::mutex mutex1;
std::mutex mutex2;
std::mutex mutex3;

// 线程A：先锁mutex1，再锁mutex2（可能导致死锁）
void FuncA() {
		std::cout << "FuncA Begin." << endl;
    std::lock_guard<std::mutex> guard1(mutex1);
    std::this_thread::sleep_for(std::chrono::seconds(1));  // 模拟耗时操作
    std::lock_guard<std::mutex> guard2(mutex2);
    std::cout << "FuncA completed." << endl;
}

// 线程B：先锁mutex2，再锁mutex3（可能导致死锁）
void FuncB() {
    std::cout << "FuncB Begin." << endl;
    std::lock_guard<std::mutex> guard2(mutex2);
    std::this_thread::sleep_for(std::chrono::seconds(1));
    std::lock_guard<std::mutex> guard3(mutex3);
    std::cout << "FuncB completed." << endl;
}

// 线程C：先锁mutex3，再锁mutex1（可能导致死锁）
void FuncC() {
    std::cout << "FuncC Begin." << endl;
    std::lock_guard<std::mutex> guard3(mutex3);
    std::this_thread::sleep_for(std::chrono::seconds(1));
    std::lock_guard<std::mutex> guard1(mutex1);
    std::cout << "FuncC completed." << endl;
}

int main() {
    // 创建三个线程
    std::thread t1(FuncA);
    std::thread t2(FuncB);
    std::thread t3(FuncC);

// 等待所有线程完成（实际可能因死锁卡死）
    t1.join();
    t2.join();
    t3.join();

cout << "All threads finished." << endl;
    return 0;
}
```

g++ --std=c++11 -g -O0 deadlock.cpp -o deadlock -lpthread

查看运行状态并生成coredump文件：

```cpp
root@iZbp1est4y0mdt6ask7pgpZ:~# ps -aux | grep dead
peter     329370  0.0  0.0  96148  1552 pts/2    Sl+  13:55   0:00 ./deadlock
root      329375  0.0  0.0   8872   656 pts/3    S+   13:55   0:00 grep --color=auto dead
root@iZbp1est4y0mdt6ask7pgpZ:~# kill -3 329370
root@iZbp1est4y0mdt6ask7pgpZ:~#

**S：进程处于 休眠状态**（Interruptible Sleep），等待资源或事件触发。
**l：进程是 多线程的**（使用 clone() 系统调用创建线程）。
**+：进程是 前台进程组** 的成员（可通过 Ctrl+C 终止）。

触发产生coredump文件：
peter@iZbp1est4y0mdt6ask7pgpZ:~/deadlock$ ./deadlock
FuncA Begin.
FuncB Begin.
FuncC Begin.
Quit (core dumped)

```

# 二、使用gdb来检测死锁

```cpp

```

## 1、info threads查看当前进程中所有线程的信息，也可以查看到部分堆栈信息

```cpp
(gdb) info thread
  Id   Target Id                          Frame
* 1    Thread 0x7f74738e0740 (LWP 329370) __pthread_clockjoin_ex (threadid=140138131617536, thread_return=0x0, clockid=<optimized out>, abstime=<optimized out>, block=<optimized out>)
    at pthread_join_common.c:145
  2    Thread 0x7f74730de700 (LWP 329372) __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1e0 <mutex3>, private=0) at lowlevellock.c:52
  3    Thread 0x7f74728dd700 (LWP 329373) __lll_lock_wait (futex=futex@entry=0x55f8c2bbb160 <mutex1>, private=0) at lowlevellock.c:52
  4    Thread 0x7f74738df700 (LWP 329371) __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1a0 <mutex2>, private=0) at lowlevellock.c:52

```

1 是主线程， 2-3是其他线程，而且都是加锁的过程，如果在生产环境中可能有很多线程在等锁，等什么锁

## 2、查看每个线程在等什么锁

```cpp
(gdb) thread 2
[Switching to thread 2 (Thread 0x7f74730de700 (LWP 329372))]
#0  **__lll_lock_wait** (futex=futex@entry=0x55f8c2bbb1e0 <**mutex3**>, private=0) at lowlevellock.c:52
52      lowlevellock.c: No such file or directory.
(gdb) bt
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1e0 <mutex3>, private=0) at lowlevellock.c:52
#1  0x00007f7473e2d0a3 in __GI___pthread_mutex_lock (mutex=0x55f8c2bbb1e0 <mutex3>) at ../nptl/pthread_mutex_lock.c:80
#2  0x000055f8c2bb6888 in __gthread_mutex_lock (__mutex=0x55f8c2bbb1e0 <mutex3>) at /usr/include/x86_64-linux-gnu/c++/9/bits/gthr-default.h:749
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb1e0 <mutex3>) at /usr/include/c++/9/bits/std_mutex.h:100
#4  0x000055f8c2bb6a78 in std::lock_guard<std::mutex>::lock_guard (this=0x7f74730dddf0, __m=...) at /usr/include/c++/9/bits/std_mutex.h:159
#5  0x000055f8c2bb6519 in FuncB () at deadlock.cpp:28
#6  0x000055f8c2bb7658 in std::__invoke_impl<void, void (*)()> (__f=@0x55f8c4797008: 0x55f8c2bb6489 <**FuncB()**>) at /usr/include/c++/9/bits/invoke.h:60
#7  0x000055f8c2bb75f0 in std::__invoke<void (*)()> (__fn=@0x55f8c4797008: 0x55f8c2bb6489 <**FuncB()**>) at /usr/include/c++/9/bits/invoke.h:95
#8  0x000055f8c2bb7582 in std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul> (this=0x55f8c4797008) at /usr/include/c++/9/thread:244
#9  0x000055f8c2bb753f in std::thread::_Invoker<std::tuple<void (*)()> >::operator() (this=0x55f8c4797008) at /usr/include/c++/9/thread:251
#10 0x000055f8c2bb7510 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run (this=0x55f8c4797000) at /usr/include/c++/9/thread:195
#11 0x00007f7473d17cb4 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f7473e2a609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#13 0x00007f7473b53353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

```

线程2【B】在给mutex3加锁，在等mutex3

```cpp
(gdb) thread 3
[Switching to thread 3 (Thread 0x7f74728dd700 (LWP 329373))]
#0  **__lll_lock_wait** (futex=futex@entry=0x55f8c2bbb160 <**mutex1**>, private=0) at lowlevellock.c:52
52      in lowlevellock.c
(gdb) bt
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb160 <mutex1>, private=0) at lowlevellock.c:52
#1  0x00007f7473e2d0a3 in __GI___pthread_mutex_lock (mutex=0x55f8c2bbb160 <mutex1>) at ../nptl/pthread_mutex_lock.c:80
#2  0x000055f8c2bb6888 in __gthread_mutex_lock (__mutex=0x55f8c2bbb160 <mutex1>) at /usr/include/x86_64-linux-gnu/c++/9/bits/gthr-default.h:749
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb160 <mutex1>) at /usr/include/c++/9/bits/std_mutex.h:100
#4  0x000055f8c2bb6a78 in std::lock_guard<std::mutex>::lock_guard (this=0x7f74728dcdf0, __m=...) at /usr/include/c++/9/bits/std_mutex.h:159
#5  0x000055f8c2bb663a in FuncC () at deadlock.cpp:37
#6  0x000055f8c2bb7658 in std::__invoke_impl<void, void (*)()> (__f=@0x55f8c4797158: 0x55f8c2bb65aa <FuncC()>) at /usr/include/c++/9/bits/invoke.h:60
#7  0x000055f8c2bb75f0 in std::__invoke<void (*)()> (__fn=@0x55f8c4797158: 0x55f8c2bb65aa <**FuncC()**>) at /usr/include/c++/9/bits/invoke.h:95
#8  0x000055f8c2bb7582 in std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul> (this=0x55f8c4797158) at /usr/include/c++/9/thread:244
#9  0x000055f8c2bb753f in std::thread::_Invoker<std::tuple<void (*)()> >::operator() (this=0x55f8c4797158) at /usr/include/c++/9/thread:251
#10 0x000055f8c2bb7510 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run (this=0x55f8c4797150) at /usr/include/c++/9/thread:195
#11 0x00007f7473d17cb4 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f7473e2a609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#13 0x00007f7473b53353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

```

线程3【\*\*C】\*\*在给mutex1加锁，在等mutex1

```cpp
(gdb) thread 4
[Switching to thread 4 (Thread 0x7f74738df700 (LWP 329371))]
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1a0 <mutex2>, private=0) at lowlevellock.c:52
52      lowlevellock.c: No such file or directory.
(gdb) bt
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1a0 <mutex2>, private=0) at lowlevellock.c:52
#1  0x00007f7473e2d0a3 in __GI___pthread_mutex_lock (mutex=0x55f8c2bbb1a0 <mutex2>) at ../nptl/pthread_mutex_lock.c:80
#2  0x000055f8c2bb6888 in __gthread_mutex_lock (__mutex=0x55f8c2bbb1a0 <mutex2>) at /usr/include/x86_64-linux-gnu/c++/9/bits/gthr-default.h:749
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb1a0 <mutex2>) at /usr/include/c++/9/bits/std_mutex.h:100
#4  0x000055f8c2bb6a78 in std::lock_guard<std::mutex>::lock_guard (this=0x7f74738dedf0, __m=...) at /usr/include/c++/9/bits/std_mutex.h:159
#5  0x000055f8c2bb63f8 in FuncA () at deadlock.cpp:19
#6  0x000055f8c2bb7658 in std::__invoke_impl<void, void (*)()> (__f=@0x55f8c4796eb8: 0x55f8c2bb6368 <FuncA()>) at /usr/include/c++/9/bits/invoke.h:60
#7  0x000055f8c2bb75f0 in std::__invoke<void (*)()> (__fn=@0x55f8c4796eb8: 0x55f8c2bb6368 <**FuncA()**>) at /usr/include/c++/9/bits/invoke.h:95
#8  0x000055f8c2bb7582 in std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul> (this=0x55f8c4796eb8) at /usr/include/c++/9/thread:244
#9  0x000055f8c2bb753f in std::thread::_Invoker<std::tuple<void (*)()> >::operator() (this=0x55f8c4796eb8) at /usr/include/c++/9/thread:251
#10 0x000055f8c2bb7510 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run (this=0x55f8c4796eb0) at /usr/include/c++/9/thread:195
#11 0x00007f7473d17cb4 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f7473e2a609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#13 0x00007f7473b53353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

```

线程4【A】在给mutex2加锁，在等mutex2

## 3、查看这些在等的锁是谁拥有的

```cpp
(gdb) thread 2
[Switching to thread 2 (Thread 0x7f74730de700 (LWP 329372))]
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1e0 <mutex3>, private=0) at lowlevellock.c:52
52      in lowlevellock.c
(gdb) bt
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1e0 <mutex3>, private=0) at lowlevellock.c:52
#1  0x00007f7473e2d0a3 in __GI___pthread_mutex_lock (mutex=0x55f8c2bbb1e0 <mutex3>) at ../nptl/pthread_mutex_lock.c:80
#2  0x000055f8c2bb6888 in __gthread_mutex_lock (__mutex=0x55f8c2bbb1e0 <mutex3>) at /usr/include/x86_64-linux-gnu/c++/9/bits/gthr-default.h:749
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb1e0 <mutex3>) at /usr/include/c++/9/bits/std_mutex.h:100
#4  0x000055f8c2bb6a78 in std::lock_guard<std::mutex>::lock_guard (this=0x7f74730dddf0, __m=...) at /usr/include/c++/9/bits/std_mutex.h:159
#5  0x000055f8c2bb6519 in FuncB () at deadlock.cpp:28
#6  0x000055f8c2bb7658 in std::__invoke_impl<void, void (*)()> (__f=@0x55f8c4797008: 0x55f8c2bb6489 <FuncB()>) at /usr/include/c++/9/bits/invoke.h:60
#7  0x000055f8c2bb75f0 in std::__invoke<void (*)()> (__fn=@0x55f8c4797008: 0x55f8c2bb6489 <FuncB()>) at /usr/include/c++/9/bits/invoke.h:95
#8  0x000055f8c2bb7582 in std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul> (this=0x55f8c4797008) at /usr/include/c++/9/thread:244
#9  0x000055f8c2bb753f in std::thread::_Invoker<std::tuple<void (*)()> >::operator() (this=0x55f8c4797008) at /usr/include/c++/9/thread:251
#10 0x000055f8c2bb7510 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run (this=0x55f8c4797000) at /usr/include/c++/9/thread:195
#11 0x00007f7473d17cb4 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f7473e2a609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#13 0x00007f7473b53353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
(gdb) f 3
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb1e0 <mutex3>) at /usr/include/c++/9/bits/std_mutex.h:100
100           int __e = __gthread_mutex_lock(&_M_mutex);
(gdb) p mutex3
$1 = {
  <std::__mutex_base> = {
    _M_mutex = {
      __data = {
        __lock = 2,
        __count = 0,
        __owner = 329373,
        __nusers = 1,
        __kind = 0,
        __spins = 0,
        __elision = 0,
        __list = {
          __prev = 0x0,
          __next = 0x0
        }
      },
      __size = "\\002\\000\\000\\000\\000\\000\\000\\000\\235\\006\\005\\000\\001", '\\000' <repeats 26 times>,
      __align = 2
    }
  }, <No data fields>}

```

进入到std::mutex::lock 这行代码所在的栈帧， 查看锁是被谁占有的，\_\_owner = **329373**, 后面如果非零，就代表这个锁被这个线程占有着。

```cpp
(gdb) info thread
  Id   Target Id                          Frame
  1    Thread 0x7f74738e0740 (LWP 329370) __pthread_clockjoin_ex (threadid=140138131617536, thread_return=0x0, clockid=<optimized out>, abstime=<optimized out>, block=<optimized out>)
    at pthread_join_common.c:145
* 2    Thread 0x7f74730de700 (LWP 329372) __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1e0 <mutex3>, private=0) at lowlevellock.c:52
  3    Thread 0x7f74728dd700 (LWP **329373**) __lll_lock_wait (futex=futex@entry=0x55f8c2bbb160 <mutex1>, private=0) at lowlevellock.c:52
  4    Thread 0x7f74738df700 (LWP 329371) __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1a0 <mutex2>, private=0) at lowlevellock.c:52

```

查看线程号，发现这把锁是被线程3  **329373**拿到的

这个线程2在等mutex3，而mutex3是被329373拿到的，也就是线程3

下一步干嘛？ 应该去排查**329373**这个线程在干嘛

### 3.1、线程**329373的状态**

```cpp
(gdb) thread 3
[Switching to thread 3 (Thread 0x7f74728dd700 (LWP 329373))]
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb160 <mutex1>, private=0) at lowlevellock.c:52
52      lowlevellock.c: No such file or directory.
(gdb) bt
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb160 <mutex1>, private=0) at lowlevellock.c:52
#1  0x00007f7473e2d0a3 in __GI___pthread_mutex_lock (mutex=0x55f8c2bbb160 <mutex1>) at ../nptl/pthread_mutex_lock.c:80
#2  0x000055f8c2bb6888 in __gthread_mutex_lock (__mutex=0x55f8c2bbb160 <mutex1>) at /usr/include/x86_64-linux-gnu/c++/9/bits/gthr-default.h:749
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb160 <mutex1>) at /usr/include/c++/9/bits/std_mutex.h:100
#4  0x000055f8c2bb6a78 in std::lock_guard<std::mutex>::lock_guard (this=0x7f74728dcdf0, __m=...) at /usr/include/c++/9/bits/std_mutex.h:159
#5  0x000055f8c2bb663a in FuncC () at deadlock.cpp:37
#6  0x000055f8c2bb7658 in std::__invoke_impl<void, void (*)()> (__f=@0x55f8c4797158: 0x55f8c2bb65aa <FuncC()>) at /usr/include/c++/9/bits/invoke.h:60
#7  0x000055f8c2bb75f0 in std::__invoke<void (*)()> (__fn=@0x55f8c4797158: 0x55f8c2bb65aa <FuncC()>) at /usr/include/c++/9/bits/invoke.h:95
#8  0x000055f8c2bb7582 in std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul> (this=0x55f8c4797158) at /usr/include/c++/9/thread:244
#9  0x000055f8c2bb753f in std::thread::_Invoker<std::tuple<void (*)()> >::operator() (this=0x55f8c4797158) at /usr/include/c++/9/thread:251
#10 0x000055f8c2bb7510 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run (this=0x55f8c4797150) at /usr/include/c++/9/thread:195
#11 0x00007f7473d17cb4 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f7473e2a609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#13 0x00007f7473b53353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
(gdb) f 3
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb160 <mutex1>) at /usr/include/c++/9/bits/std_mutex.h:100
100           int __e = __gthread_mutex_lock(&_M_mutex);
(gdb) p mutex1
$2 = {
  <std::__mutex_base> = {
    _M_mutex = {
      __data = {
        __lock = 2,
        __count = 0,
        __owner = 329371,
        __nusers = 1,
        __kind = 0,
        __spins = 0,
        __elision = 0,
        __list = {
          __prev = 0x0,
          __next = 0x0
        }
      },
      __size = "\\002\\000\\000\\000\\000\\000\\000\\000\\233\\006\\005\\000\\001", '\\000' <repeats 26 times>,
      __align = 2
    }
  }, <No data fields>}

```

这个线程3在等mutex1，而mutex1是被329371拿到的，也就是线程4

### 3.2、线程**329371的状态**

```cpp
(gdb) thread 4
[Switching to thread 4 (Thread 0x7f74738df700 (LWP 329371))]
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1a0 <mutex2>, private=0) at lowlevellock.c:52
52      lowlevellock.c: No such file or directory.
(gdb) bt
#0  __lll_lock_wait (futex=futex@entry=0x55f8c2bbb1a0 <mutex2>, private=0) at lowlevellock.c:52
#1  0x00007f7473e2d0a3 in __GI___pthread_mutex_lock (mutex=0x55f8c2bbb1a0 <mutex2>) at ../nptl/pthread_mutex_lock.c:80
#2  0x000055f8c2bb6888 in __gthread_mutex_lock (__mutex=0x55f8c2bbb1a0 <mutex2>) at /usr/include/x86_64-linux-gnu/c++/9/bits/gthr-default.h:749
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb1a0 <mutex2>) at /usr/include/c++/9/bits/std_mutex.h:100
#4  0x000055f8c2bb6a78 in std::lock_guard<std::mutex>::lock_guard (this=0x7f74738dedf0, __m=...) at /usr/include/c++/9/bits/std_mutex.h:159
#5  0x000055f8c2bb63f8 in FuncA () at deadlock.cpp:19
#6  0x000055f8c2bb7658 in std::__invoke_impl<void, void (*)()> (__f=@0x55f8c4796eb8: 0x55f8c2bb6368 <FuncA()>) at /usr/include/c++/9/bits/invoke.h:60
#7  0x000055f8c2bb75f0 in std::__invoke<void (*)()> (__fn=@0x55f8c4796eb8: 0x55f8c2bb6368 <**FuncA()**>) at /usr/include/c++/9/bits/invoke.h:95
#8  0x000055f8c2bb7582 in std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul> (this=0x55f8c4796eb8) at /usr/include/c++/9/thread:244
#9  0x000055f8c2bb753f in std::thread::_Invoker<std::tuple<void (*)()> >::operator() (this=0x55f8c4796eb8) at /usr/include/c++/9/thread:251
#10 0x000055f8c2bb7510 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run (this=0x55f8c4796eb0) at /usr/include/c++/9/thread:195
#11 0x00007f7473d17cb4 in ?? () from /lib/x86_64-linux-gnu/libstdc++.so.6
#12 0x00007f7473e2a609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#13 0x00007f7473b53353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
(gdb) f 3
#3  0x000055f8c2bb69dc in std::mutex::lock (this=0x55f8c2bbb1a0 <mutex2>) at /usr/include/c++/9/bits/std_mutex.h:100
100           int __e = __gthread_mutex_lock(&_M_mutex);
(gdb) p mutex2
$3 = {
  <std::__mutex_base> = {
    _M_mutex = {
      __data = {
        __lock = 2,
        __count = 0,
        __owner = 329372,
        __nusers = 1,
        __kind = 0,
        __spins = 0,
        __elision = 0,
        __list = {
          __prev = 0x0,
          __next = 0x0
        }
      },
      __size = "\\002\\000\\000\\000\\000\\000\\000\\000\\234\\006\\005\\000\\001", '\\000' <repeats 26 times>,
      __align = 2
    }
  }, <No data fields>}

```

这个线程4在等mutex2，而mutex2是被329372拿到的，也就是线程2

### 3.3、综上所述

```cpp
这个线程2在等mutex3，而mutex3是被329373拿到的，也就是线程3
这个线程3在等mutex1，而mutex1是被329371拿到的，也就是线程4
这个线程4在等mutex2，而mutex2是被329372拿到的，也就是线程2

其中线程2 3 4分别对应thread B C A
```

由此得出结论，出现了环形死锁的情况：

![image.png](http://121.40.244.168/usr/uploads/2025/07/2906227173.png)

还是拿上面图举例：

* 线程A已经持有mutex1，想要申请mutex2，拿到mutex2后才可以释放mutex1和mutex2，而此时mutex2被线程B占用。
* 线程B已经持有mutex2，想要申请mutex3，拿到mutex3后才可以释放mutex2和mutex3，而此时mutex3被线程C占用。
* 线程C已经持有mutex3，想要申请mutex1，拿到mutex1后才可以释放mutex3和mutex1，而此时mutex1被线程A占用。

![image.png](http://121.40.244.168/usr/uploads/2025/07/376142519.png)

如图，三个线程形成了一个环，死锁检测就是检查线程之间是否有环的存在。A->B, B->C, C->A