打印或检查 GDB 中的信号量计数值

Question

我正在尝试使用 ACE Semaphore 库来实现线程池。它不提供像 Posix 信号量中的 sem_getvalue 这样的任何 API。我需要调试一些行为不符合预期的流程。我可以检查 GDB 中的信号量吗？我正在使用 Centos 作为操作系统。

我使用提供计数 0 和 10 的默认构造函数初始化了两个信号量。我在类中将它们声明为静态，并在 cpp 文件中将其初始化为

DP_Semaphore ThreadPool::availableThreads(10);
DP_Semaphore ThreadPool::availableWork(0);

但是当我使用print 命令在 GDB 中打印信号量时，我得到了类似的输出

(gdb) p this->availableWork
$7 = {
  sema = {
    semaphore_ = {
      sema_ = 0x6fe5a0,
      name_ = 0x0
    },
    removed_ = false
  }
}
(gdb) p this->availableThreads
$8 = {
  sema = {
    semaphore_ = {
      sema_ = 0x6fe570,
      name_ = 0x0
    },
    removed_ = false
  }
}

这里有什么工具可以帮助我，或者我应该切换到 Posix 线程并重新编写我的所有代码。

编辑：根据@timrau 的要求，调用this->availableWork->dump()的输出

(gdb) p this->availableWork.dump()
[Switching to Thread 0x2aaaae97e940 (LWP 28609)]
The program stopped in another thread while making a function call from GDB.
Evaluation of the expression containing the function
(DP_Semaphore::dump()) will be abandoned.
When the function is done executing, GDB will silently stop.
(gdb) call this->availableWork.dump()
[Switching to Thread 0x2aaaaf37f940 (LWP 28612)]
The program stopped in another thread while making a function call from GDB.
Evaluation of the expression containing the function
(DP_Semaphore::dump()) will be abandoned.
When the function is done executing, GDB will silently stop.
(gdb) info threads
[New Thread 0x2aaaafd80940 (LWP 28613)]
  6 Thread 0x2aaaafd80940 (LWP 28613)  0x00002aaaac10a61e in __lll_lock_wait_private ()
   from /lib64/libpthread.so.0
* 5 Thread 0x2aaaaf37f940 (LWP 28612)  ThreadPool::fetchWork (this=0x78fef0, worker=0x2aaaaf37f038)
    at ../../CallManager/src/DP_CallControlTask.cpp:1043
  4 Thread 0x2aaaae97e940 (LWP 28609)  DP_Semaphore::dump (this=0x6e1460) at ../../Common/src/DP_Semaphore.cpp:21
  2 Thread 0x2aaaad57c940 (LWP 28607)  0x00002aaaabe01ff3 in __find_specmb () from /lib64/libc.so.6
  1 Thread 0x2aaaacb7b070 (LWP 28604)  0x00002aaaac1027c0 in __nptl_create_event () from /lib64/libpthread.so.0
(gdb)

Answer 1

sema.semaphore_.sema_ 在您的代码中看起来像一个指针。尝试在 ACE 标头中找到它的类型，然后将其转换为类型并打印：

(gdb) p *((sem_t)0x6fe570)

更新：尝试将您发布的结构中的地址转换为 sem_t。如果你使用 linux，ACE 应该使用 posix 信号量，所以类型 sem_t 必须对 gdb 可见。