Question

我正在尝试使用Distinction between processes and threads in Linux

中的一个小程序

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <pthread.h>

void* threadMethod(void* arg)
{
    int intArg = (int) *((int*) arg);

    int32_t pid = getpid();
    uint64_t pti = pthread_self();

    printf("[Thread %d] getpid() = %d\n", intArg, pid);
    printf("[Thread %d] pthread_self() = %lu\n", intArg, pti);
}

int main()
{
    pthread_t threads[2];

    int thread1 = 1;

    if ((pthread_create(&threads[0], NULL, threadMethod, (void*) &thread1))
         != 0)
    {
        fprintf(stderr, "pthread_create: error\n");
        exit(EXIT_FAILURE);
    }

    int thread2 = 2;

    if ((pthread_create(&threads[1], NULL, threadMethod, (void*) &thread2))
         != 0)
    {
        fprintf(stderr, "pthread_create: error\n");
        exit(EXIT_FAILURE);
    }

    int32_t pid = getpid();
    uint64_t pti = pthread_self();

    printf("[Process] getpid() = %d\n", pid);
    printf("[Process] pthread_self() = %lu\n", pti);

    if ((pthread_join(threads[0], NULL)) != 0)
    {
        fprintf(stderr, "Could not join thread 1\n");
        exit(EXIT_FAILURE);
    }

    if ((pthread_join(threads[1], NULL)) != 0)
    {
        fprintf(stderr, "Could not join thread 2\n");
        exit(EXIT_FAILURE);
    }

    return 0;
}

在64位Lubuntu 18.04上，我通过帖子中的同一命令对其进行了编译：

$ gcc -pthread -o thread_test thread_test.c

我还尝试遵循该帖子所说的内容：

通过在gdb中使用调度程序锁定，我可以使程序及其线程保持活动状态，这样我就可以捕获到顶部

但是由于我对gdb并不熟悉，因此该程序无需中断即可运行完成（请参阅下文）。我也尝试通过break 43设置断点，但是gdb说No line 40 in the current file。我应该怎么做才能暂停执行，以便可以使用top或ps检查线程的pid和tgid？谢谢。

$ gdb thread_test
GNU gdb (Ubuntu 8.1-0ubuntu3) 8.1.0.20180409-git
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from thread_test...(no debugging symbols found)...done.
(gdb) set scheduler-locking
Requires an argument. Valid arguments are off, on, step, replay.
(gdb) set scheduler-locking on
Target 'exec' cannot support this command.
(gdb) run
Starting program: /tmp/test/pthreads/thread_test 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7ffff77c4700 (LWP 4711)]
[New Thread 0x7ffff6fc3700 (LWP 4712)]
[Thread 1] getpid() = 4707
[Thread 1] pthread_self() = 140737345505024
[Process] getpid() = 4707
[Process] pthread_self() = 140737353951040
[Thread 0x7ffff77c4700 (LWP 4711) exited]
[Thread 2] getpid() = 4707
[Thread 2] pthread_self() = 140737337112320
[Thread 0x7ffff6fc3700 (LWP 4712) exited]
[Inferior 1 (process 4707) exited normally]
(gdb)

Answer 1

您有两个问题：

您在构建程序时未调试信息（添加-g标志），并且
您正在尝试在程序启动之前set scheduler-locking on（不起作用）。

这应该有效：

 gcc -g -pthread -o thread_test thread_test.c
 gdb -q ./thread_test
 (gdb) start
 (gdb) set scheduler-locking on

但是，您必须格外小心-从这一点继续操作将使您的程序在pthread_join中阻塞，因为只有主线程将继续运行。

Answer 2

以下是在发布的代码中使用gdb来暂停所有内容的示例：

注意：它被编译为通过以下方式查找/修复编译问题：

gcc -ggdb -Wall -Wextra -Wconversion -pedantic -std=gnu11 -c untitled.c

此文件最终通过以下方式进行编译/链接：

gcc -ggdb -Wall -o untitled untitled.c   -lpthread

然后使用调试器：gdb，从而显示我的输入和gdb的输出：

$ gdb untitled
GNU gdb (Ubuntu 8.1-0ubuntu3) 8.1.0.20180409-git
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from untitled...done.
(gdb) br main
Breakpoint 1 at 0x9a5: file untitled.c, line 20.
(gdb) br threadMethod
Breakpoint 2 at 0x946: file untitled.c, line 9.
(gdb) r
Starting program: /home/richard/Documents/forum/untitled 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Breakpoint 1, main () at untitled.c:20
20  {
(gdb) c
Continuing.
[New Thread 0x7ffff77c4700 (LWP 8645)]
[New Thread 0x7ffff6fc3700 (LWP 8646)]
[Switching to Thread 0x7ffff77c4700 (LWP 8645)]

Thread 2 "untitled" hit Breakpoint 2, threadMethod (arg=0x7fffffffdf4c)
    at untitled.c:9
9       int intArg = (int) *((int*) arg);
(gdb)

然后，您可以（在另一个终端窗口中）使用ps等来显示信息。但是，线程函数将输出（您可能会感兴趣的信息到stdout。

或者您可以（在gdb中输入以下命令：

(gdb) c
[Process] getpid() = 8641
[Process] pthread_self() = 140737353992000
[Switching to Thread 0x7ffff6fc3700 (LWP 8646)]

Thread 3 "untitled" hit Breakpoint 2, threadMethod (arg=0x7fffffffdf50)
at untitled.c:9
9       int intArg = (int) *((int*) arg);
(gdb) c
....
[Thread 1] getpid() = 8641
[Thread 1] pthread_self() = 140737345505024
....
[Thread 2] getpid() = 8641
[Thread 2] pthread_self() = 140737337112320

如何暂停pthread程序的执行，以便可以检查线程的pid和tgid？

2 个答案: