使用fork()计算接收到的命令行参数的总和时出错

Question

我试图根据从命令行接收到的一组数字来计算和，并使用一个名为worker的配套程序来完成计算。如果接收到的数字数量是奇数，它将对数字的数量添加一个零，使集合成为偶数。

这是一个可以理解的程序流程(归功于Alok)：

一个例子将使这一点更加明确：

假设您想要添加7个数字:1 2 3 4 5 6 7

1 2 3 4 5 6 7

1. input =1 2 3 4 5 6 7 0
2. n = len(input) =8
3. m = n/2 =4
4. output =0 0 0
5. 我们叉4进程，第一进程得到1 2，第二进程得到3 4，…<代码>H 210<代码>H 1114个进程返回3，7，11，7，7。
6. 输出有4个元素，因此我们为新输入分配4+1 =5个元素的空间。
7. set input =3 7 11 7 0
8. n = len(input) =5
9. m = n/2 =2
10. output =0

H 123我们分叉2个进程，首先得到3 7，第2得到11 7<代码>H 224>H 1252个进程返回10，18，这是我们分配给输出的。

1. 输出有2个元素，因此我们为新输入分配2+1 =3个元素的空间。
2. set input = 10 18 0
3. n = len(input) =3
4. m = n/2 =1
5. output =

H 137我们叉一个进程，得到10 18 <>H 238>H 139进程返回28，分配给输出。

1. 输出有一个元素，所以我们完成了。

尽管在这组特定的数字中，我得到了：

Process ID: 15195 
Sum of 1 and 2 is 3 

Process ID: 15196 
Sum of 3 and 4 is 7 

Process ID: 15197 
Sum of 5 and 6 is 11 

Process ID: 15198 
Sum of 7 and 0 is 7 

*** glibc detected *** ./coordinator: free(): invalid next size (fast): 0x080ec048 ***

后面是堆错误列表。

我认为我没有正确地重新分配指针的大小，在第一次调用next_step()之后，我试图将旧的输出重定向到新的输入。因此，它试图将数据放入内存中没有空间的部分。

更新：

@诺曼

这是我收到的输出：

==3585== Memcheck, a memory error detector
==3585== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==3585== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info
==3585== Command: ./coordinator 1 2 3 4
==3585== 
calc: 2:
input[0]: 1
input[1]: 2
input[2]: 3
input[3]: 4
==3585== Use of uninitialised value of size 4
==3585==    at 0x4076186: ??? (in /lib/tls/i686/cmov/libc-2.10.1.so)
==3585==    by 0x4079A81: vfprintf (in /lib/tls/i686/cmov/libc-2.10.1.so)
==3585==    by 0x4080F7F: printf (in /lib/tls/i686/cmov/libc-2.10.1.so)
==3585==    by 0x8048833: main (in /home/bryan/cpp/coordinator)
==3585== 
==3585== Conditional jump or move depends on uninitialised value(s)
==3585==    at 0x407618E: ??? (in /lib/tls/i686/cmov/libc-2.10.1.so)
==3585==    by 0x4079A81: vfprintf (in /lib/tls/i686/cmov/libc-2.10.1.so)
==3585==    by 0x4080F7F: printf (in /lib/tls/i686/cmov/libc-2.10.1.so)
==3585==    by 0x8048833: main (in /home/bryan/cpp/coordinator)
==3585== 
==3585== Conditional jump or move depends on uninitialised value(s)
==3585==    at 0x4077877: vfprintf (in /lib/tls/i686/cmov/libc-2.10.1.so)
==3585==    by 0x4080F7F: printf (in /lib/tls/i686/cmov/libc-2.10.1.so)
==3585==    by 0x8048833: main (in /home/bryan/cpp/coordinator)
==3585== 
==3585== Conditional jump or move depends on uninitialised value(s)
==3585==    at 0x407789B: vfprintf (in /lib/tls/i686/cmov/libc-2.10.1.so)
==3585==    by 0x4080F7F: printf (in /lib/tls/i686/cmov/libc-2.10.1.so)
==3585==    by 0x8048833: main (in /home/bryan/cpp/coordinator)
==3585== 
input[4]: 0
==3586== Memcheck, a memory error detector
==3586== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==3586== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info
==3586== Command: ./worker 1 2
==3586== 
Process ID: 3586 
Sum of 1 and 2 is 3 

==3586== 
==3586== HEAP SUMMARY:
==3586==     in use at exit: 0 bytes in 0 blocks
==3586==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==3586== 
==3586== All heap blocks were freed -- no leaks are possible
==3586== 
==3586== For counts of detected and suppressed errors, rerun with: -v
==3586== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 11 from 6)
==3587== Memcheck, a memory error detector
==3587== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==3587== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info
==3587== Command: ./worker 3 4
==3587== 
Process ID: 3587 
Sum of 3 and 4 is 7 

==3587== 
==3587== HEAP SUMMARY:
==3587==     in use at exit: 0 bytes in 0 blocks
==3587==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==3587== 
==3587== All heap blocks were freed -- no leaks are possible
==3587== 
==3587== For counts of detected and suppressed errors, rerun with: -v
==3587== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 11 from 6)
==3585== Invalid write of size 4
==3585==    at 0x8048A3A: main (in /home/bryan/cpp/coordinator)
==3585==  Address 0x417f0b4 is 8 bytes after a block of size 4 alloc'd
==3585==    at 0x4024C6C: malloc (vg_replace_malloc.c:195)
==3585==    by 0x4024CF6: realloc (vg_replace_malloc.c:476)
==3585==    by 0x8048A25: main (in /home/bryan/cpp/coordinator)
==3585== 
==3588== Memcheck, a memory error detector
==3588== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==3588== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info
==3588== Command: ./worker 3 7
==3588== 
Process ID: 3588 
Sum of 3 and 7 is 10 

==3588== 
==3588== HEAP SUMMARY:
==3588==     in use at exit: 0 bytes in 0 blocks
==3588==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==3588== 
==3588== All heap blocks were freed -- no leaks are possible
==3588== 
==3588== For counts of detected and suppressed errors, rerun with: -v
==3588== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 11 from 6)
==3585== Invalid read of size 4
==3585==    at 0x8048AB5: main (in /home/bryan/cpp/coordinator)
==3585==  Address 0x417f0e0 is 0 bytes after a block of size 0 alloc'd
==3585==    at 0x4024C6C: malloc (vg_replace_malloc.c:195)
==3585==    by 0x4024CF6: realloc (vg_replace_malloc.c:476)
==3585==    by 0x8048A77: main (in /home/bryan/cpp/coordinator)
==3585== 
The final sum is: 0==3585== 
==3585== HEAP SUMMARY:
==3585==     in use at exit: 28 bytes in 2 blocks
==3585==   total heap usage: 4 allocs, 2 frees, 32 bytes allocated
==3585== 
==3585== LEAK SUMMARY:
==3585==    definitely lost: 8 bytes in 1 blocks
==3585==    indirectly lost: 0 bytes in 0 blocks
==3585==      possibly lost: 20 bytes in 1 blocks
==3585==    still reachable: 0 bytes in 0 blocks
==3585==         suppressed: 0 bytes in 0 blocks
==3585== Rerun with --leak-check=full to see details of leaked memory
==3585== 
==3585== For counts of detected and suppressed errors, rerun with: -v
==3585== Use --track-origins=yes to see where uninitialised values come from
==3585== ERROR SUMMARY: 6 errors from 6 contexts (suppressed: 11 from 6)

Answer 1

您应该考虑编写一个函数，我们称它为step_once()，它将使用带有n数字的input，并使用m = n/2元素写入相应的output。上面的n是输入数字+ 1的数目，input的最后一个元素等于0。

在您的驱动程序函数中，假设是main()：如果output包含一个数字，那么您就完成了。否则，重新分配input以包含n_new = m+1元素，重新分配output以包含m_new = n_new/2元素，并再次调用函数step_once()。你一直这么做直到你得到一个号码：

function next_step(input, output, n, m):
    n := number of input numbers # this is 1 greater than
                                 # the number of numbers being summed
    m := n / 2 # C division
    n_children := m
    i := 0
    while i < m:
        fork worker with input[2*i] and input[2*i+1]
        get result in output[i]
        i := i + 1

function main:
    set n := length(input) + 1
    set m := n/2
    allocate memory for input # n+1 elements, last = 0
    allocate memory for output # m elements
    set values in input
    while True:
        next_step(input, output, n, m)
        if length or output == 1:
             done, return
        else:
            set n := length(output) + 1
            set m := n/2
            allocate space for new_input # n elements
            set new_input := output + [0]
            free input and output
            set input := new_input
            allocate memory for output # m elements

其优点是可以测试next_step()函数以确保其工作正常，从而使调试更容易。

一个例子将使这一点更加明确：

假设您想要添加7个数字:1 2 3 4 5 6 7

1. input =1 2 3 4 5 6 7 0
2. n = len(input) = 8
3. m = n/2 = 4
4. output =0 0 0
5. 因此，我们为新的input.
6. set input =3 7 11 7 0
7. n = len(input) = n/2 = 2
8. output =0
9. 为4+1 =5元素分配了空间--我们分叉了2个进程，第一个是37个，第二个是117个
10. ，两个进程返回10，18个，指定给output.
11. output有2个元素，因此，我们为新的input.
12. set input =1018 0
13. n = len(input) = 3
14. m = n/2 = 1
15. output =
16. 分配2+1 =3元素的空间。我们叉一个进程，得到1018
17. ，进程返回28，分配给output.
18. output有1个元素，所以就完成了。

Answer 2

如果您想要更改指针，请尝试此操作。

空ChangePointers(int **输入，int **输出)

和

ChangePointers(&input &output)；

Answer 3

雷，如果不看到更多关于错误的细节，就很难知道出了什么问题。如果如我所怀疑的那样，这些都是运行时错误，那么您能在valgrind下运行代码吗？valgrind在定位内存错误方面非常有效；在您的应用程序中，您需要

valgrind --trace-children=yes ./coordinator 1 2 3 4

编辑：好的，我们可以看到(a)将一些错误传递给printf (如果使用-g编译，您将得到确切的行号)，并且调用realloc，而不是在从malloc返回的指针上调用realloc。也许你做过一些指针运算？

在没有看到代码的情况下，我不能说更多的话，但我希望您能找到更有帮助的方法。