Question

我试图避免使用valgrind进行误报，但我使用atexit()和fork()的组合很糟糕，尽管使用了--trace-children=yes。我的代码：

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

static int * arr;

static void cleanup() {
    free(arr);
    printf("free arr as: %p\n", (void *)arr);
}

int main()
{
    arr = malloc(16 * sizeof(int));
    printf("allocated arr as: %p\n", (void *)arr);
    atexit(cleanup);

    pid_t pid = fork();
    if (pid == -1) {
        exit(1);
    } else if (pid == 0) {
        // child
        _exit(0);
    } else {
        // parent
        exit(0);
    }
}

命令行：

$ clang -Weverything leak.c 
$ valgrind --trace-children=yes ./a.out 
==3287== Memcheck, a memory error detector
==3287== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==3287== Using Valgrind-3.12.0 and LibVEX; rerun with -h for copyright info
==3287== Command: ./a.out
==3287== 
allocated arr as: 0x5202040
free arr as: 0x5202040
==3288== 
==3288== HEAP SUMMARY:
==3288==     in use at exit: 64 bytes in 1 blocks
==3288==   total heap usage: 2 allocs, 1 frees, 1,088 bytes allocated
==3288== 
==3288== LEAK SUMMARY:
==3288==    definitely lost: 0 bytes in 0 blocks
==3288==    indirectly lost: 0 bytes in 0 blocks
==3288==      possibly lost: 0 bytes in 0 blocks
==3288==    still reachable: 64 bytes in 1 blocks
==3288==         suppressed: 0 bytes in 0 blocks
==3288== Rerun with --leak-check=full to see details of leaked memory
==3288== 
==3288== For counts of detected and suppressed errors, rerun with: -v
==3288== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
==3287== 
==3287== HEAP SUMMARY:
==3287==     in use at exit: 0 bytes in 0 blocks
==3287==   total heap usage: 2 allocs, 2 frees, 1,088 bytes allocated
==3287== 
==3287== All heap blocks were freed -- no leaks are possible
==3287== 
==3287== For counts of detected and suppressed errors, rerun with: -v
==3287== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

根据printf()输出，看起来没有泄漏。我可以说服valgrind这个，还是我应该把它添加到我的valgrind抑制文件中？

Answer 1

基于printf（）输出，看起来没有泄漏。我可以说服valgrind这个，还是我应该把它添加到我的valgrind抑制文件中？

看来valgrind是对的。如果您将printf()输出解释为表示没有泄漏，那么您就不会意识到fork()的效果。

当你分叉一个孩子时，它会获得其父母地址空间的完整副本。这通常通过写时复制页面实现，但它仍构成属于子节点的内存。在您的情况下，它包括动态分配的数组arr的副本。

子进程通过调用_exit()退出，因此虽然它继承了父进程的退出处理程序注册，但在该进程中不会调用已注册的退出处理程序。您可以这样说，因为您只看到cleanup()的输出一次。因此，valgrind告诉你，从未释放属于孩子的arr副本。

但是，将这称为内存泄漏有点迂腐。当程序终止时，仍然可以访问有问题的内存，此时它将被系统回收。它只是在终止之前没有显式释放。

Answer 2

您正在子进程中使用_exit（）。根据_exit的手册页：

The function _exit() is like exit(3), but does not call any functions registered with atexit(3) or on_exit(3).

将其更改为退出（0）。它应该工作。

valgrind --trace-children = yes报告泄漏，尽管atexit清理

2 个答案: