valgrind --trace-children =是報告儘管atexit清理泄漏

Question

我試圖避免Valgrind的誤報，但我吸了atexit()和fork()的組合，儘管使用--trace-children=yes。我的代碼：

#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) 

基礎上printf()輸出，它看起來像有沒有泄漏。我可以說服valgrind這個，或者我應該只是將其添加到我的valgrind抑制文件？

Answer 1

基於printf（）輸出，看起來沒有泄漏。我可以說服valgrind這個，或者我應該只是將其添加到我的valgrind抑制文件？

看來，valgrind是正確的。如果您將printf()輸出解釋爲表示沒有泄漏，那麼您不讚賞fork()的效果。

當您分娩一個孩子時，它會獲得其父母的地址空間的完整副本。這通常是通過寫入時複製頁面實現的，但它仍構成屬於該孩子的內存。在你的情況下，它包括一個動態分配數組arr的副本。

孩子通過調用_exit()退出，所以雖然它繼承了其父母的退出處理程序註冊，但在該過程中不會調用註冊的退出處理程序。你可以知道這是因爲你只看到cleanup()的輸出。因此，valgrind告訴你，屬於孩子的arr的副本永遠不會被釋放。儘管如此，將這稱爲內存泄漏有些迂腐。當程序終止時，所討論的內存仍然可以訪問，此時它會被系統回收。它只是不是明確終止前釋放。

Answer 2

您在子進程中使用_exit（）。按照_exit的手冊頁：

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

更改它退出（0）。它應該工作。