Question

请考虑以下代码段：

#include <stdio.h>
#include <stdlib.h>
#include <readline/readline.h>

int main() {
    for (;;) {
        char *buf = readline(">>> ");
        if (!buf)
            break;

        free(buf);
    }
}

使用-lreadline进行编译，在valgrind下执行程序并输入一些行会导致巨大的内存泄漏，在我的系统上，valgrinds判决看起来像这样：

==7651== LEAK SUMMARY:
==7651==    definitely lost: 0 bytes in 0 blocks
==7651==    indirectly lost: 0 bytes in 0 blocks
==7651==      possibly lost: 0 bytes in 0 blocks
==7651==    still reachable: 213,455 bytes in 217 blocks
==7651==         suppressed: 0 bytes in 0 blocks

使用--show-leak-kinds=all运行会得到类似的结果（整个过程长数百行，我只显示开头）：

==7693== 5 bytes in 1 blocks are still reachable in loss record 1 of 57
==7693==    at 0x483777F: malloc (vg_replace_malloc.c:299)
==7693==    by 0x48CE409: xmalloc (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x48A72E6: rl_set_prompt (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x48A87E6: readline (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x10915C: main (in /home/.../a.out)
==7693== 
==7693== 5 bytes in 1 blocks are still reachable in loss record 2 of 57
==7693==    at 0x483777F: malloc (vg_replace_malloc.c:299)
==7693==    by 0x48CE409: xmalloc (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x48B95BC: ??? (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x48B9D25: rl_expand_prompt (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x48A7309: rl_set_prompt (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x48A87E6: readline (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x10915C: main (in /home/.../a.out)
==7693== 
==7693== 8 bytes in 1 blocks are still reachable in loss record 3 of 57
==7693==    at 0x483777F: malloc (vg_replace_malloc.c:299)
==7693==    by 0x496C49E: strdup (in /usr/lib/libc-2.28.so)
==7693==    by 0x4AEEDCD: _nc_trim_sgr0 (in /usr/lib/libncursesw.so.6.1)
==7693==    by 0x4AE7EA2: tgetent_sp (in /usr/lib/libncursesw.so.6.1)
==7693==    by 0x48C39BC: _rl_init_terminal_io (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x48A851C: rl_initialize (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x48A87EC: readline (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x10915C: main (in /home/.../a.out)

现在，尽管内存没有丢失，但readline并没有在程序退出之前释放大量内存，这对我来说似乎是完全荒谬的。我想念什么吗？我应该手动调用一些记录较差的清理功能吗？这是错误吗？这会在每个系统上发生吗？

Internet上似乎存在一些类似的问题，但是令我惊讶的是，即使在最简单的用例中，这种情况也会发生。

编辑：因为已经进行了很多讨论，所以我将澄清一下：bruno的答案当然是正确的，这不是传统意义上的内存泄漏，并且在几乎所有平台上都没有关系（我包括Linux标记，这是一个错误，我现在已将其删除），但我仍然想知道这是否真的有意或是否发生，因为只有在valgrind生成其统计信息之后才释放内存，并且是否有任何方法可以解决这个问题（或至少让valgrind忽略它，以免在我其余的代码中掩盖丢失的free调用）

Answer 1

GNU readline：大量内存泄漏

==7651== LEAK SUMMARY:
==7651==    definitely lost: 0 bytes in 0 blocks
==7651==    indirectly lost: 0 bytes in 0 blocks
==7651==      possibly lost: 0 bytes in 0 blocks

没有内存泄漏

==7651==    still reachable: 213,455 bytes in 217 blocks
==7651==         suppressed: 0 bytes in 0 blocks
...

可达内存不是内存泄漏

==7693== 5 bytes in 1 blocks are still reachable in loss record 1 of 57
==7693==    at 0x483777F: malloc (vg_replace_malloc.c:299)
==7693==    by 0x48CE409: xmalloc (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x48A72E6: rl_set_prompt (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x48A87E6: readline (in /usr/lib/libreadline.so.8.0)
==7693==    by 0x10915C: main (in /home/.../a.out)
...

getline 使用了内存并仍然引用它，不要忘记它管理着历史记录，可以通过调用void rl_clear_history (void)释放历史记录，在程序中添加该函数调用并重做测试

Function: void rl_clear_history (void)
  Clear the history list by deleting all of the entries, in the same
  manner as the History library's clear_history() function. This differs
  from clear_history because it frees private data Readline saves in the history list.

GNU readline：巨大的内存泄漏

1 个答案: