为什么 valgrind 在一个简单的 OCaml 程序中会出现内存泄漏？

如何解决为什么 valgrind 在一个简单的 OCaml 程序中会出现内存泄漏？

let main =
  print_endline "Hello world"

这里是一个简单的OCaml程序^

当我用 ocamlc 编译，然后在 valgrind 中运行这个程序时：

==12457== Memcheck,a memory error detector
==12457== Copyright (C) 2002-2017,and GNU GPL'd,by Julian Seward et al.
==12457== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==12457== Command: ./a.out
==12457== 
Hello world
==12457== 
==12457== HEAP SUMMARY:
==12457==     in use at exit: 7,391,113 bytes in 30 blocks
==12457==   total heap usage: 56 allocs,26 frees,7,470,447 bytes allocated
==12457== 
==12457== 256 bytes in 1 blocks are definitely lost in loss record 15 of 27
==12457==    at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==12457==    by 0x11D6BC: caml_stat_alloc (in /usr/bin/ocamlrun)
==12457==    by 0x13627C: caml_executable_name (in /usr/bin/ocamlrun)
==12457==    by 0x13C5C4: caml_main (in /usr/bin/ocamlrun)
==12457==    by 0x11CDB1: main (in /usr/bin/ocamlrun)
==12457== 
==12457== 3,936,288 bytes in 1 blocks are possibly lost in loss record 27 of 27
==12457==    at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==12457==    by 0x11D601: caml_alloc_for_heap (in /usr/bin/ocamlrun)
==12457==    by 0x13EF42: caml_init_major_heap (in /usr/bin/ocamlrun)
==12457==    by 0x12EFF5: caml_init_gc (in /usr/bin/ocamlrun)
==12457==    by 0x13C43D: caml_main (in /usr/bin/ocamlrun)
==12457==    by 0x11CDB1: main (in /usr/bin/ocamlrun)
==12457== 
==12457== LEAK SUMMARY:
==12457==    definitely lost: 256 bytes in 1 blocks
==12457==    indirectly lost: 0 bytes in 0 blocks
==12457==      possibly lost: 3,288 bytes in 1 blocks
==12457==    still reachable: 3,454,569 bytes in 28 blocks
==12457==         suppressed: 0 bytes in 0 blocks
==12457== Reachable blocks (those to which a pointer was found) are not shown.
==12457== To see them,rerun with: --leak-check=full --show-leak-kinds=all
==12457== 
==12457== For lists of detected and suppressed errors,rerun with: -s
==12457== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)

当我用 ocamlopt 编译，然后在 valgrind 中运行这个程序时：

==12562== Memcheck,a memory error detector
==12562== Copyright (C) 2002-2017,by Julian Seward et al.
==12562== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==12562== Command: ./a.out
==12562== 
Hello world
==12562== 
==12562== HEAP SUMMARY:
==12562==     in use at exit: 7,080,897 bytes in 27 blocks
==12562==   total heap usage: 27 allocs,0 frees,897 bytes allocated
==12562== 
==12562== LEAK SUMMARY:
==12562==    definitely lost: 0 bytes in 0 blocks
==12562==    indirectly lost: 0 bytes in 0 blocks
==12562==      possibly lost: 3,288 bytes in 1 blocks
==12562==    still reachable: 3,144,609 bytes in 26 blocks
==12562==         suppressed: 0 bytes in 0 blocks
==12562== Rerun with --leak-check=full to see details of leaked memory
==12562== 
==12562== For lists of detected and suppressed errors,rerun with: -s
==12562== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

为什么用ocaml编译的程序会出现内存泄漏？这些只是假内存泄漏吗？我需要担心这个吗？

解决方法

我相信 OCaml GC 比不知道 OCaml 工作原理的外部工具更明智地了解哪些内存是可访问的。此类工具需要做出非常笼统的假设，而这些假设很容易出错。

几乎没有泄漏报告，只有“可能”的泄漏（无论这意味着什么）。您可以想象 OCaml 字节码运行时在启动时分配少量全局存储。在我看来，将其称为“内存泄漏”是不正确的。退出时释放内存是没有意义的，因为这只是不必要的工作。

本机运行时没有显示泄漏（使用 ocamlopt 编译）。所以似乎没有什么需要解释的。

总之，我不会担心这个。在内存检查器的输出中，它不是一个错误，而是一个耸人听闻的术语。如果这些是 C 程序，则可能更有理由担心。

（然而，在退出之前释放全局内存仍然没有意义。因此，通过这种分析，许多 C 程序会报告类似的虚假“泄漏”。）

,

字节码解释器正在“泄漏”一个包含可执行文件名称的 256 字节字符串。由于名称在程序的整个生命周期内都拥有，所以这并不重要。

而且由于“泄漏”发生在字节码解释器中，因此本机编译程序不会发生这种情况。

更普遍地使用 valgrind 对于垃圾收集语言（在编译器开发之外）并不是真正有用，因为垃圾收集器会吞噬所有内存。最好使用了解 GC 的内存分析器，例如 statmemprof。