Question

我正在尝试编写一些单元测试来检查内存是否已被释放 - 以检查内存泄漏 - 在OS X（10.9 Mavericks）上。我正在尝试使用mstats（）和malloc_zone_statistics（）来发现我需要的信息。但似乎他们没有显示内存被释放（参见下面的示例输出......在调用free（）后内存使用率不会改变）

我怀疑这与堆管理有关，而不是与这些功能有问题。我认为堆不会释放释放的内存，也许它可以重用它而不需要删除和添加块的开销。

有没有办法告诉堆释放释放的块？为了更积极或关闭优化？
我是不是错误地使用了mstats（）或malloc_zone_statistics（）？

更新：找到的解决方案......在底部提供......

以下是我的测试程序的输出：

=== Initial conditions ===
in use: 23584, allocated: 9437184, blocks: 320
SimpleLeaker(19583,0x7fff7b2a2310) malloc: total: 9437184, used: 23584, free: 9413600
=== Before allocation ===
in use: 23584, allocated: 9437184, blocks: 320
SimpleLeaker(19583,0x7fff7b2a2310) malloc: total: 9437184, used: 23584, free: 9413600
=== After malloc ===
in use: 33824, allocated: 9437184, blocks: 321
SimpleLeaker(19583,0x7fff7b2a2310) malloc: total: 9437184, used: 33824, free: 9403360
=== After free ===
in use: 33824, allocated: 9437184, blocks: 321
SimpleLeaker(19583,0x7fff7b2a2310) malloc: total: 9437184, used: 33824, free: 9403360

以下是该程序的C代码：

    #include <stdio.h>
    #include <unistd.h>
    #include <stdlib.h>
    #include <pthread.h>
    #include <mach/mach.h>
    #include <mach/task.h>
    #include <malloc/malloc.h>
    #include <errno.h>


    /** heapStats()
     * print the output from the mstats() function: total heap bytes, 
     * used bytes, and free bytes.
     */
    void heapStats()
    {
      struct mstats ms = mstats();
      malloc_printf(
        "total: %d, used: %d, free: %d\n",
        ms.bytes_total,
        ms.bytes_used,
        ms.bytes_free);
    }

    /* heapInUse()
     * Gather the heap usage metrics from each zone, using 
     * malloc_zone_statistics().
     */
    void heapInUse(
      size_t * bytesInUse,
      size_t * blocksInUse,
      size_t * sizeAllocated)
    {
      *bytesInUse = 0;
      *blocksInUse = 0;
      *sizeAllocated = 0;
      unsigned int i;
      vm_address_t * zones;
      unsigned int count;
      kern_return_t rc =
      malloc_get_all_zones(mach_task_self(), 0, &zones, &count);
      if (0 != rc)
      {
        fprintf(stderr, "rc was %d\n", rc);
      }
      for (i = 0; i < count; ++i)
      {
        malloc_zone_t * zone = (malloc_zone_t*)zones[i];
        char const * name = malloc_get_zone_name(zone);
        if (NULL == name)
        {
          continue;
        }
        malloc_statistics_t stats;
        stats.blocks_in_use = 0;
        stats.size_in_use = 0;
        stats.max_size_in_use = 0;
        stats.size_allocated = 0;
        malloc_zone_statistics(zone, &stats);
        *bytesInUse += stats.size_in_use;
        *blocksInUse += stats.blocks_in_use;
        *sizeAllocated += stats.size_allocated;
      }
    }

    /** main()
     * entry point
     */
    int main(int argc, const char * argv[])
    {
      char * buff = (char *)0;
      size_t bytesInUse = 0;
      size_t blocksInUse = 0;
      size_t sizeAllocated = 0;
      printf("=== Initial conditions ===\n");
      heapInUse(&bytesInUse, &blocksInUse, &sizeAllocated);
      printf(
        "in use: %zu, allocated: %zu, blocks: %zu\n",
        bytesInUse, sizeAllocated, blocksInUse);
      heapStats();

      printf("=== Before allocation ===\n");
      heapInUse(&bytesInUse, &blocksInUse, &sizeAllocated);
      printf(
        "in use: %zu, allocated: %zu, blocks: %zu\n",
        bytesInUse, sizeAllocated, blocksInUse);
      heapStats();

      // Allocate the buffer
      //
      buff = (char *)malloc(10000);
      printf("=== After malloc ===\n");
      heapInUse(&bytesInUse, &blocksInUse, &sizeAllocated);
      printf(
        "in use: %zu, allocated: %zu, blocks: %zu\n",
        bytesInUse, sizeAllocated, blocksInUse);
      heapStats();

      // Free the buffer
      //
      if (NULL != buff)
      {
        free(buff);
        buff = NULL;
      }
      printf("=== After free ===\n");
      heapInUse(&bytesInUse, &blocksInUse, &sizeAllocated);
      printf(
        "in use: %zu, allocated: %zu, blocks: %zu\n",
        bytesInUse, sizeAllocated, blocksInUse);
      heapStats();

      // Get out
      //
      return 0;
    }

解决方案：感谢John Zwinck的回复，我仔细查看了malloc/malloc.h并找到了一个方法malloc_zone_pressure_relief()，我可以使用它来强制堆释放未使用的字节，以便我可以获得准确的指标。

所以我添加了这个方法：

void freeAsMuchAsPossible()
{
  vm_address_t * zones;
  unsigned int count;
  unsigned int i;

  kern_return_t rc =
    malloc_get_all_zones(mach_task_self(), 0, &zones, &count);
  if (0 != rc)
  {
    fprintf(stderr, "rc was %d\n", rc);
  }
  for (i = 0; i < count; ++i)
  {
    malloc_zone_t * zone = (malloc_zone_t*)zones[i];
    char const * name = malloc_get_zone_name(zone);
    if (NULL == name)
    {
      continue;
    }
    malloc_zone_pressure_relief(zone, 0);
  }
}

并在每次调用heapInUse()之前调用它，如下所示：

printf("=== Before allocation ===\n");
freeAsMuchAsPossible();
heapInUse(&bytesInUse, &blocksInUse, &sizeAllocated);
printf(
  "in use: %zu, allocated: %zu, blocks: %zu\n",
  bytesInUse, sizeAllocated, blocksInUse);
heapStats();

现在我得到了预期和有用的结果，例如：

=== Initial conditions ===
in use: 23584, allocated: 9437184, blocks: 4294966976
SimpleLeaker(22142,0x7fff7b2a2310) malloc: total: 9437184, used: 23584, free: 9413600
=== Before allocation ===
in use: 23584, allocated: 9437184, blocks: 4294966976
SimpleLeaker(22142,0x7fff7b2a2310) malloc: total: 9437184, used: 23584, free: 9413600
=== After malloc ===
in use: 33824, allocated: 9437184, blocks: 4294966967
SimpleLeaker(22142,0x7fff7b2a2310) malloc: total: 9437184, used: 33824, free: 9403360
=== After free ===
in use: 23584, allocated: 9437184, blocks: 4294966966
SimpleLeaker(22142,0x7fff7b2a2310) malloc: total: 9437184, used: 23584, free: 9413600

使用这种技术，我可以编写检查内存泄漏的单元测试。很好。

Answer 1

在OS X上，从10.7开始，我们可以使用malloc_zone_pressure_relief()强制堆释放未使用的字节。我已用解决方案更新了我的问题。

感谢John Zwinck的回复，促使我再次密切关注malloc.h，在那里我发现了这种方法。

Answer 2

你可能是对的：每次调用free（）时，分配器都不会将内存释放回操作系统。但您可以使用mallopt()更改此设置。尝试将M_MMAP_THRESHOLD设置为0.这将使每个单独的分配独立。您可能不希望将其用于生产，但是对于测试它可能会对您有所帮助。

Answer 3

我建议您查看OSX leaks工具以查找程序中的内存泄漏。可在此处找到介绍性文章：leaks documentation at Mac Developer Library。您可以man leaks了解更多详情。另外，仅针对您的问题1，您可以使用libgmalloc。请man libgmalloc了解详情。此外，这些手册页还包含指向malloc_history等其他工具的链接，您可能会发现这些工具对您的目的有用和/或更快。

为什么mstats和malloc_zone_statistics在免费后没有显示恢复的内存？

3 个答案: