valgrind/massif看不到从另一个线程完成的内存交易。

Question

在用Valgrind/massif分析内存使用时，我发现它似乎看不到从另一个线程完成的内存Deallocation，将其报告为泄漏。 这是一个证明：

#include <stdio.h>
#include <iostream>
#include <pthread.h>
#include <stdlib.h>

using namespace std;

struct my_struct
{
  pthread_mutex_t m_mutex;
  void* m_mem;
};

extern "C"
{
  void* my_allocation(void* p)
  {
    my_struct *ptr = (my_struct*)p;
    int error;
    if((error = pthread_mutex_lock(&ptr->m_mutex))) {
      cerr << "mutex lock failed in thread: " << error << endl;
    }
    else {
      ptr->m_mem = malloc(100);
      if((error = pthread_mutex_unlock(&ptr->m_mutex)))
        cerr << "mutex unlock failed in thread: " << error << endl;
    }

    return NULL;
  }

  void* my_deallocation(void* p)
  {
    my_struct *ptr = (my_struct*)p;
    int error;
    if((error = pthread_mutex_lock(&ptr->m_mutex))) {
      cerr << "mutex lock failed in thread: " << error << endl;
    }
    else {
      free(ptr->m_mem);
      ptr->m_mem = NULL;
      if((error = pthread_mutex_unlock(&ptr->m_mutex)))
        cerr << "mutex unlock failed in thread: " << error << endl;
    }

    return NULL;
  }
}

int main(int argc, char **argv)
{
  pthread_t alloc_thread;
  pthread_t dealloc_thread;
  my_struct value;
  value.m_mem = NULL;

  int error;
  if((error = pthread_mutex_init(&value.m_mutex, NULL))) {
    cerr << "Failed to initialize mutex: " << error << endl;
    return 1;
  }

  for(int i=0; i<300; ++i) {
    if((error = pthread_create(&alloc_thread, NULL, my_allocation, &value))) {
      cerr << "Failed to start allocation thread: " << error << endl;
      return 1;
    }

    if((error = pthread_join(alloc_thread, NULL))) {
      cerr << "Failed to join allocation thread: " << error << endl;
      return 1;
    }

    if((error = pthread_mutex_lock(&value.m_mutex))) {
      cerr << "mutex lock failed: " << error << endl;
    }
    else {
      if(!value.m_mem) {
        cerr << "Allocation thread failed to allocate the memory" << endl;
        return 1;
      }
      if((error = pthread_mutex_unlock(&value.m_mutex)))
        cerr << "mutex unlock failed: " << error << endl;
    }

    if((error = pthread_create(&dealloc_thread, NULL, my_deallocation, &value))) {
      cerr << "Failed to start deallocation thread: " << error << endl;
      return 1;
    }

    if((error = pthread_join(dealloc_thread, NULL))) {
      cerr << "Failed to join deallocation thread: " << error << endl;
      return 1;
    }

    if((error = pthread_mutex_lock(&value.m_mutex))) {
      cerr << "mutex lock failed: " << error << endl;
    }
    else {
      if(value.m_mem) {
        cerr << "Deallocation thread failed to deallocate the memory" << endl;
        return 1;
      }
      if((error = pthread_mutex_unlock(&value.m_mutex)))
        cerr << "mutex unlock failed: " << error << endl;
    }
  }

  if((error = pthread_mutex_destroy(&value.m_mutex))) {
    cerr << "Failed to destroy mutex: " << error << endl;
    return 1;
  }

  cout << "Done" << endl;
  return 0;
}

在Valgrind/massif下运行此程序后，我得到的报告似乎表明分配的内存为泄漏。

这是massif报告的片段：

--------------------------------------------------------------------------------
Command:            valgrind-threads
Massif arguments:   --heap=yes --pages-as-heap=yes --massif-out-file=/tmp/valgrind-threads.massif.31220.log
ms_print arguments: /tmp/valgrind-threads.massif.31220.log
--------------------------------------------------------------------------------

100.00% (197,083,136B) (page allocation syscalls) mmap/mremap/brk, --alloc-fns, etc.
->72.36% (142,610,432B) 0x7773FCA: mmap (in /usr/lib64/libc-2.17.so)
| ->68.10% (134,217,728B) 0x76FA2D0: new_heap (in /usr/lib64/libc-2.17.so)
| | ->68.10% (134,217,728B) 0x76FA8D3: arena_get2.isra.3 (in /usr/lib64/libc-2.17.so)
| |   ->68.10% (134,217,728B) 0x770077D: malloc (in /usr/lib64/libc-2.17.so)
| |     ->68.10% (134,217,728B) 0x40C194: my_allocation (valgrind-threads.cpp:24)
| |       ->68.10% (134,217,728B) 0x7466EA4: start_thread (in /usr/lib64/libpthread-2.17.so)
| |         ->68.10% (134,217,728B) 0x7779B0C: clone (in /usr/lib64/libc-2.17.so)
| |           
| ->04.26% (8,392,704B) 0x74677FC: pthread_create@@GLIBC_2.2.5 (in /usr/lib64/libpthread-2.17.so)
| | ->04.26% (8,392,704B) 0x40C384: main (valgrind-threads.cpp:64)
| |   
| ->00.00% (0B) in 1+ places, all below ms_print's threshold (01.00%)

valgrind版本是3.19。 用GCC 4.9.4在Red Hat Enterprise Linux服务器版本7.9（Maipo）上构建和运行。

我是错误地阅读报告，还是是valgrind/massif限制，还是我在代码中做错了什么？

Answer 1

正如它在另一个问题< /a>我发布了有关valgrind/massif未跟踪的TLS Deleclations：

如果我们使用-pages-as-as-heap，Valgrind/massif将报告每个线程Malloc Cache分配的GLIBC内存页面，至少在线程上的第一个分配时（有时在需要生长时可能会发生重新分配）。
这给人以分配的内存泄漏的印象。

如果没有运行 - 页面选项，则正确解释了交易。