秋梦无痕

from: http://blog.s135.com/post/419/

[文章作者：张宴 本文版本：v1.0 最后修改：2009-7-31 转载请注明出处：http://blog.s135.com]

Valgrind 是一款 Linux下（支持 x86、x86_64和ppc32）程序的内存调试工具，它可以对编译后的二进制程序进行内存使用监测（C语言中的malloc和free，以及C++中的new和delete），找出内存泄漏问题。

Valgrind 中包含的 Memcheck 工具可以检查以下的程序错误：
#使用未初始化的内存 (Use of uninitialised memory)
#使用已经释放了的内存 (Reading/writing memory after it has been free’d)
#使用超过malloc分配的内存空间 (Reading/writing off the end of malloc’d blocks)
#对堆栈的非法访问 (Reading/writing inappropriate areas on the stack)
#申请的空间是否有释放 (Memory leaks – where pointers to malloc’d blocks are lost forever)
#malloc/free/new/delete申请和释放内存的匹配(Mismatched use of malloc/new/new [] vs free/delete/delete [])
#src和dst的重叠(Overlapping src and dst pointers in memcpy() and related functions)
#重复free

1、编译安装 Valgrind：

wget http://valgrind.org/downloads/valgrind-3.4.1.tar.bz2
tar xvf valgrind-3.4.1.tar.bz2
cd valgrind-3.4.1/
./configure --prefix=/usr/local/webserver/valgrind
make
make install

2、使用示例：对“ls”程序进程检查，返回结果中的“definitely lost: 0 bytes in 0 blocks.”表示没有内存泄漏。

$ /usr/local/webserver/valgrind/bin/valgrind --tool=memcheck --leak-check=full ls /
==1157== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 5 from 1)
==1157== LEAK SUMMARY:
==1157== definitely lost: 0 bytes in 0 blocks.
==1157== possibly lost: 0 bytes in 0 blocks.
==1157== still reachable: 28,471 bytes in 36 blocks.
==1157== suppressed: 0 bytes in 0 blocks.
==1157== Reachable blocks (those to which a pointer was found) are not shown.
==1157== To see them, rerun with: --leak-check=full --show-reachable=yes

3、使用示例：对一个使用libevent库编写的“httptest”程序进程检查，返回结果中的“definitely lost: 255 bytes in 5 blocks.”表示发生内存泄漏。
$ /usr/local/webserver/valgrind/bin/valgrind --tool=memcheck --leak-check=full ./httptest
==1274== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 1005 from 2)
==1274== 255 bytes in 5 blocks are definitely lost in loss record 17 of 32
==1274== at 0x4A05FBB: malloc (vg_replace_malloc.c:207)
==1274== by 0x3C1D809BC6: evhttp_decode_uri (http.c:2105)
==1274== by 0x401C75: tcsql_handler (in /data0/tcsql/cankao/tcsql-0.1/tcsql)
==1274== by 0x3C1D80C88F: evhttp_get_body (http.c:1582)
==1274== by 0x3C1D8065F7: event_base_loop (event.c:392)
==1274== by 0x403E2F: main (in /data0/tcsql/cankao/tcsql-0.1/tcsql)
==1274==
==1274== LEAK SUMMARY:
==1274== definitely lost: 255 bytes in 5 blocks.
==1274== possibly lost: 0 bytes in 0 blocks.
==1274== still reachable: 402,036 bytes in 69 blocks.
==1274== suppressed: 0 bytes in 0 blocks.
==1274== Reachable blocks (those to which a pointer was found) are not shown.
==1274== To see them, rerun with: --leak-check=full --show-reachable=yes

　　检查 httptest程序，发现有一处“char *decode_uri = evhttp_decode_uri(evhttp_request_uri(req));”中的“decode_uri”没有被free，再程序处理完成后加上“free(decode_uri);”后，再使用Valgrind检查，结果已经是“definitely lost: 0 bytes in 0 blocks.”。