valgrind的DRD和Helgrind
处理一个bug时，使用strace 发现线程死锁。
但是发生死锁的位置上下文怎样快速知道呢？
使用gdb 调试 打出调用栈，只能知道运行到此处发生死锁。但是是哪里开始出现死锁呢？？
google搜索发现valgrind 的Helgrind可以解决
这个时候Helgrind就该出场了：valgrind --tool=helgrind ./nobady
Helgrind is a Valgrind tool for detecting synchronisation errors in C/C++ programs that use the POSIX threading primitives. The main abstractions in POSIX are: a set of threads sharing a common address space, thread creation, thread joining, thread exit, mutexes (locks), condition variables and barriers. Helgrind detects three types of errors: (1) misuses of the POSIX API, (2) potential deadlocks arising from lock ordering problems, and (3) data races.
http://epic-beta.kavli.tudelft.nl/share/doc/valgrind-3.8.1/html/hg-manual.html
http://www.it.uc3m.es/pbasanta/asng/course_notes/helgrind_tool_en.html
也就是说 Helgrind 可以解决 死锁、资源访问不安全等问题
所以问题也就很快解决了
gdb调试技巧：
disassemble 命令参考：blog