http://hi.baidu.com/happynwt/blog/item/1c381f46fd617d0d6a63e512.html
因爲 PTHREAD_MUTEX_RECURSIVE 變量只是 POSIX 說明應該支持的變量，但是很多版本的 linux 並沒有定義此變量，它們只有 PTHREAD_MUTEX_RECURSIVE_NP (the np stands for non-portable)，但是兩者意義是相同的。
因此，需要用宏定義解決這個問題，#define *** ***便可解決此問題。
PTHREAD_MUTEX_RECURSIVE is what posix says should be supported, but some versions of glibc have only PTHREAD_MUTEX_RECURSIVE_NP (the np stands for non-portable), when they have the same meaning.