互斥类型的困惑
根据ISO/IEC 9899:2011标准第381页第7.26.4.2 The mtx_init function节，原文内容为：
The mtx_init function creates a mutex object with properties indicated by type, which must have one of the six values: mtx_plain for a simple non-recursive mutex, mtx_timed for a non-recursive mutex that supports timeout, mtx_plain | mtx_recursive for a simple recursive mutex, or mtx_timed | mtx_recursive for a recursive mutex that suports timeout.
于是问题就产生了，互斥类型究竟是四种类型还是六种类型？
根据WG14 Document: N1372(Threads for the C Standard Library)文档第7页The mtx_init function，原文内容为：
The function creates a mutex object with properties indicated by type,which must have one of the six values: • mtx_plain—for a simple non-recursive mutex • mtx_timed—for a non-recursive mutex that supports timeout • mtx_try—for a non-recursive mutex that supports test and return • mtx_plain | mtx_recursive—for a simple recursive mutex • mtx_timed | mtx_recursive—for a recursive mutex that suports timeout • mtx_try | mtx_recursive—for a recursive mutex that suports test and return
这里提到了互斥类型的六种形式。
ISO/IEC 9899:2011标准第377页第7.26.1 Introduction节中定义了枚举常量mtx_plain、mtx_recursive、mtx_timed；并未定义mtx_try。查阅资料也发现，普遍认为C11标准的互斥类型为四种。
结论：ISO/IEC 9899:2011标准中的互斥类型应为四种，即mtx_plain、mtx_timed、mtx_plain | mtx_recursive、mtx_timed | mtx_recursive；但在实现中也可能支持mtx_try、mtx_try | mtx_recursive类型，例如：Visual Studio。
ISO/IEC 9899:2018标准第292页第7.26.4.2 The mtx_init function节对该处作了修改，具体如下：
The mtx_init function creates a mutex object with properties indicated by type, which shall have one of these values: mtx_plain for a simple non-recursive mutex, mtx_timed for a non-recursive mutex that supports timeout, mtx_plain | mtx_recursive for a simple recursive mutex, or mtx_timed | mtx_recursive for a recursive mutex that suports timeout.