在SpiderMonkey的代码库中经常可以看到一个函数名前面定义了一个宏 JS_ALWAYS_INLINE，这个宏定义在js/src/jstypes.h中：

#define JS_ALWAYS_INLINE MOZ_ALWAYS_INLINE

而 MOZ_ALWAYS_INLINE 定义在mfbt/Attributes.h中：

/* * MOZ_ALWAYS_INLINE is a macro which expands to tell the compiler that the * method decorated with it must be inlined, even if the compiler thinks * otherwise. This is only a (much) stronger version of the MOZ_INLINE hint: * compilers are not guaranteed to respect it (although they’re much more likely * to do so). */ #if defined(DEBUG)

define MOZ_ALWAYS_INLINE MOZ_INLINE

#elif defined(_MSC_VER)

define MOZ_ALWAYS_INLINE __forceinline

#elif defined(__GNUC__)

define MOZ_ALWAYS_INLINE __attribute__((always_inline)) MOZ_INLINE

#else

define MOZ_ALWAYS_INLINE MOZ_INLINE

#endif

而这里的 MOZ_INLINE 也定义在mfbt/Attributes.h中：

 

/* * MOZ_INLINE is a macro which expands to tell the compiler that the method * decorated with it should be inlined. This macro is usable from C and C++ * code, even though C89 does not support the |inline| keyword. The compiler * may ignore this directive if it chooses. */ #if defined(__cplusplus)

define MOZ_INLINE inline

#elif defined(_MSC_VER)

define MOZ_INLINE __inline

#elif defined(__GNUC__)

define MOZ_INLINE __inline__

#else

define MOZ_INLINE inline

#endif

 

这个定义文件放在mfbt目录下，这个目录的全称是“Mozilla Framework Based on Templates (MFBT)”，作用在[1]中有解释：

The Mozilla Framework Based on Templates (“mfbt”) is the central repository for macros, functions, and data structures used throughout Mozilla code, including in the JavaScript engine.

[1]: https://developer.mozilla.org/en-US/docs/Mozilla/MFBT