mutex compare latch

oracle10g引入了mutexes的概念
mutexes和latch有部分相似處
latch 和 mutexes在機制上都是一個序列概念，但是mutex在使用上比latch更加輕量級別
簡單理解
latch可以保護多個物件，當要訪問latch保護的物件時，latch本身也有可能成為一個爭用的物件
mutexes相對來說處理比較靈活，在訪問對應物件時，mutexes會衍生一個新的mutex針對要保護的物件
多個session可以共享的使用一個mutex(Shared),單個session也可以獨佔的使用一個mutex(eXclusive)

In 10.2, the only client of mutexes is kks (Kernel Kompile Shared)
i.e. the shared cursor component of the library cache.
In future releases, other clients may also start using mutexes

·In 10.2.0.1, the mutex code path for pin replacement is only activated
when _kks_use_mutex_pin is set to true (in 10.2.0.2+, this is the default).
When this code path is in effect, library cache pins are not used,
and so the 'library cache pin*' related wait events will not be seen[@more@]