Figure 3-15. First part of the pseudocode for when a process asks for a mutex. This figure contains the main Get_Mutex along with the supporting Mutex_Wait and Spin_Get functions.

Figure 3-16. Second part of the pseudocode for when a process asks for a mutex. The Fast_Get function is shown, along with the shared and exclusive mode request details.

The mutex Fast_Get function objective is the same as the latch Fast_Get function, but since mutexes are being used, the Fast_Get function can make use of the built-in and extremely quick mutex capabilities. Figure 3-17 illustrates a model of a mutex and its memory structure. If you look closely at Figure 3-17, you can see the mutex has been defined as part of the memory structure MS1. The memory structure contains two mutex variables: the holder identifier and the reference count. If an Oracle session is holding the mutex exclusively or is in the middle of running the Fast_Get function, the holder identifier contains its session identifier (v$session.sid).