Mutex Probes

Mutex Probes
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Mutexes enforce mutual exclusion to critical sections. When a thread attempts to acquire a mutex held by another thread using mutex_lock(3C) or pthread_mutex_lock(3C), it will determine if the owning thread is running on a different CPU. If it is, the acquiring thread will spin for a short while waiting for the mutex to become available. If the owner is not executing on another CPU, the acquiring thread will block.

The four plockstat probes pertaining to mutexes are listed in Table 31–1. For each probe, arg0 contains a pointer to the mutex_t or pthread_mutex_t structure (these are identical types) that represents the mutex.

Table 31.1. Mutex Probes

`mutex-acquire`	Hold event probe that fires immediately after a mutex is acquired. `arg1` contains a boolean value that indicates whether the acquisition was recursive on a recursive mutex. `arg2` indicates the number of iterations that the acquiring thread spent spinning on this mutex. `arg2` will be non-zero only if the `mutex-spin` probe fired on this mutex acquisition.
`mutex-block`	Contention event probe that fires before a thread blocks on a held mutex. Both `mutex-block` and `mutex-spin` might fire for a single lock acquisition.
`mutex-spin`	Contention event probe that fires before a thread begins spinning on a held mutex. Both `mutex-block` and `mutex-spin` might fire for a single lock acquisition.
`mutex-release`	Hold event probe that fires immediately after an mutex is released. `arg1` contains a boolean value that indicates whether the event corresponds to a recursive release on a recursive mutex.
`mutex-error`	Error event probe that fires when an error is encountered on a mutex operation. `arg1` is the `errno` value for the error encountered.