Reader/Writer Lock Probes

Reader/write locks permit multiple readers or a single writer, but not both, to be in a critical section at one time. These locks are typically used for structures that are searched more frequently than they are modified, or when threads spend substantial time in a critical section. Users interact with reader/writer locks using the Solaris rwlock(3C) or POSIX pthread_rwlock_init(3C) interfaces.

The probes pertaining to readers/writer locks are in Table 31-2. For each probe, arg0 contains a pointer to the rwlock_t or pthread_rwlock_tstructure (these are identical types) that represents the adaptive lock. arg1 contains a boolean value that indicates whether the operation was as a writer.

Table 31-2 Readers/Writer Lock Probes

`rw-acquire`	Hold event probe that fires immediately after a readers/writer lock is acquired.
`rw-block`	Contention event probe that fires before a thread blocks while attempting to acquire a lock. If enabled, the `rw-acquire` probe or the `rw-error` probe will fire after `rw-block`.
`rw-release`	Hold event probe that fires immediately after a reader/writer lock is released
`rw-error`	Error event probe that fires when an error is encountered during a reader/writer lock operation. `arg1` is the `errno` value of the error encountered.

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