Readers/Writer Lock Probes
Readers/writer locks enforce a policy of allowing multiple readers or a single writer
— but not both — to be in a critical section. These locks
are typically used for structures that are searched more frequently than they are
modified and for which there is substantial time in the critical section. If
critical section times are short, readers/writer locks will implicitly serialize over the shared
memory used to implement the lock, giving them no advantage over adaptive locks.
See rwlock(9F) for more details on readers/writer locks.
The probes pertaining to readers/writer locks are in Table 18-4. For each probe,
arg0 contains a pointer to the krwlock_t structure that represents the adaptive lock.
Table 18-4 Readers/Writer Lock Probes
rw-acquire |
Hold-event
probe that fires immediately after a readers/writer lock is acquired. arg1 contains the
constant RW_READER if the lock was acquired as a reader, and RW_WRITER if
the lock was acquired as a writer. |
rw-block |
Contention-event probe that fires after a thread
that has blocked on a held readers/writer lock has reawakened and has acquired
the lock. arg1 contains the length of time (in nanoseconds) that the
current thread had to sleep to acquire the lock. arg2 contains the constant
RW_READER if the lock was acquired as a reader, and RW_WRITER if the
lock was acquired as a writer. arg3 and arg4 contain more information on
the reason for blocking. arg3 is non-zero if and only if the lock
was held as a writer when the current thread blocked. arg4 contains
the readers count when the current thread blocked. If both the rw-block and
rw-acquire probes are enabled, rw-block fires before rw-acquire. |
rw-upgrade |
Hold-event probe that fires after a
thread has successfully upgraded a readers/writer lock from a reader to a writer.
Upgrades do not have an associated contention event because they are only possible
through a non-blocking interface, rw_tryupgrade(9F). |
rw-downgrade |
Hold-event probe that fires after a thread had
downgraded its ownership of a readers/writer lock from writer to reader. Downgrades do
not have an associated contention event because they always succeed without contention. |
rw-release |
Hold-event probe
that fires immediately after a readers/writer lock is released. arg1 contains the constant
RW_READER if the released lock was held as a reader, and RW_WRITER if the
released lock was held as a writer. Due to upgrades and downgrades,
the lock may not have been released as it was acquired. |
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