svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
rmlock(9)
RMLOCK(9) BSD Kernel Developer's Manual RMLOCK(9)
NAME
rmlock, rm_init, rm_init_flags, rm_destroy, rm_rlock, rm_try_rlock,
rm_wlock, rm_runlock, rm_wunlock, rm_wowned, rm_sleep, rm_assert,
RM_SYSINIT, RM_SYSINIT_FLAGS — kernel reader/writer lock optimized for
read-mostly access patterns
SYNOPSIS
#include <sys/param.h>
#include <sys/lock.h>
#include <sys/rmlock.h>
void
rm_init(struct rmlock *rm, const char *name);
void
rm_init_flags(struct rmlock *rm, const char *name, int opts);
void
rm_destroy(struct rmlock *rm);
void
rm_rlock(struct rmlock *rm, struct rm_priotracker* tracker);
int
rm_try_rlock(struct rmlock *rm, struct rm_priotracker* tracker);
void
rm_wlock(struct rmlock *rm);
void
rm_runlock(struct rmlock *rm, struct rm_priotracker* tracker);
void
rm_wunlock(struct rmlock *rm);
int
rm_wowned(const struct rmlock *rm);
int
rm_sleep(void *wchan, struct rmlock *rm, int priority, const char *wmesg,
int timo);
options INVARIANTS
options INVARIANT_SUPPORT
void
rm_assert(struct rmlock *rm, int what);
#include <sys/kernel.h>
RM_SYSINIT(name, struct rmlock *rm, const char *desc);
RM_SYSINIT_FLAGS(name, struct rmlock *rm, const char *desc, int flags);
DESCRIPTION
Read-mostly locks allow shared access to protected data by multiple
threads, or exclusive access by a single thread. The threads with shared
access are known as readers since they only read the protected data. A
thread with exclusive access is known as a writer since it can modify
protected data.
Read-mostly locks are designed to be efficient for locks almost exclu‐
sively used as reader locks and as such should be used for protecting
data that rarely changes. Acquiring an exclusive lock after the lock has
been locked for shared access is an expensive operation.
Normal read-mostly locks are similar to rwlock(9) locks and follow the
same lock ordering rules as rwlock(9) locks. Read-mostly locks have full
priority propagation like mutexes. Unlike rwlock(9), read-mostly locks
propagate priority to both readers and writers. This is implemented via
the rm_priotracker structure argument supplied to rm_rlock() and
rm_runlock(). Readers can recurse if the lock is initialized with the
RM_RECURSE option; however, writers are never allowed to recurse.
Sleepable read-mostly locks are created by passing RM_SLEEPABLE to
rm_init_flags(). Unlike normal read-mostly locks, sleepable read-mostly
locks follow the same lock ordering rules as sx(9) locks. Sleepable
read-mostly locks do not propagate priority to writers, but they do prop‐
agate priority to readers. Writers are permitted to sleep while holding
a read-mostly lock, but readers are not. Unlike other sleepable locks
such as sx(9) locks, readers must use try operations on other sleepable
locks to avoid sleeping.
Macros and Functions
rm_init(struct rmlock *rm, const char *name)
Initialize the read-mostly lock rm. The name description is used
solely for debugging purposes. This function must be called
before any other operations on the lock.
rm_init_flags(struct rmlock *rm, const char *name, int opts)
Similar to rm_init(), initialize the read-mostly lock rm with a
set of optional flags. The opts arguments contains one or more
of the following flags:
RM_NOWITNESS Instruct witness(4) to ignore this lock.
RM_RECURSE Allow threads to recursively acquire shared locks
for rm.
RM_SLEEPABLE Create a sleepable read-mostly lock.
RM_NEW If the kernel has been compiled with option
INVARIANTS, rm_init_flags() will assert that the rm
has not been initialized multiple times without
intervening calls to rm_destroy() unless this
option is specified.
rm_rlock(struct rmlock *rm, struct rm_priotracker* tracker)
Lock rm as a reader using tracker to track read owners of a lock
for priority propagation. This data structure is only used
internally by rmlock and must persist until rm_runlock() has been
called. This data structure can be allocated on the stack since
readers cannot sleep. If any thread holds this lock exclusively,
the current thread blocks, and its priority is propagated to the
exclusive holder. If the lock was initialized with the
RM_RECURSE option the rm_rlock() function can be called when the
current thread has already acquired reader access on rm.
rm_try_rlock(struct rmlock *rm, struct rm_priotracker* tracker)
Try to lock rm as a reader. rm_try_rlock() will return 0 if the
lock cannot be acquired immediately; otherwise, the lock will be
acquired and a non-zero value will be returned. Note that
rm_try_rlock() may fail even while the lock is not currently held
by a writer. If the lock was initialized with the RM_RECURSE
option, rm_try_rlock() will succeed if the current thread has
already acquired reader access.
rm_wlock(struct rmlock *rm)
Lock rm as a writer. If there are any shared owners of the lock,
the current thread blocks. The rm_wlock() function cannot be
called recursively.
rm_runlock(struct rmlock *rm, struct rm_priotracker* tracker)
This function releases a shared lock previously acquired by
rm_rlock(). The tracker argument must match the tracker argument
used for acquiring the shared lock
rm_wunlock(struct rmlock *rm)
This function releases an exclusive lock previously acquired by
rm_wlock().
rm_destroy(struct rmlock *rm)
This functions destroys a lock previously initialized with
rm_init(). The rm lock must be unlocked.
rm_wowned(const struct rmlock *rm)
This function returns a non-zero value if the current thread owns
an exclusive lock on rm.
rm_sleep(void *wchan, struct rmlock *rm, int priority, const char *wmesg,
int timo)
This function atomically releases rm while waiting for an event.
The rm lock must be exclusively locked. For more details on the
parameters to this function, see sleep(9).
rm_assert(struct rmlock *rm, int what)
This function asserts that the rm lock is in the state specified
by what. If the assertions are not true and the kernel is com‐
piled with options INVARIANTS and options INVARIANT_SUPPORT, the
kernel will panic. Currently the following base assertions are
supported:
RA_LOCKED Assert that current thread holds either a shared or
exclusive lock of rm.
RA_RLOCKED Assert that current thread holds a shared lock of
rm.
RA_WLOCKED Assert that current thread holds an exclusive lock
of rm.
RA_UNLOCKED Assert that current thread holds neither a shared
nor exclusive lock of rm.
In addition, one of the following optional flags may be specified
with RA_LOCKED, RA_RLOCKED, or RA_WLOCKED:
RA_RECURSED Assert that the current thread holds a recursive
lock of rm.
RA_NOTRECURSED Assert that the current thread does not hold a
recursive lock of rm.
SEE ALSO
locking(9), mutex(9), panic(9), rwlock(9), sema(9), sleep(9), sx(9)
HISTORY
These functions appeared in FreeBSD 7.0.
AUTHORS
The rmlock facility was written by Stephan Uphoff. This manual page was
written by Gleb Smirnoff for rwlock and modified to reflect rmlock by
Stephan Uphoff.
BUGS
The rmlock implementation is currently not optimized for single processor
systems.
rm_try_rlock() can fail transiently even when there is no writer, while
another reader updates the state on the local CPU.
The rmlock implementation uses a single per CPU list shared by all
rmlocks in the system. If rmlocks become popular, hashing to multiple
per CPU queues may be needed to speed up the writer lock process.
BSD November 11, 2017 BSD