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rw_wunlock (9)
  • >> rw_wunlock (9) ( FreeBSD man: Ядро )

  • BSD mandoc
     

    NAME

    
    
    rwlock
    
     
    rw_init
    
     
    rw_init_flags,
    
    rw_destroy
    
     
    rw_rlock
    
     
    rw_wlock
    
     
    rw_runlock
    
     
    rw_wunlock
    
     
    rw_try_rlock
    
     
    rw_try_upgrade
    
     
    rw_try_wlock
    
     
    rw_downgrade
    
     
    rw_sleep
    
     
    rw_initialized
    
     
    rw_wowned
    
     
    rw_assert
    
     
    RW_SYSINIT
    
     - kernel reader/writer lock
    
     
    

    SYNOPSIS

       #include <sys/param.h>
       #include <sys/lock.h>
       #include <sys/rwlock.h>
    void rw_init (struct rwlock *rw const char *name);
    void rw_init_flags (struct rwlock *rw const char *name int opts);
    void rw_destroy (struct rwlock *rw);
    void rw_rlock (struct rwlock *rw);
    void rw_wlock (struct rwlock *rw);
    int rw_try_rlock (struct rwlock *rw);
    int rw_try_wlock (struct rwlock *rw);
    void rw_runlock (struct rwlock *rw);
    void rw_wunlock (struct rwlock *rw);
    int rw_try_upgrade (struct rwlock *rw);
    void rw_downgrade (struct rwlock *rw);
    int rw_sleep (void *chan struct rwlock *rw int priority const char *wmesg int timo);
    int rw_initialized (struct rwlock *rw);
    int rw_wowned (struct rwlock *rw);

    options INVARIANTS options INVARIANT_SUPPORT void rw_assert (struct rwlock *rw int what);
       #include <sys/kernel.h>
    RW_SYSINIT (name struct rwlock *rw const char *desc);
     

    DESCRIPTION

    Reader/writer 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.

    Although reader/writer locks look very similar to sx(9) locks, their usage pattern is different. Reader/writer locks can be treated as mutexes (see mutex(9)) with shared/exclusive semantics. Unlike sx(9), an can be locked while holding a non-spin mutex, and an cannot be held while sleeping. The locks have priority propagation like mutexes, but priority can be propagated only to an exclusive holder. This limitation comes from the fact that shared owners are anonymous. Another important property is that shared holders of can recurse, and exclusive locks can be made recursive selectively.  

    Macros and Functions

    Fn rw_init struct rwlock *rw const char *name
    Initialize structure located at Fa rw as reader/writer lock, described by name Fa name . The description is used solely for debugging purposes. This function must be called before any other operations on the lock.
    Fn rw_init_flags struct rwlock *rw const char *name int opts
    Initialize the rw lock just like the rw_init ();
    function, but specifying a set of optional flags to alter the behaviour of Fa rw , through the Fa opts argument. It contains one or more of the following flags:

    RW_DUPOK
    Witness should not log messages about duplicate locks being acquired.
    RW_NOPROFILE
    Do not profile this lock.
    RW_NOWITNESS
    Instruct witness(4) to ignore this lock.
    RW_QUIET
    Do not log any operations for this lock via ktr(4).
    RW_RECURSE
    Allow threads to recursively acquire exclusive locks for Fa rw .
    Fn rw_rlock struct rwlock *rw
    Lock Fa rw as a reader. If any thread holds this lock exclusively, the current thread blocks, and its priority is propagated to the exclusive holder. The rw_rlock ();
    function can be called when the thread has already acquired reader access on Fa rw . This is called ``recursing on a lock''
    Fn rw_wlock struct rwlock *rw
    Lock Fa rw as a writer. If there are any shared owners of the lock, the current thread blocks. The rw_wlock ();
    function can be called recursively only if Fa rw has been initialized with the RW_RECURSE option enabled.
    Fn rw_try_rlock struct rwlock *rw
    Try to lock Fa rw as a reader. This function will return true if the operation succeeds, otherwise 0 will be returned.
    Fn rw_try_wlock struct rwlock *rw
    Try to lock Fa rw as a writer. This function will return true if the operation succeeds, otherwise 0 will be returned.
    Fn rw_runlock struct rwlock *rw
    This function releases a shared lock previously acquired by rw_rlock (.);
    Fn rw_wunlock struct rwlock *rw
    This function releases an exclusive lock previously acquired by rw_wlock (.);
    Fn rw_try_upgrade struct rwlock *rw
    Attempt to upgrade a single shared lock to an exclusive lock. The current thread must hold a shared lock of Fa rw . This will only succeed if the current thread holds the only shared lock on Fa rw , and it only holds a single shared lock. If the attempt succeeds rw_try_upgrade ();
    will return a non-zero value, and the current thread will hold an exclusive lock. If the attempt fails rw_try_upgrade ();
    will return zero, and the current thread will still hold a shared lock.
    Fn rw_downgrade struct rwlock *rw
    Convert an exclusive lock into a single shared lock. The current thread must hold an exclusive lock of Fa rw .
    Fn rw_sleep void *chan struct rwlock *rw int priority const char *wmesg int timo
    Atomically release Fa rw while waiting for an event. For more details on the parameters to this function, see sleep(9).
    Fn rw_initialized struct rwlock *rw
    This function returns non-zero if Fa rw has been initialized, and zero otherwise.
    Fn rw_destroy struct rwlock *rw
    This functions destroys a lock previously initialized with rw_init (.);
    The Fa rw lock must be unlocked.
    Fn rw_wowned struct rwlock *rw
    This function returns a non-zero value if the current thread owns an exclusive lock on Fa rw .
    Fn rw_assert struct rwlock *rw int what
    This function allows assertions specified in Fa what to be made about Fa rw . If the assertions are not true and the kernel is compiled with options INVARIANTS and options INVARIANT_SUPPORT the kernel will panic. Currently the following assertions are supported:

    RA_LOCKED
    Assert that current thread holds either a shared or exclusive lock of Fa rw .
    RA_RLOCKED
    Assert that current thread holds a shared lock of Fa rw .
    RA_WLOCKED
    Assert that current thread holds an exclusive lock of Fa rw .
    RA_UNLOCKED
    Assert that current thread holds neither a shared nor exclusive lock of Fa rw .

     

    SEE ALSO

    locking(9), mutex(9), panic(9), sema(9), sx(9)  

    HISTORY

    These functions appeared in Fx 7.0 .  

    AUTHORS

    An -nosplit The facility was written by An John Baldwin . This manual page was written by An Gleb Smirnoff .  

    BUGS

    If WITNESS is not included in the kernel, then it is impossible to assert that the current thread does or does not hold a read lock.    #include <the>
    non- WITNESS case, the RA_LOCKED and RA_RLOCKED assertions merely check that some thread holds a read lock.

    Reader/writer is a bit of an awkward name. An can also be called a ``Robert Watson'' lock if desired.


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    Macros and Functions
    SEE ALSO
    HISTORY
    AUTHORS
    BUGS


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