pserialize_perform(9) [netbsd man page]
PSERIALIZE(9) BSD Kernel Developer's Manual PSERIALIZE(9) NAME
pserialize -- passive serialization mechanism SYNOPSIS
#include <sys/pserialize.h> pserialize_t pserialize_create(void); void pserialize_destroy(pserialize_t psz); int pserialize_read_enter(void); void pserialize_read_exit(int s); void pserialize_perform(pserialize_t psz); DESCRIPTION
Passive serialization is a reader / writer synchronisation mechanism designed for lock-less read operations. The read operations may happen from software interrupt at IPL_SOFTCLOCK. FUNCTIONS
pserialize_create() Allocate a new synchronisation object. pserialize_destroy() Destroy the synchronisation object. No synchronisation activity should happen at this point. pserialize_read_enter() Enter the critical path of the reader side. Returns an IPL value, which must be passed to pserialize_read_exit(9). Protected code path is not allowed to block. pserialize_read_exit() Exit the critical path of the reader side. Takes the IPL value returned by pserialize_read_enter(9). pserialize_perform() Perform the passive serialization on the writer side. Passing of this function ensures that no readers are in action. Writers must be additionally serialized with a separate mechanism, e.g. mutex(9). Operation blocks and it may only be performed from thread context. EXAMPLES
Typical code fragment in the writer side: mutex_enter(&writer_psz_lock); /* * Perform the updates (e.g. remove data items from a list). */ ... pserialize_perform(object->psz); /* * At this point it is safe to destroy old data items. */ mutex_exit(&writer_psz_lock); CODE REFERENCES
The pserialize is implemented within the file sys/kern/subr_pserialize.c. SEE ALSO
membar_ops(3), condvar(9), mutex(9), rwlock(9) Hennessy, et al., Passive serialization in a multitasking environment, US Patent and Trademark Office, US Patent 4809168, February 28, 1989. HISTORY
Passive serialization mechanism first appeared in NetBSD 6.0. BSD
July 30, 2011 BSD
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MUTEX(9) BSD Kernel Developer's Manual MUTEX(9) NAME
mutex, mutex_init, mutex_destroy, mutex_enter, mutex_exit, mutex_owned, mutex_spin_enter, mutex_spin_exit, mutex_tryenter -- mutual exclusion primitives SYNOPSIS
#include <sys/mutex.h> void mutex_init(kmutex_t *mtx, kmutex_type_t type, int ipl); void mutex_destroy(kmutex_t *mtx); void mutex_enter(kmutex_t *mtx); void mutex_exit(kmutex_t *mtx); int mutex_owned(kmutex_t *mtx); void mutex_spin_enter(kmutex_t *mtx); void mutex_spin_exit(kmutex_t *mtx); int mutex_tryenter(kmutex_t *mtx); options DIAGNOSTIC options LOCKDEBUG DESCRIPTION
Mutexes are used in the kernel to implement mutual exclusion among LWPs (lightweight processes) and interrupt handlers. The kmutex_t type provides storage for the mutex object. This should be treated as an opaque object and not examined directly by consumers. Mutexes replace the spl(9) system traditionally used to provide synchronization between interrupt handlers and LWPs. OPTIONS
options DIAGNOSTIC Kernels compiled with the DIAGNOSTIC option perform basic sanity checks on mutex operations. options LOCKDEBUG Kernels compiled with the LOCKDEBUG option perform potentially CPU intensive sanity checks on mutex operations. FUNCTIONS
mutex_init(mtx, type, ipl) Dynamically initialize a mutex for use. No other operations can be performed on a mutex until it has been initialized. Once initialized, all types of mutex are manipulated using the same interface. Note that mutex_init() may block in order to allocate memory. The type argument must be given as MUTEX_DEFAULT. Other constants are defined but are for low-level system use and are not an endorsed, stable part of the interface. The type of mutex returned depends on the ipl argument: IPL_NONE, or one of the IPL_SOFT* constants An adaptive mutex will be returned. Adaptive mutexes provide mutual exclusion between LWPs, and between LWPs and soft interrupt handlers. Adaptive mutexes cannot be acquired from a hardware interrupt handler. An LWP may either sleep or busy-wait when attempting to acquire an adaptive mutex that is already held. IPL_VM, IPL_SCHED, IPL_HIGH A spin mutex will be returned. Spin mutexes provide mutual exclusion between LWPs, and between LWPs and interrupt handlers. The ipl argument is used to pass a system interrupt priority level (IPL) that will block all interrupt handlers that may try to acquire the mutex. LWPs that own spin mutexes may not sleep, and therefore must not try to acquire adaptive mutexes or other sleep locks. A processor will always busy-wait when attempting to acquire a spin mutex that is already held. See spl(9) for further information on interrupt priority levels (IPLs). mutex_destroy(mtx) Release resources used by a mutex. The mutex may not be used after it has been destroyed. mutex_destroy() may block in order to free memory. mutex_enter(mtx) Acquire a mutex. If the mutex is already held, the caller will block and not return until the mutex is acquired. Mutexes and other types of locks must always be acquired in a consistent order with respect to each other. Otherwise, the potential for system deadlock exists. Adaptive mutexes and other types of lock that can sleep may not be acquired while a spin mutex is held by the caller. When acquiring a spin mutex, the IPL of the current CPU will be raised to the level set in mutex_init() if it is not already equal or higher. mutex_exit(mtx) Release a mutex. The mutex must have been previously acquired by the caller. Mutexes may be released out of order as needed. mutex_owned(mtx) For adaptive mutexes, return non-zero if the current LWP holds the mutex. For spin mutexes, return non-zero if the mutex is held, potentially by the current processor. Otherwise, return zero. mutex_owned() is provided for making diagnostic checks to verify that a lock is held. For example: KASSERT(mutex_owned(&driver_lock)); It should not be used to make locking decisions at run time, or to verify that a lock is not held. mutex_spin_enter(mtx) Equivalent to mutex_enter(), but may only be used when it is known that mtx is a spin mutex. On some architectures, this can substan- tially reduce the cost of acquring a spin mutex. mutex_spin_exit(mtx) Equivalent to mutex_exit(), but may only be used when it is known that mtx is a spin mutex. On some architectures, this can substan- tially reduce the cost of releasing a spin mutex. mutex_tryenter(mtx) Try to acquire a mutex, but do not block if the mutex is already held. Returns non-zero if the mutex was acquired, or zero if the mutex was already held. mutex_tryenter() can be used as an optimization when acquiring locks in the wrong order. For example, in a setting where the conven- tion is that first_lock must be acquired before second_lock, the following can be used to optimistically lock in reverse order: /* We hold second_lock, but not first_lock. */ KASSERT(mutex_owned(&second_lock)); if (!mutex_tryenter(&first_lock)) { /* Failed to get it - lock in the correct order. */ mutex_exit(&second_lock); mutex_enter(&first_lock); mutex_enter(&second_lock); /* * We may need to recheck any conditions the code * path depends on, as we released second_lock * briefly. */ } CODE REFERENCES
The core of the mutex implementation is in sys/kern/kern_mutex.c. The header file sys/sys/mutex.h describes the public interface, and interfaces that machine-dependent code must provide to support mutexes. SEE ALSO
atomic_ops(3), membar_ops(3), lockstat(8), condvar(9), kpreempt(9), rwlock(9), spl(9) Jim Mauro and Richard McDougall, Solaris Internals: Core Kernel Architecture, Prentice Hall, 2001, ISBN 0-13-022496-0. HISTORY
The mutex primitives first appeared in NetBSD 5.0. BSD
September 14, 2010 BSD