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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).  Pro‐
	      tected 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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