Samy Al Bahra
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.\"
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.\" Copyright 2012 Samy Al Bahra.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\"
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.Dd March 28, 2012
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.Dt CK_HS_INIT 3
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.Sh NAME
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.Nm ck_hs_init
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.Nd initialize a hash set
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.Sh LIBRARY
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Concurrency Kit (libck, \-lck)
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.Sh SYNOPSIS
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.In ck_hs.h
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.Ft typedef unsigned long
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.Fn ck_hs_hash_cb_t "const void *key" "unsigned long seed"
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.Ft typedef bool
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.Fn ck_hs_compare_cb_t "const void *c1" "const void *c2"
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.Ft bool
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.Fn ck_hs_init "ck_hs_t *hs" "unsigned int mode" "ck_hs_hash_cb_t *hash_function" "ck_hs_compare_cb_t *compare" "struct ck_malloc *allocator" "unsigned long capacity" "unsigned long seed"
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.Sh DESCRIPTION
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The
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.Fn ck_hs_init
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function initializes the hash set pointed to by the
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.Fa hs
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pointer.
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.Pp
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The argument
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.Fa mode
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specifies the type of key-value pairs to be stored in the
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hash set as well as the expected concurrent access model.
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The value of
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.Fa mode
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consists of a bitfield of one of the following:
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.Bl -tag -width indent
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.It CK_HS_MODE_OBJECT
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The hash set is meant to store pointers to objects. This provides
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a hint that only CK_MD_VMA_BITS are necessary to encode the key
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argument. Any unused pointer bits are leveraged for internal
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optimizations.
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.It CK_HS_MODE_DIRECT
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The hash set is meant to directly store key values and that all
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bits of the key are used to encode values.
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.El
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.Pp
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The concurrent access model is specified by:
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.Bl -tag -width indent
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.It CK_HS_MODE_SPMC
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The hash set should allow for concurrent readers in the
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presence of a single writer.
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.It CK_HS_MODE_MPMC
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The hash set should allow for concurrent readers in the
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presence of concurrent writers. This is currently unsupported.
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.El
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.Pp
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The argument
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.Fa hash_function
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is a mandatory pointer to a user-specified hash function.
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A user-specified hash function takes two arguments. The
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.Fa key
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argument is a pointer to a key. The
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.Fa seed
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argument is the initial seed associated with the hash set.
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This initial seed is specified by the user in
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.Xr ck_hs_init 3 .
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.Pp
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The
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.Fa compare
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argument is an optional pointer to a user-specified
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key comparison function. If NULL is specified in this
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argument, then pointer equality will be used to determine
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key equality. A user-specified comparison function takes
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two arguments representing pointers to the objects being
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compared for equality. It is expected to return true
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if the keys are of equal value and false otherwise.
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.Pp
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The
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.Fa allocator
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argument is a pointer to a structure containing
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.Fa malloc
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and
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.Fa free
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function pointers which respectively define the memory allocation and
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destruction functions to be used by the hash set being initialized.
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.Pp
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The argument
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.Fa capacity
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represents the initial number of keys the hash
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set is expected to contain. This argument is simply a hint
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and the underlying implementation is free to allocate more
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or less memory than necessary to contain the number of entries
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.Fa capacity
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specifies.
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.Pp
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The argument
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.Fa seed
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specifies the initial seed used by the underlying hash function.
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The user is free to choose a value of their choice.
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.Sh RETURN VALUES
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Upon successful completion
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.Fn ck_hs_init
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returns a value of
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.Dv true
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and otherwise returns a value of
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.Dv false
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to indicate an error.
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.Sh ERRORS
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.Bl -tag -width Er
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.Pp
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The behavior of
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.Fn ck_hs_init
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is undefined if
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.Fa hs
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is not a pointer to a
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.Tn ck_hs_t
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object.
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.El
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.Sh SEE ALSO
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.Xr ck_hs_destroy 3 ,
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.Xr CK_HS_HASH 3 ,
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.Xr ck_hs_iterator_init 3 ,
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.Xr ck_hs_next 3 ,
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.Xr ck_hs_get 3 ,
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.Xr ck_hs_put 3 ,
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.Xr ck_hs_set 3 ,
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.Xr ck_hs_remove 3 ,
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.Xr ck_hs_grow 3 ,
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.Xr ck_hs_count 3 ,
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.Xr ck_hs_reset 3 ,
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.Xr ck_hs_stat 3
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.Pp
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Additional information available at http://concurrencykit.org/
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