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hashinit (9)

>> hashinit (9) ( FreeBSD man: Ядро )

BSD mandoc

NAME



hashinit , hashinit_flags, hashdestroy , phashinit

 - manage kernel hash tables

SYNOPSIS

   #include <sys/malloc.h>
   #include <sys/systm.h>
   #include <sys/queue.h>
void * hashinit (int nelements struct malloc_type *type u_long *hashmask);
void Fo hashinit_flags Fa int nelements struct malloc_type *type u_long *hashmask int flags Fc Ft void hashdestroy (void *hashtbl struct malloc_type *type u_long hashmask);
void * phashinit (int nelements struct malloc_type *type u_long *nentries);

DESCRIPTION

The hashinit (,);
hashinit_flags ();
and phashinit ();
functions allocate space for hash tables of size given by the argument Fa nelements .

The hashinit ();
function allocates hash tables that are sized to largest power of two less than or equal to argument Fa nelements . The phashinit ();
function allocates hash tables that are sized to the largest prime number less than or equal to argument Fa nelements . The hashinit_flags ();
function operates like hashinit ();
but also accepts an additional argument Fa flags which control various options during allocation. Allocated hash tables are contiguous arrays of LIST_HEAD3 entries, allocated using malloc(9), and initialized using LIST_INIT3. The malloc arena to be used for allocation is pointed to by argument Fa type .

The hashdestroy ();
function frees the space occupied by the hash table pointed to by argument Fa hashtbl . Argument Fa type determines the malloc arena to use when freeing space. The argument Fa hashmask should be the bit mask returned by the call to hashinit ();
that allocated the hash table. The argument Fa flags must be used with one of the following values.

HASH_NOWAIT: Any malloc performed by the hashinit_flags ();
function will not be allowed to wait, and therefore may fail.
HASH_WAITOK: Any malloc performed by the hashinit_flags ();
function is allowed to wait for memory.

IMPLEMENTATION NOTES

The largest prime hash value chosen by phashinit ();
is 32749.

RETURN VALUES

The hashinit ();
function returns a pointer to an allocated hash table and sets the location pointed to by Fa hashmask to the bit mask to be used for computing the correct slot in the hash table.

The phashinit ();
function returns a pointer to an allocated hash table and sets the location pointed to by Fa nentries to the number of rows in the hash table.

EXAMPLES

A typical example is shown below:

...
static LIST_HEAD(foo, foo) *footable;
static u_long foomask;
...
footable = hashinit(32, M_FOO, &foomask);

Here we allocate a hash table with 32 entries from the malloc arena pointed to by M_FOO The mask for the allocated hash table is returned in foomask A subsequent call to hashdestroy ();
uses the value in foomask

...
hashdestroy(footable, M_FOO, foomask);

DIAGNOSTICS

The hashinit ();
and phashinit ();
functions will panic if argument Fa nelements is less than or equal to zero.

The hashdestroy ();
function will panic if the hash table pointed to by Fa hashtbl is not empty.

BUGS

There is no phashdestroy ();
function, and using hashdestroy ();
to free a hash table allocated by phashinit ();
usually has grave consequences.

Партнёры:

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Created 1996-2024 by Maxim Chirkov
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