464 lines
19 KiB
Plaintext
464 lines
19 KiB
Plaintext
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.\" ========================================================================
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.\"
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.IX Title "OPENSSL_LH_COMPFUNC 3ossl"
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.TH OPENSSL_LH_COMPFUNC 3ossl "2024-01-30" "3.2.1" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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LHASH, LHASH_OF, DEFINE_LHASH_OF_EX, DEFINE_LHASH_OF,
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OPENSSL_LH_COMPFUNC, OPENSSL_LH_HASHFUNC, OPENSSL_LH_DOALL_FUNC,
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LHASH_DOALL_ARG_FN_TYPE,
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IMPLEMENT_LHASH_HASH_FN, IMPLEMENT_LHASH_COMP_FN,
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lh_TYPE_new, lh_TYPE_free, lh_TYPE_flush,
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lh_TYPE_insert, lh_TYPE_delete, lh_TYPE_retrieve,
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lh_TYPE_doall, lh_TYPE_doall_arg, lh_TYPE_num_items, lh_TYPE_get_down_load,
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lh_TYPE_set_down_load, lh_TYPE_error,
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OPENSSL_LH_new, OPENSSL_LH_free, OPENSSL_LH_flush,
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OPENSSL_LH_insert, OPENSSL_LH_delete, OPENSSL_LH_retrieve,
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OPENSSL_LH_doall, OPENSSL_LH_doall_arg, OPENSSL_LH_num_items,
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OPENSSL_LH_get_down_load, OPENSSL_LH_set_down_load, OPENSSL_LH_error
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\&\- dynamic hash table
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/lhash.h>
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\&
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\& LHASH_OF(TYPE)
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\&
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\& DEFINE_LHASH_OF_EX(TYPE);
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\&
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\& LHASH_OF(TYPE) *lh_TYPE_new(OPENSSL_LH_HASHFUNC hash, OPENSSL_LH_COMPFUNC compare);
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\& void lh_TYPE_free(LHASH_OF(TYPE) *table);
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\& void lh_TYPE_flush(LHASH_OF(TYPE) *table);
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\&
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\& TYPE *lh_TYPE_insert(LHASH_OF(TYPE) *table, TYPE *data);
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\& TYPE *lh_TYPE_delete(LHASH_OF(TYPE) *table, TYPE *data);
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\& TYPE *lh_TYPE_retrieve(LHASH_OF(TYPE) *table, TYPE *data);
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\&
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\& void lh_TYPE_doall(LHASH_OF(TYPE) *table, OPENSSL_LH_DOALL_FUNC func);
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\& void lh_TYPE_doall_arg(LHASH_OF(TYPE) *table, OPENSSL_LH_DOALL_FUNCARG func,
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\& TYPE *arg);
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\&
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\& unsigned long lh_TYPE_num_items(OPENSSL_LHASH *lh);
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\& unsigned long lh_TYPE_get_down_load(OPENSSL_LHASH *lh);
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\& void lh_TYPE_set_down_load(OPENSSL_LHASH *lh, unsigned long dl);
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\&
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\& int lh_TYPE_error(LHASH_OF(TYPE) *table);
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\&
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\& typedef int (*OPENSSL_LH_COMPFUNC)(const void *, const void *);
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\& typedef unsigned long (*OPENSSL_LH_HASHFUNC)(const void *);
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\& typedef void (*OPENSSL_LH_DOALL_FUNC)(const void *);
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\& typedef void (*LHASH_DOALL_ARG_FN_TYPE)(const void *, const void *);
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\&
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\& OPENSSL_LHASH *OPENSSL_LH_new(OPENSSL_LH_HASHFUNC h, OPENSSL_LH_COMPFUNC c);
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\& void OPENSSL_LH_free(OPENSSL_LHASH *lh);
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\& void OPENSSL_LH_flush(OPENSSL_LHASH *lh);
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\&
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\& void *OPENSSL_LH_insert(OPENSSL_LHASH *lh, void *data);
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\& void *OPENSSL_LH_delete(OPENSSL_LHASH *lh, const void *data);
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\& void *OPENSSL_LH_retrieve(OPENSSL_LHASH *lh, const void *data);
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\&
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\& void OPENSSL_LH_doall(OPENSSL_LHASH *lh, OPENSSL_LH_DOALL_FUNC func);
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\& void OPENSSL_LH_doall_arg(OPENSSL_LHASH *lh, OPENSSL_LH_DOALL_FUNCARG func, void *arg);
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\&
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\& unsigned long OPENSSL_LH_num_items(OPENSSL_LHASH *lh);
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\& unsigned long OPENSSL_LH_get_down_load(OPENSSL_LHASH *lh);
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\& void OPENSSL_LH_set_down_load(OPENSSL_LHASH *lh, unsigned long dl);
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\&
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\& int OPENSSL_LH_error(OPENSSL_LHASH *lh);
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\&
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\& #define LH_LOAD_MULT /* integer constant */
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.Ve
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.PP
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The following macro is deprecated:
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.PP
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.Vb 1
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\& DEFINE_LHASH_OF(TYPE);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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This library implements type-checked dynamic hash tables. The hash
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table entries can be arbitrary structures. Usually they consist of key
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and value fields. In the description here, \fB\f(BI\s-1TYPE\s0\fB\fR is used a placeholder
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for any of the OpenSSL datatypes, such as \fI\s-1SSL_SESSION\s0\fR.
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.PP
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To define a new type-checked dynamic hash table, use \fB\s-1DEFINE_LHASH_OF_EX\s0\fR().
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\&\fB\s-1DEFINE_LHASH_OF\s0\fR() was previously used for this purpose, but is now
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deprecated. The \fB\s-1DEFINE_LHASH_OF_EX\s0\fR() macro provides all functionality of
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\&\fB\s-1DEFINE_LHASH_OF\s0\fR() except for certain deprecated statistics functions (see
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\&\fIOPENSSL_LH_stats\fR\|(3)).
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.PP
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_new\fR() creates a new \fB\s-1LHASH_OF\s0\fR(\fB\f(BI\s-1TYPE\s0\fB\fR) structure to store
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arbitrary data entries, and specifies the 'hash' and 'compare'
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callbacks to be used in organising the table's entries. The \fIhash\fR
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callback takes a pointer to a table entry as its argument and returns
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an unsigned long hash value for its key field. The hash value is
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normally truncated to a power of 2, so make sure that your hash
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function returns well mixed low order bits. The \fIcompare\fR callback
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takes two arguments (pointers to two hash table entries), and returns
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0 if their keys are equal, nonzero otherwise.
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.PP
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If your hash table
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will contain items of some particular type and the \fIhash\fR and
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\&\fIcompare\fR callbacks hash/compare these types, then the
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\&\fB\s-1IMPLEMENT_LHASH_HASH_FN\s0\fR and \fB\s-1IMPLEMENT_LHASH_COMP_FN\s0\fR macros can be
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used to create callback wrappers of the prototypes required by
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_new\fR() as shown in this example:
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.PP
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.Vb 11
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\& /*
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\& * Implement the hash and compare functions; "stuff" can be any word.
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\& */
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\& static unsigned long stuff_hash(const TYPE *a)
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\& {
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\& ...
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\& }
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\& static int stuff_cmp(const TYPE *a, const TYPE *b)
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\& {
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\& ...
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\& }
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\&
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\& /*
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\& * Implement the wrapper functions.
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\& */
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\& static IMPLEMENT_LHASH_HASH_FN(stuff, TYPE)
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\& static IMPLEMENT_LHASH_COMP_FN(stuff, TYPE)
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.Ve
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.PP
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If the type is going to be used in several places, the following macros
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can be used in a common header file to declare the function wrappers:
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.PP
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.Vb 2
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\& DECLARE_LHASH_HASH_FN(stuff, TYPE)
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\& DECLARE_LHASH_COMP_FN(stuff, TYPE)
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.Ve
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.PP
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Then a hash table of \fB\f(BI\s-1TYPE\s0\fB\fR objects can be created using this:
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.PP
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.Vb 1
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\& LHASH_OF(TYPE) *htable;
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\&
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\& htable = B<lh_I<TYPE>_new>(LHASH_HASH_FN(stuff), LHASH_COMP_FN(stuff));
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.Ve
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.PP
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_free\fR() frees the \fB\s-1LHASH_OF\s0\fR(\fB\f(BI\s-1TYPE\s0\fB\fR) structure
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\&\fItable\fR. Allocated hash table entries will not be freed; consider
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using \fBlh_\f(BI\s-1TYPE\s0\fB_doall\fR() to deallocate any remaining entries in the
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hash table (see below).
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.PP
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_flush\fR() empties the \fB\s-1LHASH_OF\s0\fR(\fB\f(BI\s-1TYPE\s0\fB\fR) structure \fItable\fR. New
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entries can be added to the flushed table. Allocated hash table entries
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will not be freed; consider using \fBlh_\f(BI\s-1TYPE\s0\fB_doall\fR() to deallocate any
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remaining entries in the hash table (see below).
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.PP
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_insert\fR() inserts the structure pointed to by \fIdata\fR into
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\&\fItable\fR. If there already is an entry with the same key, the old
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value is replaced. Note that \fBlh_\f(BI\s-1TYPE\s0\fB_insert\fR() stores pointers, the
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data are not copied.
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.PP
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_delete\fR() deletes an entry from \fItable\fR.
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.PP
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_retrieve\fR() looks up an entry in \fItable\fR. Normally, \fIdata\fR
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is a structure with the key field(s) set; the function will return a
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pointer to a fully populated structure.
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.PP
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_doall\fR() will, for every entry in the hash table, call
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\&\fIfunc\fR with the data item as its parameter.
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For example:
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.PP
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.Vb 2
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\& /* Cleans up resources belonging to \*(Aqa\*(Aq (this is implemented elsewhere) */
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\& void TYPE_cleanup_doall(TYPE *a);
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\&
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\& /* Implement a prototype\-compatible wrapper for "TYPE_cleanup" */
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\& IMPLEMENT_LHASH_DOALL_FN(TYPE_cleanup, TYPE)
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\&
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\& /* Call "TYPE_cleanup" against all items in a hash table. */
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\& lh_TYPE_doall(hashtable, LHASH_DOALL_FN(TYPE_cleanup));
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\&
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\& /* Then the hash table itself can be deallocated */
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\& lh_TYPE_free(hashtable);
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.Ve
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.PP
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_doall_arg\fR() is the same as \fBlh_\f(BI\s-1TYPE\s0\fB_doall\fR() except that
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\&\fIfunc\fR will be called with \fIarg\fR as the second argument and \fIfunc\fR
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should be of type \fB\s-1LHASH_DOALL_ARG_FN\s0\fR(\fB\f(BI\s-1TYPE\s0\fB\fR) (a callback prototype
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that is passed both the table entry and an extra argument). As with
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\&\fIlh_doall()\fR, you can instead choose to declare your callback with a
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prototype matching the types you are dealing with and use the
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declare/implement macros to create compatible wrappers that cast
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variables before calling your type-specific callbacks. An example of
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this is demonstrated here (printing all hash table entries to a \s-1BIO\s0
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that is provided by the caller):
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.PP
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.Vb 2
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\& /* Prints item \*(Aqa\*(Aq to \*(Aqoutput_bio\*(Aq (this is implemented elsewhere) */
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\& void TYPE_print_doall_arg(const TYPE *a, BIO *output_bio);
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\&
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\& /* Implement a prototype\-compatible wrapper for "TYPE_print" */
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\& static IMPLEMENT_LHASH_DOALL_ARG_FN(TYPE, const TYPE, BIO)
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\&
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\& /* Print out the entire hashtable to a particular BIO */
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\& lh_TYPE_doall_arg(hashtable, LHASH_DOALL_ARG_FN(TYPE_print), BIO,
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\& logging_bio);
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.Ve
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|
.PP
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|
Note that it is by default \fBnot\fR safe to use \fBlh_\f(BI\s-1TYPE\s0\fB_delete\fR() inside a
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callback passed to \fBlh_\f(BI\s-1TYPE\s0\fB_doall\fR() or \fBlh_\f(BI\s-1TYPE\s0\fB_doall_arg\fR(). The
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reason for this is that deleting an item from the hash table may result in the
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hash table being contracted to a smaller size and rehashed.
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_doall\fR() and \fBlh_\f(BI\s-1TYPE\s0\fB_doall_arg\fR() are unsafe and will exhibit
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undefined behaviour under these conditions, as these functions assume the hash
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table size and bucket pointers do not change during the call.
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.PP
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If it is desired to use \fBlh_\f(BI\s-1TYPE\s0\fB_doall\fR() or \fBlh_\f(BI\s-1TYPE\s0\fB_doall_arg\fR() with
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_delete\fR(), it is essential that you call
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_set_down_load\fR() with a \fIdown_load\fR argument of 0 first. This
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disables hash table contraction and guarantees that it will be safe to delete
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items from a hash table during a call to \fBlh_\f(BI\s-1TYPE\s0\fB_doall\fR() or
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_doall_arg\fR().
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.PP
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It is never safe to call \fBlh_\f(BI\s-1TYPE\s0\fB_insert\fR() during a call to
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_doall\fR() or \fBlh_\f(BI\s-1TYPE\s0\fB_doall_arg\fR().
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.PP
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\&\fBlh_\f(BI\s-1TYPE\s0\fB_error\fR() can be used to determine if an error occurred in the last
|
|
operation.
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|
.PP
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|
\&\fBlh_\f(BI\s-1TYPE\s0\fB_num_items\fR() returns the number of items in the hash table.
|
|
.PP
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|
\&\fBlh_\f(BI\s-1TYPE\s0\fB_get_down_load\fR() and \fBlh_\f(BI\s-1TYPE\s0\fB_set_down_load\fR() get and set the
|
|
factor used to determine when the hash table is contracted. The factor is the
|
|
load factor at or below which hash table contraction will occur, multiplied by
|
|
\&\fB\s-1LH_LOAD_MULT\s0\fR, where the load factor is the number of items divided by the
|
|
number of nodes. Setting this value to 0 disables hash table contraction.
|
|
.PP
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|
\&\fIOPENSSL_LH_new()\fR is the same as the \fBlh_\f(BI\s-1TYPE\s0\fB_new\fR() except that it is not
|
|
type specific. So instead of returning an \fB\s-1LHASH_OF\s0(\f(BI\s-1TYPE\s0\fB)\fR value it returns
|
|
a \fBvoid *\fR. In the same way the functions \fIOPENSSL_LH_free()\fR,
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|
\&\fIOPENSSL_LH_flush()\fR, \fIOPENSSL_LH_insert()\fR, \fIOPENSSL_LH_delete()\fR,
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|
\&\fIOPENSSL_LH_retrieve()\fR, \fIOPENSSL_LH_doall()\fR, \fIOPENSSL_LH_doall_arg()\fR,
|
|
\&\fIOPENSSL_LH_num_items()\fR, \fIOPENSSL_LH_get_down_load()\fR, \fIOPENSSL_LH_set_down_load()\fR
|
|
and \fIOPENSSL_LH_error()\fR are equivalent to the similarly named \fBlh_\f(BI\s-1TYPE\s0\fB\fR
|
|
functions except that they return or use a \fBvoid *\fR where the equivalent
|
|
\&\fBlh_\f(BI\s-1TYPE\s0\fB\fR function returns or uses a \fB\f(BI\s-1TYPE\s0\fB *\fR or \fB\s-1LHASH_OF\s0(\f(BI\s-1TYPE\s0\fB) *\fR.
|
|
\&\fBlh_\f(BI\s-1TYPE\s0\fB\fR functions are implemented as type checked wrappers around the
|
|
\&\fB\s-1OPENSSL_LH\s0\fR functions. Most applications should not call the \fB\s-1OPENSSL_LH\s0\fR
|
|
functions directly.
|
|
.SH "RETURN VALUES"
|
|
.IX Header "RETURN VALUES"
|
|
\&\fBlh_\f(BI\s-1TYPE\s0\fB_new\fR() and \fIOPENSSL_LH_new()\fR return \s-1NULL\s0 on error, otherwise a
|
|
pointer to the new \fB\s-1LHASH\s0\fR structure.
|
|
.PP
|
|
When a hash table entry is replaced, \fBlh_\f(BI\s-1TYPE\s0\fB_insert\fR() or
|
|
\&\fIOPENSSL_LH_insert()\fR return the value being replaced. \s-1NULL\s0 is returned on normal
|
|
operation and on error.
|
|
.PP
|
|
\&\fBlh_\f(BI\s-1TYPE\s0\fB_delete\fR() and \fIOPENSSL_LH_delete()\fR return the entry being deleted.
|
|
\&\s-1NULL\s0 is returned if there is no such value in the hash table.
|
|
.PP
|
|
\&\fBlh_\f(BI\s-1TYPE\s0\fB_retrieve\fR() and \fIOPENSSL_LH_retrieve()\fR return the hash table entry
|
|
if it has been found, \s-1NULL\s0 otherwise.
|
|
.PP
|
|
\&\fBlh_\f(BI\s-1TYPE\s0\fB_error\fR() and \fIOPENSSL_LH_error()\fR return 1 if an error occurred in
|
|
the last operation, 0 otherwise. It's meaningful only after non-retrieve
|
|
operations.
|
|
.PP
|
|
\&\fBlh_\f(BI\s-1TYPE\s0\fB_free\fR(), \fIOPENSSL_LH_free()\fR, \fBlh_\f(BI\s-1TYPE\s0\fB_flush\fR(),
|
|
\&\fIOPENSSL_LH_flush()\fR, \fBlh_\f(BI\s-1TYPE\s0\fB_doall\fR() \fIOPENSSL_LH_doall()\fR,
|
|
\&\fBlh_\f(BI\s-1TYPE\s0\fB_doall_arg\fR() and \fIOPENSSL_LH_doall_arg()\fR return no values.
|
|
.SH "NOTE"
|
|
.IX Header "NOTE"
|
|
The \s-1LHASH\s0 code is not thread safe. All updating operations, as well as
|
|
\&\fBlh_\f(BI\s-1TYPE\s0\fB_error\fR() or \fIOPENSSL_LH_error()\fR calls must be performed under
|
|
a write lock. All retrieve operations should be performed under a read lock,
|
|
\&\fIunless\fR accurate usage statistics are desired. In which case, a write lock
|
|
should be used for retrieve operations as well. For output of the usage
|
|
statistics, using the functions from \fIOPENSSL_LH_stats\fR\|(3), a read lock
|
|
suffices.
|
|
.PP
|
|
The \s-1LHASH\s0 code regards table entries as constant data. As such, it
|
|
internally represents \fIlh_insert()\fR'd items with a \*(L"const void *\*(R"
|
|
pointer type. This is why callbacks such as those used by \fIlh_doall()\fR
|
|
and \fIlh_doall_arg()\fR declare their prototypes with \*(L"const\*(R", even for the
|
|
parameters that pass back the table items' data pointers \- for
|
|
consistency, user-provided data is \*(L"const\*(R" at all times as far as the
|
|
\&\s-1LHASH\s0 code is concerned. However, as callers are themselves providing
|
|
these pointers, they can choose whether they too should be treating
|
|
all such parameters as constant.
|
|
.PP
|
|
As an example, a hash table may be maintained by code that, for
|
|
reasons of encapsulation, has only \*(L"const\*(R" access to the data being
|
|
indexed in the hash table (i.e. it is returned as \*(L"const\*(R" from
|
|
elsewhere in their code) \- in this case the \s-1LHASH\s0 prototypes are
|
|
appropriate as-is. Conversely, if the caller is responsible for the
|
|
life-time of the data in question, then they may well wish to make
|
|
modifications to table item passed back in the \fIlh_doall()\fR or
|
|
\&\fIlh_doall_arg()\fR callbacks (see the \*(L"TYPE_cleanup\*(R" example above). If
|
|
so, the caller can either cast the \*(L"const\*(R" away (if they're providing
|
|
the raw callbacks themselves) or use the macros to declare/implement
|
|
the wrapper functions without \*(L"const\*(R" types.
|
|
.PP
|
|
Callers that only have \*(L"const\*(R" access to data they're indexing in a
|
|
table, yet declare callbacks without constant types (or cast the
|
|
\&\*(L"const\*(R" away themselves), are therefore creating their own risks/bugs
|
|
without being encouraged to do so by the \s-1API. \s0 On a related note,
|
|
those auditing code should pay special attention to any instances of
|
|
DECLARE/IMPLEMENT_LHASH_DOALL_[\s-1ARG_\s0]_FN macros that provide types
|
|
without any \*(L"const\*(R" qualifiers.
|
|
.SH "BUGS"
|
|
.IX Header "BUGS"
|
|
\&\fBlh_\f(BI\s-1TYPE\s0\fB_insert\fR() and \fIOPENSSL_LH_insert()\fR return \s-1NULL\s0 both for success
|
|
and error.
|
|
.SH "SEE ALSO"
|
|
.IX Header "SEE ALSO"
|
|
\&\fIOPENSSL_LH_stats\fR\|(3)
|
|
.SH "HISTORY"
|
|
.IX Header "HISTORY"
|
|
In OpenSSL 1.0.0, the lhash interface was revamped for better
|
|
type checking.
|
|
.PP
|
|
In OpenSSL 3.1, \fB\s-1DEFINE_LHASH_OF_EX\s0\fR() was introduced and \fB\s-1DEFINE_LHASH_OF\s0\fR()
|
|
was deprecated.
|
|
.SH "COPYRIGHT"
|
|
.IX Header "COPYRIGHT"
|
|
Copyright 2000\-2023 The OpenSSL Project Authors. All Rights Reserved.
|
|
.PP
|
|
Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
|
|
this file except in compliance with the License. You can obtain a copy
|
|
in the file \s-1LICENSE\s0 in the source distribution or at
|
|
<https://www.openssl.org/source/license.html>.
|