diff options
Diffstat (limited to 'doc/Hash.3')
| -rw-r--r-- | doc/Hash.3 | 240 |
1 files changed, 183 insertions, 57 deletions
@@ -5,19 +5,21 @@ '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" RCS: @(#) $Id: Hash.3,v 1.2 1998/09/14 18:39:49 stanton Exp $ -'\" -.so man.macros .TH Tcl_Hash 3 "" Tcl "Tcl Library Procedures" +.so man.macros .BS .SH NAME -Tcl_InitHashTable, Tcl_DeleteHashTable, Tcl_CreateHashEntry, Tcl_DeleteHashEntry, Tcl_FindHashEntry, Tcl_GetHashValue, Tcl_SetHashValue, Tcl_GetHashKey, Tcl_FirstHashEntry, Tcl_NextHashEntry, Tcl_HashStats \- procedures to manage hash tables +Tcl_InitHashTable, Tcl_InitCustomHashTable, Tcl_InitObjHashTable, Tcl_DeleteHashTable, Tcl_CreateHashEntry, Tcl_DeleteHashEntry, Tcl_FindHashEntry, Tcl_GetHashValue, Tcl_SetHashValue, Tcl_GetHashKey, Tcl_FirstHashEntry, Tcl_NextHashEntry, Tcl_HashStats \- procedures to manage hash tables .SH SYNOPSIS .nf \fB#include <tcl.h>\fR .sp \fBTcl_InitHashTable\fR(\fItablePtr, keyType\fR) .sp +\fBTcl_InitCustomHashTable\fR(\fItablePtr, keyType, typePtr\fR) +.sp +\fBTcl_InitObjHashTable\fR(\fItablePtr\fR) +.sp \fBTcl_DeleteHashTable\fR(\fItablePtr\fR) .sp Tcl_HashEntry * @@ -33,7 +35,7 @@ ClientData .sp \fBTcl_SetHashValue\fR(\fIentryPtr, value\fR) .sp -char * +void * \fBTcl_GetHashKey\fR(\fItablePtr, entryPtr\fR) .sp Tcl_HashEntry * @@ -45,16 +47,18 @@ Tcl_HashEntry * char * \fBTcl_HashStats\fR(\fItablePtr\fR) .SH ARGUMENTS -.AS Tcl_HashSearch *searchPtr +.AS "const Tcl_HashKeyType" *searchPtr out .AP Tcl_HashTable *tablePtr in Address of hash table structure (for all procedures but \fBTcl_InitHashTable\fR, this must have been initialized by previous call to \fBTcl_InitHashTable\fR). .AP int keyType in Kind of keys to use for new hash table. Must be either -TCL_STRING_KEYS, TCL_ONE_WORD_KEYS, or an integer value -greater than 1. -.AP char *key in +\fBTCL_STRING_KEYS\fR, \fBTCL_ONE_WORD_KEYS\fR, \fBTCL_CUSTOM_TYPE_KEYS\fR, +\fBTCL_CUSTOM_PTR_KEYS\fR, or an integer value greater than 1. +.AP Tcl_HashKeyType *typePtr in +Address of structure which defines the behavior of the hash table. +.AP "const void" *key in Key to use for probe into table. Exact form depends on \fIkeyType\fR used to create table. .AP int *newPtr out @@ -69,53 +73,78 @@ ClientData, but must fit in same space as ClientData. Pointer to record to use to keep track of progress in enumerating all the entries in a hash table. .BE - .SH DESCRIPTION .PP -A hash table consists of zero or more entries, each consisting of -a key and a value. -Given the key for an entry, the hashing routines can very quickly -locate the entry, and hence its value. -There may be at most one entry in a hash table with a -particular key, but many entries may have the same value. -Keys can take one of three forms: strings, -one-word values, or integer arrays. -All of the keys in a given table have the same form, which is -specified when the table is initialized. -.PP -The value of a hash table entry can be anything that fits in -the same space as a ``char *'' pointer. -Values for hash table entries are managed entirely by clients, -not by the hash module itself. -Typically each entry's value is a pointer to a data structure -managed by client code. -.PP -Hash tables grow gracefully as the number of entries increases, -so that there are always less than three entries per hash bucket, -on average. -This allows for fast lookups regardless of the number of entries -in a table. -.PP -\fBTcl_InitHashTable\fR initializes a structure that describes -a new hash table. -The space for the structure is provided by the caller, not by -the hash module. -The value of \fIkeyType\fR indicates what kinds of keys will -be used for all entries in the table. \fIKeyType\fR must have -one of the following values: +A hash table consists of zero or more entries, each consisting of a +key and a value. Given the key for an entry, the hashing routines can +very quickly locate the entry, and hence its value. There may be at +most one entry in a hash table with a particular key, but many entries +may have the same value. Keys can take one of four forms: strings, +one-word values, integer arrays, or custom keys defined by a +Tcl_HashKeyType structure (See section \fBTHE TCL_HASHKEYTYPE STRUCTURE\fR +below). All of the keys in a given table have the same +form, which is specified when the table is initialized. +.PP +The value of a hash table entry can be anything that fits in the same +space as a +.QW "char *" +pointer. Values for hash table entries are +managed entirely by clients, not by the hash module itself. Typically +each entry's value is a pointer to a data structure managed by client +code. +.PP +Hash tables grow gracefully as the number of entries increases, so +that there are always less than three entries per hash bucket, on +average. This allows for fast lookups regardless of the number of +entries in a table. +.PP +The core provides three functions for the initialization of hash +tables, Tcl_InitHashTable, Tcl_InitObjHashTable and +Tcl_InitCustomHashTable. +.PP +\fBTcl_InitHashTable\fR initializes a structure that describes a new +hash table. The space for the structure is provided by the caller, +not by the hash module. The value of \fIkeyType\fR indicates what +kinds of keys will be used for all entries in the table. All of the +key types described later are allowed, with the exception of +\fBTCL_CUSTOM_TYPE_KEYS\fR and \fBTCL_CUSTOM_PTR_KEYS\fR. +.PP +\fBTcl_InitObjHashTable\fR is a wrapper around +\fBTcl_InitCustomHashTable\fR and initializes a hash table whose keys +are Tcl_Obj *. +.PP +\fBTcl_InitCustomHashTable\fR initializes a structure that describes a +new hash table. The space for the structure is provided by the +caller, not by the hash module. The value of \fIkeyType\fR indicates +what kinds of keys will be used for all entries in the table. +\fIKeyType\fR must have one of the following values: .IP \fBTCL_STRING_KEYS\fR 25 -Keys are null-terminated ASCII strings. +Keys are null-terminated strings. They are passed to hashing routines using the address of the first character of the string. .IP \fBTCL_ONE_WORD_KEYS\fR 25 Keys are single-word values; they are passed to hashing routines -and stored in hash table entries as ``char *'' values. -The pointer value is the key; it need not (and usually doesn't) +and stored in hash table entries as +.QW "char *" +values. +The pointer value is the key; it need not (and usually does not) actually point to a string. +.IP \fBTCL_CUSTOM_TYPE_KEYS\fR 25 +Keys are of arbitrary type, and are stored in the entry. Hashing +and comparison is determined by \fItypePtr\fR. The Tcl_HashKeyType +structure is described in the section +\fBTHE TCL_HASHKEYTYPE STRUCTURE\fR below. +.IP \fBTCL_CUSTOM_PTR_KEYS\fR 25 +Keys are pointers to an arbitrary type, and are stored in the entry. Hashing +and comparison is determined by \fItypePtr\fR. The Tcl_HashKeyType +structure is described in the section +\fBTHE TCL_HASHKEYTYPE STRUCTURE\fR below. .IP \fIother\fR 25 -If \fIkeyType\fR is not TCL_STRING_KEYS or TCL_ONE_WORD_KEYS, +If \fIkeyType\fR is not one of the above, then it must be an integer value greater than 1. -In this case the keys will be arrays of ``int'' values, where +In this case the keys will be arrays of +.QW int +values, where \fIkeyType\fR gives the number of ints in each key. This allows structures to be used as keys. All keys must have the same size. @@ -136,7 +165,7 @@ before deleting the table. .PP \fBTcl_CreateHashEntry\fR locates the entry corresponding to a particular key, creating a new entry in the table if there -wasn't already one with the given key. +was not already one with the given key. If an entry already existed with the given key then \fI*newPtr\fR is set to zero. If a new entry was created, then \fI*newPtr\fR is set to a non-zero @@ -152,28 +181,34 @@ the client is responsible for any cleanup associated with the entry's value, such as freeing a structure that it points to. .PP \fBTcl_FindHashEntry\fR is similar to \fBTcl_CreateHashEntry\fR -except that it doesn't create a new entry if the key doesn't exist; +except that it does not create a new entry if the key doesn't exist; instead, it returns NULL as result. .PP \fBTcl_GetHashValue\fR and \fBTcl_SetHashValue\fR are used to read and write an entry's value, respectively. -Values are stored and retrieved as type ``ClientData'', which is +Values are stored and retrieved as type +.QW ClientData , +which is large enough to hold a pointer value. On almost all machines this is large enough to hold an integer value too. .PP \fBTcl_GetHashKey\fR returns the key for a given hash table entry, -either as a pointer to a string, a one-word (``char *'') key, or +either as a pointer to a string, a one-word +.PQ "char *" +key, or as a pointer to the first word of an array of integers, depending on the \fIkeyType\fR used to create a hash table. In all cases \fBTcl_GetHashKey\fR returns a result with type -``char *''. +.QW "char *" . When the key is a string or array, the result of \fBTcl_GetHashKey\fR points to information in the table entry; this information will remain valid until the entry is deleted or its table is deleted. .PP \fBTcl_FirstHashEntry\fR and \fBTcl_NextHashEntry\fR may be used to scan all of the entries in a hash table. -A structure of type ``Tcl_HashSearch'', provided by the client, +A structure of type +.QW Tcl_HashSearch , +provided by the client, is used to keep track of progress through the table. \fBTcl_FirstHashEntry\fR initializes the search record and returns the first entry in the table (or NULL if the table is @@ -184,16 +219,17 @@ NULL if the end of the table has been reached. A call to \fBTcl_FirstHashEntry\fR followed by calls to \fBTcl_NextHashEntry\fR will return each of the entries in the table exactly once, in an arbitrary order. -It is unadvisable to modify the structure of the table, e.g. -by creating or deleting entries, while the search is in -progress. +It is inadvisable to modify the structure of the table, e.g. +by creating or deleting entries, while the search is in progress, +with the exception of deleting the entry returned by +\fBTcl_FirstHashEntry\fR or \fBTcl_NextHashEntry\fR. .PP \fBTcl_HashStats\fR returns a dynamically-allocated string with overall information about a hash table, such as the number of entries it contains, the number of buckets in its hash array, and the utilization of the buckets. It is the caller's responsibility to free the result string -by passing it to \fBfree\fR. +by passing it to \fBckfree\fR. .PP The header file \fBtcl.h\fR defines the actual data structures used to implement hash tables. @@ -203,6 +239,96 @@ the values of entries. However, users of the hashing routines should never refer directly to any of the fields of any of the hash-related data structures; use the procedures and macros defined here. - +.SH "THE TCL_HASHKEYTYPE STRUCTURE" +.PP +Extension writers can define new hash key types by defining four procedures, +initializing a \fBTcl_HashKeyType\fR structure to describe the type, and +calling \fBTcl_InitCustomHashTable\fR. The \fBTcl_HashKeyType\fR structure is +defined as follows: +.PP +.CS +typedef struct Tcl_HashKeyType { + int \fIversion\fR; + int \fIflags\fR; + Tcl_HashKeyProc *\fIhashKeyProc\fR; + Tcl_CompareHashKeysProc *\fIcompareKeysProc\fR; + Tcl_AllocHashEntryProc *\fIallocEntryProc\fR; + Tcl_FreeHashEntryProc *\fIfreeEntryProc\fR; +} \fBTcl_HashKeyType\fR; +.CE +.PP +The \fIversion\fR member is the version of the table. If this structure is +extended in future then the version can be used to distinguish between +different structures. It should be set to \fBTCL_HASH_KEY_TYPE_VERSION\fR. +.PP +The \fIflags\fR member is 0 or one or more of the following values OR'ed +together: +.IP \fBTCL_HASH_KEY_RANDOMIZE_HASH\fR 25 +There are some things, pointers for example which do not hash well because +they do not use the lower bits. If this flag is set then the hash table will +attempt to rectify this by randomizing the bits and then using the upper N +bits as the index into the table. +.IP \fBTCL_HASH_KEY_SYSTEM_HASH\fR 25 +This flag forces Tcl to use the memory allocation procedures provided by the +operating system when allocating and freeing memory used to store the hash +table data structures, and not any of Tcl's own customized memory allocation +routines. This is important if the hash table is to be used in the +implementation of a custom set of allocation routines, or something that a +custom set of allocation routines might depend on, in order to avoid any +circular dependency. +.PP +The \fIhashKeyProc\fR member contains the address of a function called to +calculate a hash value for the key. +.PP +.CS +typedef unsigned int \fBTcl_HashKeyProc\fR( + Tcl_HashTable *\fItablePtr\fR, + void *\fIkeyPtr\fR); +.CE +.PP +If this is NULL then \fIkeyPtr\fR is used and +\fBTCL_HASH_KEY_RANDOMIZE_HASH\fR is assumed. +.PP +The \fIcompareKeysProc\fR member contains the address of a function called to +compare two keys. +.PP +.CS +typedef int \fBTcl_CompareHashKeysProc\fR( + void *\fIkeyPtr\fR, + Tcl_HashEntry *\fIhPtr\fR); +.CE +.PP +If this is NULL then the \fIkeyPtr\fR pointers are compared. If the keys do +not match then the function returns 0, otherwise it returns 1. +.PP +The \fIallocEntryProc\fR member contains the address of a function called to +allocate space for an entry and initialize the key and clientData. +.PP +.CS +typedef Tcl_HashEntry *\fBTcl_AllocHashEntryProc\fR( + Tcl_HashTable *\fItablePtr\fR, + void *\fIkeyPtr\fR); +.CE +.PP +If this is NULL then \fBTcl_Alloc\fR is used to allocate enough space for a +Tcl_HashEntry, the key pointer is assigned to key.oneWordValue and the +clientData is set to NULL. String keys and array keys use this function to +allocate enough space for the entry and the key in one block, rather than +doing it in two blocks. This saves space for a pointer to the key from the +entry and another memory allocation. Tcl_Obj* keys use this function to +allocate enough space for an entry and increment the reference count on the +value. +.PP +The \fIfreeEntryProc\fR member contains the address of a function called to +free space for an entry. +.PP +.CS +typedef void \fBTcl_FreeHashEntryProc\fR( + Tcl_HashEntry *\fIhPtr\fR); +.CE +.PP +If this is NULL then \fBTcl_Free\fR is used to free the space for the entry. +Tcl_Obj* keys use this function to decrement the reference count on the +value. .SH KEYWORDS hash table, key, lookup, search, value |