Context.c

/***********************************************************
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/*

Copyright 1987, 1988, 1990, 1994, 1998  The Open Group

Permission to use, copy, modify, distribute, and sell this software and its
documentation for any purpose is hereby granted without fee, provided that
the above copyright notice appear in all copies and that both that
copyright notice and this permission notice appear in supporting
documentation.

The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE OPEN GROUP BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

Except as contained in this notice, the name of The Open Group shall
not be used in advertising or otherwise to promote the sale, use or
other dealings in this Software without prior written authorization
from The Open Group.

*/

/* This module implements a simple sparse array.

   XSaveContext(a,b,c,d) will store d in position (a,b,c) of the array.
   XFindContext(a,b,c,&d) will set d to be the value in position (a,b,c).
   XDeleteContext(a,b,c) will delete the entry in (a,b,c).

   a is a display id, b is a resource id, and c is a Context.  d is just an
   XPointer.  This code will work with any range of parameters, but is geared
   to be most efficient with very few (one or two) different a's.

*/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include "Xlibint.h"
#include "Xutil.h"
#ifdef XTHREADS
#include "locking.h"
#endif

#define INITHASHMASK 63 /* Number of entries originally in the hash table. */

typedef struct _TableEntryRec {	/* Stores one entry. */
    XID 			rid;
    XContext			context;
    XPointer			data;
    struct _TableEntryRec	*next;
} TableEntryRec, *TableEntry;

typedef struct _XContextDB {	/* Stores hash table for one display. */
    TableEntry *table;		/* Pointer to array of hash entries. */
    int mask;			/* Current size of hash table minus 1. */
    int numentries;		/* Number of entries currently in table. */
#ifdef XTHREADS
    LockInfoRec linfo;
#endif
} DBRec, *DB;

#ifdef MOTIFBC
static DB NullDB = (DB)0;
#endif

/* Given an XID and a context, returns a value between 0 and HashSize-1.
   Currently, this requires that HashSize be a power of 2.
*/

#define Hash(db,rid,context) \
    (db)->table[(((rid) << 1) + context) & (db)->mask]

/* Resize the given db */

static void ResizeTable(DB db)
{
    TableEntry *otable;
    register TableEntry entry, next, *pold, *head;
    register int i, j;

    otable = db->table;
    for (i = INITHASHMASK+1; (i + i) < db->numentries; )
	i += i;
    db->table = Xcalloc(i, sizeof(TableEntry));
    if (!db->table) {
	db->table = otable;
	return;
    }
    j = db->mask + 1;
    db->mask = i - 1;
    for (pold = otable ; --j >= 0; pold++) {
	for (entry = *pold; entry; entry = next) {
	    next = entry->next;
	    head = &Hash(db, entry->rid, entry->context);
	    entry->next = *head;
	    *head = entry;
	}
    }
    Xfree(otable);
}

static void _XFreeContextDB(Display *display)
{
    register DB db;
    register int i;
    register TableEntry *pentry, entry, next;

    db = display->context_db;
    if (db) {
	for (i = db->mask + 1, pentry = db->table ; --i >= 0; pentry++) {
	    for (entry = *pentry; entry; entry = next) {
		next = entry->next;
		Xfree(entry);
	    }
	}
	Xfree(db->table);
	_XFreeMutex(&db->linfo);
	Xfree(db);
    }
}

/* Public routines. */

/* Save the given value of data to correspond with the keys XID and context.
   Returns nonzero error code if an error has occured, 0 otherwise.
   Possible errors are Out-of-memory.
*/

int XSaveContext(
    Display *display,
    register XID rid,
    register XContext context,
    _Xconst char* data)
{
    DB *pdb;
    register DB db;
    TableEntry *head;
    register TableEntry entry;

#ifdef MOTIFBC
    if (!display) {
	pdb = &NullDB;
	db = *pdb;
    } else
#endif
    {
	LockDisplay(display);
	pdb = &display->context_db;
	db = *pdb;
	UnlockDisplay(display);
    }
    if (!db) {
	db = Xmalloc(sizeof(DBRec));
	if (!db)
	    return XCNOMEM;
	db->mask = INITHASHMASK;
	db->table = Xcalloc(db->mask + 1, sizeof(TableEntry));
	if (!db->table) {
	    Xfree(db);
	    return XCNOMEM;
	}
	db->numentries = 0;
	_XCreateMutex(&db->linfo);
#ifdef MOTIFBC
	if (!display) *pdb = db; else
#endif
	{
	    LockDisplay(display);
	    *pdb = db;
	    display->free_funcs->context_db = _XFreeContextDB;
	    UnlockDisplay(display);
	}
    }
    _XLockMutex(&db->linfo);
    head = &Hash(db, rid, context);
    _XUnlockMutex(&db->linfo);
    for (entry = *head; entry; entry = entry->next) {
	if (entry->rid == rid && entry->context == context) {
	    entry->data = (XPointer)data;
	    return 0;
	}
    }
    entry = Xmalloc(sizeof(TableEntryRec));
    if (!entry)
	return XCNOMEM;
    entry->rid = rid;
    entry->context = context;
    entry->data = (XPointer)data;
    entry->next = *head;
    *head = entry;
    _XLockMutex(&db->linfo);
    db->numentries++;
    if (db->numentries > (db->mask << 2))
	ResizeTable(db);
    _XUnlockMutex(&db->linfo);
    return 0;
}



/* Given an XID and context, returns the associated data.  Note that data
   here is a pointer since it is a return value.  Returns nonzero error code
   if an error has occured, 0 otherwise.  Possible errors are Entry-not-found.
*/

int XFindContext(Display *display, XID rid, XContext context, XPointer *data)
{
    register DB db;
    register TableEntry entry;

#ifdef MOTIFBC
    if (!display) db = NullDB; else
#endif
    {
	LockDisplay(display);
	db = display->context_db;
	UnlockDisplay(display);
    }
    if (!db)
	return XCNOENT;
    _XLockMutex(&db->linfo);
    for (entry = Hash(db, rid, context); entry; entry = entry->next)
    {
	if (entry->rid == rid && entry->context == context) {
	    *data = (XPointer)entry->data;
	    _XUnlockMutex(&db->linfo);
	    return 0;
	}
    }
    _XUnlockMutex(&db->linfo);
    return XCNOENT;
}



/* Deletes the entry for the given XID and context from the datastructure.
   This returns the same thing that FindContext would have returned if called
   with the same arguments.
*/

int XDeleteContext(Display *display, XID rid, XContext context)
{
    register DB db;
    register TableEntry entry, *prev;

#ifdef MOTIFBC
    if (!display) db = NullDB; else
#endif
    {
	LockDisplay(display);
	db = display->context_db;
	UnlockDisplay(display);
    }
    if (!db)
	return XCNOENT;
    _XLockMutex(&db->linfo);
    for (prev = &Hash(db, rid, context);
	 (entry = *prev);
	 prev = &entry->next) {
	if (entry->rid == rid && entry->context == context) {
	    *prev = entry->next;
	    Xfree(entry);
	    db->numentries--;
	    if (db->numentries < db->mask && db->mask > INITHASHMASK)
		ResizeTable(db);
	    _XUnlockMutex(&db->linfo);
	    return 0;
	}
    }
    _XUnlockMutex(&db->linfo);
    return XCNOENT;
}