/* * Copyright (c) 2000-2004 Apple Computer, Inc. All rights reserved. * * @APPLE_OSREFERENCE_LICENSE_HEADER_START@ * * This file contains Original Code and/or Modifications of Original Code * as defined in and that are subject to the Apple Public Source License * Version 2.0 (the 'License'). You may not use this file except in * compliance with the License. The rights granted to you under the License * may not be used to create, or enable the creation or redistribution of, * unlawful or unlicensed copies of an Apple operating system, or to * circumvent, violate, or enable the circumvention or violation of, any * terms of an Apple operating system software license agreement. * * Please obtain a copy of the License at * http://www.opensource.apple.com/apsl/ and read it before using this file. * * The Original Code and all software distributed under the License are * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. * Please see the License for the specific language governing rights and * limitations under the License. * * @APPLE_OSREFERENCE_LICENSE_HEADER_END@ */ /* * @OSF_COPYRIGHT@ */ /* * Mach Operating System * Copyright (c) 1991,1990,1989 Carnegie Mellon University * All Rights Reserved. * * Permission to use, copy, modify and distribute this software and its * documentation is hereby granted, provided that both the copyright * notice and this permission notice appear in all copies of the * software, derivative works or modified versions, and any portions * thereof, and that both notices appear in supporting documentation. * * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. * * Carnegie Mellon requests users of this software to return to * * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU * School of Computer Science * Carnegie Mellon University * Pittsburgh PA 15213-3890 * * any improvements or extensions that they make and grant Carnegie Mellon * the rights to redistribute these changes. */ /* */ /* * File: ipc/ipc_hash.c * Author: Rich Draves * Date: 1989 * * Entry hash table operations. */ #include <mach/boolean.h> #include <mach/port.h> #include <kern/kalloc.h> #include <ipc/port.h> #include <ipc/ipc_space.h> #include <ipc/ipc_object.h> #include <ipc/ipc_entry.h> #include <ipc/ipc_hash.h> #include <ipc/ipc_init.h> #include <mach_ipc_debug.h> #if MACH_IPC_DEBUG #include <mach/kern_return.h> #include <mach_debug/hash_info.h> #include <vm/vm_map.h> #include <vm/vm_kern.h> #endif /* MACH_IPC_DEBUG */ /* * Forward declarations */ /* Delete an entry from the local reverse hash table */ void ipc_hash_local_delete( ipc_space_t space, ipc_object_t obj, mach_port_index_t index, ipc_entry_t entry); /* * Routine: ipc_hash_lookup * Purpose: * Converts (space, obj) -> (name, entry). * Returns TRUE if an entry was found. * Conditions: * The space must be locked (read or write) throughout. */ boolean_t ipc_hash_lookup( ipc_space_t space, ipc_object_t obj, mach_port_name_t *namep, ipc_entry_t *entryp) { return ipc_hash_table_lookup(space->is_table, space->is_table_size, obj, namep, entryp); } /* * Routine: ipc_hash_insert * Purpose: * Inserts an entry into the appropriate reverse hash table, * so that ipc_hash_lookup will find it. * Conditions: * The space must be write-locked. */ void ipc_hash_insert( ipc_space_t space, ipc_object_t obj, mach_port_name_t name, ipc_entry_t entry) { mach_port_index_t index; index = MACH_PORT_INDEX(name); ipc_hash_table_insert(space->is_table, space->is_table_size, obj, index, entry); } /* * Routine: ipc_hash_delete * Purpose: * Deletes an entry from the appropriate reverse hash table. * Conditions: * The space must be write-locked. */ void ipc_hash_delete( ipc_space_t space, ipc_object_t obj, mach_port_name_t name, ipc_entry_t entry) { mach_port_index_t index; index = MACH_PORT_INDEX(name); ipc_hash_table_delete(space->is_table, space->is_table_size, obj, index, entry); } /* * Each space has a local reverse hash table, which holds * entries from the space's table. In fact, the hash table * just uses a field (ie_index) in the table itself. * * The local hash table is an open-addressing hash table, * which means that when a collision occurs, instead of * throwing the entry into a bucket, the entry is rehashed * to another position in the table. In this case the rehash * is very simple: linear probing (ie, just increment the position). * This simple rehash makes deletions tractable (they're still a pain), * but it means that collisions tend to build up into clumps. * * Because at least one entry in the table (index 0) is always unused, * there will always be room in the reverse hash table. If a table * with n slots gets completely full, the reverse hash table will * have one giant clump of n-1 slots and one free slot somewhere. * Because entries are only entered into the reverse table if they * are pure send rights (not receive, send-once, port-set, * or dead-name rights), and free entries of course aren't entered, * I expect the reverse hash table won't get unreasonably full. * * Ordered hash tables (Amble & Knuth, Computer Journal, v. 17, no. 2, * pp. 135-142.) may be desirable here. They can dramatically help * unsuccessful lookups. But unsuccessful lookups are almost always * followed by insertions, and those slow down somewhat. They * also can help deletions somewhat. Successful lookups aren't affected. * So possibly a small win; probably nothing significant. */ #define IH_TABLE_HASH(obj, size) \ ((mach_port_index_t)((((uintptr_t) (obj)) >> 6) % (size))) /* * Routine: ipc_hash_table_lookup * Purpose: * Converts (table, obj) -> (name, entry). * Conditions: * Must have read consistency on the table. */ boolean_t ipc_hash_table_lookup( ipc_entry_t table, ipc_entry_num_t size, ipc_object_t obj, mach_port_name_t *namep, ipc_entry_t *entryp) { mach_port_index_t hindex, index; if (obj == IO_NULL) { return FALSE; } hindex = IH_TABLE_HASH(obj, size); /* * Ideally, table[hindex].ie_index is the name we want. * However, must check ie_object to verify this, * because collisions can happen. In case of a collision, * search farther along in the clump. */ while ((index = table[hindex].ie_index) != 0) { ipc_entry_t entry; assert(index < size); entry = &table[index]; if (entry->ie_object == obj) { *entryp = entry; *namep = MACH_PORT_MAKE(index, IE_BITS_GEN(entry->ie_bits)); return TRUE; } if (++hindex == size) hindex = 0; } return FALSE; } /* * Routine: ipc_hash_table_insert * Purpose: * Inserts an entry into the space's reverse hash table. * Conditions: * The space must be write-locked. */ void ipc_hash_table_insert( ipc_entry_t table, ipc_entry_num_t size, ipc_object_t obj, mach_port_index_t index, __assert_only ipc_entry_t entry) { mach_port_index_t hindex; assert(index != 0); assert(obj != IO_NULL); hindex = IH_TABLE_HASH(obj, size); assert(entry == &table[index]); assert(entry->ie_object == obj); /* * We want to insert at hindex, but there may be collisions. * If a collision occurs, search for the end of the clump * and insert there. */ while (table[hindex].ie_index != 0) { if (++hindex == size) hindex = 0; } table[hindex].ie_index = index; } /* * Routine: ipc_hash_table_delete * Purpose: * Deletes an entry from the table's reverse hash. * Conditions: * Exclusive access to the table. */ void ipc_hash_table_delete( ipc_entry_t table, ipc_entry_num_t size, ipc_object_t obj, mach_port_index_t index, __assert_only ipc_entry_t entry) { mach_port_index_t hindex, dindex; assert(index != MACH_PORT_NULL); assert(obj != IO_NULL); hindex = IH_TABLE_HASH(obj, size); assert(entry == &table[index]); assert(entry->ie_object == obj); /* * First check we have the right hindex for this index. * In case of collision, we have to search farther * along in this clump. */ while (table[hindex].ie_index != index) { if (++hindex == size) hindex = 0; } /* * Now we want to set table[hindex].ie_index = 0. * But if we aren't the last index in a clump, * this might cause problems for lookups of objects * farther along in the clump that are displaced * due to collisions. Searches for them would fail * at hindex instead of succeeding. * * So we must check the clump after hindex for objects * that are so displaced, and move one up to the new hole. * * hindex - index of new hole in the clump * dindex - index we are checking for a displaced object * * When we move a displaced object up into the hole, * it creates a new hole, and we have to repeat the process * until we get to the end of the clump. */ for (dindex = hindex; index != 0; hindex = dindex) { for (;;) { mach_port_index_t tindex; ipc_object_t tobj; if (++dindex == size) dindex = 0; assert(dindex != hindex); /* are we at the end of the clump? */ index = table[dindex].ie_index; if (index == 0) break; /* is this a displaced object? */ tobj = table[index].ie_object; assert(tobj != IO_NULL); tindex = IH_TABLE_HASH(tobj, size); if ((dindex < hindex) ? ((dindex < tindex) && (tindex <= hindex)) : ((dindex < tindex) || (tindex <= hindex))) break; } table[hindex].ie_index = index; } }