.\" $NetBSD: thmap.9,v 1.3 2020/08/28 07:03:41 riastradh Exp $ .\" .\" Copyright (c) 2018 Mindaugas Rasiukevicius .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .Dd December 11, 2018 .Dt THMAP 9 .Os .Sh NAME .Nm thmap .Nd concurrent trie-hash map .Sh SYNOPSIS .In thmap.h .\" ----- .Ft thmap_t * .Fn thmap_create "uintptr_t baseptr" "const thmap_ops_t *ops" "unsigned flags" .Ft void .Fn thmap_destroy "thmap_t *thmap" .Ft void * .Fn thmap_get "thmap_t *thmap" "const void *key" "size_t len" .Ft void * .Fn thmap_put "thmap_t *thmap" "const void *key" "size_t len" "void *val" .Ft void * .Fn thmap_del "thmap_t *thmap" "const void *key" "size_t len" .Ft void * .Fn thmap_stage_gc "thmap_t *thmap" .Ft void .Fn thmap_gc "thmap_t *thmap" "void *ref" .Ft void .Fn thmap_setroot "thmap_t *thmap" "uintptr_t root_offset" .Ft uintptr_t .Fn thmap_getroot "const thmap_t *thmap" .\" ----- .Sh DESCRIPTION Concurrent trie-hash map \(em a general purpose associative array, combining the elements of hashing and radix trie. Highlights: .Pp .Bl -hyphen -compact .It Very competitive performance, with logarithmic time complexity on average. .It Lookups are lock-free and inserts/deletes are using fine-grained locking. .It Incremental growth of the data structure (no large resizing/rehashing). .It Optional support for use with shared memory, e.g. memory-mapped file. .El .Pp Delete operations (the key/data destruction) must be synchronized with the readers using some reclamation mechanism. .\" ----- .Sh FUNCTIONS .Bl -tag -width abcd .It Fn thmap_create baseptr ops flags Construct a new trie-hash map. The optional .Fa ops parameter can used to set the custom allocate/free operations (see the description of .Vt thmap_ops_t below). In such case, the .Fa baseptr is the base (start) address of the address space mapping (it must be word-aligned). If .Fa ops is set to .Dv NULL , then .Xr malloc 3 and .Xr free 3 will be used as the default operations and .Fa baseptr should be set to zero. Currently, the supported .Fa flags are: .Bl -tag -width THMAP_SETROOT .It Dv THMAP_NOCOPY The keys on insert will not be copied and the given pointers to them will be expected to be valid and the values constant until the key is deleted; by default, the put operation will make a copy of the key. .It Dv THMAP_SETROOT Indicate that the root of the map will be manually set using the .Fn thmap_setroot routine; by default, the map is initialized and the root node is set on .Fn thmap_create . .El .\" --- .It Fn thmap_destroy thmap Destroy the map, freeing the memory it uses. .\" --- .It Fn thmap_get thmap key len Lookup the key (of a given length) and return the value associated with it. Return .Dv NULL if the key is not found (see the .Sx CAVEATS section). .\" --- .It Fn thmap_put thmap key len val Insert the key with an arbitrary value. If the key is already present, return the already existing associated value without changing it. Otherwise, on a successful insert, return the given value. Just compare the result against .Fa val to test whether the insert was successful. .\" --- .It Fn thmap_del thmap key len Remove the given key. If the key was present, return the associated value; otherwise return .Dv NULL . The memory associated with the entry is not released immediately, because in the concurrent environment (e.g., multi-threaded application) the caller may need to ensure it is safe to do so. It is managed using the .Fn thmap_stage_gc and .Fn thmap_gc routines. .\" --- .It Fn thmap_stage_gc thmap Stage the currently pending entries (the memory not yet released after the deletion) for reclamation (G/C). This operation should be called .Em before the synchronization barrier. .Pp Returns a reference which must be passed to .Fn thmap_gc . Not calling the G/C function for the returned reference would result in a memory leak. .\" --- .It Fn thmap_gc thmap ref Reclaim (G/C) the staged entries i.e. release any memory associated with the deleted keys. The reference must be the value returned by the call to .Fn thmap_stage_gc . .Pp This function must be called .Em after the synchronization barrier which guarantees that there are no active readers referencing the staged entries. .\" --- .El .Pp If the map is created using the .Fa THMAP_SETROOT flag, then the following functions are applicable: .\" --- .Bl -tag -width abcd .It Fn thmap_setroot thmap root_offset Set the root node. The address must be relative to the base address, as if allocated by the .Fn thmap_ops_t::alloc routine. Return 0 on success and \-1 on failure (if already set). .It Fn thmap_getroot thmap Get the root node address. The returned address will be relative to the base address. .El .\" --- .Pp Members of .Vt thmap_ops_t are .Bd -literal uintptr_t (*alloc)(size_t len); void (*free)(uintptr_t addr, size_t len); .Ed .\" ----- .Sh EXAMPLES Simple case backed by .Xr malloc 3 , which could be used in multi-threaded environment: .Bd -literal thmap_t *kvmap; struct obj *obj; kvmap = thmap_create(0, NULL); assert(kvmap != NULL); ... obj = obj_create(); thmap_put(kvmap, "test", sizeof("test") - 1, obj); ... obj = thmap_get(kvmap, "test", sizeof("test") - 1); ... thmap_destroy(kvmap); .Ed .\" ----- .Sh AUTHORS .An Mindaugas Rasiukevicius Aq Mt rmind@noxt.eu .Sh CAVEATS The implementation uses pointer tagging and atomic operations. This requires the base address and the allocations to provide at least word alignment. .Pp While the .Dv NULL values may be inserted, .Fn thmap_get and .Fn thmap_del cannot indicate whether the key was not found or a key with a .Dv NULL value was found. If the caller needs to indicate an "empty" value, it can use a special pointer value, such as .Li (void *)(uintptr_t)0x1 . .\" -----