Current File : //opt/imunify360-webshield/lualib/resty/lrucache/pureffi.lua
-- Copyright (C) Yichun Zhang (agentzh)
-- Copyright (C) Shuxin Yang
--[[
This module implements a key/value cache store. We adopt LRU as our
replace/evict policy. Each key/value pair is tagged with a Time-to-Live (TTL);
from user's perspective, stale pairs are automatically removed from the cache.
Why FFI
-------
In Lua, expression "table[key] = nil" does not *PHYSICALLY* remove the value
associated with the key; it just set the value to be nil! So the table will
keep growing with large number of the key/nil pairs which will be purged until
resize() operator is called.
This "feature" is terribly ill-suited to what we need. Therefore we have to
rely on FFI to build a hash-table where any entry can be physically deleted
immediately.
Under the hood:
--------------
In concept, we introduce three data structures to implement the cache store:
1. key/value vector for storing keys and values.
2. a queue to mimic the LRU.
3. hash-table for looking up the value for a given key.
Unfortunately, efficiency and clarity usually come at each other cost. The
data strucutres we are using are slightly more complicated than what we
described above.
o. Lua does not have efficient way to store a vector of pair. So, we use
two vectors for key/value pair: one for keys and the other for values
(_M.key_v and _M.val_v, respectively), and i-th key corresponds to
i-th value.
A key/value pair is identified by the "id" field in a "node" (we shall
discuss node later)
o. The queue is nothing more than a doubly-linked list of "node" linked via
lrucache_pureffi_queue_s::{next|prev} fields.
o. The hash-table has two parts:
- the _M.bucket_v[] a vector of bucket, indiced by hash-value, and
- a bucket is a singly-linked list of "node" via the
lrucache_pureffi_queue_s::conflict field.
A key must be a string, and the hash value of a key is evaluated by:
crc32(key-cast-to-pointer) % size(_M.bucket_v).
We mandate size(_M.bucket_v) being a power-of-two in order to avoid
expensive modulo operation.
At the heart of the module is an array of "node" (of type
lrucache_pureffi_queue_s). A node:
- keeps the meta-data of its corresponding key/value pair
(embodied by the "id", and "expire" field);
- is a part of LRU queue (embodied by "prev" and "next" fields);
- is a part of hash-table (embodied by the "conflict" field).
]]
local ffi = require "ffi"
local bit = require "bit"
local ffi_new = ffi.new
local ffi_sizeof = ffi.sizeof
local ffi_cast = ffi.cast
local ffi_fill = ffi.fill
local ngx_now = ngx.now
local uintptr_t = ffi.typeof("uintptr_t")
local c_str_t = ffi.typeof("const char*")
local int_t = ffi.typeof("int")
local int_array_t = ffi.typeof("int[?]")
local crc_tab = ffi.new("const unsigned int[256]", {
0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419, 0x706AF48F,
0xE963A535, 0x9E6495A3, 0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988,
0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91, 0x1DB71064, 0x6AB020F2,
0xF3B97148, 0x84BE41DE, 0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7,
0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 0x63066CD9,
0xFA0F3D63, 0x8D080DF5, 0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172,
0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B, 0x35B5A8FA, 0x42B2986C,
0xDBBBC9D6, 0xACBCF940, 0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59,
0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423,
0xCFBA9599, 0xB8BDA50F, 0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924,
0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D, 0x76DC4190, 0x01DB7106,
0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433,
0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818, 0x7F6A0DBB, 0x086D3D2D,
0x91646C97, 0xE6635C01, 0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E,
0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457, 0x65B0D9C6, 0x12B7E950,
0x8BBEB8EA, 0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65,
0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2, 0x4ADFA541, 0x3DD895D7,
0xA4D1C46D, 0xD3D6F4FB, 0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0,
0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9, 0x5005713C, 0x270241AA,
0xBE0B1010, 0xC90C2086, 0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,
0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17, 0x2EB40D81,
0xB7BD5C3B, 0xC0BA6CAD, 0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A,
0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683, 0xE3630B12, 0x94643B84,
0x0D6D6A3E, 0x7A6A5AA8, 0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1,
0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB,
0x196C3671, 0x6E6B06E7, 0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC,
0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5, 0xD6D6A3E8, 0xA1D1937E,
0x38D8C2C4, 0x4FDFF252, 0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B,
0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60, 0xDF60EFC3, 0xA867DF55,
0x316E8EEF, 0x4669BE79, 0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236,
0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F, 0xC5BA3BBE, 0xB2BD0B28,
0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D,
0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A, 0x9C0906A9, 0xEB0E363F,
0x72076785, 0x05005713, 0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38,
0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21, 0x86D3D2D4, 0xF1D4E242,
0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777,
0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C, 0x8F659EFF, 0xF862AE69,
0x616BFFD3, 0x166CCF45, 0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2,
0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB, 0xAED16A4A, 0xD9D65ADC,
0x40DF0B66, 0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,
0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6, 0xBAD03605, 0xCDD70693,
0x54DE5729, 0x23D967BF, 0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94,
0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D });
local setmetatable = setmetatable
local tonumber = tonumber
local tostring = tostring
local type = type
local brshift = bit.rshift
local bxor = bit.bxor
local band = bit.band
local new_tab
do
local ok
ok, new_tab = pcall(require, "table.new")
if not ok then
new_tab = function(narr, nrec) return {} end
end
end
-- queue data types
--
-- this queue is a double-ended queue and the first node
-- is reserved for the queue itself.
-- the implementation is mostly borrowed from nginx's ngx_queue_t data
-- structure.
ffi.cdef[[
/* A lrucache_pureffi_queue_s node hook together three data structures:
* o. the key/value store as embodied by the "id" (which is in essence the
* indentifier of key/pair pair) and the "expire" (which is a metadata
* of the corresponding key/pair pair).
* o. The LRU queue via the prev/next fields.
* o. The hash-tabble as embodied by the "conflict" field.
*/
typedef struct lrucache_pureffi_queue_s lrucache_pureffi_queue_t;
struct lrucache_pureffi_queue_s {
/* Each node is assigned a unique ID at construction time, and the
* ID remain immutatble, regardless the node is in active-list or
* free-list. The queue header is assigned ID 0. Since queue-header
* is a sentinel node, 0 denodes "invalid ID".
*
* Intuitively, we can view the "id" as the identifier of key/value
* pair.
*/
int id;
/* The bucket of the hash-table is implemented as a singly-linked list.
* The "conflict" refers to the ID of the next node in the bucket.
*/
int conflict;
uint32_t user_flags;
double expire; /* in seconds */
lrucache_pureffi_queue_t *prev;
lrucache_pureffi_queue_t *next;
};
]]
local queue_arr_type = ffi.typeof("lrucache_pureffi_queue_t[?]")
--local queue_ptr_type = ffi.typeof("lrucache_pureffi_queue_t*")
local queue_type = ffi.typeof("lrucache_pureffi_queue_t")
local NULL = ffi.null
--========================================================================
--
-- Queue utility functions
--
--========================================================================
-- Append the element "x" to the given queue "h".
local function queue_insert_tail(h, x)
local last = h[0].prev
x.prev = last
last.next = x
x.next = h
h[0].prev = x
end
--[[
Allocate a queue with size + 1 elements. Elements are linked together in a
circular way, i.e. the last element's "next" points to the first element,
while the first element's "prev" element points to the last element.
]]
local function queue_init(size)
if not size then
size = 0
end
local q = ffi_new(queue_arr_type, size + 1)
ffi_fill(q, ffi_sizeof(queue_type, size + 1), 0)
if size == 0 then
q[0].prev = q
q[0].next = q
else
local prev = q[0]
for i = 1, size do
local e = q[i]
e.id = i
e.user_flags = 0
prev.next = e
e.prev = prev
prev = e
end
local last = q[size]
last.next = q
q[0].prev = last
end
return q
end
local function queue_is_empty(q)
-- print("q: ", tostring(q), "q.prev: ", tostring(q), ": ", q == q.prev)
return q == q[0].prev
end
local function queue_remove(x)
local prev = x.prev
local next = x.next
next.prev = prev
prev.next = next
-- for debugging purpose only:
x.prev = NULL
x.next = NULL
end
-- Insert the element "x" the to the given queue "h"
local function queue_insert_head(h, x)
x.next = h[0].next
x.next.prev = x
x.prev = h
h[0].next = x
end
local function queue_last(h)
return h[0].prev
end
local function queue_head(h)
return h[0].next
end
--========================================================================
--
-- Miscellaneous Utility Functions
--
--========================================================================
local function ptr2num(ptr)
return tonumber(ffi_cast(uintptr_t, ptr))
end
local function crc32_ptr(ptr)
local p = brshift(ptr2num(ptr), 3)
local b = band(p, 255)
local crc32 = crc_tab[b]
b = band(brshift(p, 8), 255)
crc32 = bxor(brshift(crc32, 8), crc_tab[band(bxor(crc32, b), 255)])
b = band(brshift(p, 16), 255)
crc32 = bxor(brshift(crc32, 8), crc_tab[band(bxor(crc32, b), 255)])
--b = band(brshift(p, 24), 255)
--crc32 = bxor(brshift(crc32, 8), crc_tab[band(bxor(crc32, b), 255)])
return crc32
end
--========================================================================
--
-- Implementation of "export" functions
--
--========================================================================
local _M = {
_VERSION = '0.13'
}
local mt = { __index = _M }
-- "size" specifies the maximum number of entries in the LRU queue, and the
-- "load_factor" designates the 'load factor' of the hash-table we are using
-- internally. The default value of load-factor is 0.5 (i.e. 50%); if the
-- load-factor is specified, it will be clamped to the range of [0.1, 1](i.e.
-- if load-factor is greater than 1, it will be saturated to 1, likewise,
-- if load-factor is smaller than 0.1, it will be clamped to 0.1).
function _M.new(size, load_factor)
if size < 1 then
return nil, "size too small"
end
-- Determine bucket size, which must be power of two.
local load_f = load_factor
if not load_factor then
load_f = 0.5
elseif load_factor > 1 then
load_f = 1
elseif load_factor < 0.1 then
load_f = 0.1
end
local bs_min = size / load_f
-- The bucket_sz *MUST* be a power-of-two. See the hash_string().
local bucket_sz = 1
repeat
bucket_sz = bucket_sz * 2
until bucket_sz >= bs_min
local self = {
size = size,
bucket_sz = bucket_sz,
free_queue = queue_init(size),
cache_queue = queue_init(0),
node_v = nil,
key_v = new_tab(size, 0),
val_v = new_tab(size, 0),
bucket_v = ffi_new(int_array_t, bucket_sz),
num_items = 0,
}
-- "node_v" is an array of all the nodes used in the LRU queue. Exprpession
-- node_v[i] evaluates to the element of ID "i".
self.node_v = self.free_queue
-- Allocate the array-part of the key_v, val_v, bucket_v.
--local key_v = self.key_v
--local val_v = self.val_v
--local bucket_v = self.bucket_v
ffi_fill(self.bucket_v, ffi_sizeof(int_t, bucket_sz), 0)
return setmetatable(self, mt)
end
function _M.count(self)
return self.num_items
end
function _M.capacity(self)
return self.size
end
local function hash_string(self, str)
local c_str = ffi_cast(c_str_t, str)
local hv = crc32_ptr(c_str)
hv = band(hv, self.bucket_sz - 1)
-- Hint: bucket is 0-based
return hv
end
-- Search the node associated with the key in the bucket, if found returns
-- the the id of the node, and the id of its previous node in the conflict list.
-- The "bucket_hdr_id" is the ID of the first node in the bucket
local function _find_node_in_bucket(key, key_v, node_v, bucket_hdr_id)
if bucket_hdr_id ~= 0 then
local prev = 0
local cur = bucket_hdr_id
while cur ~= 0 and key_v[cur] ~= key do
prev = cur
cur = node_v[cur].conflict
end
if cur ~= 0 then
return cur, prev
end
end
end
-- Return the node corresponding to the key/val.
local function find_key(self, key)
local key_hash = hash_string(self, key)
return _find_node_in_bucket(key, self.key_v, self.node_v,
self.bucket_v[key_hash])
end
--[[ This function tries to
1. Remove the given key and the associated value from the key/value store,
2. Remove the entry associated with the key from the hash-table.
NOTE: all queues remain intact.
If there was a node bound to the key/val, return that node; otherwise,
nil is returned.
]]
local function remove_key(self, key)
local key_v = self.key_v
local val_v = self.val_v
local node_v = self.node_v
local bucket_v = self.bucket_v
local key_hash = hash_string(self, key)
local cur, prev =
_find_node_in_bucket(key, key_v, node_v, bucket_v[key_hash])
if cur then
-- In an attempt to make key and val dead.
key_v[cur] = nil
val_v[cur] = nil
self.num_items = self.num_items - 1
-- Remove the node from the hash table
local next_node = node_v[cur].conflict
if prev ~= 0 then
node_v[prev].conflict = next_node
else
bucket_v[key_hash] = next_node
end
node_v[cur].conflict = 0
return cur
end
end
--[[ Bind the key/val with the given node, and insert the node into the Hashtab.
NOTE: this function does not touch any queue
]]
local function insert_key(self, key, val, node)
-- Bind the key/val with the node
local node_id = node.id
self.key_v[node_id] = key
self.val_v[node_id] = val
-- Insert the node into the hash-table
local key_hash = hash_string(self, key)
local bucket_v = self.bucket_v
node.conflict = bucket_v[key_hash]
bucket_v[key_hash] = node_id
self.num_items = self.num_items + 1
end
function _M.get(self, key)
if type(key) ~= "string" then
key = tostring(key)
end
local node_id = find_key(self, key)
if not node_id then
return nil
end
-- print(key, ": moving node ", tostring(node), " to cache queue head")
local cache_queue = self.cache_queue
local node = self.node_v + node_id
queue_remove(node)
queue_insert_head(cache_queue, node)
local expire = node.expire
if expire >= 0 and expire < ngx_now() then
-- print("expired: ", node.expire, " > ", ngx_now())
return nil, self.val_v[node_id], node.user_flags
end
return self.val_v[node_id], nil, node.user_flags
end
function _M.delete(self, key)
if type(key) ~= "string" then
key = tostring(key)
end
local node_id = remove_key(self, key);
if not node_id then
return false
end
local node = self.node_v + node_id
queue_remove(node)
queue_insert_tail(self.free_queue, node)
return true
end
function _M.set(self, key, value, ttl, flags)
if type(key) ~= "string" then
key = tostring(key)
end
local node_id = find_key(self, key)
local node
if not node_id then
local free_queue = self.free_queue
if queue_is_empty(free_queue) then
-- evict the least recently used key
-- assert(not queue_is_empty(self.cache_queue))
node = queue_last(self.cache_queue)
remove_key(self, self.key_v[node.id])
else
-- take a free queue node
node = queue_head(free_queue)
-- print(key, ": get a new free node: ", tostring(node))
end
-- insert the key
insert_key(self, key, value, node)
else
node = self.node_v + node_id
self.val_v[node_id] = value
end
queue_remove(node)
queue_insert_head(self.cache_queue, node)
if ttl then
node.expire = ngx_now() + ttl
else
node.expire = -1
end
if type(flags) == "number" and flags >= 0 then
node.user_flags = flags
else
node.user_flags = 0
end
end
function _M.get_keys(self, max_count, res)
if not max_count or max_count == 0 then
max_count = self.num_items
end
if not res then
res = new_tab(max_count + 1, 0) -- + 1 for trailing hole
end
local cache_queue = self.cache_queue
local key_v = self.key_v
local i = 0
local node = queue_head(cache_queue)
while node ~= cache_queue do
if i >= max_count then
break
end
i = i + 1
res[i] = key_v[node.id]
node = node.next
end
res[i + 1] = nil
return res
end
function _M.flush_all(self)
local cache_queue = self.cache_queue
local key_v = self.key_v
local node = queue_head(cache_queue)
while node ~= cache_queue do
local key = key_v[node.id]
node = node.next
_M.delete(self, key)
end
end
return _M
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