memcached: use own slab arena

Historically memcached module uses slab cache created by Tarantool.
Fibers get access to it via call of function cord_slab_cache() that is a
part of Tarantool C API. The problem is happen when memcached and
Tarantool use different versions of Small library where ABI is broken.
Issues #59 and #96 are examples of such problems.

We decided use independent slab arena in memcached module to avoid such
problems in future and this patch implements it.

Below I'll describe what is important in switching to own arena.

memcached module uses different types of Small's allocators (ibuf and
obuf used for every network connection, one slab cache used per fiber).
There are two important things with used Small's allocators:

1. some allocators depends on other and sequence of allocations should
   be correct. README in small source code repository has a clear
   description of relationships between allocators [1].
2. some allocators are thread-safe and others not. slab arena is shared
   between all memcached instances, when slab cache allocated on top of
   slab arena is not thread-safe and must be used in scope of fiber.

memcached performs memory allocations and deallocations on different
stages and I would list all these stages explicitly:

- memcached module initialization
- memcached module deinitialization
- memcached instance gc
- memcached instance initialization
- memcached instance start
- memcached instance stop
- memcached instance deinitialization

Most part of these cases covered in tests
test/common/instance_api.test.lua and test/common/module_api.test.lua
that were added in previous commits. The exception here is gc that was
checked manually.

In tests function is_port_open() has been replaced to memcached
minimalistic client that do set value, get value with the same key and
compare both values. This check is more rigorous than check port
openess.

1. https://github.com/tarantool/small

Fixes #96

memcached/init.lua

@@ -82,6 +82,10 @@ memcached_get_stat (struct memcached_service *);
 struct memcached_service *
 memcached_create(const char *, uint32_t);
 
+void memcached_slab_arena_create();
+
+void memcached_slab_cache_create();
+
 int    memcached_start     (struct memcached_service *);
 void   memcached_stop      (struct memcached_service *);
 void   memcached_free      (struct memcached_service *);
@@ -386,6 +390,13 @@ local function memcached_get(name)
     return memcached_services[name]
 end
 
+local function memcached_init()
+    memcached_internal.memcached_slab_arena_create()
+    memcached_internal.memcached_slab_cache_create()
+end
+
+memcached_init()
+
 return {
     create = memcached_create_instance,
     get    = memcached_get,

memcached/internal/alloc.c

@@ -1,2 +1,58 @@
 #include <tarantool/module.h>
 #include <small/slab_cache.h>
+#include <small/quota.h>
+
+static struct slab_arena arena;
+static struct slab_cache slabc;
+static struct quota quota;
+
+void
+memcached_slab_arena_create()
+{
+	static __thread bool inited = false;
+	if (inited) return;
+	size_t quota_size = QUOTA_MAX;
+	quota_init(&quota, quota_size);
+	/* Parameters are the same as in src/lib/core/memory.c:memory_init() */
+	const size_t SLAB_SIZE = 4 * 1024 * 1024;
+	slab_arena_create(&arena, &quota, 0, SLAB_SIZE, SLAB_ARENA_PRIVATE);
+	say_info("creating arena with %zu bytes...", quota_size);
+	inited = 1;
+}
+
+void
+memcached_slab_arena_destroy()
+{
+	static __thread bool freed = false;
+	if (freed) return;
+	say_info("destroying arena...");
+	slab_arena_destroy(&arena);
+	freed = 1;
+}
+
+void
+memcached_slab_cache_create()
+{
+	static __thread bool inited = false;
+	if (inited) return;
+	slab_cache_set_thread(&slabc);
+	slab_cache_create(&slabc, &arena);
+	say_info("allocate slab cache with slab size %u", arena.slab_size);
+	inited = 1;
+}
+
+void
+memcached_slab_cache_destroy()
+{
+	static __thread bool freed = false;
+	if (freed) return;
+	say_info("destroying slab cache");
+	slab_cache_destroy(&slabc);
+	freed = 1;
+}
+
+struct slab_cache *
+memcached_slab_cache()
+{
+	return &slabc;
+}

memcached/internal/alloc.h

@@ -1,4 +1,19 @@
 #ifndef   ALLOC_H_INCLUDED
 #define   ALLOC_H_INCLUDED
 
+void
+memcached_slab_arena_create();
+
+void
+memcached_slab_arena_destroy();
+
+void
+memcached_slab_cache_create();
+
+void
+memcached_slab_cache_destroy();
+
+struct slab_cache *
+memcached_slab_cache();
+
 #endif /* ALLOC_H_INCLUDED */

memcached/internal/memcached.c

@@ -37,6 +37,7 @@
 #include <small/ibuf.h>
 #include <small/obuf.h>
 
+#include "alloc.h"
 #include "memcached.h"
 #include "memcached_layer.h"
 #include "error.h"
@@ -46,6 +47,12 @@
 #include "expiration.h"
 #include "mc_sasl.h"
 
+__attribute__((destructor)) static void
+destroy_allocations()  {
+	memcached_slab_cache_destroy();
+	memcached_slab_arena_destroy();
+}
+
 static inline int
 memcached_skip_request(struct memcached_connection *con) {
 	struct ibuf *in = con->in;
@@ -250,7 +257,7 @@ memcached_handler(struct memcached_service *p, int fd)
 		assert(0); /* unreacheable */
 	}
 
-	region_create(&con.gc, cord_slab_cache());
+	region_create(&con.gc, memcached_slab_cache());
 
 	/* read-write cycle */
 	con.cfg->stat.curr_conns++;

memcached/internal/network.c

@@ -14,6 +14,7 @@
 #include <small/ibuf.h>
 #include <small/obuf.h>
 
+#include "alloc.h"
 #include "memcached.h"
 #include "constants.h"
 #include "network.h"
@@ -31,8 +32,8 @@ iobuf_mempool_create()
 {
 	static __thread bool inited = false;
 	if (inited) return;
-	mempool_create(&ibuf_pool, cord_slab_cache(), sizeof(struct ibuf));
-	mempool_create(&obuf_pool, cord_slab_cache(), sizeof(struct obuf));
+	mempool_create(&ibuf_pool, memcached_slab_cache(), sizeof(struct ibuf));
+	mempool_create(&obuf_pool, memcached_slab_cache(), sizeof(struct obuf));
 	inited = 1;
 }
 
@@ -48,7 +49,7 @@ ibuf_new()
 {
 	void *ibuf = mempool_alloc(&ibuf_pool);
 	if (ibuf == NULL) return NULL;
-	ibuf_create((struct ibuf *)ibuf, cord_slab_cache(), iobuf_readahead);
+	ibuf_create((struct ibuf *)ibuf, memcached_slab_cache(), iobuf_readahead);
 	return ibuf;
 }
 
@@ -57,7 +58,7 @@ obuf_new()
 {
 	void *obuf = mempool_alloc(&obuf_pool);
 	if (obuf == NULL) return NULL;
-	obuf_create((struct obuf *)obuf, cord_slab_cache(), iobuf_readahead);
+	obuf_create((struct obuf *)obuf, memcached_slab_cache(), iobuf_readahead);
 	return obuf;
 }
 

test/common/module_api.test.lua

@@ -6,12 +6,36 @@ package.cpath = './?.so;' .. package.cpath
 local memcached = require('memcached')
 local test = tap.test('memcached module api')
 
-local function is_port_open(port)
-    local sock, _ = socket.tcp_connect('127.0.0.1', port)
+-- 1. Open connection to memcached instance.
+-- 2. Set a key 'key' to value 5.
+-- 3. Get a value of key 'key'.
+-- 4. Make sure value is equal to 5.
+-- 5. Close connection.
+local function check_memcached(port, timeout)
+    timeout = timeout or 0.5
+    local sock, err = socket.tcp_connect('127.0.0.1', port, timeout)
     if sock == nil then
+        print(err)
         return false
     end
-    return sock:sysconnect(0, port) and true or false
+    sock:nonblock(true)
+
+    -- Set a value.
+    local cmd = 'set key 0 60 5\r\nvalue\r\n'
+    local send = sock:send(cmd)
+    assert(send > 0)
+
+    -- Get a value.
+    send = sock:send('get key\r\n')
+    assert(send > 0)
+    local read = sock:read(23)
+    local v = read:match('VALUE key 0 ([0-9])')
+    assert(v == '5')
+
+    -- Close connection.
+    sock:close()
+
+    return tonumber(v) == 5
 end
 
 if type(box.cfg) == 'function' then
@@ -39,7 +63,7 @@ local mc_1 = memcached.create(mc_1_name, tostring(mc_1_port), {
     space_name = mc_1_space_name
 })
 test:isnt(mc_1, nil, '1st memcached instance object is not nil')
-test:is(is_port_open(mc_1_port), true, '1st memcached instance is started')
+test:is(check_memcached(mc_1_port), true, 'connected to 1st memcached instance')
 mc_1:stop()
 
 -- memcached.create(): instance 2
@@ -52,7 +76,7 @@ local mc_2 = memcached.create(mc_2_name, tostring(mc_2_port), {
     space_name = mc_2_space_name
 })
 test:isnt(mc_2, nil, '2nd memcached instance object is not nil')
-test:is(is_port_open(mc_2_port), true, '2nd memcached instance is started')
+test:is(check_memcached(mc_2_port), true, 'connected to 2nd memcached instance')
 mc_2:stop()
 
 -- memcached.server with created and started instances