src/lib-sql/sql-db-cache.c

/* Copyright (c) 2004-2018 Dovecot authors, see the included COPYING file */

#include "lib.h"
#include "array.h"
#include "hash.h"
#include "sql-api-private.h"
#include "sql-db-cache.h"

#define SQL_DB_CACHE_CONTEXT(obj) \
    MODULE_CONTEXT_REQUIRE(obj, sql_db_cache_module)

struct sql_db_cache_context {
    union sql_db_module_context module_ctx;
    struct sql_db *prev, *next; /* These are set while refcount=0 */

    struct sql_db_cache *cache;
    int refcount;
    char *key;
    void (*orig_deinit)(struct sql_db *db);
};

struct sql_db_cache {
    HASH_TABLE(char *, struct sql_db *) dbs;
    unsigned int unused_count, max_unused_connections;
    struct sql_db *unused_tail, *unused_head;
};

static MODULE_CONTEXT_DEFINE_INIT(sql_db_cache_module, &sql_db_module_register);

static void sql_db_cache_db_deinit(struct sql_db *db)
{
    struct sql_db_cache_context *ctx = SQL_DB_CACHE_CONTEXT(db);
    struct sql_db_cache_context *head_ctx;

    if (--ctx->refcount > 0)
        return;

    ctx->cache->unused_count++;
    if (ctx->cache->unused_tail == NULL)
        ctx->cache->unused_tail = db;
    else {
        head_ctx = SQL_DB_CACHE_CONTEXT(ctx->cache->unused_head);
        head_ctx->next = db;
    }
    ctx->prev = ctx->cache->unused_head;
    ctx->cache->unused_head = db;
}

static void sql_db_cache_unlink(struct sql_db_cache_context *ctx)
{
    struct sql_db_cache_context *prev_ctx, *next_ctx;

    i_assert(ctx->refcount == 0);

    if (ctx->prev == NULL)
        ctx->cache->unused_tail = ctx->next;
    else {
        prev_ctx = SQL_DB_CACHE_CONTEXT(ctx->prev);
        prev_ctx->next = ctx->next;
    }
    if (ctx->next == NULL)
        ctx->cache->unused_head = ctx->prev;
    else {
        next_ctx = SQL_DB_CACHE_CONTEXT(ctx->next);
        next_ctx->prev = ctx->prev;
    }
    ctx->cache->unused_count--;
}

static void sql_db_cache_free_tail(struct sql_db_cache *cache)
{
    struct sql_db *db;
    struct sql_db_cache_context *ctx;

    db = cache->unused_tail;
    ctx = SQL_DB_CACHE_CONTEXT(db);
    sql_db_cache_unlink(ctx);
    hash_table_remove(cache->dbs, ctx->key);

    i_free(ctx->key);
    ctx->orig_deinit(db);
    i_free(ctx);
}

static void sql_db_cache_drop_oldest(struct sql_db_cache *cache)
{
    while (cache->unused_count >= cache->max_unused_connections)
        sql_db_cache_free_tail(cache);
}

struct sql_db *
sql_db_cache_new(struct sql_db_cache *cache,
         const char *db_driver, const char *connect_string)
{
    struct sql_db_cache_context *ctx;
    struct sql_db *db;
    char *key;

    key = i_strdup_printf("%s\t%s", db_driver, connect_string);
    db = hash_table_lookup(cache->dbs, key);
    if (db != NULL) {
        ctx = SQL_DB_CACHE_CONTEXT(db);
        if (ctx->refcount == 0) {
            sql_db_cache_unlink(ctx);
            ctx->prev = ctx->next = NULL;
        }
        i_free(key);
    } else {
        sql_db_cache_drop_oldest(cache);

        ctx = i_new(struct sql_db_cache_context, 1);
        ctx->cache = cache;
        ctx->key = key;

        db = sql_init(db_driver, connect_string);
        ctx->orig_deinit = db->v.deinit;
        db->v.deinit = sql_db_cache_db_deinit;

        MODULE_CONTEXT_SET(db, sql_db_cache_module, ctx);
        hash_table_insert(cache->dbs, ctx->key, db);
    }

    ctx->refcount++;
    return db;
}

struct sql_db_cache *sql_db_cache_init(unsigned int max_unused_connections)
{
    struct sql_db_cache *cache;

    cache = i_new(struct sql_db_cache, 1);
    hash_table_create(&cache->dbs, default_pool, 0, str_hash, strcmp);
    cache->max_unused_connections = max_unused_connections;
    return cache;
}

void sql_db_cache_deinit(struct sql_db_cache **_cache)
{
    struct sql_db_cache *cache = *_cache;

    *_cache = NULL;
    while (cache->unused_tail != NULL)
        sql_db_cache_free_tail(cache);
    hash_table_destroy(&cache->dbs);
    i_free(cache);
}