polardbxengine/mysys/mf_keycaches.cc

/* Copyright (c) 2003, 2019, Oracle and/or its affiliates. All rights reserved.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

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   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
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   Without limiting anything contained in the foregoing, this file,
   which is part of C Driver for MySQL (Connector/C), is also subject to the
   Universal FOSS Exception, version 1.0, a copy of which can be found at
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   This program is distributed in the hope that it will be useful,
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   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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   You should have received a copy of the GNU General Public License
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   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

/**
  @file mysys/mf_keycaches.cc
  Handling of multiple key caches.

  The idea is to have a thread safe hash on the table name,
  with a default key cache value that is returned if the table name is not in
  the cache.
*/

#include <string.h>
#include <sys/types.h>
#include <string>

#include "keycache.h"
#include "m_ctype.h"
#include "map_helpers.h"
#include "my_dbug.h"
#include "my_inttypes.h"
#include "my_sys.h"
#include "mysql/psi/mysql_rwlock.h"
#include "mysql/service_mysql_alloc.h"
#include "mysys/mysys_priv.h"
#include "template_utils.h"

using std::string;

/*****************************************************************************
  General functions to handle SAFE_HASH objects.

  A SAFE_HASH object is used to store the hash, the lock and default value
  needed by the rest of the key cache code.
  This is a separate struct to make it easy to later reuse the code for other
  purposes

  All entries are linked in a list to allow us to traverse all elements
  and delete selected ones. (HASH doesn't allow any easy ways to do this).
*****************************************************************************/

/*
  Struct to store a key and pointer to object
*/

struct SAFE_HASH_ENTRY {
  char *key;
  uint length;
  uchar *data;
  SAFE_HASH_ENTRY *next, **prev;
};

struct SAFE_HASH {
  mysql_rwlock_t lock;
  malloc_unordered_map<string, unique_ptr_my_free<SAFE_HASH_ENTRY>> hash{
      key_memory_SAFE_HASH_ENTRY};
  uchar *default_value;
  SAFE_HASH_ENTRY *root;
};

/*
  Init a SAFE_HASH object

  SYNOPSIS
    safe_hash_init()
    hash		safe_hash handler
    elements		Expected max number of elements
    default_value	default value

  NOTES
    In case of error we set hash->default_value to 0 to allow one to call
    safe_hash_free on an object that couldn't be initialized.

  RETURN
    0  ok
    1  error
*/

static bool safe_hash_init(SAFE_HASH *hash, uchar *default_value) {
  DBUG_TRACE;
  mysql_rwlock_init(key_SAFE_HASH_lock, &hash->lock);
  hash->default_value = default_value;
  hash->root = 0;
  return 0;
}

/*
  Free a SAFE_HASH object

  NOTES
    This is safe to call on any object that has been sent to safe_hash_init()
*/

static void safe_hash_free(SAFE_HASH *hash) {
  /*
    Test if safe_hash_init succeeded. This will also guard us against multiple
    free calls.
  */
  if (hash->default_value) {
    hash->hash.clear();
    mysql_rwlock_destroy(&hash->lock);
    hash->default_value = 0;
  }
}

/*
  Return the value stored for a key or default value if no key
*/

static uchar *safe_hash_search(SAFE_HASH *hash, const uchar *key, uint length) {
  uchar *result;
  DBUG_TRACE;
  mysql_rwlock_rdlock(&hash->lock);
  auto it = hash->hash.find(string(pointer_cast<const char *>(key), length));
  if (it == hash->hash.end())
    result = hash->default_value;
  else
    result = it->second->data;
  mysql_rwlock_unlock(&hash->lock);
  DBUG_PRINT("exit", ("data: %p", result));
  return result;
}

/*
  Associate a key with some data

  SYONOPSIS
    safe_hash_set()
    hash			Hash handle
    key				key (path to table etc..)
    length			Length of key
    data			data to to associate with the data

  NOTES
    This can be used both to insert a new entry and change an existing
    entry.
    If one associates a key with the default key cache, the key is deleted

  RETURN
    0  ok
    1  error (Can only be EOM). In this case my_message() is called.
*/

static bool safe_hash_set(SAFE_HASH *hash, const uchar *key, uint length,
                          uchar *data) {
  SAFE_HASH_ENTRY *entry;
  bool error = 0;
  DBUG_TRACE;
  DBUG_PRINT("enter", ("key: %.*s  data: %p", length, key, data));
  string key_str(pointer_cast<const char *>(key), length);

  mysql_rwlock_wrlock(&hash->lock);
  entry = find_or_nullptr(hash->hash, key_str);

  if (data == hash->default_value) {
    /*
      The key is to be associated with the default entry. In this case
      we can just delete the entry (if it existed) from the hash as a
      search will return the default entry
    */
    if (!entry) /* nothing to do */
      goto end;
    /* unlink entry from list */
    if ((*entry->prev = entry->next)) entry->next->prev = entry->prev;
    hash->hash.erase(key_str);
    goto end;
  }
  if (entry) {
    /* Entry existed;  Just change the pointer to point at the new data */
    entry->data = data;
  } else {
    if (!(entry = (SAFE_HASH_ENTRY *)my_malloc(key_memory_SAFE_HASH_ENTRY,
                                               sizeof(*entry) + length,
                                               MYF(MY_WME)))) {
      error = 1;
      goto end;
    }
    entry->key = (char *)(entry + 1);
    memcpy(entry->key, key, length);
    entry->length = length;
    entry->data = data;
    /* Link entry to list */
    if ((entry->next = hash->root)) entry->next->prev = &entry->next;
    entry->prev = &hash->root;
    hash->root = entry;
    hash->hash.emplace(
        string(pointer_cast<const char *>(entry->key), entry->length),
        unique_ptr_my_free<SAFE_HASH_ENTRY>(entry));
  }

end:
  mysql_rwlock_unlock(&hash->lock);
  return error;
}

/*
  Change all entres with one data value to another data value

  SYONOPSIS
    safe_hash_change()
    hash			Hash handle
    old_data			Old data
    new_data			Change all 'old_data' to this

  NOTES
    We use the linked list to traverse all elements in the hash as
    this allows us to delete elements in the case where 'new_data' is the
    default value.
*/

static void safe_hash_change(SAFE_HASH *hash, uchar *old_data,
                             uchar *new_data) {
  SAFE_HASH_ENTRY *entry, *next;
  DBUG_TRACE;

  mysql_rwlock_wrlock(&hash->lock);

  for (entry = hash->root; entry; entry = next) {
    next = entry->next;
    if (entry->data == old_data) {
      if (new_data == hash->default_value) {
        if ((*entry->prev = entry->next)) entry->next->prev = entry->prev;
        hash->hash.erase(string(entry->key, entry->length));
      } else
        entry->data = new_data;
    }
  }

  mysql_rwlock_unlock(&hash->lock);
}

/*****************************************************************************
  Functions to handle the key cache objects
*****************************************************************************/

/* Variable to store all key cache objects */
static SAFE_HASH key_cache_hash;

bool multi_keycache_init(void) {
  return safe_hash_init(&key_cache_hash, (uchar *)dflt_key_cache);
}

void multi_keycache_free(void) { safe_hash_free(&key_cache_hash); }

/*
  Get a key cache to be used for a specific table.

  SYNOPSIS
    multi_key_cache_search()
    key				key to find (usually table path)
    uint length			Length of key.

  NOTES
    This function is coded in such a way that we will return the
    default key cache even if one never called multi_keycache_init.
    This will ensure that it works with old MyISAM clients.

  RETURN
    key cache to use
*/

KEY_CACHE *multi_key_cache_search(uchar *key, uint length) {
  if (key_cache_hash.hash.empty()) return dflt_key_cache;
  return (KEY_CACHE *)safe_hash_search(&key_cache_hash, key, length);
}

/*
  Assosiate a key cache with a key


  SYONOPSIS
    multi_key_cache_set()
    key				key (path to table etc..)
    length			Length of key
    key_cache			cache to assococite with the table

  NOTES
    This can be used both to insert a new entry and change an existing
    entry
*/

bool multi_key_cache_set(const uchar *key, uint length, KEY_CACHE *key_cache) {
  return safe_hash_set(&key_cache_hash, key, length, (uchar *)key_cache);
}

void multi_key_cache_change(KEY_CACHE *old_data, KEY_CACHE *new_data) {
  safe_hash_change(&key_cache_hash, (uchar *)old_data, (uchar *)new_data);
}