path: root/storage/perfschema/table_uvar_by_thread.cc

/* Copyright (c) 2013, 2023, Oracle and/or its affiliates.

  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.

  This program is also distributed with certain software (including
  but not limited to OpenSSL) that is licensed under separate terms,
  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
  separately licensed software that they have included with MySQL.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License, version 2.0, for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

/**
  @file storage/perfschema/table_uvar_by_thread.cc
  Table USER_VARIABLES_BY_THREAD (implementation).
*/

#include "my_global.h"
#include "my_thread.h"
#include "pfs_instr_class.h"
#include "pfs_column_types.h"
#include "pfs_column_values.h"
#include "table_uvar_by_thread.h"
#include "pfs_global.h"
#include "pfs_visitor.h"
#include "pfs_buffer_container.h"

/* Iteration on THD from the sql layer. */
#include "sql_class.h"
#include "mysqld_thd_manager.h"

class Find_thd_user_var : public Find_THD_Impl
{
public:
  Find_thd_user_var(THD *unsafe_thd)
    : m_unsafe_thd(unsafe_thd)
  {}

  virtual bool operator()(THD *thd)
  {
    if (thd != m_unsafe_thd)
      return false;

    if (thd->user_vars.records == 0)
      return false;

    mysql_mutex_lock(&thd->LOCK_thd_data);
    return true;
  }

private:
  THD *m_unsafe_thd;
};

void User_variables::materialize(PFS_thread *pfs, THD *thd)
{
  reset();

  m_pfs= pfs;
  m_thread_internal_id= pfs->m_thread_internal_id;
  m_array.reserve(thd->user_vars.records);

  user_var_entry *sql_uvar;

  uint index= 0;
  User_variable empty;

  /* Protects thd->user_vars. */
  mysql_mutex_assert_owner(&thd->LOCK_thd_data);

  for (;;)
  {
    sql_uvar= reinterpret_cast<user_var_entry*> (my_hash_element(& thd->user_vars, index));
    if (sql_uvar == NULL)
      break;

    /*
      m_array is a container of objects (not pointers)

      Naive code can:
      - build locally a new entry
      - add it to the container
      but this causes useless object construction, destruction, and deep copies.

      What we do here:
      - add a dummy (empty) entry
      - the container does a deep copy on something empty,
        so that there is nothing to copy.
      - get a reference to the entry added in the container
      - complete -- in place -- the entry initialization
    */
    m_array.push(empty);
    User_variable & pfs_uvar= *m_array.back();

    /* Copy VARIABLE_NAME */
    const char *name= sql_uvar->name.str;
    size_t name_length= sql_uvar->name.length;
    DBUG_ASSERT(name_length <= sizeof(pfs_uvar.m_name));
    pfs_uvar.m_name.make_row(name, name_length);

    /* Copy VARIABLE_VALUE */
    bool null_value;
    String *str_value;
    String str_buffer;
    uint decimals= 0;
    str_value= sql_uvar->val_str(& null_value, & str_buffer, decimals);
    if (str_value != NULL)
    {
      pfs_uvar.m_value.make_row(str_value->ptr(), str_value->length());
    }
    else
    {
      pfs_uvar.m_value.make_row(NULL, 0);
    }

    index++;
  }
}

THR_LOCK table_uvar_by_thread::m_table_lock;

PFS_engine_table_share_state
table_uvar_by_thread::m_share_state = {
  false /* m_checked */
};

PFS_engine_table_share
table_uvar_by_thread::m_share=
{
  { C_STRING_WITH_LEN("user_variables_by_thread") },
  &pfs_readonly_acl,
  table_uvar_by_thread::create,
  NULL, /* write_row */
  NULL, /* delete_all_rows */
  table_uvar_by_thread::get_row_count,
  sizeof(pos_t),
  &m_table_lock,
  { C_STRING_WITH_LEN("CREATE TABLE user_variables_by_thread("
  "THREAD_ID BIGINT unsigned not null comment 'The thread identifier of the session in which the variable is defined.',"
  "VARIABLE_NAME VARCHAR(64) not null comment 'The variable name, without the leading @ character.',"
  "VARIABLE_VALUE LONGBLOB comment 'The variable value')") },
  false, /* m_perpetual */
  false, /* m_optional */
  &m_share_state
};

PFS_engine_table*
table_uvar_by_thread::create(void)
{
  return new table_uvar_by_thread();
}

ha_rows
table_uvar_by_thread::get_row_count(void)
{
  /*
    This is an estimate only, not a hard limit.
    The row count is given as a multiple of thread_max,
    so that a join between:
    - table performance_schema.threads
    - table performance_schema.user_variables_by_thread
    will still evaluate relative table sizes correctly
    when deciding a join order.
  */
  return global_thread_container.get_row_count() * 10;
}

table_uvar_by_thread::table_uvar_by_thread()
  : PFS_engine_table(&m_share, &m_pos),
    m_row_exists(false), m_pos(), m_next_pos()
{}

void table_uvar_by_thread::reset_position(void)
{
  m_pos.reset();
  m_next_pos.reset();
}

int table_uvar_by_thread::rnd_next(void)
{
  PFS_thread *thread;
  bool has_more_thread= true;

  for (m_pos.set_at(&m_next_pos);
       has_more_thread;
       m_pos.next_thread())
  {
    thread= global_thread_container.get(m_pos.m_index_1, & has_more_thread);
    if (thread != NULL)
    {
      if (materialize(thread) == 0)
      {
        const User_variable *uvar= m_THD_cache.get(m_pos.m_index_2);
        if (uvar != NULL)
        {
          make_row(thread, uvar);
          m_next_pos.set_after(&m_pos);
          return 0;
        }
      }
    }
  }

  return HA_ERR_END_OF_FILE;
}

int
table_uvar_by_thread::rnd_pos(const void *pos)
{
  PFS_thread *thread;

  set_position(pos);

  thread= global_thread_container.get(m_pos.m_index_1);
  if (thread != NULL)
  {
    if (materialize(thread) == 0)
    {
      const User_variable *uvar= m_THD_cache.get(m_pos.m_index_2);
      if (uvar != NULL)
      {
        make_row(thread, uvar);
        return 0;
      }
    }
  }

  return HA_ERR_RECORD_DELETED;
}

int table_uvar_by_thread::materialize(PFS_thread *thread)
{
  if (m_THD_cache.is_materialized(thread))
    return 0;

  if (! thread->m_lock.is_populated())
    return 1;

  THD *unsafe_thd= thread->m_thd;
  if (unsafe_thd == NULL)
    return 1;

  Find_thd_user_var finder(unsafe_thd);
  THD *safe_thd= Global_THD_manager::get_instance()->find_thd(&finder);
  if (safe_thd == NULL)
    return 1;

  m_THD_cache.materialize(thread, safe_thd);
  mysql_mutex_unlock(&safe_thd->LOCK_thd_data);
  return 0;
}

void table_uvar_by_thread
::make_row(PFS_thread *thread, const User_variable *uvar)
{
  pfs_optimistic_state lock;
  m_row_exists= false;

  /* Protect this reader against a thread termination */
  thread->m_lock.begin_optimistic_lock(&lock);

  m_row.m_thread_internal_id= thread->m_thread_internal_id;

  /* uvar is materialized, pointing to it directly. */
  m_row.m_variable_name= & uvar->m_name;
  m_row.m_variable_value= & uvar->m_value;

  if (! thread->m_lock.end_optimistic_lock(&lock))
    return;

  m_row_exists= true;
}

int table_uvar_by_thread
::read_row_values(TABLE *table,
                  unsigned char *buf,
                  Field **fields,
                  bool read_all)
{
  Field *f;

  if (unlikely(! m_row_exists))
    return HA_ERR_RECORD_DELETED;

  /* Set the null bits */
  assert(table->s->null_bytes == 1);
  buf[0]= 0;

  assert(m_row.m_variable_name != NULL);
  assert(m_row.m_variable_value != NULL);

  for (; (f= *fields) ; fields++)
  {
    if (read_all || bitmap_is_set(table->read_set, f->field_index))
    {
      switch(f->field_index)
      {
      case 0: /* THREAD_ID */
        set_field_ulonglong(f, m_row.m_thread_internal_id);
        break;
      case 1: /* VARIABLE_NAME */
        set_field_varchar_utf8(f,
                               m_row.m_variable_name->m_str,
                               m_row.m_variable_name->m_length);
        break;
      case 2: /* VARIABLE_VALUE */
        if (m_row.m_variable_value->get_value_length() > 0)
        {
          set_field_blob(f,
                         m_row.m_variable_value->get_value(),
              static_cast<uint>(m_row.m_variable_value->get_value_length()));
        }
        else
        {
          f->set_null();
        }
        break;
      default:
        assert(false);
      }
    }
  }

  return 0;
}