mdl.h

#ifndef MDL_H
#define MDL_H
/* Copyright (c) 2009, 2012, 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 as published by
   the Free Software Foundation; version 2 of the License.

   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 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,
   51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA */

#if defined(__IBMC__) || defined(__IBMCPP__)
/* Further down, "next_in_lock" and "next_in_context" have the same type,
   and in "sql_plist.h" this leads to an identical signature, which causes
   problems in function overloading.
*/
#pragma namemangling(v5)
#endif


#include "sql_plist.h"
#include <my_sys.h>
#include <m_string.h>
#include <mysql_com.h>

#include <algorithm>

class THD;

class MDL_context;
class MDL_lock;
class MDL_ticket;

#define ENTER_COND(C, M, S, O) enter_cond(C, M, S, O, __func__, __FILE__, __LINE__)

#define EXIT_COND(S) exit_cond(S, __func__, __FILE__, __LINE__)

class MDL_context_owner
{
public:
  virtual ~MDL_context_owner() {}

  virtual void enter_cond(mysql_cond_t *cond, mysql_mutex_t *mutex,
                          const PSI_stage_info *stage, PSI_stage_info *old_stage,
                          const char *src_function, const char *src_file,
                          int src_line) = 0;

  virtual void exit_cond(const PSI_stage_info *stage,
                         const char *src_function, const char *src_file,
                         int src_line) = 0;
  virtual int  is_killed() = 0;

  virtual THD* get_thd() = 0;

  virtual bool notify_shared_lock(MDL_context_owner *in_use,
                                  bool needs_thr_lock_abort) = 0;
};

enum enum_mdl_type {
  /*
    An intention exclusive metadata lock. Used only for scoped locks.
    Owner of this type of lock can acquire upgradable exclusive locks on
    individual objects.
    Compatible with other IX locks, but is incompatible with scoped S and
    X locks.
  */
  MDL_INTENTION_EXCLUSIVE= 0,
  /*
    A shared metadata lock.
    To be used in cases when we are interested in object metadata only
    and there is no intention to access object data (e.g. for stored
    routines or during preparing prepared statements).
    We also mis-use this type of lock for open HANDLERs, since lock
    acquired by this statement has to be compatible with lock acquired
    by LOCK TABLES ... WRITE statement, i.e. SNRW (We can't get by by
    acquiring S lock at HANDLER ... OPEN time and upgrading it to SR
    lock for HANDLER ... READ as it doesn't solve problem with need
    to abort DML statements which wait on table level lock while having
    open HANDLER in the same connection).
    To avoid deadlock which may occur when SNRW lock is being upgraded to
    X lock for table on which there is an active S lock which is owned by
    thread which waits in its turn for table-level lock owned by thread
    performing upgrade we have to use thr_abort_locks_for_thread()
    facility in such situation.
    This problem does not arise for locks on stored routines as we don't
    use SNRW locks for them. It also does not arise when S locks are used
    during PREPARE calls as table-level locks are not acquired in this
    case.
  */
  MDL_SHARED,
  /*
    A high priority shared metadata lock.
    Used for cases when there is no intention to access object data (i.e.
    data in the table).
    "High priority" means that, unlike other shared locks, it is granted
    ignoring pending requests for exclusive locks. Intended for use in
    cases when we only need to access metadata and not data, e.g. when
    filling an INFORMATION_SCHEMA table.
    Since SH lock is compatible with SNRW lock, the connection that
    holds SH lock lock should not try to acquire any kind of table-level
    or row-level lock, as this can lead to a deadlock. Moreover, after
    acquiring SH lock, the connection should not wait for any other
    resource, as it might cause starvation for X locks and a potential
    deadlock during upgrade of SNW or SNRW to X lock (e.g. if the
    upgrading connection holds the resource that is being waited for).
  */
  MDL_SHARED_HIGH_PRIO,
  /*
    A shared metadata lock for cases when there is an intention to read data
    from table.
    A connection holding this kind of lock can read table metadata and read
    table data (after acquiring appropriate table and row-level locks).
    This means that one can only acquire TL_READ, TL_READ_NO_INSERT, and
    similar table-level locks on table if one holds SR MDL lock on it.
    To be used for tables in SELECTs, subqueries, and LOCK TABLE ...  READ
    statements.
  */
  MDL_SHARED_READ,
  /*
    A shared metadata lock for cases when there is an intention to modify
    (and not just read) data in the table.
    A connection holding SW lock can read table metadata and modify or read
    table data (after acquiring appropriate table and row-level locks).
    To be used for tables to be modified by INSERT, UPDATE, DELETE
    statements, but not LOCK TABLE ... WRITE or DDL). Also taken by
    SELECT ... FOR UPDATE.
  */
  MDL_SHARED_WRITE,
  /*
    An upgradable shared metadata lock for cases when there is an intention
    to modify (and not just read) data in the table.
    Can be upgraded to MDL_SHARED_NO_WRITE and MDL_EXCLUSIVE.
    A connection holding SU lock can read table metadata and modify or read
    table data (after acquiring appropriate table and row-level locks).
    To be used for the first phase of ALTER TABLE.
  */
  MDL_SHARED_UPGRADABLE,
  /*
    An upgradable shared metadata lock which blocks all attempts to update
    table data, allowing reads.
    A connection holding this kind of lock can read table metadata and read
    table data.
    Can be upgraded to X metadata lock.
    Note, that since this type of lock is not compatible with SNRW or SW
    lock types, acquiring appropriate engine-level locks for reading
    (TL_READ* for MyISAM, shared row locks in InnoDB) should be
    contention-free.
    To be used for the first phase of ALTER TABLE, when copying data between
    tables, to allow concurrent SELECTs from the table, but not UPDATEs.
  */
  MDL_SHARED_NO_WRITE,
  /*
    An upgradable shared metadata lock which allows other connections
    to access table metadata, but not data.
    It blocks all attempts to read or update table data, while allowing
    INFORMATION_SCHEMA and SHOW queries.
    A connection holding this kind of lock can read table metadata modify and
    read table data.
    Can be upgraded to X metadata lock.
    To be used for LOCK TABLES WRITE statement.
    Not compatible with any other lock type except S and SH.
  */
  MDL_SHARED_NO_READ_WRITE,
  /*
    An exclusive metadata lock.
    A connection holding this lock can modify both table's metadata and data.
    No other type of metadata lock can be granted while this lock is held.
    To be used for CREATE/DROP/RENAME TABLE statements and for execution of
    certain phases of other DDL statements.
  */
  MDL_EXCLUSIVE,
  /* This should be the last !!! */
  MDL_TYPE_END};


enum enum_mdl_duration {
  MDL_STATEMENT= 0,
  MDL_TRANSACTION,
  MDL_EXPLICIT,
  /* This should be the last ! */
  MDL_DURATION_END };


#define MAX_MDLKEY_LENGTH (1 + NAME_LEN + 1 + NAME_LEN + 1)


class MDL_key
{
public:
#ifdef HAVE_PSI_INTERFACE
  static void init_psi_keys();
#endif

  enum enum_mdl_namespace { GLOBAL=0,
                            SCHEMA,
                            TABLE,
                            FUNCTION,
                            PROCEDURE,
                            TRIGGER,
                            EVENT,
                            COMMIT,
                            /* This should be the last ! */
                            NAMESPACE_END };

  const uchar *ptr() const { return (uchar*) m_ptr; }
  uint length() const { return m_length; }

  const char *db_name() const { return m_ptr + 1; }
  uint db_name_length() const { return m_db_name_length; }

  const char *name() const { return m_ptr + m_db_name_length + 2; }
  uint name_length() const { return m_length - m_db_name_length - 3; }

  enum_mdl_namespace mdl_namespace() const
  { return (enum_mdl_namespace)(m_ptr[0]); }

  void mdl_key_init(enum_mdl_namespace mdl_namespace,
                    const char *db, const char *name)
  {
    m_ptr[0]= (char) mdl_namespace;
    /*
      It is responsibility of caller to ensure that db and object names
      are not longer than NAME_LEN. Still we play safe and try to avoid
      buffer overruns.
    */
    DBUG_ASSERT(strlen(db) <= NAME_LEN && strlen(name) <= NAME_LEN);
    m_db_name_length= static_cast<uint16>(strmake(m_ptr + 1, db, NAME_LEN) -
                                          m_ptr - 1);
    m_length= static_cast<uint16>(strmake(m_ptr + m_db_name_length + 2, name,
                                          NAME_LEN) - m_ptr + 1);
  }
  void mdl_key_init(const MDL_key *rhs)
  {
    memcpy(m_ptr, rhs->m_ptr, rhs->m_length);
    m_length= rhs->m_length;
    m_db_name_length= rhs->m_db_name_length;
  }
  bool is_equal(const MDL_key *rhs) const
  {
    return (m_length == rhs->m_length &&
            memcmp(m_ptr, rhs->m_ptr, m_length) == 0);
  }
  int cmp(const MDL_key *rhs) const
  {
    /*
      The key buffer is always '\0'-terminated. Since key
      character set is utf-8, we can safely assume that no
      character starts with a zero byte.
    */
    using std::min;
    return memcmp(m_ptr, rhs->m_ptr, min(m_length, rhs->m_length));
  }

  MDL_key(const MDL_key *rhs)
  {
    mdl_key_init(rhs);
  }
  MDL_key(enum_mdl_namespace namespace_arg,
          const char *db_arg, const char *name_arg)
  {
    mdl_key_init(namespace_arg, db_arg, name_arg);
  }
  MDL_key() {} /* To use when part of MDL_request. */

  const PSI_stage_info * get_wait_state_name() const
  {
    return & m_namespace_to_wait_state_name[(int)mdl_namespace()];
  }

private:
  uint16 m_length;
  uint16 m_db_name_length;
  char m_ptr[MAX_MDLKEY_LENGTH];
  static PSI_stage_info m_namespace_to_wait_state_name[NAMESPACE_END];
private:
  MDL_key(const MDL_key &);                     /* not implemented */
  MDL_key &operator=(const MDL_key &);          /* not implemented */
};


class MDL_request
{
public:
  enum          enum_mdl_type type;
  enum enum_mdl_duration duration;

  MDL_request *next_in_list;
  MDL_request **prev_in_list;
  MDL_ticket *ticket;

  MDL_key key;

public:
  static void *operator new(size_t size, MEM_ROOT *mem_root) throw ()
  { return alloc_root(mem_root, size); }
  static void operator delete(void *ptr, MEM_ROOT *mem_root) {}

  void init(MDL_key::enum_mdl_namespace namespace_arg,
            const char *db_arg, const char *name_arg,
            enum_mdl_type mdl_type_arg,
            enum_mdl_duration mdl_duration_arg);
  void init(const MDL_key *key_arg, enum_mdl_type mdl_type_arg,
            enum_mdl_duration mdl_duration_arg);
  inline void set_type(enum_mdl_type type_arg)
  {
    DBUG_ASSERT(ticket == NULL);
    type= type_arg;
  }

  /*
    This is to work around the ugliness of TABLE_LIST
    compiler-generated assignment operator. It is currently used
    in several places to quickly copy "most" of the members of the
    table list. These places currently never assume that the mdl
    request is carried over to the new TABLE_LIST, or shared
    between lists.

    This method does not initialize the instance being assigned!
    Use of init() for initialization after this assignment operator
    is mandatory. Can only be used before the request has been
    granted.
  */
  MDL_request& operator=(const MDL_request &rhs)
  {
    ticket= NULL;
    /* Do nothing, in particular, don't try to copy the key. */
    return *this;
  }
  /* Another piece of ugliness for TABLE_LIST constructor */
  MDL_request() {}

  MDL_request(const MDL_request *rhs)
    :type(rhs->type),
    duration(rhs->duration),
    ticket(NULL),
    key(&rhs->key)
  {}
};


typedef void (*mdl_cached_object_release_hook)(void *);


class MDL_wait_for_graph_visitor
{
public:
  virtual bool enter_node(MDL_context *node) = 0;
  virtual void leave_node(MDL_context *node) = 0;

  virtual bool inspect_edge(MDL_context *dest) = 0;
  virtual ~MDL_wait_for_graph_visitor();
  MDL_wait_for_graph_visitor() :m_lock_open_count(0) {}
public:
  uint m_lock_open_count;
};

class MDL_wait_for_subgraph
{
public:
  virtual ~MDL_wait_for_subgraph();

  virtual bool accept_visitor(MDL_wait_for_graph_visitor *gvisitor) = 0;

  enum enum_deadlock_weight
  {
    DEADLOCK_WEIGHT_DML= 0,
    DEADLOCK_WEIGHT_DDL= 100
  };
  /* A helper used to determine which lock request should be aborted. */
  virtual uint get_deadlock_weight() const = 0;
};


class MDL_ticket : public MDL_wait_for_subgraph
{
public:
  MDL_ticket *next_in_context;
  MDL_ticket **prev_in_context;
  MDL_ticket *next_in_lock;
  MDL_ticket **prev_in_lock;
public:
  bool has_pending_conflicting_lock() const;

  MDL_context *get_ctx() const { return m_ctx; }
  bool is_upgradable_or_exclusive() const
  {
    return m_type == MDL_SHARED_UPGRADABLE ||
           m_type == MDL_SHARED_NO_WRITE ||
           m_type == MDL_SHARED_NO_READ_WRITE ||
           m_type == MDL_EXCLUSIVE;
  }
  enum_mdl_type get_type() const { return m_type; }
  MDL_lock *get_lock() const { return m_lock; }
  void downgrade_lock(enum_mdl_type type);

  bool has_stronger_or_equal_type(enum_mdl_type type) const;

  bool is_incompatible_when_granted(enum_mdl_type type) const;
  bool is_incompatible_when_waiting(enum_mdl_type type) const;

  virtual bool accept_visitor(MDL_wait_for_graph_visitor *dvisitor);
  virtual uint get_deadlock_weight() const;
private:
  friend class MDL_context;

  MDL_ticket(MDL_context *ctx_arg, enum_mdl_type type_arg
#ifndef DBUG_OFF
             , enum_mdl_duration duration_arg
#endif
            )
   : m_type(type_arg),
#ifndef DBUG_OFF
     m_duration(duration_arg),
#endif
     m_ctx(ctx_arg),
     m_lock(NULL)
  {}

  static MDL_ticket *create(MDL_context *ctx_arg, enum_mdl_type type_arg
#ifndef DBUG_OFF
                            , enum_mdl_duration duration_arg
#endif
                            );
  static void destroy(MDL_ticket *ticket);
private:
  enum enum_mdl_type m_type;
#ifndef DBUG_OFF

  enum_mdl_duration m_duration;
#endif

  MDL_context *m_ctx;

  MDL_lock *m_lock;

private:
  MDL_ticket(const MDL_ticket &);               /* not implemented */
  MDL_ticket &operator=(const MDL_ticket &);    /* not implemented */
};


class MDL_savepoint
{
public:
  MDL_savepoint() {};

private:
  MDL_savepoint(MDL_ticket *stmt_ticket, MDL_ticket *trans_ticket)
    : m_stmt_ticket(stmt_ticket), m_trans_ticket(trans_ticket)
  {}

  friend class MDL_context;

private:
  MDL_ticket *m_stmt_ticket;
  MDL_ticket *m_trans_ticket;
};


class MDL_wait
{
public:
  MDL_wait();
  ~MDL_wait();

  enum enum_wait_status { EMPTY = 0, GRANTED, VICTIM, TIMEOUT, KILLED };

  bool set_status(enum_wait_status result_arg);
  enum_wait_status get_status();
  void reset_status();
  enum_wait_status timed_wait(MDL_context_owner *owner,
                              struct timespec *abs_timeout,
                              bool signal_timeout,
                              const PSI_stage_info *wait_state_name);
private:
  mysql_mutex_t m_LOCK_wait_status;
  mysql_cond_t m_COND_wait_status;
  enum_wait_status m_wait_status;
};


typedef I_P_List<MDL_request, I_P_List_adapter<MDL_request,
                 &MDL_request::next_in_list,
                 &MDL_request::prev_in_list>,
                 I_P_List_counter>
        MDL_request_list;

class MDL_context
{
public:
  typedef I_P_List<MDL_ticket,
                   I_P_List_adapter<MDL_ticket,
                                    &MDL_ticket::next_in_context,
                                    &MDL_ticket::prev_in_context> >
          Ticket_list;

  typedef Ticket_list::Iterator Ticket_iterator;

  MDL_context();
  void destroy();

  bool try_acquire_lock(MDL_request *mdl_request);
  bool acquire_lock(MDL_request *mdl_request, ulong lock_wait_timeout);
  bool acquire_locks(MDL_request_list *requests, ulong lock_wait_timeout);
  bool upgrade_shared_lock(MDL_ticket *mdl_ticket,
                           enum_mdl_type new_type,
                           ulong lock_wait_timeout);

  bool clone_ticket(MDL_request *mdl_request);

  void release_all_locks_for_name(MDL_ticket *ticket);
  void release_lock(MDL_ticket *ticket);

  bool is_lock_owner(MDL_key::enum_mdl_namespace mdl_namespace,
                     const char *db, const char *name,
                     enum_mdl_type mdl_type);

  bool has_lock(const MDL_savepoint &mdl_savepoint, MDL_ticket *mdl_ticket);

  inline bool has_locks() const
  {
    return !(m_tickets[MDL_STATEMENT].is_empty() &&
             m_tickets[MDL_TRANSACTION].is_empty() &&
             m_tickets[MDL_EXPLICIT].is_empty());
  }

  MDL_savepoint mdl_savepoint()
  {
    return MDL_savepoint(m_tickets[MDL_STATEMENT].front(),
                         m_tickets[MDL_TRANSACTION].front());
  }

  void set_explicit_duration_for_all_locks();
  void set_transaction_duration_for_all_locks();
  void set_lock_duration(MDL_ticket *mdl_ticket, enum_mdl_duration duration);

  void release_statement_locks();
  void release_transactional_locks();
  void rollback_to_savepoint(const MDL_savepoint &mdl_savepoint);

  MDL_context_owner *get_owner() { return m_owner; }

  inline uint get_deadlock_weight() const
  { return m_waiting_for->get_deadlock_weight(); }
  void init(MDL_context_owner *arg) { m_owner= arg; }

  void set_needs_thr_lock_abort(bool needs_thr_lock_abort)
  {
    /*
      @note In theory, this member should be modified under protection
            of some lock since it can be accessed from different threads.
            In practice, this is not necessary as code which reads this
            value and so might miss the fact that value was changed will
            always re-try reading it after small timeout and therefore
            will see the new value eventually.
    */
    m_needs_thr_lock_abort= needs_thr_lock_abort;
  }
  bool get_needs_thr_lock_abort() const
  {
    return m_needs_thr_lock_abort;
  }
public:
  MDL_wait m_wait;
private:
  Ticket_list m_tickets[MDL_DURATION_END];
  MDL_context_owner *m_owner;
  bool m_needs_thr_lock_abort;

  mysql_prlock_t m_LOCK_waiting_for;
  MDL_wait_for_subgraph *m_waiting_for;
private:
  THD *get_thd() const { return m_owner->get_thd(); }
  MDL_ticket *find_ticket(MDL_request *mdl_req,
                          enum_mdl_duration *duration);
  void release_locks_stored_before(enum_mdl_duration duration, MDL_ticket *sentinel);
  void release_lock(enum_mdl_duration duration, MDL_ticket *ticket);
  bool try_acquire_lock_impl(MDL_request *mdl_request,
                             MDL_ticket **out_ticket);

public:
  void find_deadlock();

  bool visit_subgraph(MDL_wait_for_graph_visitor *dvisitor);

  void will_wait_for(MDL_wait_for_subgraph *waiting_for_arg)
  {
    mysql_prlock_wrlock(&m_LOCK_waiting_for);
    m_waiting_for=  waiting_for_arg;
    mysql_prlock_unlock(&m_LOCK_waiting_for);
  }

  void done_waiting_for()
  {
    mysql_prlock_wrlock(&m_LOCK_waiting_for);
    m_waiting_for= NULL;
    mysql_prlock_unlock(&m_LOCK_waiting_for);
  }
  void lock_deadlock_victim()
  {
    mysql_prlock_rdlock(&m_LOCK_waiting_for);
  }
  void unlock_deadlock_victim()
  {
    mysql_prlock_unlock(&m_LOCK_waiting_for);
  }
private:
  MDL_context(const MDL_context &rhs);          /* not implemented */
  MDL_context &operator=(MDL_context &rhs);     /* not implemented */
};


void mdl_init();
void mdl_destroy();


#ifndef DBUG_OFF
extern mysql_mutex_t LOCK_open;
#endif


/*
  Start-up parameter for the maximum size of the unused MDL_lock objects cache
  and a constant for its default value.
*/
extern ulong mdl_locks_cache_size;
static const ulong MDL_LOCKS_CACHE_SIZE_DEFAULT = 1024;

/*
  Start-up parameter for the number of partitions of the hash
  containing all the MDL_lock objects and a constant for
  its default value.
*/
extern ulong mdl_locks_hash_partitions;
static const ulong MDL_LOCKS_HASH_PARTITIONS_DEFAULT = 8;

/*
  Metadata locking subsystem tries not to grant more than
  max_write_lock_count high-prio, strong locks successively,
  to avoid starving out weak, low-prio locks.
*/
extern "C" ulong max_write_lock_count;
#endif