/* Copyright (c) 2000, 2011, Oracle and/or its affiliates.
   Copyright (c) 2012, Monty Program Ab.

   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, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */

/*
Read and write locks for Posix threads. All tread must acquire
all locks it needs through thr_multi_lock() to avoid dead-locks.
A lock consists of a master lock (THR_LOCK), and lock instances
(THR_LOCK_DATA).
Any thread can have any number of lock instances (read and write:s) on
any lock. All lock instances must be freed.
Locks are prioritized according to:

The current lock types are:

TL_READ                 # Low priority read
TL_READ_WITH_SHARED_LOCKS
TL_READ_HIGH_PRIORITY	# High priority read
TL_READ_NO_INSERT	# Read without concurrent inserts
TL_WRITE_ALLOW_WRITE	# Write lock that allows other writers
TL_WRITE_CONCURRENT_INSERT
			# Insert that can be mixed when selects
TL_WRITE_DELAYED	# Used by delayed insert
			# Allows lower locks to take over
TL_WRITE_LOW_PRIORITY	# Low priority write
TL_WRITE		# High priority write
TL_WRITE_ONLY		# High priority write
			# Abort all new lock request with an error

Locks are prioritized according to:

WRITE_ALLOW_WRITE, WRITE_CONCURRENT_INSERT, WRITE_DELAYED,
WRITE_LOW_PRIORITY, READ, WRITE, READ_HIGH_PRIORITY and WRITE_ONLY

Locks in the same privilege level are scheduled in first-in-first-out order.

To allow concurrent read/writes locks, with 'WRITE_CONCURRENT_INSERT' one
should put a pointer to the following functions in the lock structure:
(If the pointer is zero (default), the function is not called)

check_status:
	 Before giving a lock of type TL_WRITE_CONCURRENT_INSERT,
         we check if this function exists and returns 0.
	 If not, then the lock is upgraded to TL_WRITE_LOCK
	 In MyISAM this is a simple check if the insert can be done
	 at the end of the datafile.
update_status:
        in thr_reschedule_write_lock(), when an insert delayed thread
        downgrades TL_WRITE lock to TL_WRITE_DELAYED, to allow SELECT
        threads to proceed.
        A storage engine should also call update_status internally
        in the ::external_lock(F_UNLCK) method.
        In MyISAM and CSV this functions updates the length of the datafile.
        MySQL does in some exceptional cases (when doing DLL statements on
        open tables calls thr_unlock() followed by thr_lock() without calling
        ::external_lock() in between. In this case thr_unlock() is called with
        the THR_UNLOCK_UPDATE_STATUS flag and thr_unlock() will call
        update_status for write locks.
get_status:
	When one gets a lock this functions is called.
	In MyISAM this stores the number of rows and size of the datafile
	for concurrent reads.

The lock algorithm allows one to have one TL_WRITE_CONCURRENT_INSERT or
one TL_WRITE_DELAYED lock at the same time as multiple read locks.

In addition, if lock->allow_multiple_concurrent_insert is set then there can
be any number of TL_WRITE_CONCURRENT_INSERT locks aktive at the same time.
*/

#if !defined(MAIN) && !defined(DBUG_OFF) && !defined(EXTRA_DEBUG)
#define FORCE_DBUG_OFF
#endif

#include "mysys_priv.h"

#include "thr_lock.h"
#include "mysql/psi/mysql_table.h"
#include <m_string.h>
#include <errno.h>

my_bool thr_lock_inited=0;
ulong locks_immediate = 0L, locks_waited = 0L;
enum thr_lock_type thr_upgraded_concurrent_insert_lock = TL_WRITE;

/* The following constants are only for debug output */
#define MAX_THREADS 1000
#define MAX_LOCKS   1000


LIST *thr_lock_thread_list;			/* List of threads in use */
ulong max_write_lock_count= ~(ulong) 0L;

static void (*before_lock_wait)(void)= 0;
static void (*after_lock_wait)(void)= 0;

void thr_set_lock_wait_callback(void (*before_wait)(void),
                                void (*after_wait)(void))
{
  before_lock_wait= before_wait;
  after_lock_wait= after_wait;
}

static inline mysql_cond_t *get_cond(void)
{
  return &my_thread_var->suspend;
}


/*
  Sort locks in priority order

  LOCK_CMP()
    A       First lock
    B       Second lock

  Return:
      0 if A >= B
      1 if A < B

  Priority for locks (decides in which order locks are locked)
  We want all write locks to be first, followed by read locks.
  Locks from MERGE tables has a little lower priority than other
  locks, to allow one to release merge tables without having
  to unlock and re-lock other locks.
  The lower the number, the higher the priority for the lock.
  For MERGE tables we add 2 (THR_LOCK_MERGE_PRIV) to the lock priority.
  THR_LOCK_LATE_PRIV (1) is used when one locks other tables to be merged
  with existing locks. This way we prioritize the original locks over the
  new locks.
*/


static inline int LOCK_CMP(THR_LOCK_DATA *a, THR_LOCK_DATA *b)
{
  if (a->lock != b->lock)
    return a->lock < b->lock;

  if (a->type != b->type)
    return a->type > b->type;

  return a->priority < b->priority;
}


/*
  For the future (now the thread specific cond is alloced by my_pthread.c)
*/

my_bool init_thr_lock()
{
  thr_lock_inited=1;
  return 0;
}

static inline my_bool
thr_lock_owner_equal(THR_LOCK_INFO *rhs, THR_LOCK_INFO *lhs)
{
  return rhs == lhs;
}


#ifdef EXTRA_DEBUG
#define MAX_FOUND_ERRORS	10		/* Report 10 first errors */
static uint found_errors=0;

static int check_lock(struct st_lock_list *list, const char* lock_type,
		      const char *where, my_bool same_owner, my_bool no_cond,
                      my_bool read_lock)
{
  THR_LOCK_DATA *data,**prev;
  uint count=0;

  prev= &list->data;
  if (list->data)
  {
    enum thr_lock_type last_lock_type= list->data->type;
    THR_LOCK_INFO *first_owner= list->data->owner;

    for (data=list->data; data && count++ < MAX_LOCKS ; data=data->next)
    {
      if (data->type == TL_UNLOCK)
      {
	fprintf(stderr,
		"Warning: Found unlocked lock at %s: %s\n",
                lock_type, where);
        return 1;
      }
      if ((read_lock && data->type >= TL_FIRST_WRITE) ||
          (!read_lock && data->type < TL_FIRST_WRITE))
      {
	fprintf(stderr,
		"Warning: Found %s lock in %s queue at %s: %s\n",
                read_lock ? "write" : "read",
                read_lock ? "read" : "write",
                lock_type, where);
        return 1;
      }
      if (data->type != last_lock_type)
	last_lock_type=TL_IGNORE;
      if (data->prev != prev)
      {
	fprintf(stderr,
		"Warning: prev link %d didn't point at previous lock at %s: %s\n",
		count, lock_type, where);
	return 1;
      }
      if (same_owner &&
          !thr_lock_owner_equal(data->owner, first_owner) &&
	  last_lock_type != TL_WRITE_ALLOW_WRITE &&
          last_lock_type != TL_WRITE_CONCURRENT_INSERT)
      {
	fprintf(stderr,
		"Warning: Found locks from different threads for lock '%s' in '%s' at '%s'.  org_lock_type: %d  last_lock_type: %d  new_lock_type: %d\n",
                data->lock->name ? data->lock->name : "",
		lock_type, where, list->data->type, last_lock_type,
                data->type);
	return 1;
      }
      if (no_cond && data->cond)
      {
	fprintf(stderr,
		"Warning: Found active lock with not reset cond %s: %s\n",
		lock_type,where);
	return 1;
      }
      prev= &data->next;
    }
    if (data)
    {
      fprintf(stderr,"Warning: found too many locks at %s: %s\n",
	      lock_type,where);
      return 1;
    }
  }
  if (prev != list->last)
  {
    fprintf(stderr,"Warning: last didn't point at last lock at %s: %s\n",
	    lock_type, where);
    return 1;
  }
  return 0;
}


static void check_locks(THR_LOCK *lock, const char *where,
                        enum thr_lock_type type,
			my_bool allow_no_locks)
{
  uint old_found_errors=found_errors;
  DBUG_ENTER("check_locks");

  if (found_errors < MAX_FOUND_ERRORS)
  {
    if (check_lock(&lock->write,"write",where,1,1,0) |
	check_lock(&lock->write_wait,"write_wait",where,0,0,0) |
	check_lock(&lock->read,"read",where,0,1,1) |
	check_lock(&lock->read_wait,"read_wait",where,0,0,1))
    {
      DBUG_ASSERT(my_assert_on_error == 0);
      found_errors++;
    }

    if (found_errors < MAX_FOUND_ERRORS)
    {
      uint count=0, count2= 0;
      THR_LOCK_DATA *data;
      for (data=lock->read.data ; data ; data=data->next)
      {
        count2++;
	if (data->type == TL_READ_NO_INSERT)
	  count++;
        /* Protect against infinite loop. */
        DBUG_ASSERT(count <= lock->read_no_write_count &&
                    count2 <= MAX_LOCKS);
      }
      if (count != lock->read_no_write_count)
      {
	found_errors++;
	fprintf(stderr,
		"Warning at '%s': Locks read_no_write_count was %u when it should have been %u\n", where, lock->read_no_write_count,count);
      }      

      if (!lock->write.data)
      {
	if (!allow_no_locks && !lock->read.data &&
	    (lock->write_wait.data || lock->read_wait.data))
	{
	  found_errors++;
	  fprintf(stderr,
		  "Warning at '%s': No locks in use but locks are in wait queue\n",
		  where);
	}
	if (!lock->write_wait.data)
	{
	  if (!allow_no_locks && lock->read_wait.data)
	  {
	    found_errors++;
	    fprintf(stderr,
		    "Warning at '%s': No write locks and waiting read locks\n",
		    where);
	  }
	}
	else
	{
	  if (!allow_no_locks &&
	      (((lock->write_wait.data->type == TL_WRITE_CONCURRENT_INSERT ||
		 lock->write_wait.data->type == TL_WRITE_ALLOW_WRITE) &&
		!lock->read_no_write_count) ||
	       (lock->write_wait.data->type == TL_WRITE_DELAYED &&
		!lock->read.data)))
	  {
	    found_errors++;
	    fprintf(stderr,
		    "Warning at '%s': Write lock %d waiting while no exclusive read locks\n",where,(int) lock->write_wait.data->type);
            DBUG_PRINT("warning", ("Warning at '%s': Write lock %d waiting while no exclusive read locks",where,(int) lock->write_wait.data->type));
	  }
        }
      }
      else
      {
        /* We have at least one write lock */
        if (lock->write.data->type == TL_WRITE_CONCURRENT_INSERT)
        {
          count= 0;
          for (data=lock->write.data->next;
               data && count < MAX_LOCKS;
               data=data->next)
          {
            if (data->type != TL_WRITE_CONCURRENT_INSERT &&
                data->type != TL_WRITE_ALLOW_WRITE)
            {
              fprintf(stderr,
                      "Warning at '%s': Found TL_WRITE_CONCURRENT_INSERT lock mixed with other write lock: %d\n",
                      where, data->type);
              DBUG_PRINT("warning", ("Warning at '%s': Found TL_WRITE_CONCURRENT_INSERT lock mixed with other write lock: %d",
                                     where, data->type));
              break;
            }
          }
        }
	if (lock->write_wait.data)
	{
	  if (!allow_no_locks && 
	      lock->write.data->type == TL_WRITE_ALLOW_WRITE &&
	      lock->write_wait.data->type == TL_WRITE_ALLOW_WRITE)
	  {
	    found_errors++;
	    fprintf(stderr,
		    "Warning at '%s': Found WRITE_ALLOW_WRITE lock waiting for WRITE_ALLOW_WRITE lock\n",
		    where);
            DBUG_PRINT("warning", ("Warning at '%s': Found WRITE_ALLOW_WRITE lock waiting for WRITE_ALLOW_WRITE lock",
                                   where));

	  }
	}
	if (lock->read.data)
	{
          for (data=lock->read.data ; data ; data=data->next)
          {
            if (!thr_lock_owner_equal(lock->write.data->owner,
                                      data->owner) &&
	      ((lock->write.data->type > TL_WRITE_DELAYED &&
		lock->write.data->type != TL_WRITE_ONLY) ||
	       ((lock->write.data->type == TL_WRITE_CONCURRENT_INSERT ||
		 lock->write.data->type == TL_WRITE_ALLOW_WRITE) &&
                data->type == TL_READ_NO_INSERT)))
            {
              found_errors++;
              fprintf(stderr,
                      "Warning at '%s' for lock: %d: Found lock of type %d that is write and read locked. Read_no_write_count: %d\n",
                      where, (int) type, lock->write.data->type,
                      lock->read_no_write_count);
              DBUG_PRINT("warning",("At '%s' for lock %d: Found lock of type %d that is write and read locked",
                                    where, (int) type,
                                    lock->write.data->type));
            }
          }
	}
	if (lock->read_wait.data)
	{
	  if (!allow_no_locks && lock->write.data->type <= TL_WRITE_DELAYED &&
	      lock->read_wait.data->type <= TL_READ_HIGH_PRIORITY)
	  {
	    found_errors++;
	    fprintf(stderr,
		    "Warning at '%s': Found read lock of type %d waiting for write lock of type %d\n",
		    where,
		    (int) lock->read_wait.data->type,
		    (int) lock->write.data->type);
	  }
	}
      }
    }
    if (found_errors != old_found_errors)
    {
      DBUG_PRINT("error",("Found wrong lock"));
    }
  }
  DBUG_VOID_RETURN;
}

#else /* EXTRA_DEBUG */
#define check_locks(A,B,C,D)
#endif


	/* Initialize a lock */

void thr_lock_init(THR_LOCK *lock)
{
  DBUG_ENTER("thr_lock_init");
  bzero((char*) lock,sizeof(*lock));
  mysql_mutex_init(key_THR_LOCK_mutex, &lock->mutex, MY_MUTEX_INIT_FAST);
  lock->read.last= &lock->read.data;
  lock->read_wait.last= &lock->read_wait.data;
  lock->write_wait.last= &lock->write_wait.data;
  lock->write.last= &lock->write.data;

  mysql_mutex_lock(&THR_LOCK_lock);              /* Add to locks in use */
  lock->list.data=(void*) lock;
  thr_lock_thread_list=list_add(thr_lock_thread_list,&lock->list);
  mysql_mutex_unlock(&THR_LOCK_lock);
  DBUG_VOID_RETURN;
}


void thr_lock_delete(THR_LOCK *lock)
{
  DBUG_ENTER("thr_lock_delete");
  mysql_mutex_lock(&THR_LOCK_lock);
  thr_lock_thread_list=list_delete(thr_lock_thread_list,&lock->list);
  mysql_mutex_unlock(&THR_LOCK_lock);
  mysql_mutex_destroy(&lock->mutex);
  DBUG_VOID_RETURN;
}


void thr_lock_info_init(THR_LOCK_INFO *info, struct st_my_thread_var *tmp)
{
  if (!tmp)
    tmp= my_thread_var;
  info->thread=    tmp->pthread_self;
  info->thread_id= tmp->id;
}

	/* Initialize a lock instance */

void thr_lock_data_init(THR_LOCK *lock,THR_LOCK_DATA *data, void *param)
{
  data->lock=lock;
  data->type=TL_UNLOCK;
  data->owner= 0;                               /* no owner yet */
  data->status_param=param;
  data->cond=0;
  data->priority= 0;
  data->debug_print_param= 0;
}


static inline my_bool
has_old_lock(THR_LOCK_DATA *data, THR_LOCK_INFO *owner)
{
  for ( ; data ; data=data->next)
  {
    if (thr_lock_owner_equal(data->owner, owner))
      return 1;					/* Already locked by thread */
  }
  return 0;
}

static void wake_up_waiters(THR_LOCK *lock);


static enum enum_thr_lock_result
wait_for_lock(struct st_lock_list *wait, THR_LOCK_DATA *data,
              my_bool in_wait_list, ulong lock_wait_timeout)
{
  struct st_my_thread_var *thread_var= my_thread_var;
  mysql_cond_t *cond= &thread_var->suspend;
  struct timespec wait_timeout;
  enum enum_thr_lock_result result= THR_LOCK_ABORTED;
  PSI_stage_info old_stage;
  my_bool use_wait_callbacks= FALSE;
  DBUG_ENTER("wait_for_lock");

  /*
    One can use this to signal when a thread is going to wait for a lock.
    See debug_sync.cc.

    Beware of waiting for a signal here. The lock has acquired its mutex.
    While waiting on a signal here, the locking thread could not acquire
    the mutex to release the lock. One could lock up the table
    completely.

    In detail it works so: When thr_lock() tries to acquire a table
    lock, it locks the lock->mutex, checks if it can have the lock, and
    if not, it calls wait_for_lock(). Here it unlocks the table lock
    while waiting on a condition. The sync point is located before this
    wait for condition. If we have a waiting action here, we hold the
    the table locks mutex all the time. Any attempt to look at the table
    lock by another thread blocks it immediately on lock->mutex. This
    can easily become an unexpected and unobvious blockage. So be
    warned: Do not request a WAIT_FOR action for the 'wait_for_lock'
    sync point unless you really know what you do.
  */
  DEBUG_SYNC_C("wait_for_lock");

  if (!in_wait_list)
  {
    (*wait->last)=data;				/* Wait for lock */
    data->prev= wait->last;
    wait->last= &data->next;
  }

  statistic_increment(locks_waited, &THR_LOCK_lock);

  /* Set up control struct to allow others to abort locks */
  thread_var->current_mutex= &data->lock->mutex;
  thread_var->current_cond=  cond;
  data->cond= cond;

  proc_info_hook(NULL, &stage_waiting_for_table_level_lock,
                 &old_stage,
                               __func__, __FILE__, __LINE__);

  /*
    Since before_lock_wait potentially can create more threads to
    scheduler work for, we don't want to call the before_lock_wait
    callback unless it will really start to wait.

    For similar reasons, we do not want to call before_lock_wait and
    after_lock_wait for each lap around the loop, so we restrict
    ourselves to call it before_lock_wait once before starting to wait
    and once after the thread has exited the wait loop.
   */
  if ((!thread_var->abort || in_wait_list) && before_lock_wait)
  {
    use_wait_callbacks= TRUE;
    (*before_lock_wait)();
  }

  set_timespec(wait_timeout, lock_wait_timeout);
  while (!thread_var->abort || in_wait_list)
  {
    int rc= mysql_cond_timedwait(cond, &data->lock->mutex, &wait_timeout);
    /*
      We must break the wait if one of the following occurs:
      - the connection has been aborted (!thread_var->abort), but
        this is not a delayed insert thread (in_wait_list). For a delayed
        insert thread the proper action at shutdown is, apparently, to
        acquire the lock and complete the insert.
      - the lock has been granted (data->cond is set to NULL by the granter),
        or the waiting has been aborted (additionally data->type is set to
        TL_UNLOCK).
      - the wait has timed out (rc == ETIMEDOUT)
      Order of checks below is important to not report about timeout
      if the predicate is true.
    */
    if (data->cond == 0)
    {
      DBUG_PRINT("thr_lock", ("lock granted/aborted"));
      break;
    }
    if (rc == ETIMEDOUT || rc == ETIME)
    {
      /* purecov: begin inspected */
      DBUG_PRINT("thr_lock", ("lock timed out"));
      result= THR_LOCK_WAIT_TIMEOUT;
      break;
      /* purecov: end */
    }
  }

  /*
    We call the after_lock_wait callback once the wait loop has
    finished.
   */
  if (after_lock_wait && use_wait_callbacks)
    (*after_lock_wait)();

  DBUG_PRINT("thr_lock", ("aborted: %d  in_wait_list: %d",
                          thread_var->abort, in_wait_list));

  if (data->cond || data->type == TL_UNLOCK)
  {
    if (data->cond)                             /* aborted or timed out */
    {
      if (((*data->prev)=data->next))		/* remove from wait-list */
	data->next->prev= data->prev;
      else
	wait->last=data->prev;
      data->type= TL_UNLOCK;                    /* No lock */
      check_locks(data->lock, "killed or timed out wait_for_lock", data->type,
                  1);
      wake_up_waiters(data->lock);
    }
    else
    {
      DBUG_PRINT("thr_lock", ("lock aborted"));
      check_locks(data->lock, "aborted wait_for_lock", data->type, 0);
    }
  }
  else
  {
    result= THR_LOCK_SUCCESS;
    if (data->lock->get_status &&
        (*data->lock->get_status)(data->status_param,
                                  data->type == TL_WRITE_CONCURRENT_INSERT))
        result= THR_LOCK_ABORTED;
    check_locks(data->lock,"got wait_for_lock", data->type, 0);
  }
  mysql_mutex_unlock(&data->lock->mutex);

  /* The following must be done after unlock of lock->mutex */
  mysql_mutex_lock(&thread_var->mutex);
  thread_var->current_mutex= 0;
  thread_var->current_cond=  0;
  mysql_mutex_unlock(&thread_var->mutex);

  proc_info_hook(NULL, &old_stage, NULL, __func__, __FILE__, __LINE__);

  DBUG_RETURN(result);
}

static enum enum_thr_lock_result
thr_lock(THR_LOCK_DATA *data, THR_LOCK_INFO *owner, ulong lock_wait_timeout)
{
  THR_LOCK *lock=data->lock;
  enum enum_thr_lock_result result= THR_LOCK_SUCCESS;
  struct st_lock_list *wait_queue;
  enum thr_lock_type lock_type= data->type;
  MYSQL_TABLE_WAIT_VARIABLES(locker, state) /* no ';' */
  DBUG_ENTER("thr_lock");

  data->next=0;
  data->cond=0;					/* safety */
  data->owner= owner;                           /* Must be reset ! */
  data->priority&= ~THR_LOCK_LATE_PRIV;

  MYSQL_START_TABLE_LOCK_WAIT(locker, &state, data->m_psi,
                              PSI_TABLE_LOCK, lock_type);

  mysql_mutex_lock(&lock->mutex);
  DBUG_PRINT("lock",("data:%p  thread:%lu  lock:%p  type: %d",
                     data, (ulong) data->owner->thread_id,
                     lock, (int) lock_type));
  check_locks(lock,(uint) lock_type < (uint) TL_FIRST_WRITE ?
	      "enter read_lock" : "enter write_lock", lock_type, 0);
  if ((int) lock_type < (int) TL_FIRST_WRITE)
  {
    /* Request for READ lock */
    if (lock->write.data)
    {
      /*
        We can allow a read lock even if there is already a
        write lock on the table if they are owned by the same
        thread or if they satisfy the following lock
        compatibility matrix:

           Request
          /-------
         H|++++  WRITE_ALLOW_WRITE
         e|+++-  WRITE_CONCURRENT_INSERT
         l|++++  WRITE_DELAYED
         d ||||
           |||\= READ_NO_INSERT
           ||\ = READ_HIGH_PRIORITY
           |\  = READ_WITH_SHARED_LOCKS
           \   = READ
          

        + = Request can be satisfied.
        - = Request cannot be satisfied.

        READ_NO_INSERT and WRITE_ALLOW_WRITE should in principle
        be incompatible. However this will cause starvation of
        LOCK TABLE READ in InnoDB under high write load.
        See Bug#42147 for more information.
      */

      DBUG_PRINT("lock",("write locked 1 by thread:%lu",
			 (ulong) lock->write.data->owner->thread_id));
      if (thr_lock_owner_equal(data->owner, lock->write.data->owner) ||
	  (lock->write.data->type <= TL_WRITE_DELAYED &&
	   (((int) lock_type <= (int) TL_READ_HIGH_PRIORITY) ||
	    (lock->write.data->type != TL_WRITE_CONCURRENT_INSERT))))
      {						/* Already got a write lock */
	(*lock->read.last)=data;		/* Add to running FIFO */
	data->prev=lock->read.last;
	lock->read.last= &data->next;
	if (lock_type == TL_READ_NO_INSERT)
	  lock->read_no_write_count++;
	check_locks(lock,"read lock with old write lock", lock_type, 0);
	if ((lock->get_status) && (*lock->get_status)(data->status_param, 0))
          result= THR_LOCK_ABORTED;
	statistic_increment(locks_immediate,&THR_LOCK_lock);
	goto end;
      }
      if (lock->write.data->type == TL_WRITE_ONLY)
      {
	/* We are not allowed to get a READ lock in this case */
	data->type=TL_UNLOCK;
        result= THR_LOCK_ABORTED;               /* Can't wait for this one */
	goto end;
      }
    }
    else if (!lock->write_wait.data ||
	     lock->write_wait.data->type <= TL_WRITE_LOW_PRIORITY ||
	     lock_type == TL_READ_HIGH_PRIORITY ||
	     has_old_lock(lock->read.data, data->owner)) /* Has old read lock */
    {						/* No important write-locks */
      (*lock->read.last)=data;			/* Add to running FIFO */
      data->prev=lock->read.last;
      lock->read.last= &data->next;
      if (lock_type == TL_READ_NO_INSERT)
	lock->read_no_write_count++;
      check_locks(lock,"read lock with no write locks", lock_type, 0);
      if ((lock->get_status) && (*lock->get_status)(data->status_param, 0))
        result= THR_LOCK_ABORTED;
      statistic_increment(locks_immediate,&THR_LOCK_lock);
      goto end;
    }
    /*
      We're here if there is an active write lock or no write
      lock but a high priority write waiting in the write_wait queue.
      In the latter case we should yield the lock to the writer.
    */
    wait_queue= &lock->read_wait;
  }
  else						/* Request for WRITE lock */
  {
    if (lock_type == TL_WRITE_DELAYED)
    {
      if (lock->write.data && lock->write.data->type == TL_WRITE_ONLY)
      {
	data->type=TL_UNLOCK;
        result= THR_LOCK_ABORTED;               /* Can't wait for this one */
	goto end;
      }
      if (lock->write.data || lock->read.data)
      {
	/* Add delayed write lock to write_wait queue, and return at once */
	(*lock->write_wait.last)=data;
	data->prev=lock->write_wait.last;
	lock->write_wait.last= &data->next;
	data->cond=get_cond();
        /*
          We don't have to do get_status here as we will do it when we change
          the delayed lock to a real write lock
        */
	statistic_increment(locks_immediate,&THR_LOCK_lock);
	goto end;
      }
    }
    else if (lock_type == TL_WRITE_CONCURRENT_INSERT && ! lock->check_status)
      data->type=lock_type= thr_upgraded_concurrent_insert_lock;

    if (lock->write.data)			/* If there is a write lock */
    {
      if (lock->write.data->type == TL_WRITE_ONLY)
      {
        /* purecov: begin tested */
        /* Allow lock owner to bypass TL_WRITE_ONLY. */
        if (!thr_lock_owner_equal(data->owner, lock->write.data->owner))
        {
          /* We are not allowed to get a lock in this case */
          data->type=TL_UNLOCK;
          result= THR_LOCK_ABORTED;               /* Can't wait for this one */
          goto end;
        }
        /* purecov: end */
      }

      /*
        The idea is to allow us to get a lock at once if we already have
        a write lock or if there is no pending write locks and if all
        write locks are of the same type and are either
        TL_WRITE_ALLOW_WRITE or TL_WRITE_CONCURRENT_INSERT and
        there is no TL_READ_NO_INSERT lock.

        Note that, since lock requests for the same table are sorted in
        such way that requests with higher thr_lock_type value come first
        (with one exception (*)), lock being requested usually (**) has
        equal or "weaker" type than one which thread might have already
        acquired.
        *)  The only exception to this rule is case when type of old lock
            is TL_WRITE_LOW_PRIORITY and type of new lock is changed inside
            of thr_lock() from TL_WRITE_CONCURRENT_INSERT to TL_WRITE since
            engine turns out to be not supporting concurrent inserts.
            Note that since TL_WRITE has the same compatibility rules as
            TL_WRITE_LOW_PRIORITY (their only difference is priority),
            it is OK to grant new lock without additional checks in such
            situation.
        **) The exceptions are situations when:
            - when old lock type is TL_WRITE_DELAYED
            But these should never happen within MariaDB.
        Therefore it is OK to allow acquiring write lock on the table if
        this thread already holds some write lock on it.

        (INSERT INTO t1 VALUES (f1()), where f1() is stored function which
        tries to update t1, is an example of statement which requests two
        different types of write lock on the same table).
      */
      DBUG_ASSERT(! has_old_lock(lock->write.data, data->owner) ||
                  ((lock_type <= lock->write.data->type ||
                    (lock_type == TL_WRITE &&
                     lock->write.data->type == TL_WRITE_LOW_PRIORITY)) &&
                   lock->write.data->type != TL_WRITE_DELAYED));

      if (((lock_type == TL_WRITE_ALLOW_WRITE ||
           (lock_type == TL_WRITE_CONCURRENT_INSERT &&
             lock->allow_multiple_concurrent_insert &&
            !lock->read_no_write_count)) &&
           ! lock->write_wait.data &&
           lock->write.data->type == lock_type &&
           ! lock->read_no_write_count) ||
          has_old_lock(lock->write.data, data->owner))
      {
        DBUG_PRINT("info", ("write_wait.data: %p  old_type: %d",
                            lock->write_wait.data,
                            lock->write.data->type));

	(*lock->write.last)=data;	/* Add to running fifo */
	data->prev=lock->write.last;
	lock->write.last= &data->next;
	check_locks(lock,"second write lock", lock_type, 0);
	if ((lock->get_status) &&
            (*lock->get_status)(data->status_param,
                                lock_type == TL_WRITE_CONCURRENT_INSERT))
          result= THR_LOCK_ABORTED;
	statistic_increment(locks_immediate,&THR_LOCK_lock);
	goto end;
      }
      DBUG_PRINT("lock",("write locked 2 by thread: %lu",
			 (ulong) lock->write.data->owner->thread_id));
    }
    else
    {
      DBUG_PRINT("info", ("write_wait.data:%p",
                          lock->write_wait.data));
      if (!lock->write_wait.data)
      {						/* no scheduled write locks */
        my_bool concurrent_insert= 0;
	if (lock_type == TL_WRITE_CONCURRENT_INSERT)
        {
          concurrent_insert= 1;
          if ((*lock->check_status)(data->status_param))
          {
            concurrent_insert= 0;
            data->type=lock_type= thr_upgraded_concurrent_insert_lock;
          }
        }

	if (!lock->read.data ||
	    (lock_type <= TL_WRITE_DELAYED &&
	     ((lock_type != TL_WRITE_CONCURRENT_INSERT &&
	       lock_type != TL_WRITE_ALLOW_WRITE) ||
	      !lock->read_no_write_count)))
	{
	  (*lock->write.last)=data;		/* Add as current write lock */
	  data->prev=lock->write.last;
	  lock->write.last= &data->next;
	  if ((lock->get_status) &&
              (*lock->get_status)(data->status_param, concurrent_insert))
            result= THR_LOCK_ABORTED;
	  check_locks(lock,"only write lock", lock_type, 0);
	  statistic_increment(locks_immediate,&THR_LOCK_lock);
	  goto end;
	}
      }
      DBUG_PRINT("lock",("write locked 3 by thread:%lu  type: %d",
			 (ulong) lock->read.data->owner->thread_id,
                         data->type));
    }
    wait_queue= &lock->write_wait;
  }
  result= wait_for_lock(wait_queue, data, 0, lock_wait_timeout);
  MYSQL_END_TABLE_LOCK_WAIT(locker);
  DBUG_RETURN(result);
end:
  mysql_mutex_unlock(&lock->mutex);
  MYSQL_END_TABLE_LOCK_WAIT(locker);
  DBUG_RETURN(result);
}


static inline void free_all_read_locks(THR_LOCK *lock,
				       my_bool using_concurrent_insert)
{
  THR_LOCK_DATA *data=lock->read_wait.data;

  check_locks(lock,"before freeing read locks", TL_UNLOCK, 1);

  /* move all locks from read_wait list to read list */
  (*lock->read.last)=data;
  data->prev=lock->read.last;
  lock->read.last=lock->read_wait.last;

  /* Clear read_wait list */
  lock->read_wait.last= &lock->read_wait.data;

  do
  {
    mysql_cond_t *cond= data->cond;
    if ((int) data->type == (int) TL_READ_NO_INSERT)
    {
      if (using_concurrent_insert)
      {
	/*
	  We can't free this lock; 
	  Link lock away from read chain back into read_wait chain
	*/
	if (((*data->prev)=data->next))
	  data->next->prev=data->prev;
	else
	  lock->read.last=data->prev;
	*lock->read_wait.last= data;
	data->prev= lock->read_wait.last;
	lock->read_wait.last= &data->next;
	continue;
      }
      lock->read_no_write_count++;
    }      
    /* purecov: begin inspected */
    DBUG_PRINT("lock",("giving read lock to thread: %lu",
		      (ulong)data->owner->thread_id));
    /* purecov: end */
    data->cond=0;				/* Mark thread free */
    mysql_cond_signal(cond);
  } while ((data=data->next));
  *lock->read_wait.last=0;
  if (!lock->read_wait.data)
    lock->write_lock_count=0;
  check_locks(lock,"after giving read locks", TL_UNLOCK, 0);
}

	/* Unlock lock and free next thread on same lock */

void thr_unlock(THR_LOCK_DATA *data, uint unlock_flags)
{
  THR_LOCK *lock=data->lock;
  enum thr_lock_type lock_type=data->type;
  DBUG_ENTER("thr_unlock");
  DBUG_PRINT("lock",("data: %p  thread: %lu  lock: %p",
                     data, (ulong) data->owner->thread_id,
                     lock));
  mysql_mutex_lock(&lock->mutex);
  check_locks(lock,"start of release lock", lock_type, 0);

  if (((*data->prev)=data->next))		/* remove from lock-list */
    data->next->prev= data->prev;
  else if (lock_type <= TL_READ_NO_INSERT)
    lock->read.last=data->prev;
  else if (lock_type == TL_WRITE_DELAYED && data->cond)
  {
    /*
      This only happens in extreme circumstances when a 
      write delayed lock that is waiting for a lock
    */
    lock->write_wait.last=data->prev;		/* Put it on wait queue */
  }
  else
    lock->write.last=data->prev;
 
  if (unlock_flags & THR_UNLOCK_UPDATE_STATUS)
  {
    /* External lock was not called; Update or restore status */
    if (lock_type >= TL_WRITE_CONCURRENT_INSERT)
    {
      if (lock->update_status)
        (*lock->update_status)(data->status_param);
    }
    else
    {
      if (lock->restore_status)
        (*lock->restore_status)(data->status_param);
    }
  }
  if (lock_type == TL_READ_NO_INSERT)
    lock->read_no_write_count--;
  data->type=TL_UNLOCK;				/* Mark unlocked */
  wake_up_waiters(lock);
  mysql_mutex_unlock(&lock->mutex);
  DBUG_VOID_RETURN;
}


/**
  @brief  Wake up all threads which pending requests for the lock
          can be satisfied.

  @param  lock  Lock for which threads should be woken up

*/

static void wake_up_waiters(THR_LOCK *lock)
{
  THR_LOCK_DATA *data;
  enum thr_lock_type lock_type;
  DBUG_ENTER("wake_up_waiters");

  check_locks(lock, "before waking up waiters", TL_UNLOCK, 1);
  if (!lock->write.data)			/* If no active write locks */
  {
    data=lock->write_wait.data;
    if (!lock->read.data)			/* If no more locks in use */
    {
      /* Release write-locks with TL_WRITE or TL_WRITE_ONLY priority first */
      if (data &&
	  (data->type != TL_WRITE_LOW_PRIORITY || !lock->read_wait.data ||
	   lock->read_wait.data->type < TL_READ_HIGH_PRIORITY))
      {
	if (lock->write_lock_count++ > max_write_lock_count)
	{
	  /* Too many write locks in a row;  Release all waiting read locks */
	  lock->write_lock_count=0;
	  if (lock->read_wait.data)
	  {
	    DBUG_PRINT("info",("Freeing all read_locks because of max_write_lock_count"));
	    free_all_read_locks(lock,0);
	    goto end;
	  }
	}
	for (;;)
	{
	  if (((*data->prev)=data->next))	/* remove from wait-list */
	    data->next->prev= data->prev;
	  else
	    lock->write_wait.last=data->prev;
	  (*lock->write.last)=data;		/* Put in execute list */
	  data->prev=lock->write.last;
	  data->next=0;
	  lock->write.last= &data->next;
	  if (data->type == TL_WRITE_CONCURRENT_INSERT &&
	      (*lock->check_status)(data->status_param))
	    data->type=TL_WRITE;			/* Upgrade lock */
          /* purecov: begin inspected */
	  DBUG_PRINT("lock",("giving write lock of type %d to thread: %lu",
			     data->type, (ulong) data->owner->thread_id));
          /* purecov: end */
	  {
            mysql_cond_t *cond= data->cond;
	    data->cond=0;				/* Mark thread free */
            mysql_cond_signal(cond);                    /* Start waiting thread */
	  }
	  if (data->type != TL_WRITE_ALLOW_WRITE ||
	      !lock->write_wait.data ||
	      lock->write_wait.data->type != TL_WRITE_ALLOW_WRITE)
	    break;
	  data=lock->write_wait.data;		/* Free this too */
	}
	if (data->type >= TL_WRITE_LOW_PRIORITY)
          goto end;
	/* Release possible read locks together with the write lock */
      }
      if (lock->read_wait.data)
	free_all_read_locks(lock,
			    data &&
			    (data->type == TL_WRITE_CONCURRENT_INSERT ||
			     data->type == TL_WRITE_ALLOW_WRITE));
      else
      {
	DBUG_PRINT("lock",("No waiting read locks to free"));
      }
    }
    else if (data &&
	     (lock_type=data->type) <= TL_WRITE_DELAYED &&
	     ((lock_type != TL_WRITE_CONCURRENT_INSERT &&
	       lock_type != TL_WRITE_ALLOW_WRITE) ||
	      !lock->read_no_write_count))
    {
      /*
	For DELAYED, ALLOW_READ, WRITE_ALLOW_WRITE or CONCURRENT_INSERT locks
	start WRITE locks together with the READ locks
      */
      if (lock_type == TL_WRITE_CONCURRENT_INSERT &&
	  (*lock->check_status)(data->status_param))
      {
	data->type=TL_WRITE;			/* Upgrade lock */
	if (lock->read_wait.data)
	  free_all_read_locks(lock,0);
	goto end;
      }
      do {
        mysql_cond_t *cond= data->cond;
	if (((*data->prev)=data->next))		/* remove from wait-list */
	  data->next->prev= data->prev;
	else
	  lock->write_wait.last=data->prev;
	(*lock->write.last)=data;		/* Put in execute list */
	data->prev=lock->write.last;
	lock->write.last= &data->next;
	data->next=0;				/* Only one write lock */
	data->cond=0;				/* Mark thread free */
        mysql_cond_signal(cond);                /* Start waiting thread */
      } while (lock_type == TL_WRITE_ALLOW_WRITE &&
	       (data=lock->write_wait.data) &&
	       data->type == TL_WRITE_ALLOW_WRITE);
      if (lock->read_wait.data)
	free_all_read_locks(lock,
			    (lock_type == TL_WRITE_CONCURRENT_INSERT ||
			     lock_type == TL_WRITE_ALLOW_WRITE));
    }
    else if (!data && lock->read_wait.data)
      free_all_read_locks(lock,0);
  }
end:
  check_locks(lock, "after waking up waiters", TL_UNLOCK, 0);
  DBUG_VOID_RETURN;
}


/*
  Get all locks in a specific order to avoid dead-locks
  Sort according to lock position and put write_locks before read_locks if
  lock on same lock. Locks on MERGE tables has lower priority than other
  locks of the same type. See comment for lock_priority.
*/

static void sort_locks(THR_LOCK_DATA **data,uint count)
{
  THR_LOCK_DATA **pos,**end,**prev,*tmp;

  /* Sort locks with insertion sort (fast because almost always few locks) */

  for (pos=data+1,end=data+count; pos < end ; pos++)
  {
    tmp= *pos;
    if (LOCK_CMP(tmp,pos[-1]))
    {
      prev=pos;
      do {
	prev[0]=prev[-1];
      } while (--prev != data && LOCK_CMP(tmp,prev[-1]));
      prev[0]=tmp;
    }
  }
}


enum enum_thr_lock_result
thr_multi_lock(THR_LOCK_DATA **data, uint count, THR_LOCK_INFO *owner,
               ulong lock_wait_timeout)
{
  THR_LOCK_DATA **pos, **end, **first_lock;
  DBUG_ENTER("thr_multi_lock");
  DBUG_PRINT("lock",("data: %p  count: %d", data, count));

  if (count > 1)
    sort_locks(data,count);
  else if (count == 0)
    DBUG_RETURN(THR_LOCK_SUCCESS);

  /* lock everything */
  DEBUG_SYNC_C("thr_multi_lock_before_thr_lock");
  for (pos=data,end=data+count; pos < end ; pos++)
  {
    enum enum_thr_lock_result result= thr_lock(*pos, owner, lock_wait_timeout);
    if (result != THR_LOCK_SUCCESS)
    {						/* Aborted */
      thr_multi_unlock(data,(uint) (pos-data), 0);
      /* Mark all requested locks as TL_UNLOCK (to simplify lock checking) */
      for ( ; pos < end ; pos++)
        (*pos)->type= TL_UNLOCK;
      DBUG_RETURN(result);
    }
#ifdef MAIN
    printf("Thread: %s  Got lock:%p  type: %d\n",my_thread_name(),
	   pos[0]->lock, pos[0]->type); fflush(stdout);
#endif
  }
  DEBUG_SYNC_C("thr_multi_lock_after_thr_lock");

  /*
    Call start_trans for all locks.
    If we lock the same table multiple times, we must use the same
    status_param; We ensure this by calling copy_status() for all
    copies of the same tables.
  */
  if ((*data)->lock->start_trans)
    ((*data)->lock->start_trans)((*data)->status_param);
  for (first_lock=data, pos= data+1 ; pos < end ; pos++)
  {
    /* Get the current status (row count, checksum, trid etc) */
    if ((*pos)->lock->start_trans)
      (*(*pos)->lock->start_trans)((*pos)->status_param);
    /*
      If same table as previous table use pointer to previous status
      information to ensure that all read/write tables shares same
      state.
    */
    if (pos[0]->lock == pos[-1]->lock && pos[0]->lock->copy_status)
      (pos[0]->lock->copy_status)((*pos)->status_param,
                                  (*first_lock)->status_param);
    else
    {
      /* Different lock, use this as base for next lock */
      first_lock= pos;
    }
  }
  DBUG_RETURN(THR_LOCK_SUCCESS);
}


/**
  Merge two sets of locks.

  @param data       All locks. First old locks, then new locks.
  @param old_count  Original number of locks. These are first in 'data'.
  @param new_count  How many new locks

  The merge is needed if the new locks contains same tables as the old
  locks, in which case we have to ensure that same tables shares the
  same status (as after a thr_multi_lock()).
*/

void thr_merge_locks(THR_LOCK_DATA **data, uint old_count, uint new_count)
{
  THR_LOCK_DATA **pos, **end, **first_lock= 0;
  DBUG_ENTER("thr_merge_lock");

  /* Remove marks on old locks to make them sort before new ones */
  for (pos=data, end= pos + old_count; pos < end ; pos++)
    (*pos)->priority&= ~THR_LOCK_LATE_PRIV;

  /* Mark new locks with LATE_PRIV to make them sort after org ones */
  for (pos=data + old_count, end= pos + new_count; pos < end ; pos++)
    (*pos)->priority|= THR_LOCK_LATE_PRIV;

  sort_locks(data, old_count + new_count);

  for (pos=data ; pos < end ; pos++)
  {
    /* Check if lock was unlocked before */
    if (pos[0]->type == TL_UNLOCK || ! pos[0]->lock->fix_status)
    {
      DBUG_PRINT("info", ("lock skipped.  unlocked: %d  fix_status: %d",
                          pos[0]->type == TL_UNLOCK,
                          pos[0]->lock->fix_status == 0));
      continue;
    }

    /*
      If same table as previous table use pointer to previous status
      information to ensure that all read/write tables shares same
      state.
    */
    if (first_lock && pos[0]->lock == first_lock[0]->lock)
      (pos[0]->lock->fix_status)((*first_lock)->status_param,
                                 (*pos)->status_param);
    else
    {
      /* Different lock, use this as base for next lock */
      first_lock= pos;
      (pos[0]->lock->fix_status)((*first_lock)->status_param, 0);
    }
  }
  DBUG_VOID_RETURN;
}


/* Unlock all locks */

void thr_multi_unlock(THR_LOCK_DATA **data,uint count, uint unlock_flags)
{
  THR_LOCK_DATA **pos,**end;
  DBUG_ENTER("thr_multi_unlock");
  DBUG_PRINT("lock",("data: %p  count: %d  flags: %u", data, count,
                     unlock_flags));

  for (pos=data,end=data+count; pos < end ; pos++)
  {
#ifdef MAIN
    printf("Thread: %s  Rel lock: %p  type: %d\n",
	   my_thread_name(), pos[0]->lock, pos[0]->type);
    fflush(stdout);
#endif
    if ((*pos)->type != TL_UNLOCK)
      thr_unlock(*pos, unlock_flags);
    else
    {
      DBUG_PRINT("lock",("Free lock: data: %p  thread:%lu  lock: %p",
                         *pos, (ulong) (*pos)->owner->thread_id,
                         (*pos)->lock));
    }
  }
  DBUG_VOID_RETURN;
}

/*
  Abort all threads waiting for a lock. The lock will be upgraded to
  TL_WRITE_ONLY to abort any new accesses to the lock
*/

void thr_abort_locks(THR_LOCK *lock, my_bool upgrade_lock)
{
  THR_LOCK_DATA *data;
  DBUG_ENTER("thr_abort_locks");
  mysql_mutex_lock(&lock->mutex);

  for (data=lock->read_wait.data; data ; data=data->next)
  {
    data->type=TL_UNLOCK;			/* Mark killed */
    /* It's safe to signal the cond first: we're still holding the mutex. */
    mysql_cond_signal(data->cond);
    data->cond=0;				/* Removed from list */
  }
  for (data=lock->write_wait.data; data ; data=data->next)
  {
    data->type=TL_UNLOCK;
    mysql_cond_signal(data->cond);
    data->cond=0;
  }
  lock->read_wait.last= &lock->read_wait.data;
  lock->write_wait.last= &lock->write_wait.data;
  lock->read_wait.data=lock->write_wait.data=0;
  if (upgrade_lock && lock->write.data)
    lock->write.data->type=TL_WRITE_ONLY;
  mysql_mutex_unlock(&lock->mutex);
  DBUG_VOID_RETURN;
}


/*
  Abort all locks for specific table/thread combination

  This is used to abort all locks for a specific thread
*/

my_bool thr_abort_locks_for_thread(THR_LOCK *lock, my_thread_id thread_id)
{
  THR_LOCK_DATA *data;
  my_bool found= FALSE;
  DBUG_ENTER("thr_abort_locks_for_thread");

  mysql_mutex_lock(&lock->mutex);
  for (data= lock->read_wait.data; data ; data= data->next)
  {
    if (data->owner->thread_id == thread_id)    /* purecov: tested */
    {
      DBUG_PRINT("info",("Aborting read-wait lock"));
      data->type= TL_UNLOCK;			/* Mark killed */
      /* It's safe to signal the cond first: we're still holding the mutex. */
      found= TRUE;
      mysql_cond_signal(data->cond);
      data->cond= 0;				/* Removed from list */

      if (((*data->prev)= data->next))
	data->next->prev= data->prev;
      else
	lock->read_wait.last= data->prev;
    }
  }
  for (data= lock->write_wait.data; data ; data= data->next)
  {
    if (data->owner->thread_id == thread_id) /* purecov: tested */
    {
      DBUG_PRINT("info",("Aborting write-wait lock"));
      data->type= TL_UNLOCK;
      found= TRUE;
      mysql_cond_signal(data->cond);
      data->cond= 0;

      if (((*data->prev)= data->next))
	data->next->prev= data->prev;
      else
	lock->write_wait.last= data->prev;
    }
  }
  wake_up_waiters(lock);
  mysql_mutex_unlock(&lock->mutex);
  DBUG_RETURN(found);
}


/*
  Downgrade a WRITE_* to a lower WRITE level
  SYNOPSIS
    thr_downgrade_write_lock()
    in_data                   Lock data of thread downgrading its lock
    new_lock_type             New write lock type
  RETURN VALUE
    NONE
  DESCRIPTION
    This can be used to downgrade a lock already owned. When the downgrade
    occurs also other waiters, both readers and writers can be allowed to
    start.
    The previous lock is often TL_WRITE_ONLY but can also be
    TL_WRITE. The normal downgrade variants are:
    TL_WRITE_ONLY => TL_WRITE after a short exclusive lock while holding a
    write table lock
    TL_WRITE_ONLY => TL_WRITE_ALLOW_WRITE After a short exclusive lock after
    already earlier having dongraded lock to TL_WRITE_ALLOW_WRITE
    The implementation is conservative and rather don't start rather than
    go on unknown paths to start, the common cases are handled.

    NOTE:
    In its current implementation it is only allowed to downgrade from
    TL_WRITE_ONLY. In this case there are no waiters. Thus no wake up
    logic is required.
*/

void thr_downgrade_write_lock(THR_LOCK_DATA *in_data,
                              enum thr_lock_type new_lock_type)
{
  THR_LOCK *lock=in_data->lock;
#ifdef DBUG_ASSERT_EXISTS
  enum thr_lock_type old_lock_type= in_data->type;
#endif
  DBUG_ENTER("thr_downgrade_write_only_lock");

  mysql_mutex_lock(&lock->mutex);
  DBUG_ASSERT(old_lock_type == TL_WRITE_ONLY);
  DBUG_ASSERT(old_lock_type > new_lock_type);
  in_data->type= new_lock_type;
  check_locks(lock,"after downgrading lock", old_lock_type, 0);

  mysql_mutex_unlock(&lock->mutex);
  DBUG_VOID_RETURN;
}

/* Upgrade a WRITE_DELAY lock to a WRITE_LOCK */

my_bool thr_upgrade_write_delay_lock(THR_LOCK_DATA *data,
                                     enum thr_lock_type new_lock_type,
                                     ulong lock_wait_timeout)
{
  THR_LOCK *lock=data->lock;
  enum enum_thr_lock_result res;
  DBUG_ENTER("thr_upgrade_write_delay_lock");

  mysql_mutex_lock(&lock->mutex);
  if (data->type == TL_UNLOCK || data->type >= TL_WRITE_LOW_PRIORITY)
  {
    mysql_mutex_unlock(&lock->mutex);
    DBUG_RETURN(data->type == TL_UNLOCK);	/* Test if Aborted */
  }
  check_locks(lock,"before upgrading lock", data->type, 0);
  /* TODO:  Upgrade to TL_WRITE_CONCURRENT_INSERT in some cases */
  data->type= new_lock_type;                    /* Upgrade lock */

  /* Check if someone has given us the lock */
  if (!data->cond)
  {
    if (!lock->read.data)			/* No read locks */
    {						/* We have the lock */
      /* For this function, get_status is not allowed to fail */
      if (data->lock->get_status)
	(*data->lock->get_status)(data->status_param, 0);
      mysql_mutex_unlock(&lock->mutex);
      if (lock->start_trans)
	(*lock->start_trans)(data->status_param);
      DBUG_RETURN(0);
    }

    if (((*data->prev)=data->next))		/* remove from lock-list */
      data->next->prev= data->prev;
    else
      lock->write.last=data->prev;

    if ((data->next=lock->write_wait.data))	/* Put first in lock_list */
      data->next->prev= &data->next;
    else
      lock->write_wait.last= &data->next;
    data->prev= &lock->write_wait.data;
    lock->write_wait.data=data;
    check_locks(lock,"upgrading lock", new_lock_type, 0);
  }
  else
  {
    check_locks(lock,"waiting for lock", new_lock_type, 0);
  }
  res= wait_for_lock(&lock->write_wait, data, 1, lock_wait_timeout);
  if (res == THR_LOCK_SUCCESS && lock->start_trans)
    DBUG_RETURN((*lock->start_trans)(data->status_param));
  DBUG_RETURN(0);
}


/* downgrade a WRITE lock to a WRITE_DELAY lock if there is pending locks */

my_bool thr_reschedule_write_lock(THR_LOCK_DATA *data,
                                  ulong lock_wait_timeout)
{
  THR_LOCK *lock=data->lock;
  enum thr_lock_type write_lock_type;
  DBUG_ENTER("thr_reschedule_write_lock");

  mysql_mutex_lock(&lock->mutex);
  if (!lock->read_wait.data)			/* No waiting read locks */
  {
    mysql_mutex_unlock(&lock->mutex);
    DBUG_RETURN(0);
  }

  write_lock_type= data->type;
  data->type=TL_WRITE_DELAYED;
  if (lock->update_status)
    (*lock->update_status)(data->status_param);
  if (((*data->prev)=data->next))		/* remove from lock-list */
    data->next->prev= data->prev;
  else
    lock->write.last=data->prev;

  if ((data->next=lock->write_wait.data))	/* Put first in lock_list */
    data->next->prev= &data->next;
  else
    lock->write_wait.last= &data->next;
  data->prev= &lock->write_wait.data;
  data->cond=get_cond();			/* This was zero */
  lock->write_wait.data=data;
  free_all_read_locks(lock,0);

  mysql_mutex_unlock(&lock->mutex);
  DBUG_RETURN(thr_upgrade_write_delay_lock(data, write_lock_type,
                                           lock_wait_timeout));
}


#include <my_sys.h>

static void thr_print_lock(const char* name,struct st_lock_list *list)
{
  THR_LOCK_DATA *data,**prev;
  uint count=0;

  if (list->data)
  {
    printf("%-10s: ",name);
    prev= &list->data;
    for (data=list->data; data && count++ < MAX_LOCKS ; data=data->next)
    {
      printf("%p (%lu:%d); ", data, (ulong) data->owner->thread_id,
             (int) data->type);
      if (data->prev != prev)
	printf("\nWarning: prev didn't point at previous lock\n");
      prev= &data->next;
    }
    puts("");
    if (prev != list->last)
      printf("Warning: last didn't point at last lock\n");
  }
}

void thr_print_locks(void)
{
  LIST *list;
  uint count=0;

  mysql_mutex_lock(&THR_LOCK_lock);
  puts("Current active THR (table level locks):");
  for (list= thr_lock_thread_list; list && count++ < MAX_THREADS;
       list= list_rest(list))
  {
    THR_LOCK *lock=(THR_LOCK*) list->data;
    mysql_mutex_lock(&lock->mutex);
    if ((lock->write.data || lock->read.data ||
         lock->write_wait.data || lock->read_wait.data))
    {
      printf("lock: %p:", lock);
      if ((lock->write_wait.data || lock->read_wait.data) &&
          (! lock->read.data && ! lock->write.data))
        printf(" WARNING: ");
      if (lock->write.data)
        printf(" write");
      if (lock->write_wait.data)
        printf(" write_wait");
      if (lock->read.data)
        printf(" read");
      if (lock->read_wait.data)
        printf(" read_wait");
      puts("");
      thr_print_lock("write",&lock->write);
      thr_print_lock("write_wait",&lock->write_wait);
      thr_print_lock("read",&lock->read);
      thr_print_lock("read_wait",&lock->read_wait);
      puts("");
    }
    mysql_mutex_unlock(&lock->mutex);
  }
  fflush(stdout);
  mysql_mutex_unlock(&THR_LOCK_lock);
}


/*****************************************************************************
** Test of thread locks
****************************************************************************/

#ifdef MAIN

struct st_test {
  uint lock_nr;
  enum thr_lock_type lock_type;
};

THR_LOCK locks[6];			/* Number of locks +1 */

struct st_test test_0[] = {{0,TL_READ}};	/* One lock */
struct st_test test_1[] = {{0,TL_READ},{0,TL_WRITE}}; /* Read and write lock of lock 0 */
struct st_test test_2[] = {{1,TL_WRITE},{0,TL_READ},{2,TL_READ}};
struct st_test test_3[] = {{2,TL_WRITE},{1,TL_READ},{0,TL_READ}}; /* Deadlock with test_2 ? */
struct st_test test_4[] = {{0,TL_WRITE},{0,TL_READ},{0,TL_WRITE},{0,TL_READ}};
struct st_test test_5[] = {{0,TL_READ},{1,TL_READ},{2,TL_READ},{3,TL_READ}}; /* Many reads */
struct st_test test_6[] = {{0,TL_WRITE},{1,TL_WRITE},{2,TL_WRITE},{3,TL_WRITE}}; /* Many writes */
struct st_test test_7[] = {{3,TL_READ}};
struct st_test test_8[] = {{1,TL_READ_NO_INSERT},{2,TL_READ_NO_INSERT},{3,TL_READ_NO_INSERT}};	/* Should be quick */
struct st_test test_9[] = {{4,TL_READ_HIGH_PRIORITY}};
struct st_test test_10[] ={{4,TL_WRITE}};
struct st_test test_11[] = {{0,TL_WRITE_LOW_PRIORITY},{1,TL_WRITE_LOW_PRIORITY},{2,TL_WRITE_LOW_PRIORITY},{3,TL_WRITE_LOW_PRIORITY}}; /* Many writes */
struct st_test test_12[] = {{0,TL_WRITE_CONCURRENT_INSERT},{1,TL_WRITE_CONCURRENT_INSERT},{2,TL_WRITE_CONCURRENT_INSERT},{3,TL_WRITE_CONCURRENT_INSERT}};
struct st_test test_13[] = {{0,TL_WRITE_CONCURRENT_INSERT},{1,TL_READ}};
struct st_test test_14[] = {{0,TL_WRITE_ALLOW_WRITE},{1,TL_READ}};
struct st_test test_15[] = {{0,TL_WRITE_ALLOW_WRITE},{1,TL_WRITE_ALLOW_WRITE}};

struct st_test *tests[] = {test_0,test_1,test_2,test_3,test_4,test_5,test_6,
			   test_7,test_8,test_9,test_10,test_11,test_12,
			   test_13,test_14,test_15};
int lock_counts[]= {sizeof(test_0)/sizeof(struct st_test),
		    sizeof(test_1)/sizeof(struct st_test),
		    sizeof(test_2)/sizeof(struct st_test),
		    sizeof(test_3)/sizeof(struct st_test),
		    sizeof(test_4)/sizeof(struct st_test),
		    sizeof(test_5)/sizeof(struct st_test),
		    sizeof(test_6)/sizeof(struct st_test),
		    sizeof(test_7)/sizeof(struct st_test),
		    sizeof(test_8)/sizeof(struct st_test),
		    sizeof(test_9)/sizeof(struct st_test),
		    sizeof(test_10)/sizeof(struct st_test),
		    sizeof(test_11)/sizeof(struct st_test),
		    sizeof(test_12)/sizeof(struct st_test),
		    sizeof(test_13)/sizeof(struct st_test),
		    sizeof(test_14)/sizeof(struct st_test),
		    sizeof(test_15)/sizeof(struct st_test)
};


static mysql_cond_t COND_thread_count;
static mysql_mutex_t LOCK_thread_count;
static uint thread_count;
static ulong sum=0;

#define MAX_LOCK_COUNT 8
#define TEST_TIMEOUT 100000

/* The following functions is for WRITE_CONCURRENT_INSERT */

static my_bool test_get_status(void* param __attribute__((unused)),
                               my_bool concurrent_insert __attribute__((unused)))
{
  return 0;
}

static void test_update_status(void* param __attribute__((unused)))
{
}

static void test_copy_status(void* to __attribute__((unused)) ,
			     void *from __attribute__((unused)))
{
}

static my_bool test_check_status(void* param __attribute__((unused)))
{
  return 0;
}


static void *test_thread(void *arg)
{
  int i,j,param=*((int*) arg);
  THR_LOCK_DATA data[MAX_LOCK_COUNT];
  THR_LOCK_INFO lock_info;
  THR_LOCK_DATA *multi_locks[MAX_LOCK_COUNT];
  my_thread_init();

  printf("Thread %s (%d) started\n",my_thread_name(),param); fflush(stdout);

  thr_lock_info_init(&lock_info, 0);
  for (i=0; i < lock_counts[param] ; i++)
    thr_lock_data_init(locks+tests[param][i].lock_nr,data+i,NULL);
  for (j=1 ; j < 10 ; j++)		/* try locking 10 times */
  {
    for (i=0; i < lock_counts[param] ; i++)
    {					/* Init multi locks */
      multi_locks[i]= &data[i];
      data[i].type= tests[param][i].lock_type;
    }
    thr_multi_lock(multi_locks, lock_counts[param], &lock_info, TEST_TIMEOUT);
    mysql_mutex_lock(&LOCK_thread_count);
    {
      int tmp=rand() & 7;			/* Do something from 0-2 sec */
      if (tmp == 0)
	sleep(1);
      else if (tmp == 1)
	sleep(2);
      else
      {
	ulong k;
	for (k=0 ; k < (ulong) (tmp-2)*100000L ; k++)
	  sum+=k;
      }
    }
    mysql_mutex_unlock(&LOCK_thread_count);
    thr_multi_unlock(multi_locks,lock_counts[param], THR_UNLOCK_UPDATE_STATUS);
  }

  printf("Thread %s (%d) ended\n",my_thread_name(),param); fflush(stdout);
  thr_print_locks();
  mysql_mutex_lock(&LOCK_thread_count);
  thread_count--;
  mysql_cond_signal(&COND_thread_count); /* Tell main we are ready */
  mysql_mutex_unlock(&LOCK_thread_count);
  my_thread_end();
  return 0;
}


int main(int argc __attribute__((unused)),char **argv __attribute__((unused)))
{
  pthread_t tid;
  pthread_attr_t thr_attr;
  int param[array_elements(lock_counts)], error;
  uint i;
  MY_INIT(argv[0]);
  if (argc > 1 && argv[1][0] == '-' && argv[1][1] == '#')
    DBUG_PUSH(argv[1]+2);

  printf("Main thread: %s\n",my_thread_name());

  if ((error= mysql_cond_init(0, &COND_thread_count, NULL)))
  {
    fprintf(stderr, "Got error: %d from mysql_cond_init (errno: %d)",
	    error,errno);
    exit(1);
  }
  if ((error= mysql_mutex_init(0, &LOCK_thread_count, MY_MUTEX_INIT_FAST)))
  {
    fprintf(stderr, "Got error: %d from mysql_cond_init (errno: %d)",
	    error,errno);
    exit(1);
  }

  for (i=0 ; i < array_elements(locks) ; i++)
  {
    thr_lock_init(locks+i);
    locks[i].check_status= test_check_status;
    locks[i].update_status=test_update_status;
    locks[i].copy_status=  test_copy_status;
    locks[i].get_status=   test_get_status;
    locks[i].allow_multiple_concurrent_insert= 1;
  }
  if ((error=pthread_attr_init(&thr_attr)))
  {
    fprintf(stderr,"Got error: %d from pthread_attr_init (errno: %d)",
	    error,errno);
    exit(1);
  }
  if ((error=pthread_attr_setdetachstate(&thr_attr,PTHREAD_CREATE_DETACHED)))
  {
    fprintf(stderr,
	    "Got error: %d from pthread_attr_setdetachstate (errno: %d)",
	    error,errno);
    exit(1);
  }
#ifndef pthread_attr_setstacksize		/* void return value */
  if ((error=pthread_attr_setstacksize(&thr_attr,65536L)))
  {
    fprintf(stderr,"Got error: %d from pthread_attr_setstacksize (errno: %d)",
	    error,errno);
    exit(1);
  }
#endif
  for (i=0 ; i < array_elements(lock_counts) ; i++)
  {
    param[i]= i;

    if ((error= mysql_mutex_lock(&LOCK_thread_count)))
    {
      fprintf(stderr, "Got error: %d from mysql_mutex_lock (errno: %d)",
              error, errno);
      exit(1);
    }
    if ((error= mysql_thread_create(0,
                                    &tid, &thr_attr, test_thread,
                                    (void*) &param[i])))
    {
      fprintf(stderr, "Got error: %d from mysql_thread_create (errno: %d)\n",
              error, errno);
      mysql_mutex_unlock(&LOCK_thread_count);
      exit(1);
    }
    thread_count++;
    mysql_mutex_unlock(&LOCK_thread_count);
  }

  pthread_attr_destroy(&thr_attr);
  if ((error= mysql_mutex_lock(&LOCK_thread_count)))
    fprintf(stderr, "Got error: %d from mysql_mutex_lock\n", error);
  while (thread_count)
  {
    if ((error= mysql_cond_wait(&COND_thread_count, &LOCK_thread_count)))
      fprintf(stderr, "Got error: %d from mysql_cond_wait\n", error);
  }
  if ((error= mysql_mutex_unlock(&LOCK_thread_count)))
    fprintf(stderr, "Got error: %d from mysql_mutex_unlock\n", error);
  for (i=0 ; i < array_elements(locks) ; i++)
    thr_lock_delete(locks+i);
#ifdef EXTRA_DEBUG
  if (found_errors)
    printf("Got %d warnings\n",found_errors);
  else
#endif
    printf("Test succeeded\n");
  mysql_cond_destroy(&COND_thread_count);
  mysql_mutex_destroy(&LOCK_thread_count);
  my_end(MY_CHECK_ERROR);
  return 0;
}

#endif /* MAIN */
