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diff --git a/storage/perfschema/pfs_lock.h b/storage/perfschema/pfs_lock.h
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+/* Copyright (c) 2009, 2016, 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.
+
+  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,
+  51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */
+
+#ifndef PFS_LOCK_H
+#define PFS_LOCK_H
+
+/**
+  @file storage/perfschema/pfs_lock.h
+  Performance schema internal locks (declarations).
+*/
+
+#include "my_global.h"
+
+#include "pfs_atomic.h"
+
+/* to cause bugs, testing */
+// #define MEM(X) std::memory_order_relaxed
+/* correct code */
+#define MEM(X) X
+
+/**
+  @addtogroup Performance_schema_buffers
+  @{
+*/
+
+/**
+  State of a free record.
+  Values of a free record should not be read by a reader.
+  Writers can concurrently attempt to allocate a free record.
+*/
+#define PFS_LOCK_FREE 0x00
+/**
+  State of a dirty record.
+  Values of a dirty record should not be read by a reader,
+  as the record is currently being modified.
+  Only one writer, the writer which owns the record, should
+  modify the record content.
+*/
+#define PFS_LOCK_DIRTY 0x01
+/**
+  State of an allocated record.
+  Values of an allocated record are safe to read by a reader.
+  A writer may modify some but not all properties of the record:
+  only modifying values that can never cause the reader to crash is allowed.
+*/
+#define PFS_LOCK_ALLOCATED 0x02
+
+#define VERSION_MASK 0xFFFFFFFC
+#define STATE_MASK   0x00000003
+#define VERSION_INC  4
+
+struct pfs_optimistic_state
+{
+  uint32 m_version_state;
+};
+
+struct pfs_dirty_state
+{
+  uint32 m_version_state;
+};
+
+/**
+  A 'lock' protecting performance schema internal buffers.
+  This lock is used to mark the state of a record.
+  Access to the record is not enforced here,
+  it's up to the readers and writers to look at the record state
+  before making an actual read or write operation.
+*/
+struct pfs_lock
+{
+  /**
+    The record internal version and state
+    @sa PFS_LOCK_FREE
+    @sa PFS_LOCK_DIRTY
+    @sa PFS_LOCK_ALLOCATED
+    The version number is to transform the 'ABA' problem
+    (see http://en.wikipedia.org/wiki/ABA_problem)
+    into an 'A(n)BA(n + 1)' problem, where 'n' is the m_version number.
+    When the performance schema instrumentation deletes a record,
+    then create a different record reusing the same memory allocation,
+    the version number is incremented, so that a reader can detect that
+    the record was changed. Note that the version number is never
+    reset to zero when a new record is created.
+    The version number is stored in the high 30 bits.
+    The state is stored in the low 2 bits.
+  */
+  uint32 m_version_state;
+
+  uint32 copy_version_state()
+  {
+    uint32 copy;
+
+    copy= m_version_state; /* dirty read */
+
+    return copy;
+  }
+
+  /** Returns true if the record is free. */
+  bool is_free(void)
+  {
+    uint32 copy;
+
+    copy= PFS_atomic::load_u32(&m_version_state);
+
+    return ((copy & STATE_MASK) == PFS_LOCK_FREE);
+  }
+
+  /** Returns true if the record contains values that can be read. */
+  bool is_populated(void)
+  {
+    uint32 copy;
+
+    copy= PFS_atomic::load_u32(&m_version_state);
+
+    return ((copy & STATE_MASK) == PFS_LOCK_ALLOCATED);
+  }
+
+  /**
+    Execute a free to dirty transition.
+    This transition is safe to execute concurrently by multiple writers.
+    Only one writer will succeed to acquire the record.
+    @return true if the operation succeed
+  */
+  bool free_to_dirty(pfs_dirty_state *copy_ptr)
+  {
+    uint32 old_val;
+
+    old_val= PFS_atomic::load_u32(&m_version_state);
+
+    if ((old_val & STATE_MASK) != PFS_LOCK_FREE)
+    {
+      return false;
+    }
+
+    uint32 new_val= (old_val & VERSION_MASK) + PFS_LOCK_DIRTY;
+    bool pass;
+
+    pass= PFS_atomic::cas_u32(&m_version_state, &old_val, new_val);
+
+    if (pass)
+    {
+      copy_ptr->m_version_state= new_val;
+    }
+
+    return pass;
+  }
+
+  /**
+    Execute an allocated to dirty transition.
+    This transition should be executed by the writer that owns the record,
+    before the record is modified.
+  */
+  void allocated_to_dirty(pfs_dirty_state *copy_ptr)
+  {
+    uint32 copy= copy_version_state();
+    /* Make sure the record was ALLOCATED. */
+    DBUG_ASSERT((copy & STATE_MASK) == PFS_LOCK_ALLOCATED);
+    /* Keep the same version, set the DIRTY state */
+    uint32 new_val= (copy & VERSION_MASK) + PFS_LOCK_DIRTY;
+    /* We own the record, no need to use compare and swap. */
+
+    PFS_atomic::store_u32(&m_version_state, new_val);
+
+    copy_ptr->m_version_state= new_val;
+  }
+
+  /**
+    Execute a dirty to allocated transition.
+    This transition should be executed by the writer that owns the record,
+    after the record is in a state ready to be read.
+  */
+  void dirty_to_allocated(const pfs_dirty_state *copy)
+  {
+    /* Make sure the record was DIRTY. */
+    DBUG_ASSERT((copy->m_version_state & STATE_MASK) == PFS_LOCK_DIRTY);
+    /* Increment the version, set the ALLOCATED state */
+    uint32 new_val= (copy->m_version_state & VERSION_MASK) + VERSION_INC + PFS_LOCK_ALLOCATED;
+
+    PFS_atomic::store_u32(&m_version_state, new_val);
+  }
+
+  /**
+    Initialize a lock to allocated.
+    This transition should be executed by the writer that owns the record and the lock,
+    after the record is in a state ready to be read.
+  */
+  void set_allocated(void)
+  {
+    /* Do not set the version to 0, read the previous value. */
+    uint32 copy= copy_version_state();
+    /* Increment the version, set the ALLOCATED state */
+    uint32 new_val= (copy & VERSION_MASK) + VERSION_INC + PFS_LOCK_ALLOCATED;
+
+    PFS_atomic::store_u32(&m_version_state, new_val);
+  }
+
+  /**
+    Initialize a lock to dirty.
+  */
+  void set_dirty(pfs_dirty_state *copy_ptr)
+  {
+    /* Do not set the version to 0, read the previous value. */
+    uint32 copy= PFS_atomic::load_u32(&m_version_state);
+    /* Increment the version, set the DIRTY state */
+    uint32 new_val= (copy & VERSION_MASK) + VERSION_INC + PFS_LOCK_DIRTY;
+    PFS_atomic::store_u32(&m_version_state, new_val);
+
+    copy_ptr->m_version_state= new_val;
+  }
+
+  /**
+    Execute a dirty to free transition.
+    This transition should be executed by the writer that owns the record.
+  */
+  void dirty_to_free(const pfs_dirty_state *copy)
+  {
+    /* Make sure the record was DIRTY. */
+    DBUG_ASSERT((copy->m_version_state & STATE_MASK) == PFS_LOCK_DIRTY);
+    /* Keep the same version, set the FREE state */
+    uint32 new_val= (copy->m_version_state & VERSION_MASK) + PFS_LOCK_FREE;
+
+    PFS_atomic::store_u32(&m_version_state, new_val);
+  }
+
+  /**
+    Execute an allocated to free transition.
+    This transition should be executed by the writer that owns the record.
+  */
+  void allocated_to_free(void)
+  {
+    /*
+      If this record is not in the ALLOCATED state and the caller is trying
+      to free it, this is a bug: the caller is confused,
+      and potentially damaging data owned by another thread or object.
+    */
+    uint32 copy= copy_version_state();
+    /* Make sure the record was ALLOCATED. */
+    DBUG_ASSERT(((copy & STATE_MASK) == PFS_LOCK_ALLOCATED));
+    /* Keep the same version, set the FREE state */
+    uint32 new_val= (copy & VERSION_MASK) + PFS_LOCK_FREE;
+
+    PFS_atomic::store_u32(&m_version_state, new_val);
+  }
+
+  /**
+    Start an optimistic read operation.
+    @param [out] copy Saved lock state
+    @sa end_optimist_lock.
+  */
+  void begin_optimistic_lock(struct pfs_optimistic_state *copy)
+  {
+    copy->m_version_state= PFS_atomic::load_u32(&m_version_state);
+  }
+
+  /**
+    End an optimistic read operation.
+    @sa begin_optimist_lock.
+    @param copy Saved lock state
+    @return true if the data read is safe to use.
+  */
+  bool end_optimistic_lock(const struct pfs_optimistic_state *copy)
+  {
+    uint32 version_state;
+
+    /* Check there was valid data to look at. */
+    if ((copy->m_version_state & STATE_MASK) != PFS_LOCK_ALLOCATED)
+      return false;
+
+    version_state= PFS_atomic::load_u32(&m_version_state);
+
+    /* Check the version + state has not changed. */
+    if (copy->m_version_state != version_state)
+      return false;
+
+    return true;
+  }
+
+  uint32 get_version()
+  {
+    uint32 version_state;
+
+    version_state= PFS_atomic::load_u32(&m_version_state);
+
+    return (version_state & VERSION_MASK);
+  }
+};
+
+
+/** @} */
+#endif
+