diff options
Diffstat (limited to 'storage/perfschema/pfs_lock.h')
| -rw-r--r-- | storage/perfschema/pfs_lock.h | 240 |
1 files changed, 240 insertions, 0 deletions
diff --git a/storage/perfschema/pfs_lock.h b/storage/perfschema/pfs_lock.h new file mode 100644 index 00000000000..c429d934702 --- /dev/null +++ b/storage/perfschema/pfs_lock.h @@ -0,0 +1,240 @@ +/* Copyright (c) 2009, 2010, 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 */ + +#ifndef PFS_LOCK_H +#define PFS_LOCK_H + +/** + @file storage/perfschema/pfs_lock.h + Performance schema internal locks (declarations). +*/ + +#include "pfs_atomic.h" + +/** + @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 + +/** + 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. + */ + volatile uint32 m_version_state; + + /** Returns true if the record is free. */ + bool is_free(void) + { + uint32 copy= m_version_state; /* non volatile copy, and dirty read */ + return ((copy & STATE_MASK) == PFS_LOCK_FREE); + } + + /** Returns true if the record contains values that can be read. */ + bool is_populated(void) + { + uint32 copy= m_version_state; /* non volatile copy, and dirty read */ + 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(void) + { + uint32 copy= m_version_state; /* non volatile copy, and dirty read */ + uint32 old_val= (copy & VERSION_MASK) + PFS_LOCK_FREE; + uint32 new_val= (copy & VERSION_MASK) + PFS_LOCK_DIRTY; + + return (PFS_atomic::cas_u32(&m_version_state, &old_val, new_val)); + } + + /** + 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(void) + { + uint32 copy= PFS_atomic::load_u32(&m_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); + } + + /** + 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(void) + { + uint32 copy= PFS_atomic::load_u32(&m_version_state); + /* Make sure the record was DIRTY. */ + DBUG_ASSERT((copy & STATE_MASK) == PFS_LOCK_DIRTY); + /* 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 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= PFS_atomic::load_u32(&m_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); + } + + /** + Execute a dirty to free transition. + This transition should be executed by the writer that owns the record. + */ + void dirty_to_free(void) + { + uint32 copy= PFS_atomic::load_u32(&m_version_state); + /* Make sure the record was DIRTY. */ + DBUG_ASSERT((copy & STATE_MASK) == PFS_LOCK_DIRTY); + /* 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); + } + + /** + Execute an allocated to free transition. + This transition should be executed by the writer that owns the record. + */ + void allocated_to_free(void) + { +#ifndef DBUG_OFF + extern volatile bool ready_to_exit; +#endif + + /* + 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. + The correct assert to use here to guarantee data integrity is simply: + DBUG_ASSERT(m_state == PFS_LOCK_ALLOCATED); + Now, because of Bug#56666 (Race condition between the server main thread + and the kill server thread), this assert actually fails during shutdown, + and the failure is legitimate, on concurrent calls to mysql_*_destroy(), + when destroying the instrumentation of an object ... twice. + During shutdown this has no consequences for the performance schema, + so the assert is relaxed with the "|| ready_to_exit" condition as a work + around until Bug#56666 is fixed. + */ + uint32 copy= PFS_atomic::load_u32(&m_version_state); + /* Make sure the record was ALLOCATED. */ + DBUG_ASSERT(((copy & STATE_MASK) == PFS_LOCK_ALLOCATED) || ready_to_exit); + /* 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. + @sa end_optimist_lock. + */ + void begin_optimistic_lock(struct pfs_lock *copy) + { + copy->m_version_state= PFS_atomic::load_u32(&m_version_state); + } + + /** + End an optimistic read operation. + @sa begin_optimist_lock. + @return true if the data read is safe to use. + */ + bool end_optimistic_lock(struct pfs_lock *copy) + { + /* Check there was valid data to look at. */ + if ((copy->m_version_state & STATE_MASK) != PFS_LOCK_ALLOCATED) + return false; + + /* Check the version + state has not changed. */ + if (copy->m_version_state != PFS_atomic::load_u32(&m_version_state)) + return false; + + return true; + } + + uint32 get_version() + { + return (PFS_atomic::load_u32(&m_version_state) & VERSION_MASK); + } +}; + + +/** @} */ +#endif + |