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/*****************************************************************************
Copyright (c) 1995, 2009, Innobase Oy. All Rights Reserved.
Copyright (c) 2008, Google Inc.
Portions of this file contain modifications contributed and copyrighted by
Google, Inc. Those modifications are gratefully acknowledged and are described
briefly in the InnoDB documentation. The contributions by Google are
incorporated with their permission, and subject to the conditions contained in
the file COPYING.Google.
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., 59 Temple
Place, Suite 330, Boston, MA 02111-1307 USA
*****************************************************************************/
/**************************************************//**
@file include/sync0sync.ic
Mutex, the basic synchronization primitive
Created 9/5/1995 Heikki Tuuri
*******************************************************/
/******************************************************************//**
Sets the waiters field in a mutex. */
UNIV_INTERN
void
mutex_set_waiters(
/*==============*/
mutex_t* mutex, /*!< in: mutex */
ulint n); /*!< in: value to set */
/******************************************************************//**
Reserves a mutex for the current thread. If the mutex is reserved, the
function spins a preset time (controlled by SYNC_SPIN_ROUNDS) waiting
for the mutex before suspending the thread. */
UNIV_INTERN
void
mutex_spin_wait(
/*============*/
mutex_t* mutex, /*!< in: pointer to mutex */
const char* file_name, /*!< in: file name where mutex
requested */
ulint line); /*!< in: line where requested */
#ifdef UNIV_SYNC_DEBUG
/******************************************************************//**
Sets the debug information for a reserved mutex. */
UNIV_INTERN
void
mutex_set_debug_info(
/*=================*/
mutex_t* mutex, /*!< in: mutex */
const char* file_name, /*!< in: file where requested */
ulint line); /*!< in: line where requested */
#endif /* UNIV_SYNC_DEBUG */
/******************************************************************//**
Releases the threads waiting in the primary wait array for this mutex. */
UNIV_INTERN
void
mutex_signal_object(
/*================*/
mutex_t* mutex); /*!< in: mutex */
/******************************************************************//**
Performs an atomic test-and-set instruction to the lock_word field of a
mutex.
@return the previous value of lock_word: 0 or 1 */
UNIV_INLINE
byte
mutex_test_and_set(
/*===============*/
mutex_t* mutex) /*!< in: mutex */
{
#if defined(HAVE_ATOMIC_BUILTINS)
return(os_atomic_test_and_set_byte(&mutex->lock_word, 1));
#else
ibool ret;
ret = os_fast_mutex_trylock(&(mutex->os_fast_mutex));
if (ret == 0) {
/* We check that os_fast_mutex_trylock does not leak
and allow race conditions */
ut_a(mutex->lock_word == 0);
mutex->lock_word = 1;
}
return((byte)ret);
#endif
}
/******************************************************************//**
Performs a reset instruction to the lock_word field of a mutex. This
instruction also serializes memory operations to the program order. */
UNIV_INLINE
void
mutex_reset_lock_word(
/*==================*/
mutex_t* mutex) /*!< in: mutex */
{
#if defined(HAVE_ATOMIC_BUILTINS)
/* In theory __sync_lock_release should be used to release the lock.
Unfortunately, it does not work properly alone. The workaround is
that more conservative __sync_lock_test_and_set is used instead. */
os_atomic_test_and_set_byte(&mutex->lock_word, 0);
#else
mutex->lock_word = 0;
os_fast_mutex_unlock(&(mutex->os_fast_mutex));
#endif
}
/******************************************************************//**
Gets the value of the lock word. */
UNIV_INLINE
lock_word_t
mutex_get_lock_word(
/*================*/
const mutex_t* mutex) /*!< in: mutex */
{
ut_ad(mutex);
return(mutex->lock_word);
}
/******************************************************************//**
Gets the waiters field in a mutex.
@return value to set */
UNIV_INLINE
ulint
mutex_get_waiters(
/*==============*/
const mutex_t* mutex) /*!< in: mutex */
{
const volatile ulint* ptr; /*!< declared volatile to ensure that
the value is read from memory */
ut_ad(mutex);
ptr = &(mutex->waiters);
return(*ptr); /* Here we assume that the read of a single
word from memory is atomic */
}
/******************************************************************//**
Unlocks a mutex owned by the current thread. */
UNIV_INLINE
void
mutex_exit(
/*=======*/
mutex_t* mutex) /*!< in: pointer to mutex */
{
ut_ad(mutex_own(mutex));
ut_d(mutex->thread_id = (os_thread_id_t) ULINT_UNDEFINED);
#ifdef UNIV_SYNC_DEBUG
sync_thread_reset_level(mutex);
#endif
mutex_reset_lock_word(mutex);
/* A problem: we assume that mutex_reset_lock word
is a memory barrier, that is when we read the waiters
field next, the read must be serialized in memory
after the reset. A speculative processor might
perform the read first, which could leave a waiting
thread hanging indefinitely.
Our current solution call every second
sync_arr_wake_threads_if_sema_free()
to wake up possible hanging threads if
they are missed in mutex_signal_object. */
if (mutex_get_waiters(mutex) != 0) {
mutex_signal_object(mutex);
}
#ifdef UNIV_SYNC_PERF_STAT
mutex_exit_count++;
#endif
}
/******************************************************************//**
Locks a mutex for the current thread. If the mutex is reserved, the function
spins a preset time (controlled by SYNC_SPIN_ROUNDS), waiting for the mutex
before suspending the thread. */
UNIV_INLINE
void
mutex_enter_func(
/*=============*/
mutex_t* mutex, /*!< in: pointer to mutex */
const char* file_name, /*!< in: file name where locked */
ulint line) /*!< in: line where locked */
{
ut_ad(mutex_validate(mutex));
ut_ad(!mutex_own(mutex));
/* Note that we do not peek at the value of lock_word before trying
the atomic test_and_set; we could peek, and possibly save time. */
ut_d(mutex->count_using++);
if (!mutex_test_and_set(mutex)) {
ut_d(mutex->thread_id = os_thread_get_curr_id());
#ifdef UNIV_SYNC_DEBUG
mutex_set_debug_info(mutex, file_name, line);
#endif
return; /* Succeeded! */
}
mutex_spin_wait(mutex, file_name, line);
}
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