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/******************************************************
The read-write lock (for threads)
(c) 1995 Innobase Oy
Created 9/11/1995 Heikki Tuuri
*******************************************************/
/**********************************************************************
Lock an rw-lock in shared mode for the current thread. If the rw-lock is
locked in exclusive mode, or there is an exclusive lock request waiting,
the function spins a preset time (controlled by SYNC_SPIN_ROUNDS),
waiting for the lock before suspending the thread. */
void
rw_lock_s_lock_spin(
/*================*/
rw_lock_t* lock, /* in: pointer to rw-lock */
ulint pass, /* in: pass value; != 0, if the lock will
be passed to another thread to unlock */
const char* file_name,/* in: file name where lock requested */
ulint line); /* in: line where requested */
#ifdef UNIV_SYNC_DEBUG
/**********************************************************************
Inserts the debug information for an rw-lock. */
void
rw_lock_add_debug_info(
/*===================*/
rw_lock_t* lock, /* in: rw-lock */
ulint pass, /* in: pass value */
ulint lock_type, /* in: lock type */
const char* file_name, /* in: file where requested */
ulint line); /* in: line where requested */
/**********************************************************************
Removes a debug information struct for an rw-lock. */
void
rw_lock_remove_debug_info(
/*======================*/
rw_lock_t* lock, /* in: rw-lock */
ulint pass, /* in: pass value */
ulint lock_type); /* in: lock type */
#endif /* UNIV_SYNC_DEBUG */
/************************************************************************
Accessor functions for rw lock. */
UNIV_INLINE
ulint
rw_lock_get_waiters(
/*================*/
rw_lock_t* lock)
{
return(lock->waiters);
}
UNIV_INLINE
void
rw_lock_set_waiters(
/*================*/
rw_lock_t* lock,
ulint flag)
{
lock->waiters = flag;
}
UNIV_INLINE
ulint
rw_lock_get_writer(
/*===============*/
rw_lock_t* lock)
{
return(lock->writer);
}
UNIV_INLINE
void
rw_lock_set_writer(
/*===============*/
rw_lock_t* lock,
ulint flag)
{
lock->writer = flag;
}
UNIV_INLINE
ulint
rw_lock_get_reader_count(
/*=====================*/
rw_lock_t* lock)
{
return(lock->reader_count);
}
UNIV_INLINE
void
rw_lock_set_reader_count(
/*=====================*/
rw_lock_t* lock,
ulint count)
{
lock->reader_count = count;
}
UNIV_INLINE
mutex_t*
rw_lock_get_mutex(
/*==============*/
rw_lock_t* lock)
{
return(&(lock->mutex));
}
/**********************************************************************
Returns the value of writer_count for the lock. Does not reserve the lock
mutex, so the caller must be sure it is not changed during the call. */
UNIV_INLINE
ulint
rw_lock_get_x_lock_count(
/*=====================*/
/* out: value of writer_count */
rw_lock_t* lock) /* in: rw-lock */
{
return(lock->writer_count);
}
/**********************************************************************
Low-level function which tries to lock an rw-lock in s-mode. Performs no
spinning. */
UNIV_INLINE
ibool
rw_lock_s_lock_low(
/*===============*/
/* out: TRUE if success */
rw_lock_t* lock, /* in: pointer to rw-lock */
ulint pass __attribute__((unused)),
/* in: pass value; != 0, if the lock will be
passed to another thread to unlock */
const char* file_name, /* in: file name where lock requested */
ulint line) /* in: line where requested */
{
#ifdef UNIV_SYNC_DEBUG
ut_ad(mutex_own(rw_lock_get_mutex(lock)));
#endif /* UNIV_SYNC_DEBUG */
/* Check if the writer field is free */
if (UNIV_LIKELY(lock->writer == RW_LOCK_NOT_LOCKED)) {
/* Set the shared lock by incrementing the reader count */
lock->reader_count++;
#ifdef UNIV_SYNC_DEBUG
rw_lock_add_debug_info(lock, pass, RW_LOCK_SHARED, file_name,
line);
#endif
lock->last_s_file_name = file_name;
lock->last_s_line = line;
return(TRUE); /* locking succeeded */
}
return(FALSE); /* locking did not succeed */
}
/**********************************************************************
Low-level function which locks an rw-lock in s-mode when we know that it
is possible and none else is currently accessing the rw-lock structure.
Then we can do the locking without reserving the mutex. */
UNIV_INLINE
void
rw_lock_s_lock_direct(
/*==================*/
rw_lock_t* lock, /* in: pointer to rw-lock */
const char* file_name, /* in: file name where requested */
ulint line) /* in: line where lock requested */
{
ut_ad(lock->writer == RW_LOCK_NOT_LOCKED);
ut_ad(rw_lock_get_reader_count(lock) == 0);
/* Set the shared lock by incrementing the reader count */
lock->reader_count++;
lock->last_s_file_name = file_name;
lock->last_s_line = line;
#ifdef UNIV_SYNC_DEBUG
rw_lock_add_debug_info(lock, 0, RW_LOCK_SHARED, file_name, line);
#endif
}
/**********************************************************************
Low-level function which locks an rw-lock in x-mode when we know that it
is not locked and none else is currently accessing the rw-lock structure.
Then we can do the locking without reserving the mutex. */
UNIV_INLINE
void
rw_lock_x_lock_direct(
/*==================*/
rw_lock_t* lock, /* in: pointer to rw-lock */
const char* file_name, /* in: file name where requested */
ulint line) /* in: line where lock requested */
{
ut_ad(rw_lock_validate(lock));
ut_ad(rw_lock_get_reader_count(lock) == 0);
ut_ad(rw_lock_get_writer(lock) == RW_LOCK_NOT_LOCKED);
rw_lock_set_writer(lock, RW_LOCK_EX);
lock->writer_thread = os_thread_get_curr_id();
lock->writer_count++;
lock->pass = 0;
lock->last_x_file_name = file_name;
lock->last_x_line = line;
#ifdef UNIV_SYNC_DEBUG
rw_lock_add_debug_info(lock, 0, RW_LOCK_EX, file_name, line);
#endif
}
/**********************************************************************
NOTE! Use the corresponding macro, not directly this function! Lock an
rw-lock in shared mode for the current thread. If the rw-lock is locked
in exclusive mode, or there is an exclusive lock request waiting, the
function spins a preset time (controlled by SYNC_SPIN_ROUNDS), waiting for
the lock, before suspending the thread. */
UNIV_INLINE
void
rw_lock_s_lock_func(
/*================*/
rw_lock_t* lock, /* in: pointer to rw-lock */
ulint pass, /* in: pass value; != 0, if the lock will
be passed to another thread to unlock */
const char* file_name,/* in: file name where lock requested */
ulint line) /* in: line where requested */
{
/* NOTE: As we do not know the thread ids for threads which have
s-locked a latch, and s-lockers will be served only after waiting
x-lock requests have been fulfilled, then if this thread already
owns an s-lock here, it may end up in a deadlock with another thread
which requests an x-lock here. Therefore, we will forbid recursive
s-locking of a latch: the following assert will warn the programmer
of the possibility of a tjis kind of deadlock. If we want to implement
safe recursive s-locking, we should keep in a list the thread ids of
the threads which have s-locked a latch. This would use some CPU
time. */
#ifdef UNIV_SYNC_DEBUG
ut_ad(!rw_lock_own(lock, RW_LOCK_SHARED)); /* see NOTE above */
#endif /* UNIV_SYNC_DEBUG */
mutex_enter(rw_lock_get_mutex(lock));
if (UNIV_LIKELY(rw_lock_s_lock_low(lock, pass, file_name, line))) {
mutex_exit(rw_lock_get_mutex(lock));
return; /* Success */
} else {
/* Did not succeed, try spin wait */
mutex_exit(rw_lock_get_mutex(lock));
rw_lock_s_lock_spin(lock, pass, file_name, line);
return;
}
}
/**********************************************************************
NOTE! Use the corresponding macro, not directly this function! Lock an
rw-lock in shared mode for the current thread if the lock can be acquired
immediately. */
UNIV_INLINE
ibool
rw_lock_s_lock_func_nowait(
/*=======================*/
/* out: TRUE if success */
rw_lock_t* lock, /* in: pointer to rw-lock */
const char* file_name,/* in: file name where lock requested */
ulint line) /* in: line where requested */
{
ibool success = FALSE;
mutex_enter(rw_lock_get_mutex(lock));
if (lock->writer == RW_LOCK_NOT_LOCKED) {
/* Set the shared lock by incrementing the reader count */
lock->reader_count++;
#ifdef UNIV_SYNC_DEBUG
rw_lock_add_debug_info(lock, 0, RW_LOCK_SHARED, file_name,
line);
#endif
lock->last_s_file_name = file_name;
lock->last_s_line = line;
success = TRUE;
}
mutex_exit(rw_lock_get_mutex(lock));
return(success);
}
/**********************************************************************
NOTE! Use the corresponding macro, not directly this function! Lock an
rw-lock in exclusive mode for the current thread if the lock can be
obtained immediately. */
UNIV_INLINE
ibool
rw_lock_x_lock_func_nowait(
/*=======================*/
/* out: TRUE if success */
rw_lock_t* lock, /* in: pointer to rw-lock */
const char* file_name,/* in: file name where lock requested */
ulint line) /* in: line where requested */
{
ibool success = FALSE;
os_thread_id_t curr_thread = os_thread_get_curr_id();
mutex_enter(rw_lock_get_mutex(lock));
if (UNIV_UNLIKELY(rw_lock_get_reader_count(lock) != 0)) {
} else if (UNIV_LIKELY(rw_lock_get_writer(lock)
== RW_LOCK_NOT_LOCKED)) {
rw_lock_set_writer(lock, RW_LOCK_EX);
lock->writer_thread = curr_thread;
lock->pass = 0;
relock:
lock->writer_count++;
#ifdef UNIV_SYNC_DEBUG
rw_lock_add_debug_info(lock, 0, RW_LOCK_EX, file_name, line);
#endif
lock->last_x_file_name = file_name;
lock->last_x_line = line;
success = TRUE;
} else if (rw_lock_get_writer(lock) == RW_LOCK_EX
&& lock->pass == 0
&& os_thread_eq(lock->writer_thread, curr_thread)) {
goto relock;
}
mutex_exit(rw_lock_get_mutex(lock));
ut_ad(rw_lock_validate(lock));
return(success);
}
/**********************************************************************
Releases a shared mode lock. */
UNIV_INLINE
void
rw_lock_s_unlock_func(
/*==================*/
rw_lock_t* lock /* in: rw-lock */
#ifdef UNIV_SYNC_DEBUG
,ulint pass /* in: pass value; != 0, if the lock may have
been passed to another thread to unlock */
#endif
)
{
mutex_t* mutex = &(lock->mutex);
ibool sg = FALSE;
/* Acquire the mutex protecting the rw-lock fields */
mutex_enter(mutex);
/* Reset the shared lock by decrementing the reader count */
ut_ad(lock->reader_count > 0);
lock->reader_count--;
#ifdef UNIV_SYNC_DEBUG
rw_lock_remove_debug_info(lock, pass, RW_LOCK_SHARED);
#endif
/* If there may be waiters and this was the last s-lock,
signal the object */
if (UNIV_UNLIKELY(lock->waiters)
&& lock->reader_count == 0) {
sg = TRUE;
rw_lock_set_waiters(lock, 0);
}
mutex_exit(mutex);
if (UNIV_UNLIKELY(sg)) {
sync_array_signal_object(sync_primary_wait_array, lock);
}
ut_ad(rw_lock_validate(lock));
#ifdef UNIV_SYNC_PERF_STAT
rw_s_exit_count++;
#endif
}
/**********************************************************************
Releases a shared mode lock when we know there are no waiters and none
else will access the lock during the time this function is executed. */
UNIV_INLINE
void
rw_lock_s_unlock_direct(
/*====================*/
rw_lock_t* lock) /* in: rw-lock */
{
/* Reset the shared lock by decrementing the reader count */
ut_ad(lock->reader_count > 0);
lock->reader_count--;
#ifdef UNIV_SYNC_DEBUG
rw_lock_remove_debug_info(lock, 0, RW_LOCK_SHARED);
#endif
ut_ad(!lock->waiters);
ut_ad(rw_lock_validate(lock));
#ifdef UNIV_SYNC_PERF_STAT
rw_s_exit_count++;
#endif
}
/**********************************************************************
Releases an exclusive mode lock. */
UNIV_INLINE
void
rw_lock_x_unlock_func(
/*==================*/
rw_lock_t* lock /* in: rw-lock */
#ifdef UNIV_SYNC_DEBUG
,ulint pass /* in: pass value; != 0, if the lock may have
been passed to another thread to unlock */
#endif
)
{
ibool sg = FALSE;
/* Acquire the mutex protecting the rw-lock fields */
mutex_enter(&(lock->mutex));
/* Reset the exclusive lock if this thread no longer has an x-mode
lock */
ut_ad(lock->writer_count > 0);
lock->writer_count--;
if (lock->writer_count == 0) {
rw_lock_set_writer(lock, RW_LOCK_NOT_LOCKED);
}
#ifdef UNIV_SYNC_DEBUG
rw_lock_remove_debug_info(lock, pass, RW_LOCK_EX);
#endif
/* If there may be waiters, signal the lock */
if (UNIV_UNLIKELY(lock->waiters)
&& lock->writer_count == 0) {
sg = TRUE;
rw_lock_set_waiters(lock, 0);
}
mutex_exit(&(lock->mutex));
if (UNIV_UNLIKELY(sg)) {
sync_array_signal_object(sync_primary_wait_array, lock);
}
ut_ad(rw_lock_validate(lock));
#ifdef UNIV_SYNC_PERF_STAT
rw_x_exit_count++;
#endif
}
/**********************************************************************
Releases an exclusive mode lock when we know there are no waiters, and
none else will access the lock durint the time this function is executed. */
UNIV_INLINE
void
rw_lock_x_unlock_direct(
/*====================*/
rw_lock_t* lock) /* in: rw-lock */
{
/* Reset the exclusive lock if this thread no longer has an x-mode
lock */
ut_ad(lock->writer_count > 0);
lock->writer_count--;
if (lock->writer_count == 0) {
rw_lock_set_writer(lock, RW_LOCK_NOT_LOCKED);
}
#ifdef UNIV_SYNC_DEBUG
rw_lock_remove_debug_info(lock, 0, RW_LOCK_EX);
#endif
ut_ad(!lock->waiters);
ut_ad(rw_lock_validate(lock));
#ifdef UNIV_SYNC_PERF_STAT
rw_x_exit_count++;
#endif
}