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/*
Copyright (C) 2020 MariaDB Foundation
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
*/
/**
MariaDB thread cache for "one thread per connection" scheduler.
Thread cache allows to re-use threads (as well as THD objects) for
subsequent connections.
*/
class Thread_cache
{
mutable mysql_cond_t COND_thread_cache;
mutable mysql_cond_t COND_flush_thread_cache;
mutable mysql_mutex_t LOCK_thread_cache;
/** Queue of new connection requests. */
I_List<CONNECT> list;
/** Number of threads parked in the cache. */
ulong cached_thread_count;
/** Number of active flush requests. */
uint32_t kill_cached_threads;
/**
PFS stuff, only used during initialization.
Unfortunately needs to survive till destruction.
*/
PSI_cond_key key_COND_thread_cache, key_COND_flush_thread_cache;
PSI_mutex_key key_LOCK_thread_cache;
public:
void init()
{
#ifdef HAVE_PSI_INTERFACE
PSI_cond_info conds[]=
{
{ &key_COND_thread_cache, "COND_thread_cache", PSI_FLAG_GLOBAL },
{ &key_COND_flush_thread_cache, "COND_flush_thread_cache",
PSI_FLAG_GLOBAL }
};
PSI_mutex_info mutexes[]=
{
{ &key_LOCK_thread_cache, "LOCK_thread_cache", PSI_FLAG_GLOBAL }
};
mysql_mutex_register("sql", mutexes, array_elements(mutexes));
mysql_cond_register("sql", conds, array_elements(conds));
#endif
mysql_mutex_init(key_LOCK_thread_cache, &LOCK_thread_cache,
MY_MUTEX_INIT_FAST);
mysql_cond_init(key_COND_thread_cache, &COND_thread_cache, 0);
mysql_cond_init(key_COND_flush_thread_cache, &COND_flush_thread_cache, 0);
list.empty();
kill_cached_threads= 0;
cached_thread_count= 0;
}
void destroy()
{
DBUG_ASSERT(cached_thread_count == 0);
DBUG_ASSERT(list.is_empty());
mysql_cond_destroy(&COND_flush_thread_cache);
mysql_cond_destroy(&COND_thread_cache);
mysql_mutex_destroy(&LOCK_thread_cache);
}
/**
Flushes thread cache.
Awakes parked threads and requests them to shutdown.
Waits until last parked thread leaves the cache.
*/
void flush()
{
mysql_mutex_lock(&LOCK_thread_cache);
kill_cached_threads++;
while (cached_thread_count)
{
mysql_cond_broadcast(&COND_thread_cache);
mysql_cond_wait(&COND_flush_thread_cache, &LOCK_thread_cache);
}
kill_cached_threads--;
mysql_mutex_unlock(&LOCK_thread_cache);
}
/**
Flushes thread cache and forbids threads parking in the cache.
This is a pre-shutdown hook.
*/
void final_flush()
{
kill_cached_threads++;
flush();
}
/**
Requests parked thread to serve new connection.
@return
@retval true connection is enqueued and parked thread is about to serve it
@retval false thread cache is empty
*/
bool enqueue(CONNECT *connect)
{
mysql_mutex_lock(&LOCK_thread_cache);
if (cached_thread_count)
{
list.push_back(connect);
cached_thread_count--;
mysql_mutex_unlock(&LOCK_thread_cache);
mysql_cond_signal(&COND_thread_cache);
return true;
}
mysql_mutex_unlock(&LOCK_thread_cache);
return false;
}
/**
Parks thread in the cache.
Thread execution is suspended until either of the following occurs:
- thread is requested to serve new connection;
- thread cache is flushed;
- THREAD_CACHE_TIMEOUT elapsed.
@return
@retval pointer to CONNECT if requested to serve new connection
@retval 0 if thread cache is flushed or on timeout
*/
CONNECT *park()
{
struct timespec abstime;
CONNECT *connect;
bool flushed= false;
DBUG_ENTER("Thread_cache::park");
set_timespec(abstime, THREAD_CACHE_TIMEOUT);
/*
Delete the instrumentation for the job that just completed,
before parking this pthread in the cache (blocked on COND_thread_cache).
*/
PSI_CALL_delete_current_thread();
#ifndef DBUG_OFF
while (_db_is_pushed_())
_db_pop_();
#endif
mysql_mutex_lock(&LOCK_thread_cache);
if ((connect= list.get()))
cached_thread_count++;
else if (cached_thread_count < thread_cache_size && !kill_cached_threads)
{
/* Don't kill the thread, just put it in cache for reuse */
DBUG_PRINT("info", ("Adding thread to cache"));
cached_thread_count++;
for (;;)
{
int error= mysql_cond_timedwait(&COND_thread_cache, &LOCK_thread_cache,
&abstime);
flushed= kill_cached_threads;
if ((connect= list.get()))
break;
else if (flushed || error == ETIMEDOUT || error == ETIME)
{
/*
If timeout, end thread.
If a new thread is requested, we will handle the call, even if we
got a timeout (as we are already awake and free)
*/
cached_thread_count--;
break;
}
}
}
mysql_mutex_unlock(&LOCK_thread_cache);
if (flushed)
mysql_cond_signal(&COND_flush_thread_cache);
DBUG_RETURN(connect);
}
/** Returns the number of parked threads. */
ulong size() const
{
mysql_mutex_lock(&LOCK_thread_cache);
ulong r= cached_thread_count;
mysql_mutex_unlock(&LOCK_thread_cache);
return r;
}
};
extern Thread_cache thread_cache;