Edit: thread_cache.h
/* 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;
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