Adding upstream version 1:10.5.12.upstream/1%10.5.12upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 210 insertions, 0 deletions

diff --git a/sql/thread_cache.h b/sql/thread_cache.h
new file mode 100644
index 00000000..5cb6c0fe
--- /dev/null
+++ b/sql/thread_cache.h
@@ -0,0 +1,210 @@
+/*
+  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;