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diff --git a/sql/my_apc.h b/sql/my_apc.h
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+#ifndef SQL_MY_APC_INCLUDED
+#define SQL_MY_APC_INCLUDED
+/*
+   Copyright (c) 2011, 2013 Monty Program Ab.
+
+   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 Street, Fifth Floor, Boston, MA 02110-1335 USA */
+
+/*
+  Interface
+  ~~~~~~~~~
+   (
+    - This is an APC request queue
+    - We assume there is a particular owner thread which periodically calls
+      process_apc_requests() to serve the call requests.
+    - Other threads can post call requests, and block until they are exectued.
+  )
+
+  Implementation
+  ~~~~~~~~~~~~~~
+  - The target has a mutex-guarded request queue.
+
+  - After the request has been put into queue, the requestor waits for request
+    to be satisfied. The worker satisifes the request and signals the
+    requestor.
+*/
+
+class THD;
+
+/*
+  Target for asynchronous procedure calls (APCs). 
+   - A target is running in some particular thread, 
+   - One can make calls to it from other threads.
+*/
+class Apc_target
+{
+  mysql_mutex_t *LOCK_thd_kill_ptr;
+public:
+  Apc_target() : enabled(0), apc_calls(NULL) {} 
+  ~Apc_target() { DBUG_ASSERT(!enabled && !apc_calls);}
+
+  void init(mysql_mutex_t *target_mutex);
+
+  /* Destroy the target. The target must be disabled when this call is made. */
+  void destroy() { DBUG_ASSERT(!enabled); }
+
+  /* Enter ther state where the target is available for serving APC requests */
+  void enable() { enabled++; }
+
+  /*
+    Make the target unavailable for serving APC requests.
+
+    @note
+      This call will serve all requests that were already enqueued
+  */
+  void disable()
+  {
+    DBUG_ASSERT(enabled);
+    mysql_mutex_lock(LOCK_thd_kill_ptr);
+    bool process= !--enabled && have_apc_requests();
+    mysql_mutex_unlock(LOCK_thd_kill_ptr);
+    if (unlikely(process))
+      process_apc_requests(true);
+  }
+
+  void process_apc_requests(bool force);
+  /* 
+    A lightweight function, intended to be used in frequent checks like this:
+
+      if (apc_target.have_requests()) apc_target.process_apc_requests()
+  */
+  inline bool have_apc_requests()
+  {
+    return MY_TEST(apc_calls);
+  }
+
+  inline bool is_enabled() { return enabled; }
+  
+  /* Functor class for calls you can schedule */
+  class Apc_call
+  {
+  public:
+    /* This function will be called in the target thread */
+    virtual void call_in_target_thread()= 0;
+    virtual ~Apc_call() = default;
+  };
+  
+  /* Make a call in the target thread (see function definition for details) */
+  bool make_apc_call(THD *caller_thd, Apc_call *call, int timeout_sec, bool *timed_out);
+
+#ifndef DBUG_OFF
+  int n_calls_processed; /* Number of calls served by this target */
+#endif
+private:
+  class Call_request;
+
+  /* 
+    Non-zero value means we're enabled. It's an int, not bool, because one can
+    call enable() N times (and then needs to call disable() N times before the 
+    target is really disabled)
+  */
+  int enabled;
+
+  /* 
+    Circular, double-linked list of all enqueued call requests. 
+    We use this structure, because we 
+     - process requests sequentially: requests are added at the end of the 
+       list and removed from the front. With circular list, we can keep one
+       pointer, and access both front an back of the list with it.
+     - a thread that has posted a request may time out (or be KILLed) and 
+       cancel the request, which means we need a fast request-removal
+       operation.
+  */
+  Call_request *apc_calls;
+ 
+  class Call_request
+  {
+  public:
+    Apc_call *call; /* Functor to be called */
+
+    /* The caller will actually wait for "processed==TRUE" */
+    bool processed;
+
+    /* Condition that will be signalled when the request has been served */
+    mysql_cond_t COND_request;
+    
+    /* Double linked-list linkage */
+    Call_request *next;
+    Call_request *prev;
+    
+    const char *what; /* (debug) state of the request */
+  };
+
+  void enqueue_request(Call_request *qe);
+  void dequeue_request(Call_request *qe);
+
+  /* return the first call request in queue, or NULL if there are none enqueued */
+  Call_request *get_first_in_queue()
+  {
+    return apc_calls;
+  }
+};
+
+#ifdef HAVE_PSI_INTERFACE
+void init_show_explain_psi_keys(void);
+#else
+#define init_show_explain_psi_keys() /* no-op */
+#endif
+
+#endif //SQL_MY_APC_INCLUDED
+