MWL#182: Explain running statements

First code
- "Asynchronous procedure call" system
- new THD::check_killed() that serves APC request is called from within most important loops
- EXPLAIN code is now able to generate EXPLAIN output on-the-fly [incomplete]

Parts that are still missing:
- put THD::check_killed() call into every loop where we could spend significant amount of time
- Make sure EXPLAIN code works for group-by queries that replace JOIN::join_tab with make_simple_join() 
  and other such cases.
- User interface: what error code to use, where to get timeout settings from, etc.

1 files changed, 98 insertions, 0 deletions

diff --git a/sql/my_apc.h b/sql/my_apc.h
new file mode 100644
index 00000000000..3783bd28f54
--- /dev/null
+++ b/sql/my_apc.h
@@ -0,0 +1,98 @@
+/*
+  TODO: MP AB Copyright
+*/
+
+/*
+  Design
+  - Mutex-guarded request queue (it belongs to the target), which can be enabled/
+    disabled (when empty).
+
+  - 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.
+*/
+
+/*
+  Target for asynchronous calls.
+*/
+class Apc_target
+{
+public:
+  Apc_target() : enabled(0), apc_calls(NULL) /*, call_queue_size(0)*/ {} 
+  ~Apc_target() { DBUG_ASSERT(!enabled && !apc_calls);}
+
+  /* 
+    Initialize the target. This must be called before anything else. Right
+    after initialization, the target is disabled.
+  */
+  void init();
+
+  /* 
+    Destroy the target. The target must be disabled when this call is made.
+  */
+  void destroy();
+  
+  /* 
+    Enter into state where this target will be serving APC requests
+  */
+  void enable();
+
+  /* 
+    Leave the state where we could serve APC requests (will serve all already 
+    enqueued requests)
+  */
+  void disable();
+  
+  /*
+    This should be called periodically to serve observation requests.
+  */
+  void process_apc_requests();
+
+  typedef void (*apc_func_t)(void *arg);
+  
+  /*
+    Make an APC call: schedule it for execution and wait until the target
+    thread has executed it. This function must not be called from a thread
+    that's different from the target thread.
+
+    @retval FALSE - Ok, the call has been made
+    @retval TRUE  - Call wasnt made (either the target is in disabled state or
+                    timeout occured)
+  */
+  bool make_apc_call(apc_func_t func, void *func_arg, 
+                     int timeout_sec, bool *timed_out);
+
+private:
+  class Call_request;
+  int enabled;
+
+  Call_request *apc_calls;
+  pthread_mutex_t LOCK_apc_queue;
+  //int call_queue_size;
+
+  class Call_request
+  {
+  public:
+    apc_func_t func;
+    void *func_arg;
+    bool done;
+
+    pthread_mutex_t LOCK_request;
+    pthread_cond_t COND_request;
+
+    Call_request *next;
+    Call_request *prev;
+    
+    const char *what;
+  };
+
+  void enqueue_request(Call_request *qe);
+  void dequeue_request(Call_request *qe);
+  Call_request *get_first_in_queue()
+  { 
+    return apc_calls;
+  }
+};
+
+///////////////////////////////////////////////////////////////////////
+