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-<HTML>
-<HEAD>
- <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
- <META NAME="Author" CONTENT="James CE Johnson">
- <TITLE>ACE Tutorial 012</TITLE>
-</HEAD>
-<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#000FFF" VLINK="#FF0F0F">
-
-<CENTER><B><FONT SIZE=+2>ACE Tutorial 012</FONT></B></CENTER>
-
-<CENTER><B><FONT SIZE=+2>Passing classes through ACE_Message_Queue</FONT></B></CENTER>
-
-
-<P>
-<HR WIDTH="100%">
-<P>
-The Task is the only object we've not been through yet. I'll go ahead
-and show both the header and cpp on this one page since the header
-isn't very large.
-<P>
-<HR WIDTH="100%">
-<PRE>
-
-/*
- This is our basic thread-pool Task. We have a choice of pool size
- on the open() and the usual svc() and close() methods.
-
- A new addition is the ACE_Barrier object. This will allow the
- synchronization of our svc() methods so that they all start at the
- "same" time. The normal case may allow one thread to start working
- earlier than others. There's no real harm in it but you can get
- better "work by thread" statistics if they start out together.
-*/
-class Task : public ACE_Task < ACE_MT_SYNCH >
-{
-public:
-
- typedef ACE_Task < ACE_MT_SYNCH > inherited;
-
- Task (void);
- ~Task (void);
-
- int open (int threads = 1);
-
- int svc (void);
-
- int close (u_long flags = 0);
-
-protected:
- ACE_Barrier * barrier_;
-};
-</PRE>
-<HR WIDTH="50%">
-<PRE>
-/*
- Boring default constructor. Be sure our barrier_ is initialized in
- case we get destructed before opened.
-*/
-Task::Task (void)
-: barrier_ (0)
-{
- ACE_DEBUG ((LM_DEBUG, "(%P|%t) Task ctor 0x%x\n", (void *) this));
-}
-
-/*
- You'll see in the svc() method that when we get a shutdown request,
- we always putq() it back into our message queue. The last thread in
- the pool will do this also and result in there always being one
- shutdown request left in the queue when we get here. Just to be
- polite, we'll go ahead and get that message and release it.
-
- We also delete the barrier_ object we used to synch the svc()
- methods.
-*/
-Task::~Task (void)
-{
- ACE_DEBUG ((LM_DEBUG, "(%P|%t) Task dtor 0x%x\n", (void *) this));
-
- ACE_Message_Block *message;
- this->getq (message);
- message->release ();
-
- delete barrier_;
-}
-
-/*
- The ACE_Barrier needs to know how many threads it will be working
- for. For that reason, we have to put off it's construction until we
- get here. We then pass the thread count through to our base class'
- activate().
-*/
-int Task::open (int threads)
-{
- barrier_ = new ACE_Barrier (threads);
- return this->activate (THR_NEW_LWP, threads);
-}
-
-/*
- We don't really do anything here but I wanted to provide a message
- in the output.
-*/
-int Task::close (u_long flags)
-{
- ACE_DEBUG ((LM_DEBUG, "(%P|%t) Task close 0x%x\n", (void *) this));
- return inherited::close (flags);
-}
-
-/*
- Now the svc() method where everything interesting happens.
-*/
-int Task::svc (void)
-{
- /*
- All of the threads will block here until the last thread
- arrives. They will all then be free to begin doing work.
- */
- this->barrier_->wait ();
-
- ACE_DEBUG ((LM_DEBUG, "(%P|%t) Task 0x%x starts in thread %u\n", (void *) this, ACE_Thread::self ()));
-
- // Where we getq() the message
- ACE_Message_Block *message;
- // What we really put into the queue is a Message_Block, so we'll
- // cast the 'message' to 'message_block' after getting it. I'm
- // going through some extra steps here just to be explicit
- Message_Block * message_block;
- // The baseclass of the work object we put into the queue. Notice
- // that we can use this and not bother with the Work object at all.
- Unit_Of_Work * unit_of_work;
-
- while (1)
- {
- // Get the message...
- if (this->getq (message) == -1)
- {
- ACE_ERROR_RETURN ((LM_ERROR, "%p\n", "getq"), -1);
- }
-
- // Is it a shutdown request?
- if (message->msg_type () == ACE_Message_Block::MB_HANGUP)
- {
- // Send the shutdown to all of our pool peers
- this->putq (message);
- break;
- }
-
- // Cast the pointer to our specialized Message_Block. We could
- // have done this at the getq() call but I wanted to be explicit
- // about what we're doing here
- message_block = (Message_Block*)message;
-
- /*
- Since we left alone the ACE_Data_Block used by the
- Message_Block we have chosen to use it to send arbitrary data
- as well.
- */
- const char *cp = message_block->rd_ptr ();
- // Don't forget to skip the NULL we inserted
- message_block->rd_ptr (strlen (cp) + 1);
-
- /*
- Get the Unit_Of_Work pointer out of our specialized
- Message_Block. Since the methods of interest are virtual, we
- don't have to know what kind of work we're to do.
- */
- unit_of_work = message_block->data();
-
- /*
- Invoke a couple of method calls on the object we constructed.
- */
- unit_of_work->who_am_i ();
- unit_of_work->what_am_i ();
-
- ACE_DEBUG ((LM_DEBUG, "(%P|%t) Block 0x%x contains (%s)\n", (void *) message, cp));
-
- /*
- Pretend that the work takes a little time to process. This
- prevents one thread from getting all of the action. In a real
- system you wouldn't need to do this since the work really
- would take time to complete.
- */
- ACE_OS::sleep (ACE_Time_Value (0, 5000));
-
- /*
- Release the message block and allow the unit of work to also go
- away.
- */
- message->release ();
- }
-
- return (0);
-}
-</PRE>
-<HR WIDTH="100%">
-<P>
-Like main() this is actually simpler than the previous tutorial. It's
-much cleaner to carry around a pointer to the object we're working
-with than to try copying data.
-<P>
-The only complication is the new ACE_Barrier. It's a pretty simple
-object that makes it easy for you to synch threads in this way. You
-could do some fancy tricks with mutexes, counters & semaphores but why
-bother when the Barrier already exists.
-<P>
-<HR WIDTH="100%">
-<P>
-<CENTER>[<A HREF="..">Tutorial Index</A>] [<A HREF="page06.html">Continue
-This Tutorial</A>]</CENTER>
-
-</BODY>
-</HTML>