<!-- page04.html,v 1.10 2000/03/19 20:09:25 jcej Exp --> <HTML> <HEAD> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <META NAME="Author" CONTENT="James CE Johnson"> <TITLE>ACE Tutorial 010</TITLE> </HEAD> <BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#000FFF" VLINK="#FF0F0F"> <CENTER><B><FONT SIZE=+2>ACE Tutorial 010</FONT></B></CENTER> <CENTER><B><FONT SIZE=+2>Passing chunks of data through an ACE_Message_Queue</FONT></B></CENTER> <P> <HR WIDTH="100%"> Our <A HREF="task.h">Task</A> object executes in one or more threads and reads from the message queue it contains. <P> <HR WIDTH="100%"> <PRE> <font color=red>// page04.html,v 1.10 2000/03/19 20:09:25 jcej Exp</font> <font color=blue>#ifndef</font> <font color=purple>TASK_H</font> <font color=blue>#define</font> <font color=purple>TASK_H</font> <font color=blue>#include</font> "<A HREF="../../../ace/Task.h">ace/Task.h</A>" <font color=blue>#if !defined</font> (<font color=purple>ACE_LACKS_PRAGMA_ONCE</font>) <font color=blue># pragma</font> <font color=purple>once</font> <font color=blue>#endif</font> <font color=red>/* ACE_LACKS_PRAGMA_ONCE */</font> <font color=red>/* Like the thread-pool server tutorial, we'll derive from ACE_Task<>. Our goal here is to show off the ACE_Message_Queue and the best way to do that is to use one to pass data between threads. The easiest way to create threads is with ACE_Task<> */</font> class Task : public ACE_Task <ACE_MT_SYNCH> { public: typedef ACE_Task <ACE_MT_SYNCH> inherited; <font color=red>/* The constructor/destructor are simple but take care of some necessary housekeeping. */</font> Task (size_t n_threads); ~Task (void); <font color=red>/* open() will kick off our thread pool for us. */</font> int open (void * = 0); <font color=red>/* Our worker method */</font> int svc (void); <font color=red>/* All we'll do here is print a message to the user. */</font> int close (u_long flags = 0); protected: <font color=red>/* Just to be clever, I'll use an ACE_Barrier to cause the threads to sync in svc() before doing any real work. */</font> ACE_Barrier barrier_; size_t n_threads_; <font color=red>// Number of threads in the pool.</font> }; <font color=blue>#endif</font> <font color=red>/* TASK_H */</font> </PRE> <HR WIDTH="100%"> <P> The only thing here that we didn't see in the thread-pool server is the ACE_Barrier. The application logic really doesn't need it but it is a handy way to synchronize the threads at the beginning of svc(). In testing I found that if I didn't sync svc(), the first thread to get activated would tend to get all of the messages before the other threads came alive. <P><HR WIDTH="100%"> <CENTER>[<A HREF="../online-tutorials.html">Tutorial Index</A>] [<A HREF="page05.html">Continue This Tutorial</A>]</CENTER>