Our Task object definition:
#include "task.h" #include "block.h" /* Set our housekeeping pointer to NULL and tell the user we exist. */ Task::Task (void) : barrier_ (0) { ACE_DEBUG ((LM_DEBUG, "(%P|%t) Task ctor 0x%x\n", (void *) this)); } /* Take care of cleanup & tell the user we're going away. */ Task::~Task (void) { ACE_DEBUG ((LM_DEBUG, "(%P|%t) Task dtor 0x%x\n", (void *) this)); /* Get our shutdown notification out of the queue and release it. */ ACE_Message_Block * message; this->getq(message); message->release(); delete barrier_; } /* Open the object to do work. We create the Barrier object and tell it how many threads we'll be using. Next, we activate the Task into the number of requested threads. */ int Task::open (int threads) { barrier_ = new ACE_Barrier (threads); return this->activate (THR_NEW_LWP, threads); } /* Tell the user we're closing and invoke the baseclass' close() to take care of things. */ int Task::close (u_long flags) { ACE_DEBUG ((LM_DEBUG, "(%P|%t) Task close 0x%x\n", (void *) this)); return inherited::close (flags); } /* Our svc() method waits for work on the queue and then processes that work. */ int Task::svc (void) { /* This will cause all of the threads to wait on this line until all have invoked this method. The net result is that no thread in the Task will get a shot at the queue until all of the threads are active. There's no real need to do this but it's an easy intro into the use of ACE_Barrier. */ this->barrier_->wait (); ACE_DEBUG ((LM_DEBUG, "(%P|%t) Task 0x%x starts in thread %d\n", (void *) this, ACE_Thread::self ())); /* Remember that get() needs a reference to a pointer. To save stack thrashing we'll go ahead and create a pointer outside of the almost- infinite loop. */ ACE_Message_Block *message; while (1) { /* Get a message from the queue. */ if (this->getq (message) == -1) { ACE_ERROR_RETURN ((LM_ERROR, "%p\n", "getq"), -1); } /* If we got the shutdown request, we need to go away. */ if (message->msg_type () == ACE_Message_Block::MB_HANGUP) { /* Forward the request to any peer threads. */ this->putq (message); /* Leave the infinite loop so that the thread exits. */ break; } /* The message queue stores char* data. We use rd_ptr() to get to the beginning of the data. */ const char *cp = message->rd_ptr (); /* Move the rd_ptr() past the data we read. This isn't real useful here since we won't be reading any more from the block but it's a good habit to get into. */ message->rd_ptr( strlen(cp) ); /* Display the block's address and data to the user. */ ACE_DEBUG ((LM_DEBUG, "(%P|%t) Block 0x%x contains (%s)\n", (void *) message, cp)); /* Pretend that it takes a while to process the data. */ ACE_OS::sleep (ACE_Time_Value (0, 5000)); /* Release the message block. Notice that we never delete a message block. Blocks are reference counted & the release() method will take care of the delete when there are no more references to the data. */ message->release (); } return (0); }
This is all pretty straight-forward too. One gottcha we avoided was a memory leak due to our shutdown message. Notice that svc() enqueues that block without bothering to see if there are any more threads to dequeue it. Thats why our dtor can call getq() without worrying about blocking infinitely: it knows the message block will be there.