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<CENTER><B><FONT SIZE=+2>ACE Tutorial 017</FONT></B></CENTER>
<CENTER><B><FONT SIZE=+2>Using the ACE_Barrier synch object</FONT></B></CENTER>
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First, lets take a look at the main() routine and how it will use the
Barrier wrapper class. A simple ACE_Task derivative is used so that
we can perform work in multiple threads. These threads will use the
barrier to synch in a couple of places.
<P>
Obviously this isn't a very realistic example but you should be able
to get the idea of how to use a Barrier without getting hung up in
application-level details.
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<PRE>
<font color=red>// page02.html,v 1.10 2000/03/19 20:09:32 jcej Exp</font>
<font color=blue>#include</font> "<font color=green>Barrier_i.h</font>"
<font color=blue>#include</font> "<A HREF="../../../ace/Task.h">ace/Task.h</A>"
<font color=red>/* We'll use a simple Task<> derivative to test our new Barrier
object.
*/</font>
class Test : public ACE_Task<ACE_NULL_SYNCH>
{
public:
<font color=red>// Construct the object with a desired thread count</font>
Test(int _threads);
<font color=red>// Open/begin the test. As usual, we have to match the</font>
<font color=red>// ACE_Task signature.</font>
int open(void * _unused = 0);
<font color=red>// Change the threads_ value for the next invocation of open()</font>
void threads(int _threads);
<font color=red>// Get the current threads_ value.</font>
int threads(void);
<font color=red>// Perform the test</font>
int svc(void);
protected:
<font color=red>// How many threads the barrier will test.</font>
int threads_;
<font color=red>// The Barrier object we'll use in our tests below</font>
Barrier barrier_;
};
<font color=red>/* Construct the object & initialize the threads value for open() to
use.
*/</font>
<font color=#008888>Test::Test</font>(int _threads)
: threads_(_threads)
{
}
<font color=red>/* As usual, our open() will create one or more threads where we'll do
the interesting work.
*/</font>
int <font color=#008888>Test::open</font>(void * _unused)
{
ACE_UNUSED_ARG(_unused);
<font color=red>// One thing about the barrier: You have to tell it how many</font>
<font color=red>// threads it will be synching. The threads() mutator on my</font>
<font color=red>// Barrier class lets you do that and hides the implementation</font>
<font color=red>// details at the same time.</font>
barrier_.threads(threads_);
<font color=red>// Activate the tasks as usual... Like the other cases where</font>
<font color=red>// we're joining (or waiting for) our threads, we can't use</font>
<font color=red>// THR_DETACHED.</font>
return this->activate(THR_NEW_LWP, threads_);
}
void <font color=#008888>Test::threads</font>(int _threads)
{
threads_ = _threads;
}
int <font color=#008888>Test::threads</font>(void)
{
return threads_;
}
<font color=red>/* svc() will execute in each thread & do a few things with the
Barrier we have.
*/</font>
int <font color=#008888>Test::svc</font>(void)
{
ACE_DEBUG ((LM_INFO, "<font color=green>(%P|%t|%T)\<font color=#008888>tTest::svc</font>() Entry\n</font>"));
<font color=red>// Initialize the random number generator. We'll use this to</font>
<font color=red>// create sleep() times in each thread. This will help us see</font>
<font color=red>// if the barrier synch is working.</font>
ACE_Time_Value now(<font color=#008888>ACE_OS::gettimeofday</font>());
ACE_RANDR_TYPE seed = now.usec();
<font color=#008888>ACE_OS::srand</font>(seed);
int delay;
<font color=red>// After saying hello above, sleep for a random amount of time</font>
<font color=red>// from 1 to 6 seconds. That will cause the next message</font>
<font color=red>// "<font color=green>Entering wait()</font>" to be staggered on the output as each</font>
<font color=red>// thread's sleep() returns.</font>
delay = <font color=#008888>ACE_OS::rand_r</font>(seed)%5;
<font color=#008888>ACE_OS::sleep</font>(abs(delay)+1);
<font color=red>// When executing the app you should see these messages</font>
<font color=red>// staggered in an at-most 6 second window. That is, you</font>
<font color=red>// won't likely see them all at once.</font>
ACE_DEBUG ((LM_INFO, "<font color=green>(%P|%t|%T)\<font color=#008888>tTest::svc</font>() Entering wait()\n</font>"));
<font color=red>// All of the threads will now wait at this point. As each</font>
<font color=red>// thread finishes the sleep() above it will join the waiters.</font>
if( barrier_.wait() == -1 )
{
ACE_DEBUG ((LM_INFO, "<font color=green>(%P|%t|%T)\tbarrier_.wait() failed!\n</font>"));
return 0;
}
<font color=red>// When all threads have reached wait() they will give us this</font>
<font color=red>// message. If you execute this, you should see all of the</font>
<font color=red>// "<font color=green>Everybody together</font>" messages at about the same time.</font>
ACE_DEBUG ((LM_INFO, "<font color=green>(%P|%t|%T)\<font color=#008888>tTest::svc</font>() Everybody together?\n</font>"));
<font color=red>// Now we do the sleep() cycle again...</font>
delay = <font color=#008888>ACE_OS::rand_r</font>(seed)%5;
<font color=#008888>ACE_OS::sleep</font>(abs(delay)+1);
<font color=red>// As before, these will trickle in over a few seconds.</font>
ACE_DEBUG ((LM_INFO, "<font color=green>(%P|%t|%T)\<font color=#008888>tTest::svc</font>() Entering done()\n</font>"));
<font color=red>// This time we call done() instead of wait(). done()</font>
<font color=red>// actually invokes wait() but before returning here, it will</font>
<font color=red>// clean up a few resources. The goal is to prevent carrying</font>
<font color=red>// around objects you don't need.</font>
if( barrier_.done() == -1 )
{
ACE_DEBUG ((LM_INFO, "<font color=green>(%P|%t|%T)\tbarrier_.done() failed!\n</font>"));
return 0;
}
<font color=red>// Since done() invokes wait() internally, we'll see this</font>
<font color=red>// message from each thread simultaneously</font>
ACE_DEBUG ((LM_INFO, "<font color=green>(%P|%t|%T)\<font color=#008888>tTest::svc</font>() Is everyone still here?\n</font>"));
<font color=red>// A final sleep()</font>
delay = <font color=#008888>ACE_OS::rand_r</font>(seed)%5;
<font color=#008888>ACE_OS::sleep</font>(abs(delay)+1);
<font color=red>// These should be randomly spaced like all of the other</font>
<font color=red>// post-sleep messages.</font>
ACE_DEBUG ((LM_INFO, "<font color=green>(%P|%t|%T)\<font color=#008888>tTest::svc</font>() Chaos and anarchy for all!\n</font>"));
return(0);
}
<font color=red>/* Our test application...
*/</font>
int main(int, char**)
{
<font color=red>// Create the test object with 10 threads</font>
Test test(10);
<font color=red>// and open it to test the barrier.</font>
test.open();
<font color=red>// Now wait for them all to exit.</font>
test.wait();
<font color=red>// Re-open the Test object with just 5 threads</font>
test.threads(5);
test.open();
<font color=red>// and wait for them to complete also.</font>
test.wait();
return(0);
}
</PRE>
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