Author: James CE Johnson

ACE Tutorial 016
Making ACE_Condition easier to use

We finally get to the main() application. I create a simple Task derivative that will serve as a baseclass for other objects that test specific functions of the Condition class. Notice how easy it is to integrate a Condition into the application without keeping track of three related member variables.

    // page04.html,v 1.6 1999/04/03 21:56:31 jcej Exp

    #include "Condition_i.h"
    #include "ace/Task.h"

    /* In order to test our Condition we'll derive from ACE_Task<> so that
       we can have several threads accessing the condition variable
       together.
     */
    class Test : public ACE_Task<ACE_NULL_SYNCH>
    {
    public:
         // Construct the condition variable with an initial value.
        Test( int _max_threads, Condition::value_t _value );
        ~Test(void);

         // Open the Task with enough threads to make a useful test.
        int open(void);

    protected:
         // Each thread will do work on the Condition.
        int svc(void);

         // Override this method to modify the Condition in some way.
        virtual void modify(void) = 0;

         // Override this to test the Condition in some way.
        virtual void test(void) = 0;

         // How many threads to use in the test.  This is also used in the
         // modify() and test() methods of the derivatives.
        int max_threads_;

         // We want to sleep for a random amount of time to simulate
         // work.  The seed is necessary for proper random number generation.
        ACE_RANDR_TYPE seed_;

         // This is the actual condition variable set.
        Condition condition_;
    };

    // Initialize the condition variable.
    Test::Test( int _max_threads, Condition::value_t _value )
            : max_threads_(_max_threads), condition_(_value)
    {
        ;
    }

    Test::~Test(void)
    {
        ;
    }

    // Seed the random number generator and start the threads.
    int Test::open(void)
    {
        seed_ = ACE_OS::gettimeofday().usec();

        ACE_OS::srand( seed_ );

        return this->activate(THR_NEW_LWP, max_threads_);
    }

    /* Each thread will modify the condition variable in some way and then
       wait for the condition to be satisfied.  The derived classes
       overload modify() and test() to implement a specific test of the
       Condition class.
     */
    int Test::svc(void)
    {
            // Take a moment before we modify the condition.  This will
            // cause test() in other threads to delay a bit.
        int stime = ACE_OS::rand_r( seed_ ) % 5;
        ACE_OS::sleep(abs(stime)+2);

        ACE_DEBUG ((LM_INFO, "(%P|%t|%T)\tTest::svc() befor modify, condition_ is:  %d\n", (int)condition_ ));

         // Change the condition variable's value
        modify();

        ACE_DEBUG ((LM_INFO, "(%P|%t|%T)\tTest::svc() after modify, condition_ is:  %d\n", (int)condition_ ));

         // Test for the condition we want
        test();

        ACE_DEBUG ((LM_INFO, "(%P|%t|%T)\tTest::svc() leaving.\n" ));

        return(0);
    }

    /* Test Condition::operator!=()
       The task's svc() method will increment the condition variable and
       then wait until the variable's value reaches max_threads_.
     */
    class Test_ne : public Test
    {
    public:
         // Initialize the condition variable to zero since we're counting up.
        Test_ne( int _max_threads )
                : Test(_max_threads,0)
            {
                ACE_DEBUG ((LM_INFO, "\n(%P|%t|%T)\tTesting condition_ != %d\n", max_threads_));
            }

         // Increment the variable
        void modify(void)
            {
                ++condition_;
            }

         // Wait until it equals max_threads_
        void test(void)
            {
                condition_ != max_threads_;
            }
    };

    /* Test Condition::operator>=()
       Each svc() method will decrement the condition variable and wait
       until it is less than max_threads_.  To do this correctly, we have
       to be careful where we start the condition variable.
     */
    class Test_ge : public Test
    {
    public:
         // For max_threads_ == 5, we will start the condition variable at
         // the value 9.  When the "last" thread decrements it, the value
         // will be 4 which satisfies the condition.
        Test_ge( int _max_threads )
                : Test(_max_threads,_max_threads*2-1)
            {
                ACE_DEBUG ((LM_INFO, "\n(%P|%t|%T)\tTesting condition_ >= %d\n", max_threads_));
            }

         // Decrement by one...
        void modify(void)
            {
                --condition_;
            }

         // while( value >= max_threads_ ) wait();
        void test(void)
            {
                condition_ >= max_threads_;
            }
    };

    /* Test Condition::operator<=()
       This time we will increment the condition until it is greater than
       max_threads_.  Again, we have to be careful where we start the
       value and how we increment.
     */
    class Test_le : public Test
    {
    public:
         // I'm starting the value at 1 so that if we increment by one in
         // each thread, the "last" thread (of 5) will set the value to
         // 6.  Since I actually increment by 2, we could start somewhat lower.
        Test_le( int _max_threads )
                : Test( _max_threads, 1 )
            {
                ACE_DEBUG ((LM_INFO, "\n(%P|%t|%T)\tTesting condition_ <= %d\n", max_threads_));
            }

         // Try out Condition::operator+=(int)
         // This will cause the third thread to satisfy the condition.
        void modify(void)
            {
                condition_ += 2;
            }

         // while( value <= max_threads_ ) wait();
        void test(void)
            {
                condition_ <= max_threads_;
            }
    };

    /* For our final test, we'll go after Condition::operator=(Condition::Compare)
       By deriving from Condition::Compare we can perform any arbitrary
       test on the value of the condition variable.
     */
    class Test_fo : public Test
    {
    public:
         // We'll be using operator*=(int) to increment the condition
         // variable, so we need to start with a non-zero value.
        Test_fo( int _max_threads )
                : Test( _max_threads, 1 )
            {
                ACE_DEBUG ((LM_INFO, "\n(%P|%t|%T)\tTesting condition_ == FunctionObject\n" ));
            }

         // Double the value for each thread that we have.
        void modify(void)
            {
                condition_ *= 2;
            }

         /* Derive our CompareFunction and provide the operator() that
            performs our test.  In this case, we'll compare the value to
            the number 32.
          */
        class CompareFunction : public Condition::Compare
        {
        public:
             // When this returns non-zero, the condition test operator
             // will unblock in each thread.
             // Note that 32 was chosen because 2**5 == 32.  That is, the
             // fifth thread will modify() the value to 32.
            int operator() ( Condition::value_t _value )
                {
                    return _value == 32;
                }
        };

         // Create the CompareFunction and wait for the condition variable
         // to reach the state we want.
        void test(void)
            {
                CompareFunction compare;
                condition_ == compare;
            }
    };

    /* In main() we just instantiate each of the four test objects that we
       created.  After open()ing each, we wait() for it's threads to exit.
     */
    int main(int, char **)
    {
        Test_ne test_ne(5);
        test_ne.open();
        test_ne.wait();

        Test_ge test_ge(5);
        test_ge.open();
        test_ge.wait();

        Test_le test_le(5);
        test_le.open();
        test_le.wait();

        Test_fo test_fo(5);
        test_fo.open();
        test_fo.wait();

        return(0);
    }

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