Author: James CE Johnson

ACE Tutorial 018
The FIFO Nature of ACE_Token

Our Test object is a simple derivative of ACE_Task. Although we've certainly used templates in other tutorials, this is the first time we've created one of our own.

In a lot of ways, you can think of templates as the sophisticated cousin of the old C-style pre-processor macros. With templates, however, you get better type-checking and much easier debugging. There are certainly other benefits but these are my favorites.

Our template's MUTEX parameter is used to set the mutex type mutex_t. That'll be used in svc() so that we can protect shared resources needed during the processing of data received on our message queue.

Note at the bottom how we have to include the cpp file associated with us. Most compilers have to see the definition of templated classes along with their declaration. You might be tempted, therefore, to just put the definitions in the header file. Resist that temptation because templates are one of the fastest growing areas of compilers. Including the definition like we do here leads to long compile times and overly-large binaries. With luck, the compilers will get smarter in the future and we won't need definition inclusion. If you've already got them broken out then you'll save yourself a lot of time!

    // page03.html,v 1.5 1999/04/03 21:56:32 jcej Exp

    #ifndef TEST_T_H
    #define TEST_T_H

    #include "ace/Task.h"

    /* We'll create a simple ACE_Task derivative for testing a couple of
       different locking mechanisms.  We've hidden the open() method to
       force our client into using the run() method instead.

       The naming convention *_T is fairly typical for ACE.  The _T suffix
       on the object name (and it's source files) indicates that this is a
       templated class.  Generally, there is a non-templated class defined
       also such as foobar.h that would be included instead of foobar_T.h.
     */

    template <class MUTEX>
    class Test_T : public ACE_Task<ACE_MT_SYNCH>
    {
    public:
      // Allow our derivative to name the class so that we can tell the
      // user what's going on as we test the lock.
      Test_T (const char *name);

      // This will run the entire test.  open() will be called to activate
      // the task's threads.  We then add a number of messages to the
      // queue for svc() to process.
      int run (void);

    protected:

      // Activate a few threads
      int open (void *arg = 0);

      // Read some things from the message queue and exercise the lock.
      int svc (void);

      // Send a message block to svc().  If _message is 0 then send a
      // shutdown request (e.g., MB_HANGUP)
      int send (ACE_Message_Block * message = 0);

      // The object's name.  Typically provided by a derivative.
      const char *name_;

      // We want to barrier the svc() methods to give all of the threads a
      // fair chance
      ACE_Barrier barrier_;

      // As each thread enters svc() it will increment this.  While we
      // have a thread id available to us, I wanted a simple value to
      // display in debug messages.
      ACE_Atomic_Op<ACE_Mutex,int> thread_num_;

      // Set our mutex type based on the template parameter.  We then
      // build a guard type based on that type.
      typedef MUTEX mutex_t;
      typedef ACE_Guard<mutex_t> guard_t;

      // Our mutex.  We'll use this in svc() to protect imaginary shared
      // resources.
      mutex_t mutex_;
    };

    /* Although different compilers differ in their details, almost all of
       them require that you provide the definition of the templated
       object along with the declaration.  With any luck, this will change
       someday & we'll have smaller object files.  Until then, the lines
       below will take care of you.
     */

    #if defined (ACE_TEMPLATES_REQUIRE_SOURCE)
    #include "Test_T.cpp"
    #endif /* ACE_TEMPLATES_REQUIRE_SOURCE */

    #if defined (ACE_TEMPLATES_REQUIRE_PRAGMA)
    #pragma implementation ("Test_T.cpp")
    #endif /* ACE_TEMPLATES_REQUIRE_PRAGMA */

    #endif /* TEST_T_H */

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