[Home]	[About]
[Screenshots]	[Download]
[News]	[Community]
[Documentation]	[Manual]
[Bugs & Requests]	[Wiki]

/home/tetron/hack/vos/apps/tutorials/vostut2.cc

Go to the documentation of this file.

/* Second VOS tutorial.  Introduction to Vobjects.

   This tutorial covers:
   - Setting a default access control
   - Creating a Vobject on a site
   - Reference counting in VOS
   - Simple Vobject methods

   This file (vostut2.cc) is released into the public domain.  No
   restrictions are placed on its use, distribution or inclusion into
   other works.
*/

#include <vos/vos/vos.hh>

using namespace VUtil;
using namespace VOS;

#ifdef WIN32
#define sleep _sleep
#endif

int main(int argc, char** argv)
{
    std::cout << "VOS Tutorial 2\n\n";

    Site localsite;
    localsite.addSiteExtension(new LocalVipSiteExtension());

    /* Remote users are denied access to objects by default unless a Vobject's 
       access control policy gives them permission.  Here, we set the default 
       policy for new objects on this site to "accept-all" for demonstration 
       purposes.  Access control policies and access control lists are be 
       covered in detail in tutorialXXX.
     */
    localsite.setDefaultPolicy("core:accept-all");

    /* The fundamental abstraction in VOS is the "Vobject" (pronounced
       Vee-Object).  A Vobject is an entity which can exchange
       messages with other Vobjects.  Every Vobject is associated with
       a site, and the site provides the means by which the Vobject
       may communicate over a network using standards such as TCP/IP
       sockets.  A Vobject is created by using the createVobject()
       method (or variants createVobjectA() and createVobjectT()) 
       and assigning the returned object to a vRef<> template (explained below).
    */
    vRef<Vobject> primus = localsite.createVobjectA("primus");

    /* -- About Reference Counting --

       Memory management in VOS uses a technique known as Reference
       Counting.  The idea is simple: an object stores the number of
       times it's refered to (via a C++ pointer or reference, the two
       are essentially interchangeable) in other parts of the program.
       When an object is constructed, its reference is initially 1.
       As additional pointers to the object are created, the reference
       count is increased, and as those pointers go away the count is
       decreased.  When the count reaches 0, this means the object is
       no longer refered to anywhere in the program and can be safely
       deleted without leaving any dangling pointers.

       To simplify reference counting you can use the smart pointer
       class vRef<>.  It is a template class whose purpose is simply
       to ensure that a reference which you have acquired is released
       when you are done with it.  The way it works is very simple:
       the template holds a pointer to the object.  When the vRef
       object is destroyed (usually by going out of scope) it calls
       release() on the pointer it holds, thereby decreasing the reference
       count.  By using operator overloading, the use of the smart pointer 
       class is nearly identical to as if it were a normal raw pointer.  
       Methods in VOS that return reference counted objects generally 
       return them wrapped in a vRef<> for safety.

     */

    /* Now, let's look at a few simple methods you can use on Vobjects: */

    /* Get the Vobject's site name.  This is the name it was created
       with, and is unique on its site.
    */
    std::cout << "Vobject site name is: " << primus->getSiteName() << "\n";

    /* Get the URL you can use to refer to this Vobject.  It should
       consist of the hostname of your site and the vobject's unique
       name.
    */
    std::cout << "Vobject URL is: " << primus->getURLstr() << "\n";

    /* Get the site the Vobject is associated with, which is our
       localsite object.  Sites are a subclass of Vobjects, so you can
       use the entire Vobject API (described in this and following
       tutorials) with sites.
    */
    vRef<Site> site = primus->getSite();
    std::cout << "Vobject site is: " << site->getURLstr() << "\n";
    std::cout << "Our local site is: " << localsite.getURLstr() << "\n";

    /* Now, if you access this site with a VOS browser such as Mesh or
       Metalurgy you will see a single vobject named "primus".
    */
    std::cout << "Going into idle loop...\n";
    while(true) sleep(1000);
}