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Editing: simpleprogramlisting.html

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <title>Program Listing</title>
    <link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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    <link rel="start" href="index.html" title="Getting Started with Replicated Berkeley DB Applications" />
    <link rel="up" href="txnapp.html" title="Chapter 2. Transactional Application" />
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    <div xmlns="" class="navheader">
      <div class="libver">
        <p>Library Version 11.2.5.3</p>
      </div>
      <table width="100%" summary="Navigation header">
        <tr>
          <th colspan="3" align="center">Program Listing</th>
        </tr>
        <tr>
          <td width="20%" align="left"><a accesskey="p" href="txnapp.html">Prev</a> </td>
          <th width="60%" align="center">Chapter 2. Transactional Application</th>
          <td width="20%" align="right"> <a accesskey="n" href="repapp.html">Next</a></td>
        </tr>
      </table>
      <hr />
    </div>
    <div class="sect1" lang="en" xml:lang="en">
      <div class="titlepage">
        <div>
          <div>
            <h2 class="title" style="clear: both"><a id="simpleprogramlisting"></a>Program Listing</h2>
          </div>
        </div>
      </div>
      <div class="toc">
        <dl>
          <dt>
            <span class="sect2">
              <a href="simpleprogramlisting.html#repconfiginfo_cxx">
                            <span>Class: RepConfigInfo</span>
                            
                    </a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="simpleprogramlisting.html#repmgr_cxx">Class: excxx_repquote_gsg_simple</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="simpleprogramlisting.html#usage_cxx">Function: usage()</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="simpleprogramlisting.html#main_cxx">Function: main()</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="simpleprogramlisting.html#repmgr_init_cxx">Method: SimpleTxn::init()</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="simpleprogramlisting.html#doloop_cxx">Method: SimpleTxn::doloop()</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="simpleprogramlisting.html#printstocks_c">
                            
                            <span>Method: SimpleTxn::print_stocks()</span>
                            
                    </a>
            </span>
          </dt>
        </dl>
      </div>
      <p>
                Our example program is a fairly simple transactional
                application. At this early stage of its development, the
                application contains no hint that it must be network-aware
                so the only command line argument that it takes is one that
                allows us to specify the environment home directory.
                (Eventually, we will specify things like host names and
                ports from the command line).
            </p>
      <p>
                Note that the application performs all writes under the
                protection of a transaction; however, multiple database
                operations are not performed per transaction. Consequently,
                we simplify things a bit by using autocommit for our 
                database writes.
            </p>
      <p>
                Also, this application is single-threaded. It is possible
                to write a multi-threaded or multi-process application that 
                performs replication. That said, the concepts described in
                this book are applicable to both single threaded and
                multi-threaded applications so nothing
                is gained by multi-threading this application other than
                distracting complexity. This manual
                does, however, identify where care must be taken when
                performing replication with a non-single threaded
                application.
            </p>
      <p>
                Finally, remember that transaction processing is not described in
                this manual. Rather, see the 
                <em class="citetitle">Berkeley DB Getting Started with Transaction Processing</em> guide for details on 
                that topic.
            </p>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="repconfiginfo_cxx"></a>
                            <span>Class: RepConfigInfo</span>
                            
                    </h3>
            </div>
          </div>
        </div>
        <p>
                            Before we begin, we present a 
                            class that we will use to maintain useful
                            information for us. Under normal circumstances,
                            this class would not be necessary for a simple
                            transactional example such as this. However, this code will
                            grow into a replicated example that needs to
                            track a lot more information for the
                            application, and so we lay the groundwork for
                            it here.
                    </p>
        <p>
                            The class that we create is called
                            <code class="classname">RepConfigInfo</code>
                            
                            and its only purpose at this time is to track
                            the location of our environment home directory.
                    </p>
        <pre class="programlisting">#include &lt;db_cxx.h&gt;

class RepConfigInfo {
public:
    RepConfigInfo();
    virtual ~RepConfigInfo();

public:
    char* home;
};

RepConfigInfo::RepConfigInfo()
{
    home = "TESTDIR";
}

RepConfigInfo::~RepConfigInfo()
{
}  </pre>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="repmgr_cxx"></a>Class: excxx_repquote_gsg_simple</h3>
            </div>
          </div>
        </div>
        <p>
                            Our transactional example will 
                            instantiate a class,
                            <code class="classname">SimpleTxn</code>, that performs
                            all our work for us. Before we implement our
                            <code class="function">main()</code> function, we show
                            the <code class="classname">SimpleTxn</code> class
                            declaration.
                    </p>
        <p>
                            First, we provide some declarations and
                            definitions that are needed later in
                            our example:
                    </p>
        <pre class="programlisting">#include &lt;iostream&gt;
#include &lt;db_cxx.h&gt;
#include "RepConfig.h"

using std::cout;
using std::cin;
using std::cerr;
using std::endl;
using std::flush;

#define CACHESIZE   (10 * 1024 * 1024)
#define DATABASE    "quote.db"

const char *progname = "excxx_reqquote_gsg_simple";

#ifdef _WIN32
#define WIN32_LEAN_AND_MEAN
#include &lt;windows.h&gt;
#include &lt;direct.h&gt;

extern "C" {
  extern int getopt(int, char * const *, const char *);
  extern char *optarg;
}
#else
#include &lt;errno.h&gt;
#endif  </pre>
        <p>
        And then we define our <code class="classname">SimpleTxn</code> class:
</p>
        <pre class="programlisting">class SimpleTxn
{
public:
    // Constructor.
    SimpleTxn();
    // Initialization method. Creates and opens our environment handle.
    int init(RepConfigInfo* config);
    // The doloop is where all the work is performed.
    int doloop();
    // terminate() provides our shutdown code.
    int terminate();

private:
    // disable copy constructor.
    SimpleTxn(const SimpleTxn &amp;);
    void operator = (const SimpleTxn &amp;);

// internal data members.
    RepConfigInfo   *app_config;
    DbEnv           dbenv;

// private methods.
    // print_stocks() is used to display the contents of our database.
    static int print_stocks(Db *dbp);
};  </pre>
        <p>
            Note that we show the implementation of the various
            <code class="classname">SimpleTxn</code> methods later in this section.
    </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="usage_cxx"></a>Function: usage()</h3>
            </div>
          </div>
        </div>
        <p>
                            Our <code class="function">usage()</code> is at this
                            stage of development trivial because we only
                            have one command line argument to manage.
                            Still, we show it here for the sake of
                            completeness.
                    </p>
        <pre class="programlisting">static void usage()
{
    cerr &lt;&lt; "usage: " &lt;&lt; progname &lt;&lt; endl
         &lt;&lt; "-h home" &lt;&lt; endl;

exit(EXIT_FAILURE);
}  </pre>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="main_cxx"></a>Function: main()</h3>
            </div>
          </div>
        </div>
        <p>
                            Now we provide our <code class="function">main()</code>
                            function. This is a trivial function whose only
                            job is to collect command line information,
                            then instantiate a <code class="classname">SimpleTxn</code>
                            object, run it, then terminate it.
                    </p>
        <p>
                            We begin by declaring some useful variables. Of
                            these, note that we instantiate our
                            <code class="classname">RepConfigInfo</code>
                            object here. Recall that this is used to store
                            information useful to our code. This class becomes more
                            interesting later in this book.
                    </p>
        <pre class="programlisting">int main(int argc, char **argv)
{
    RepConfigInfo config;
    char ch;
    int ret;  </pre>
        <p>
            Then we collect our command line information. Again, this is at
            this point fairly trivial:
    </p>
        <pre class="programlisting">    // Extract the command line parameters
    while ((ch = getopt(argc, argv, "h:")) != EOF) {
        switch (ch) {
        case 'h':
            config.home = optarg;
            break;
        case '?':
        default:
            usage();
        }
    }

// Error check command line.
    if (config.home == NULL)
        usage();  </pre>
        <p>
        Now we instantiate and initialize our <code class="classname">SimpleTxn</code>
        class, which is what is responsible for doing all our real work.
        The <code class="methodname">SimpleTxn::init()</code> method creates and
        opens our environment handle.
</p>
        <pre class="programlisting">    SimpleTxn runner;
    try {
        if((ret = runner.init(&amp;config)) != 0)
            goto err;  </pre>
        <p>
            Then we call the <code class="methodname">SimpleTxn::doloop()</code>
            method, which is where the actual transactional work is
            performed for this application.
    </p>
        <pre class="programlisting">        if((ret = runner.doloop()) != 0)
            goto err;  </pre>
        <p>
                Finally, catch exceptions and terminate the program:
        </p>
        <pre class="programlisting">    } catch (DbException dbe) {
        cerr &lt;&lt; "Caught an exception during initialization or"
            &lt;&lt; " processing: " &lt;&lt; dbe.what() &lt;&lt; endl;
    }
err:
    runner.terminate();
    return 0;
}  </pre>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="repmgr_init_cxx"></a>Method: SimpleTxn::init()</h3>
            </div>
          </div>
        </div>
        <p>
                        The <code class="methodname">SimpleTxn::init()</code>
                        method is used to create and open our environment handle.
                        For readers familiar with writing transactional
                        DB applications, there should be no surprises
                        here. However, we will be adding to this in later
                        chapters as we roll replication into this example.
                </p>
        <p>
                        First, we show the class constructor
                        implementation, which is only used to initialize a
                        few variables:
                </p>
        <pre class="programlisting">SimpleTxn::SimpleTxn() : app_config(0), dbenv(0)
{
}  </pre>
        <p>
        We now provide the <code class="methodname">init()</code> method
        implementation. The only thing of interest here is that we specify
        <code class="literal">DB_TXN_NOSYNC</code> to our environment. This causes
        our transactional commits to become non-durable, which is something
        that we are doing only because of the nature of our example.
</p>
        <pre class="programlisting">int SimpleTxn::init(RepConfigInfo *config)
{
    int ret = 0;

app_config = config;

dbenv.set_errfile(stderr);
    dbenv.set_errpfx(progname);

/*
     * We can now open our environment.
     */
    dbenv.set_cachesize(0, CACHESIZE, 0);
    dbenv.set_flags(DB_TXN_NOSYNC, 1);

try {
        dbenv.open(app_config-&gt;home, 
            DB_CREATE | 
            DB_RECOVER |
            DB_INIT_LOCK | 
            DB_INIT_LOG |
            DB_INIT_MPOOL | 
            DB_INIT_TXN, 
            0);
    } catch(DbException dbe) {
        cerr &lt;&lt; "Caught an exception during DB environment open." &lt;&lt; endl
            &lt;&lt; "Ensure that the home directory is created prior to"
            &lt;&lt; " starting the application." &lt;&lt; endl;
        ret = ENOENT;
        goto err;
    }

err:
    return ret;
}  </pre>
        <p>
        Finally, we present the <code class="methodname">SimpleTxn::terminate()</code>
        method here. All this does is close the environment handle. Again,
        there should be no surprises here, but we provide the
        implementation for the sake of completeness anyway.
</p>
        <pre class="programlisting">int SimpleTxn::terminate()
{
    try {
        dbenv.close(0);
    } catch (DbException dbe) {
        cerr &lt;&lt; "error closing environment: " &lt;&lt; dbe.what() &lt;&lt; endl;
    }
    return 0;
}  </pre>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="doloop_cxx"></a>Method: SimpleTxn::doloop()</h3>
            </div>
          </div>
        </div>
        <p>
                        Having written our <code class="function">main()</code>
                        function and support utility methods, we now implement 
                        our application's
                        primary data processing method. This
                        method provides a command prompt at which the
                        user can enter a stock ticker value and a price for
                        that value. This information is then entered to the
                        database.
                    </p>
        <p>
                            To display the database, simply enter
                            <code class="literal">return</code> at the prompt.
                    </p>
        <p>
                        To begin, we declare a database pointer,
                        several <code class="classname">Dbt</code> variables, and
                        the usual assortment of variables used for buffers
                        and return codes. We also initialize all of this.
                    </p>
        <pre class="programlisting">#define BUFSIZE 1024
int SimpleTxn::doloop()
{
    Db *dbp;
    Dbt key, data;
    char buf[BUFSIZE], *rbuf;
    int ret;

dbp = NULL;
    memset(&amp;key, 0, sizeof(key));
    memset(&amp;data, 0, sizeof(data));
    ret = 0;  </pre>
        <p>
                    Next, we begin the loop and we immediately open our
                    database if it has not already been opened. Notice that
                    we specify autocommit when we open the database. In
                    this case, autocommit is important because we will only
                    ever write to our database using it. There is no need
                    for explicit transaction handles and commit/abort code
                    in this application, because we are not combining
                    multiple database operations together under a single
                    transaction.
                </p>
        <p>
                    Autocommit is described in greater detail in the 
                    <em class="citetitle">Berkeley DB Getting Started with Transaction Processing</em> guide.
                </p>
        <pre class="programlisting">    for (;;) {
        if (dbp == NULL) {
            dbp = new Db(&amp;dbenv, 0);

try {
                dbp-&gt;open(NULL, DATABASE, NULL, DB_BTREE,
                    DB_CREATE | DB_AUTO_COMMIT, 0);
            } catch(DbException dbe) {
                dbenv.err(ret, "DB-&gt;open");
                throw dbe;
            }
        }  </pre>
        <p>
            Now we implement our command prompt. This is a simple and not
            very robust implementation of a command prompt.
            If the user enters the keywords <code class="literal">exit</code>
            or <code class="literal">quit</code>, the loop is exited and the
            application ends. If the user enters nothing and instead simply
            presses <code class="literal">return</code>, the entire contents of the
            database is displayed. We use our
            <code class="function">print_stocks()</code> method to display the
            database. (That implementation is shown next in this chapter.)
        </p>
        <p>
           Notice that very little error checking is performed on the data
           entered at this prompt.  If the user fails to enter at least one 
            space in the value string, a simple help message is printed and
            the prompt is returned to the user. That is the only error
            checking performed here. In a real-world application,
            at a minimum the application would probably check to ensure
            that the price was in fact an integer or float value. 
            However, in order to keep this example code as simple as
            possible, we refrain from implementing a thorough user interface.
        </p>
        <pre class="programlisting">        cout &lt;&lt; "QUOTESERVER" ;
        cout &lt;&lt; "&gt; " &lt;&lt; flush;

if (fgets(buf, sizeof(buf), stdin) == NULL)
            break;
        if (strtok(&amp;buf[0], " \t\n") == NULL) {
            switch ((ret = print_stocks(dbp))) {
            case 0:
                continue;
            default:
                dbp-&gt;err(ret, "Error traversing data");
                goto err;
            }
        }
        rbuf = strtok(NULL, " \t\n");
        if (rbuf == NULL || rbuf[0] == '\0') {
            if (strncmp(buf, "exit", 4) == 0 ||
                strncmp(buf, "quit", 4) == 0)
                break;
            dbenv.errx("Format: TICKER VALUE");
            continue;
        }  </pre>
        <p>
                Now we assign data to the <code class="classname">Dbt</code>s that
                we will use to write the new information to the database.
            </p>
        <pre class="programlisting">        key.set_data(buf);
        key.set_size((u_int32_t)strlen(buf));

data.set_data(rbuf);
        data.set_size((u_int32_t)strlen(rbuf));  </pre>
        <p>
                Having done that, we can write the new information to the
                database. Remember that this application uses autocommit,
                so no explicit transaction management is required. Also,
                the database is not configured for duplicate records, so
                the data portion of a record is overwritten if the provided
                key already exists in the database. However, in this case
                DB returns <code class="literal">DB_KEYEXIST</code> — which
                we ignore.
            </p>
        <pre class="programlisting">        if ((ret = dbp-&gt;put(NULL, &amp;key, &amp;data, 0)) != 0)
        {
            dbp-&gt;err(ret, "DB-&gt;put");
            if (ret != DB_KEYEXIST)
                goto err;
        }
    }  </pre>
        <p>
            Finally, we close our database before returning from the
            method.
        </p>
        <pre class="programlisting">err:    if (dbp != NULL) {
        (void)dbp-&gt;close(DB_NOSYNC);
        cout &lt;&lt; "database closed" &lt;&lt; endl;
        }

return (ret);
}  </pre>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="printstocks_c"></a>
                            
                            <span>Method: SimpleTxn::print_stocks()</span>
                            
                    </h3>
            </div>
          </div>
        </div>
        <p>
                        The <code class="function">print_stocks()</code> 
                          
                        
                        <span>method</span>
                        simply takes a database handle, opens a cursor, and uses 
                        it to display all the information it finds in a database.
                        This is trivial cursor operation that should hold
                        no surprises for you. We simply provide it here for
                        the sake of completeness.
                    </p>
        <p>
                        If you are unfamiliar with basic cursor operations,
                        please see the <em class="citetitle">Getting Started with Berkeley DB</em>
                        guide.
                    </p>
        <pre class="programlisting">int SimpleTxn::print_stocks(Db *dbp)
{
    Dbc *dbc;
    Dbt key, data;
#define MAXKEYSIZE  10
#define MAXDATASIZE 20
    char keybuf[MAXKEYSIZE + 1], databuf[MAXDATASIZE + 1];
    int ret, t_ret;
    u_int32_t keysize, datasize;

if ((ret = dbp-&gt;cursor(NULL, &amp;dbc, 0)) != 0) {
        dbp-&gt;err(ret, "can't open cursor");
        return (ret);
    }

memset(&amp;key, 0, sizeof(key));
    memset(&amp;data, 0, sizeof(data));

cout &lt;&lt; "\tSymbol\tPrice" &lt;&lt; endl
        &lt;&lt; "\t======\t=====" &lt;&lt; endl;

for (ret = dbc-&gt;get(&amp;key, &amp;data, DB_FIRST);
        ret == 0;
        ret = dbc-&gt;get(&amp;key, &amp;data, DB_NEXT)) {
        keysize = key.get_size() &gt; MAXKEYSIZE ? MAXKEYSIZE : 
                                   key.get_size();
        memcpy(keybuf, key.get_data(), keysize);
        keybuf[keysize] = '\0';

datasize = data.get_size() &gt;=
            MAXDATASIZE ? MAXDATASIZE : data.get_size();
        memcpy(databuf, data.get_data(), datasize);
        databuf[datasize] = '\0';

cout &lt;&lt; "\t" &lt;&lt; keybuf &lt;&lt; "\t" &lt;&lt; databuf &lt;&lt; endl;
    }
    cout &lt;&lt; endl &lt;&lt; flush;

if ((t_ret = dbc-&gt;close()) != 0 &amp;&amp; ret == 0) {
        cout &lt;&lt; "closed cursor" &lt;&lt; endl;
        ret = t_ret;
    }

switch (ret) {
    case 0:
    case DB_NOTFOUND:
        return (0);
    default:
        return (ret);
    }
}  </pre>
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