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<html><!-- #BeginTemplate "/Templates/tmpl.dwt" --><!-- DW6 --><head><!-- #BeginEditable "doctitle" --> <title>PTypes: multithreading: examples</title><!-- #EndEditable --> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link rel="stylesheet" href="styles.css"></head><body bgcolor="#FFFFFF" leftmargin="40" marginwidth="40"><p><a href="../index.html"><img src="title-20.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.0" border="0"></a> <hr size="1" noshade><!-- #BeginEditable "body" --> <p class="hpath"><a href="index.html">Top</a>: <a href="async.html">Multithreading</a>: Examples </p><p><b>Example 1</b>. This simple example shows the use of mutex objects to safely perform calculation that involves more than one global variable. Note that using the <span class="lang">rwlock</span> class instead of <span class="lang">mutex</span> can improve performance by allowing multiple threads call <span class="lang">avg_get()</span> at once.</p><blockquote> <pre>int avg_sum = 0;int avg_cnt = 0;mutex avg_lock;void avg_add(int v){    scopelock lock(avg_lock);    avg_sum += v;    avg_cnt++;}int avg_get(){    int result;    {        scopelock lock(avg_lock);        if (avg_cnt == 0)            result = 0;        else            result = avg_sum / avg_cnt;    }    return result;}</pre></blockquote><p><br><b>Example 2</b>. A multithreaded TCP server that uses the <span class="lang">jobqueue</span> class to maintain a thread pool - a fixed list of reusable threads that receive job `assignments' from a queue. The code below can be used as a template for a multithreaded network server.</p><blockquote> <pre>#include &lt;ptypes.h&gt;#include &lt;ptime.h&gt;#include &lt;pasync.h&gt;#include &lt;pinet.h&gt;USING_PTYPESconst int testport = 8085;const int maxthreads = 30;const int maxtoken = 4096;const int MSG_MYJOB = MSG_USER + 1;class myjobthread: public thread{protected:    int id;    jobqueue* jq;    virtual void execute();public:    myjobthread(int iid, jobqueue* ijq)        : thread(false), id(iid), jq(ijq)  {}    ~myjobthread()  { waitfor(); }};class myjob: public message{public:    ipstream* client;    myjob(ipstream* iclient)        : message(MSG_MYJOB), client(iclient)  {}    ~myjob()  { delete client; }};void myjobthread::execute(){    bool quit = false;    while (!quit)    {        <span class="comment">// get the next message from the queue</span>        message* msg = jq->getmessage();        try        {            switch (msg->id)            {            case MSG_MYJOB:                {                    ipstream* client = ((myjob*)msg)->client;                    <span class="comment">// read the request line</span>                    string req = lowercase(client->line(maxtoken));                    if (req == "hello")                    {                        <span class="comment">// send our greeting to the client</span>                        client->putline("Hello, " + iptostring(client->get_ip()) + ", nice to see you!");                        client->flush();                        <span class="comment">// log this request</span>                        pout.putf("%t  greeting received from %a, handled by thread %d\n",                            now(), long(client->get_ip()), id);                    }                    client->close();                }                break;            case MSG_QUIT:                <span class="comment">// MSG_QUIT is not used in our example</span>                quit = true;                break;            }        }        catch(exception*)        {            <span class="comment">// the message object must be freed!</span>            delete msg;            throw;        }        delete msg;    }}void servermain(ipstmserver& svr){    jobqueue jq;    tobjlist&lt;myjobthread&gt; threads(true);    <span class="comment">// create the thread pool</span>    int i;    for(i = 0; i < maxthreads; i++)    {        myjobthread* j = new myjobthread(i + 1, &jq);        j->start();        threads.add(j);    }    ipstream* client = new ipstream();    pout.putf("Ready to answer queries on port %d\n", testport);    while(true)    {        svr.serve(*client);        if (client->get_active())        {            <span class="comment">// post the job to the queue; the client object will be freed            // automatically by the job object</span>            jq.post(new myjob(client));            client = new ipstream();        }    }}int main(){    ipstmserver svr;    try    {        <span class="comment">// bind to all local addresses on port 8085</span>        svr.bindall(testport);        <span class="comment">// enter an infinite loop of serving requests</span>        servermain(svr);    }    catch(estream* e)    {        perr.putf("FATAL: %s\n", pconst(e->get_message()));        delete e;    }    return 0;}</pre></blockquote><p class="seealso">See also: <a href="async.thread.html">thread</a>, <a href="async.mutex.html">mutex</a>, <a href="async.rwlock.html">rwlock</a>, <a href="async.jobqueue.html">jobqueue</a>, <a href="async.message.html">message</a>, <a href="inet.examples.html">Networking examples</a></p><!-- #EndEditable --><hr size="1"><a href="../index.html" class="ns">PTypes home</a></body><!-- #EndTemplate --></html>
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