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<title>PTypes: multithreading: examples</title>
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<p><a href="../index.html"><img src="title-21.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.1" border="0"></a>
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<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 <ptypes.h>
#include <ptime.h>
#include <pasync.h>
#include <pinet.h>
USING_PTYPES
const 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<myjobthread> 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>
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