<html><!-- Created using the cpp_pretty_printer from the dlib C++ library. See http://dlib.net for updates. --><head><title>dlib C++ Library - pipe_ex_2.cpp</title></head><body bgcolor='white'><pre>
<font color='#009900'>// The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt
</font>
<font color='#009900'>/*
This is an example showing how to use the type_safe_union and pipe object from
from the dlib C++ Library to send messages between threads.
In this example we will create a class with a single thread in it. This thread
will receive messages from a pipe object and simply print them to the screen.
The interesting thing about this example is that it shows how to use a pipe and
type_safe_union to create a message channel between threads that can send many
different types of objects in a type safe manner.
Program output:
got a float: 4.567
got a string: string message
got an int: 7
got a string: yet another string message
*/</font>
<font color='#0000FF'>#include</font> <font color='#5555FF'><</font>dlib<font color='#5555FF'>/</font>threads.h<font color='#5555FF'>></font>
<font color='#0000FF'>#include</font> <font color='#5555FF'><</font>dlib<font color='#5555FF'>/</font>pipe.h<font color='#5555FF'>></font>
<font color='#0000FF'>#include</font> <font color='#5555FF'><</font>dlib<font color='#5555FF'>/</font>type_safe_union.h<font color='#5555FF'>></font>
<font color='#0000FF'>#include</font> <font color='#5555FF'><</font>iostream<font color='#5555FF'>></font>
<font color='#0000FF'>using</font> <font color='#0000FF'>namespace</font> dlib;
<font color='#0000FF'>using</font> <font color='#0000FF'>namespace</font> std;
<font color='#009900'>// ----------------------------------------------------------------------------------------
</font>
<font color='#0000FF'>typedef</font> type_safe_union<font color='#5555FF'><</font><font color='#0000FF'><u>int</u></font>, <font color='#0000FF'><u>float</u></font>, std::string<font color='#5555FF'>></font> tsu_type;
<font color='#009900'>/* This is a typedef for the type_safe_union we will be using in this example.
This type_safe_union object is a type-safe analogue of a union declared as follows:
union our_union_type
{
int a;
float b;
std::string c;
};
Note that the above union isn't actually valid C++ code because it contains a
non-POD type. That is, you can't put a std::string or any non-trivial
C++ class in a union. The type_safe_union, however, enables you to store non-POD
types such as the std::string.
*/</font>
<font color='#009900'>// ----------------------------------------------------------------------------------------
</font>
<font color='#0000FF'>class</font> <b><a name='pipe_example'></a>pipe_example</b> : <font color='#0000FF'>private</font> threaded_object
<b>{</b>
<font color='#0000FF'>public</font>:
<b><a name='pipe_example'></a>pipe_example</b><font face='Lucida Console'>(</font>
<font face='Lucida Console'>)</font> :
message_pipe<font face='Lucida Console'>(</font><font color='#979000'>4</font><font face='Lucida Console'>)</font> <font color='#009900'>// This 4 here is the size of our message_pipe. The significance is that
</font> <font color='#009900'>// if you try to enqueue more than 4 messages onto the pipe then enqueue() will
</font> <font color='#009900'>// block until there is room.
</font> <b>{</b>
<font color='#009900'>// start the thread
</font> <font color='#BB00BB'>start</font><font face='Lucida Console'>(</font><font face='Lucida Console'>)</font>;
<b>}</b>
~<b><a name='pipe_example'></a>pipe_example</b> <font face='Lucida Console'>(</font>
<font face='Lucida Console'>)</font>
<b>{</b>
<font color='#009900'>// wait for all the messages to be processed
</font> message_pipe.<font color='#BB00BB'>wait_until_empty</font><font face='Lucida Console'>(</font><font face='Lucida Console'>)</font>;
<font color='#009900'>// Now disable the message_pipe. Doing this will cause all calls to
</font> <font color='#009900'>// message_pipe.dequeue() to return false so our thread will terminate
</font> message_pipe.<font color='#BB00BB'>disable</font><font face='Lucida Console'>(</font><font face='Lucida Console'>)</font>;
<font color='#009900'>// now block until our thread has terminated
</font> <font color='#BB00BB'>wait</font><font face='Lucida Console'>(</font><font face='Lucida Console'>)</font>;
<b>}</b>
<font color='#009900'>// Here we declare our pipe object. It will contain our messages.
</font> dlib::pipe<font color='#5555FF'><</font>tsu_type<font color='#5555FF'>></font> message_pipe;
<font color='#0000FF'>private</font>:
<font color='#009900'>// When we call apply_to_contents() below these are the
</font> <font color='#009900'>// functions which get called.
</font> <font color='#0000FF'><u>void</u></font> <b><a name='operator'></a>operator</b><font face='Lucida Console'>(</font><font face='Lucida Console'>)</font> <font face='Lucida Console'>(</font><font color='#0000FF'><u>int</u></font> val<font face='Lucida Console'>)</font>
<b>{</b>
cout <font color='#5555FF'><</font><font color='#5555FF'><</font> "<font color='#CC0000'>got an int: </font>" <font color='#5555FF'><</font><font color='#5555FF'><</font> val <font color='#5555FF'><</font><font color='#5555FF'><</font> endl;
<b>}</b>
<font color='#0000FF'><u>void</u></font> <b><a name='operator'></a>operator</b><font face='Lucida Console'>(</font><font face='Lucida Console'>)</font> <font face='Lucida Console'>(</font><font color='#0000FF'><u>float</u></font> val<font face='Lucida Console'>)</font>
<b>{</b>
cout <font color='#5555FF'><</font><font color='#5555FF'><</font> "<font color='#CC0000'>got a float: </font>" <font color='#5555FF'><</font><font color='#5555FF'><</font> val <font color='#5555FF'><</font><font color='#5555FF'><</font> endl;
<b>}</b>
<font color='#0000FF'><u>void</u></font> <b><a name='operator'></a>operator</b><font face='Lucida Console'>(</font><font face='Lucida Console'>)</font> <font face='Lucida Console'>(</font>std::string val<font face='Lucida Console'>)</font>
<b>{</b>
cout <font color='#5555FF'><</font><font color='#5555FF'><</font> "<font color='#CC0000'>got a string: </font>" <font color='#5555FF'><</font><font color='#5555FF'><</font> val <font color='#5555FF'><</font><font color='#5555FF'><</font> endl;
<b>}</b>
<font color='#0000FF'><u>void</u></font> <b><a name='thread'></a>thread</b> <font face='Lucida Console'>(</font><font face='Lucida Console'>)</font>
<b>{</b>
tsu_type msg;
<font color='#009900'>// Here we loop on messages from the message_pipe.
</font> <font color='#0000FF'>while</font> <font face='Lucida Console'>(</font>message_pipe.<font color='#BB00BB'>dequeue</font><font face='Lucida Console'>(</font>msg<font face='Lucida Console'>)</font><font face='Lucida Console'>)</font>
<b>{</b>
<font color='#009900'>// Here we call the apply_to_contents() function on our type_safe_union.
</font> <font color='#009900'>// It takes a function object and applies that function object
</font> <font color='#009900'>// to the contents of the union. In our case we have setup
</font> <font color='#009900'>// the pipe_example class as our function object and so below we
</font> <font color='#009900'>// tell the msg object to take whatever it contains and
</font> <font color='#009900'>// call (*this)(contained_object); So what happens here is
</font> <font color='#009900'>// one of the three above functions gets called with the message
</font> <font color='#009900'>// we just got.
</font> msg.<font color='#BB00BB'>apply_to_contents</font><font face='Lucida Console'>(</font><font color='#5555FF'>*</font><font color='#0000FF'>this</font><font face='Lucida Console'>)</font>;
<b>}</b>
<b>}</b>
<font color='#009900'>// Finally, note that since we declared the operator() member functions
</font> <font color='#009900'>// private we need to declare the type_safe_union as a friend of this
</font> <font color='#009900'>// class so that it will be able to call them.
</font> <font color='#0000FF'>friend</font> <font color='#0000FF'>class</font> <b><a name='type_safe_union'></a>type_safe_union</b><font color='#5555FF'><</font><font color='#0000FF'><u>int</u></font>, <font color='#0000FF'><u>float</u></font>, std::string<font color='#5555FF'>></font>;
<b>}</b>;
<font color='#009900'>// ----------------------------------------------------------------------------------------
</font>
<font color='#0000FF'><u>int</u></font> <b><a name='main'></a>main</b><font face='Lucida Console'>(</font><font face='Lucida Console'>)</font>
<b>{</b>
pipe_example pe;
<font color='#009900'>// Make one of our type_safe_union objects
</font> tsu_type msg;
<font color='#009900'>// Treat our msg as a float and assign it 4.567
</font> msg.get<font color='#5555FF'><</font><font color='#0000FF'><u>float</u></font><font color='#5555FF'>></font><font face='Lucida Console'>(</font><font face='Lucida Console'>)</font> <font color='#5555FF'>=</font> <font color='#979000'>4.567f</font>;
<font color='#009900'>// Now put the message into the pipe
</font> pe.message_pipe.<font color='#BB00BB'>enqueue</font><font face='Lucida Console'>(</font>msg<font face='Lucida Console'>)</font>;
<font color='#009900'>// Put a string into the pipe
</font> msg.get<font color='#5555FF'><</font>std::string<font color='#5555FF'>></font><font face='Lucida Console'>(</font><font face='Lucida Console'>)</font> <font color='#5555FF'>=</font> "<font color='#CC0000'>string message</font>";
pe.message_pipe.<font color='#BB00BB'>enqueue</font><font face='Lucida Console'>(</font>msg<font face='Lucida Console'>)</font>;
<font color='#009900'>// And now an int
</font> msg.get<font color='#5555FF'><</font><font color='#0000FF'><u>int</u></font><font color='#5555FF'>></font><font face='Lucida Console'>(</font><font face='Lucida Console'>)</font> <font color='#5555FF'>=</font> <font color='#979000'>7</font>;
pe.message_pipe.<font color='#BB00BB'>enqueue</font><font face='Lucida Console'>(</font>msg<font face='Lucida Console'>)</font>;
<font color='#009900'>// And another string
</font> msg.get<font color='#5555FF'><</font>std::string<font color='#5555FF'>></font><font face='Lucida Console'>(</font><font face='Lucida Console'>)</font> <font color='#5555FF'>=</font> "<font color='#CC0000'>yet another string message</font>";
pe.message_pipe.<font color='#BB00BB'>enqueue</font><font face='Lucida Console'>(</font>msg<font face='Lucida Console'>)</font>;
<font color='#009900'>// the main function won't really terminate here. It will call the destructor for pe
</font> <font color='#009900'>// which will block until all the messages have been processed.
</font><b>}</b>
<font color='#009900'>// ----------------------------------------------------------------------------------------
</font>
</pre></body></html>