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<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.io_service"></a><a class="link" href="io_service.html" title="io_service">io_service</a>
</h3></div></div></div>
<p>
Provides core I/O functionality.
</p>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">io_service</span> <span class="special">:</span>
<span class="identifier">noncopyable</span>
</pre>
<h5>
<a name="boost_asio.reference.io_service.h0"></a>
<span class="phrase"><a name="boost_asio.reference.io_service.types"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.types">Types</a>
</h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<a class="link" href="io_service__id.html" title="io_service::id"><span class="bold"><strong>id</strong></span></a>
</p>
</td>
<td>
<p>
Class used to uniquely identify a service.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service__service.html" title="io_service::service"><span class="bold"><strong>service</strong></span></a>
</p>
</td>
<td>
<p>
Base class for all io_service services.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service__strand.html" title="io_service::strand"><span class="bold"><strong>strand</strong></span></a>
</p>
</td>
<td>
<p>
Provides serialised handler execution.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service__work.html" title="io_service::work"><span class="bold"><strong>work</strong></span></a>
</p>
</td>
<td>
<p>
Class to inform the io_service when it has work to do.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/fork_event.html" title="io_service::fork_event"><span class="bold"><strong>fork_event</strong></span></a>
</p>
</td>
<td>
<p>
Fork-related event notifications.
</p>
</td>
</tr>
</tbody>
</table></div>
<h5>
<a name="boost_asio.reference.io_service.h1"></a>
<span class="phrase"><a name="boost_asio.reference.io_service.member_functions"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.member_functions">Member
Functions</a>
</h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<a class="link" href="io_service/dispatch.html" title="io_service::dispatch"><span class="bold"><strong>dispatch</strong></span></a>
</p>
</td>
<td>
<p>
Request the io_service to invoke the given handler.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/io_service.html" title="io_service::io_service"><span class="bold"><strong>io_service</strong></span></a>
</p>
</td>
<td>
<p>
Constructor.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/notify_fork.html" title="io_service::notify_fork"><span class="bold"><strong>notify_fork</strong></span></a>
</p>
</td>
<td>
<p>
Notify the io_service of a fork-related event.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/poll.html" title="io_service::poll"><span class="bold"><strong>poll</strong></span></a>
</p>
</td>
<td>
<p>
Run the io_service object's event processing loop to execute ready
handlers.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/poll_one.html" title="io_service::poll_one"><span class="bold"><strong>poll_one</strong></span></a>
</p>
</td>
<td>
<p>
Run the io_service object's event processing loop to execute one
ready handler.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/post.html" title="io_service::post"><span class="bold"><strong>post</strong></span></a>
</p>
</td>
<td>
<p>
Request the io_service to invoke the given handler and return immediately.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/reset.html" title="io_service::reset"><span class="bold"><strong>reset</strong></span></a>
</p>
</td>
<td>
<p>
Reset the io_service in preparation for a subsequent run() invocation.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/run.html" title="io_service::run"><span class="bold"><strong>run</strong></span></a>
</p>
</td>
<td>
<p>
Run the io_service object's event processing loop.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/run_one.html" title="io_service::run_one"><span class="bold"><strong>run_one</strong></span></a>
</p>
</td>
<td>
<p>
Run the io_service object's event processing loop to execute at
most one handler.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/stop.html" title="io_service::stop"><span class="bold"><strong>stop</strong></span></a>
</p>
</td>
<td>
<p>
Stop the io_service object's event processing loop.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/stopped.html" title="io_service::stopped"><span class="bold"><strong>stopped</strong></span></a>
</p>
</td>
<td>
<p>
Determine whether the io_service object has been stopped.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/wrap.html" title="io_service::wrap"><span class="bold"><strong>wrap</strong></span></a>
</p>
</td>
<td>
<p>
Create a new handler that automatically dispatches the wrapped
handler on the io_service.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/_io_service.html" title="io_service::~io_service"><span class="bold"><strong>~io_service</strong></span></a>
</p>
</td>
<td>
<p>
Destructor.
</p>
</td>
</tr>
</tbody>
</table></div>
<h5>
<a name="boost_asio.reference.io_service.h2"></a>
<span class="phrase"><a name="boost_asio.reference.io_service.friends"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.friends">Friends</a>
</h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<a class="link" href="io_service/add_service.html" title="io_service::add_service"><span class="bold"><strong>add_service</strong></span></a>
</p>
</td>
<td>
<p>
Add a service object to the io_service.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/has_service.html" title="io_service::has_service"><span class="bold"><strong>has_service</strong></span></a>
</p>
</td>
<td>
<p>
Determine if an io_service contains a specified service type.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service/use_service.html" title="io_service::use_service"><span class="bold"><strong>use_service</strong></span></a>
</p>
</td>
<td>
<p>
Obtain the service object corresponding to the given type.
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
The <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a>
class provides the core I/O functionality for users of the asynchronous I/O
objects, including:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span></code>
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">acceptor</span></code>
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">socket</span></code>
</li>
<li class="listitem">
<a class="link" href="deadline_timer.html" title="deadline_timer"><code class="computeroutput"><span class="identifier">deadline_timer</span></code></a>.
</li>
</ul></div>
<p>
The <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a>
class also includes facilities intended for developers of custom asynchronous
services.
</p>
<h5>
<a name="boost_asio.reference.io_service.h3"></a>
<span class="phrase"><a name="boost_asio.reference.io_service.thread_safety"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.thread_safety">Thread
Safety</a>
</h5>
<p>
<span class="emphasis"><em>Distinct</em></span> <span class="emphasis"><em>objects:</em></span> Safe.
</p>
<p>
<span class="emphasis"><em>Shared</em></span> <span class="emphasis"><em>objects:</em></span> Safe, with the
specific exceptions of the <code class="computeroutput"><span class="identifier">reset</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">notify_fork</span><span class="special">()</span></code> functions. Calling <code class="computeroutput"><span class="identifier">reset</span><span class="special">()</span></code> while there are unfinished <code class="computeroutput"><span class="identifier">run</span><span class="special">()</span></code>,
<code class="computeroutput"><span class="identifier">run_one</span><span class="special">()</span></code>,
<code class="computeroutput"><span class="identifier">poll</span><span class="special">()</span></code>
or <code class="computeroutput"><span class="identifier">poll_one</span><span class="special">()</span></code>
calls results in undefined behaviour. The <code class="computeroutput"><span class="identifier">notify_fork</span><span class="special">()</span></code> function should not be called while any
<a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a>
function, or any function on an I/O object that is associated with the <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a>,
is being called in another thread.
</p>
<h5>
<a name="boost_asio.reference.io_service.h4"></a>
<span class="phrase"><a name="boost_asio.reference.io_service.synchronous_and_asynchronous_operations"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.synchronous_and_asynchronous_operations">Synchronous
and asynchronous operations</a>
</h5>
<p>
Synchronous operations on I/O objects implicitly run the <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> object for an individual
operation. The <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> functions <code class="computeroutput"><span class="identifier">run</span><span class="special">()</span></code>,
<code class="computeroutput"><span class="identifier">run_one</span><span class="special">()</span></code>,
<code class="computeroutput"><span class="identifier">poll</span><span class="special">()</span></code>
or <code class="computeroutput"><span class="identifier">poll_one</span><span class="special">()</span></code>
must be called for the <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> to perform asynchronous
operations on behalf of a C++ program. Notification that an asynchronous
operation has completed is delivered by invocation of the associated handler.
Handlers are invoked only by a thread that is currently calling any overload
of <code class="computeroutput"><span class="identifier">run</span><span class="special">()</span></code>,
<code class="computeroutput"><span class="identifier">run_one</span><span class="special">()</span></code>,
<code class="computeroutput"><span class="identifier">poll</span><span class="special">()</span></code>
or <code class="computeroutput"><span class="identifier">poll_one</span><span class="special">()</span></code>
for the <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a>.
</p>
<h5>
<a name="boost_asio.reference.io_service.h5"></a>
<span class="phrase"><a name="boost_asio.reference.io_service.effect_of_exceptions_thrown_from_handlers"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.effect_of_exceptions_thrown_from_handlers">Effect
of exceptions thrown from handlers</a>
</h5>
<p>
If an exception is thrown from a handler, the exception is allowed to propagate
through the throwing thread's invocation of <code class="computeroutput"><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">poll_one</span><span class="special">()</span></code>. No other threads that are calling any
of these functions are affected. It is then the responsibility of the application
to catch the exception.
</p>
<p>
After the exception has been caught, the <code class="computeroutput"><span class="identifier">run</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">run_one</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">poll</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">poll_one</span><span class="special">()</span></code> call may be restarted <span class="emphasis"><em>without</em></span>
the need for an intervening call to <code class="computeroutput"><span class="identifier">reset</span><span class="special">()</span></code>. This allows the thread to rejoin the
<a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a>
object's thread pool without impacting any other threads in the pool.
</p>
<p>
For example:
</p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span> <span class="identifier">io_service</span><span class="special">;</span>
<span class="special">...</span>
<span class="keyword">for</span> <span class="special">(;;)</span>
<span class="special">{</span>
<span class="keyword">try</span>
<span class="special">{</span>
<span class="identifier">io_service</span><span class="special">.</span><span class="identifier">run</span><span class="special">();</span>
<span class="keyword">break</span><span class="special">;</span> <span class="comment">// run() exited normally</span>
<span class="special">}</span>
<span class="keyword">catch</span> <span class="special">(</span><span class="identifier">my_exception</span><span class="special">&</span> <span class="identifier">e</span><span class="special">)</span>
<span class="special">{</span>
<span class="comment">// Deal with exception as appropriate.</span>
<span class="special">}</span>
<span class="special">}</span>
</pre>
<h5>
<a name="boost_asio.reference.io_service.h6"></a>
<span class="phrase"><a name="boost_asio.reference.io_service.stopping_the_io_service_from_running_out_of_work"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.stopping_the_io_service_from_running_out_of_work">Stopping
the io_service from running out of work</a>
</h5>
<p>
Some applications may need to prevent an <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> object's <code class="computeroutput"><span class="identifier">run</span><span class="special">()</span></code> call
from returning when there is no more work to do. For example, the <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> may be being run in a
background thread that is launched prior to the application's asynchronous
operations. The <code class="computeroutput"><span class="identifier">run</span><span class="special">()</span></code>
call may be kept running by creating an object of type <a class="link" href="io_service__work.html" title="io_service::work"><code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">work</span></code></a>:
</p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span> <span class="identifier">io_service</span><span class="special">;</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">work</span> <span class="identifier">work</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">);</span>
<span class="special">...</span>
</pre>
<p>
To effect a shutdown, the application will then need to call the <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> object's <code class="computeroutput"><span class="identifier">stop</span><span class="special">()</span></code>
member function. This will cause the <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> <code class="computeroutput"><span class="identifier">run</span><span class="special">()</span></code> call to return as soon as possible, abandoning
unfinished operations and without permitting ready handlers to be dispatched.
</p>
<p>
Alternatively, if the application requires that all operations and handlers
be allowed to finish normally, the work object may be explicitly destroyed.
</p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span> <span class="identifier">io_service</span><span class="special">;</span>
<span class="identifier">auto_ptr</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">work</span><span class="special">></span> <span class="identifier">work</span><span class="special">(</span>
<span class="keyword">new</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">work</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">));</span>
<span class="special">...</span>
<span class="identifier">work</span><span class="special">.</span><span class="identifier">reset</span><span class="special">();</span> <span class="comment">// Allow run() to exit. </span>
</pre>
<h5>
<a name="boost_asio.reference.io_service.h7"></a>
<span class="phrase"><a name="boost_asio.reference.io_service.the_io_service_class_and_i_o_services"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.the_io_service_class_and_i_o_services">The
io_service class and I/O services</a>
</h5>
<p>
Class <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a>
implements an extensible, type-safe, polymorphic set of I/O services, indexed
by service type. An object of class <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> must be initialised before
I/O objects such as sockets, resolvers and timers can be used. These I/O
objects are distinguished by having constructors that accept an <code class="computeroutput"><span class="identifier">io_service</span><span class="special">&</span></code>
parameter.
</p>
<p>
I/O services exist to manage the logical interface to the operating system
on behalf of the I/O objects. In particular, there are resources that are
shared across a class of I/O objects. For example, timers may be implemented
in terms of a single timer queue. The I/O services manage these shared resources.
</p>
<p>
Access to the services of an <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> is via three function
templates, <code class="computeroutput"><span class="identifier">use_service</span><span class="special">()</span></code>,
<code class="computeroutput"><span class="identifier">add_service</span><span class="special">()</span></code>
and <code class="computeroutput"><span class="identifier">has_service</span><span class="special">()</span></code>.
</p>
<p>
In a call to <code class="computeroutput"><span class="identifier">use_service</span><span class="special"><</span><span class="identifier">Service</span><span class="special">>()</span></code>, the type argument chooses a service,
making available all members of the named type. If <code class="computeroutput"><span class="identifier">Service</span></code>
is not present in an <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a>, an object of type <code class="computeroutput"><span class="identifier">Service</span></code> is created and added to the <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a>.
A C++ program can check if an <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> implements a particular
service with the function template <code class="computeroutput"><span class="identifier">has_service</span><span class="special"><</span><span class="identifier">Service</span><span class="special">>()</span></code>.
</p>
<p>
Service objects may be explicitly added to an <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> using the function template
<code class="computeroutput"><span class="identifier">add_service</span><span class="special"><</span><span class="identifier">Service</span><span class="special">>()</span></code>.
If the <code class="computeroutput"><span class="identifier">Service</span></code> is already
present, the <a class="link" href="service_already_exists.html" title="service_already_exists"><code class="computeroutput"><span class="identifier">service_already_exists</span></code></a> exception
is thrown. If the owner of the service is not the same object as the <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a>
parameter, the <a class="link" href="invalid_service_owner.html" title="invalid_service_owner"><code class="computeroutput"><span class="identifier">invalid_service_owner</span></code></a> exception
is thrown.
</p>
<p>
Once a service reference is obtained from an <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> object by calling <code class="computeroutput"><span class="identifier">use_service</span><span class="special">()</span></code>,
that reference remains usable as long as the owning <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> object exists.
</p>
<p>
All I/O service implementations have <a class="link" href="io_service__service.html" title="io_service::service"><code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">service</span></code></a> as a public base class.
Custom I/O services may be implemented by deriving from this class and then
added to an <a class="link" href="io_service.html" title="io_service"><code class="computeroutput"><span class="identifier">io_service</span></code></a> using the facilities
described above.
</p>
<h5>
<a name="boost_asio.reference.io_service.h8"></a>
<span class="phrase"><a name="boost_asio.reference.io_service.requirements"></a></span><a class="link" href="io_service.html#boost_asio.reference.io_service.requirements">Requirements</a>
</h5>
<p>
<span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/io_service.hpp</code>
</p>
<p>
<span class="emphasis"><em>Convenience header: </em></span><code class="literal">boost/asio.hpp</code>
</p>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2015 Christopher M.
Kohlhoff<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
</div></td>
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