[boost-doc-zh] r293 committed - [No log message]

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Date: Tue, 25 Aug 2009 03:40:44 +0000

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Date: Mon Aug 24 20:40:18 2009
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http://code.google.com/p/boost-doc-zh/source/detail?r=293

Modified:
 /trunk/doc/html/boost_asio/tutorial/tuttimer5.html

=======================================

--- /trunk/doc/html/boost_asio/tutorial/tuttimer5.html Wed May 27 03:09:502009+++ /trunk/doc/html/boost_asio/tutorial/tuttimer5.html Mon Aug 24 20:40:182009

@@ -1,6 +1,6 @@
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Timer.5 - Synchronising handlers in multithreaded programs</title>
 <link rel="stylesheet" href="../../boostbook.css" type="text/css">
 <meta name="generator" content="DocBook XSL Stylesheets V1.74.3">
@@ -24,41 +24,35 @@
 </div>
 <div class="section" lang="en">
 <div class="titlepage"><div><div><h3 class="title">

-<a name="boost_asio.tutorial.tuttimer5"></a><a class="link"href="tuttimer5.html" title="Timer.5 - Synchronising handlers inmultithreaded programs"> Timer.5 - Synchronising

-      handlers in multithreaded programs</a>

+<a name="boost_asio.tutorial.tuttimer5"></a><a class="link"href="tuttimer5.html" title="Timer.5 - Synchronising handlers inmultithreaded programs"> Timer.5 - 多线程同步回调</a>

 </h3></div></div></div>
 <p>

- This tutorial demonstrates the use of the boost::asio::strandclass to synchronise

-        callback handlers in a multithreaded program.

+ 本示例程序示范了使用boost::asio::strand 类来创建多线程程序中的同步回调句柄。

       </p>
 <p>

- The previous four tutorials avoided the issue of handlersynchronisation- by calling the <a class="link"href="../reference/io_service/run.html"title="io_service::run">io_service::run()</a>- function from one thread only. As you already know, the asiolibrary provides- a guarantee that callback handlers will only be called fromthreads that- are currently calling <a class="link"href="../reference/io_service/run.html"title="io_service::run">io_service::run()</a>.- Consequently, calling <a class="link"href="../reference/io_service/run.html"title="io_service::run">io_service::run()</a>- from only one thread ensures that callback handlers cannot runconcurrently.+ 前四个例程只是在单线程下使用<a class="link"href="../reference/io_service/run.html"title="io_service::run">io_service::run()</a>

+        函数来避免处理函同步。
+         如你所见，Asio库保证回调句柄仅能被当前正在调用

+ <a class="link" href="../reference/io_service/run.html"title="io_service::run">io_service::run()</a>.

+        函数的线程调用。

+ 因此，在单线程中调用<a class="link"href="../reference/io_service/run.html"title="io_service::run">io_service::run()</a>

+        能确保回调句柄不被并发运行。
       </p>
 <p>

- The single threaded approach is usually the best place to startwhen developing- applications using asio. The downside is the limitations it placeson programs,

-        particularly servers, including:

+ 单线程通常是使用Asio开发应用程序最好的方式。下面是Asio在程序中的局限性，尤其是服务器方面，包括：

       </p>
 <div class="itemizedlist"><ul type="disc">
 <li>

- Poor responsiveness when handlers can take a long time tocomplete.

+          操作需要较长时间处理才能完成时弱响应。
         </li>
 <li>
-          An inability to scale on multiprocessor systems.
+         在大规模的多处理机系统中表现不佳。
         </li>
 </ul></div>
 <p>

- If you find yourself running into these limitations, analternative approach- is to have a pool of threads calling <a class="link"href="../reference/io_service/run.html"title="io_service::run">io_service::run()</a>.- However, as this allows handlers to execute concurrently, we needa method- of synchronisation when handlers might be accessing a shared,thread-unsafe

-        resource.

+ 如果你发现自己陷入这些局限时，一个可供选择的方法是创建一个每个线程都调用<a class="link" href="../reference/io_service/run.html"title="io_service::run">io_service::run()</a>

+        的线程池。

+ 不过，因为这允许并发操作，当访问一个共享、非线程安全的资源时，我们需要一个同步方式。

       </p>

<pre class="programlisting">#include<<spanclass="identifier">iostream>#include <spanclass="special"><boost<spanclass="special">/asio<spanclass="special">.hpp<spanclass="special">>

@@ -67,27 +61,21 @@

#include <spanclass="special"><boost<spanclass="special">/date_time<spanclass="special">/posix_time<spanclass="special">/posix_time<spanclass="special">.hpp<spanclass="special">>

 </pre>
 <p>

- We start by defining a class called <codeclass="computeroutput">printer</code>,- similar to the class in the previous tutorial. This class willextend the

-        previous tutorial by running two timers in parallel.

+ 让我们从定义一个名为<code class="computeroutput"><spanclass="identifier">printer</code>的类开始，这与前一个示例中的类很相似。这个类是上一个例子的扩展，这里我们使用两个并行的定时器。

       </p>

<pre class="programlisting">class <spanclass="identifier">printer

 <span class="special">{</span>
 <span class="keyword">public</span><span class="special">:</span>
 </pre>
 <p>

- In addition to initialising a pair of boost::asio::deadline_timermembers,- the constructor initialises the <code class="computeroutput"><spanclass="identifier">strand_</code>

-        member, an object of type boost::asio::strand.

+ 除了初始化一对boost::asio::deadline_timer 成员变量外，构造函数还初始化一个boost::asio::strand类型<code class="computeroutput"><spanclass="identifier">strand_</code>

+        成员变量。
       </p>
 <p>

- An boost::asio::strand guarantees that, for those handlers thatare dispatched- through it, an executing handler will be allowed to completebefore the next- one is started. This is guaranteed irrespective of the number ofthreads- that are calling <a class="link"href="../reference/io_service/run.html"title="io_service::run">io_service::run()</a>.- Of course, the handlers may still execute concurrently with otherhandlers- that were not dispatched through an boost::asio::strand, or weredispatched

-        through a different boost::asio::strand object.

+ boost::asio::strand 对象保证：对于通过它来分派执行的众操作中，只有一个操作执行完成之后才允许进入下一个操作。+ 这种保证与多少个线程调用<a class="link"href="../reference/io_service/run.html"title="io_service::run">io_service::run()</a>

+        无关。当然，如果不是通过一个boost::asio::strand对象分派，

+ 或者通过其它不同的boost::asio::strand对象分派，这些操作仍旧可能是并发的。

       </p>

<pre class="programlisting"> printer<spanclass="special">(boost<spanclass="special">::asio<spanclass="special">::io_service<spanclass="special">& io<spanclass="special">): <spanclass="identifier">strand_(<spanclass="identifier">io),

@@ -97,12 +85,9 @@
   <span class="special">{</span>
 </pre>
 <p>

- When initiating the asynchronous operations, each callback handleris "wrapped"- using the boost::asio::strand object. The <a class="link"href="../reference/io_service__strand/wrap.html"title="io_service::strand::wrap">strand::wrap()</a>- function returns a new handler that automatically dispatches itscontained- handler through the boost::asio::strand object. By wrapping thehandlers- using the same boost::asio::strand, we are ensuring that theycannot execute

-        concurrently.

+ 当开始同步操作时，每一个回调句柄都使用boost::asio::strand对象进行“包装”。<a class="link" href="../reference/io_service__strand/wrap.html"title="io_service::strand::wrap">strand::wrap()</a>

+        函数返回一个新的通过boost::asio::strand对象自动分派的内部句柄。

+ 通过同一boost::asio::strand对象对句柄进行“ 包装”，我们可以保证操作不会并发执行。

       </p>

<pre class="programlisting"> <spanclass="identifier">timer1_.<spanclass="identifier">async_wait(<spanclass="identifier">strand_.<spanclass="identifier">wrap(<spanclass="identifier">boost::<spanclass="identifier">bind(&<spanclass="identifier">printer::<spanclass="identifier">print1, <spanclass="keyword">this)));timer2_<spanclass="special">.async_wait<spanclass="special">(strand_<spanclass="special">.wrap<spanclass="special">(boost<spanclass="special">::bind<spanclass="special">(&printer<spanclass="special">::print2<spanclass="special">, this<spanclass="special">)));

@@ -114,11 +99,9 @@
   <span class="special">}</span>
 </pre>
 <p>

- In a multithreaded program, the handlers for asynchronousoperations should- be synchronised if they access shared resources. In this tutorial,the shared- resources used by the handlers (<code class="computeroutput"><spanclass="identifier">print1</code>- and <code class="computeroutput"><spanclass="identifier">print2</code>) are <codeclass="computeroutput">std<spanclass="special">::cout</code>- and the <code class="computeroutput"><spanclass="identifier">count_</code> data member.+ 在一个多线程程序中，当访问同一共享资源时，异步操作必须是同步的。在本例中，<code class="computeroutput"><spanclass="identifier">print1</code>+ 和<code class="computeroutput"><spanclass="identifier">print2</code>)函数使用的共享资源<codeclass="computeroutput">std<spanclass="special">::cout</code>+ 和<code class="computeroutput"><spanclass="identifier">count_</code>数据成员。

       </p>

<pre class="programlisting"> void <spanclass="identifier">print1()

   <span class="special">{</span>
@@ -152,15 +135,12 @@
 <span class="special">};</span>
 </pre>
 <p>

- The <code class="computeroutput"><spanclass="identifier">main</code> function now causes+ <code class="computeroutput"><spanclass="identifier">main</code>函数中，<a class="link" href="../reference/io_service/run.html"title="io_service::run">io_service::run()</a>- to be called from two threads: the main thread and one additionalthread.

-        This is accomplished using an boost::thread object.

+ 现在被两个线程调用：主线程和一个附加线程。这一切依赖于boost::thread对象来完成。

       </p>
 <p>

- Just as it would with a call from a single thread, concurrentcalls to <a class="link" href="../reference/io_service/run.html"title="io_service::run">io_service::run()</a> will- continue to execute while there is "work" left to do. Thebackground- thread will not exit until all asynchronous operations havecompleted.+ 正如它被一个单线程调用一样，<a class="link"href="../reference/io_service/run.html"title="io_service::run">io_service::run()</a>的并发调用会一直持续到无任何“工作”可做。后台线程直到所有异步操作都完成后才会退出。

       </p>

<pre class="programlisting">int <spanclass="identifier">main()

 <span class="special">{</span>
@@ -174,14 +154,13 @@
 <span class="special">}</span>
 </pre>
 <p>

- See the <a class="link" href="tuttimer5/src.html" title="Sourcelisting for Timer.5">full source listing</a>+ 查看<a class="link" href="tuttimer5/src.html" title="Sourcelisting for Timer.5">本例全部源代码</a>

       </p>
 <p>

- Return to the <a class="link" href="../tutorial.html"title="Tutorial">tutorial index</a>+ 返回<a class="link" href="../tutorial.html" title="Tutorial">指南</a>

       </p>
 <p>

- Previous: <a class="link" href="tuttimer4.html" title="Timer.4 -Using a member function as a handler">Timer.4 - Using a

-        member function as a handler</a>

+ 前一例: <a class="link" href="tuttimer4.html" title="Timer.4 -Using a member function as a handler">Timer.4 - 成员函数作为回调函数</a>

       </p>
 </div>

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