ch4.htm

汤子瀛《操作系统》电子教案

      <p><font color="#FFFFFF"><span lang="EN-US">&nbsp;</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt">4．4．1<span style="mso-spacerun: yes">&nbsp; 
      </span>进程调度<o:p>
      </o:p>
      </span></font></p>
      <p><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><font color="#FFFFFF">一、同构型多处理机系统中的进程调度</font></span></p>
      <p><font color="#FFFFFF"><span lang="EN-US">1</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．静态分配（</span><span lang="EN-US">Static 
      Assignment</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">）</span></font></p>
      <p><font color="#FFFFFF"><span lang="EN-US">2</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．动态分配（</span><span lang="EN-US">Dynamic 
      Assignment</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">）</span></font></p>
      <p><font color="#FFFFFF"><span lang="EN-US">3</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．自调度（</span><span lang="EN-US">Self-Scheduling</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">）</span></font></p>
      <p><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><font color="#FFFFFF">二、异构型多处理机系统中的进程调度</font></span></p>
      <p><span lang="EN-US"><font color="#FFFFFF">&nbsp;<o:p>
      </o:p>
      </font></span></p>
      <p><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><font color="#FFFFFF">4．4．2<span style="mso-spacerun: yes">&nbsp; 
      </span>自调度<o:p>
      </o:p>
      </font></span></p>
      <p><font color="#FFFFFF"><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">（</span><span lang="EN-US">1</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">）自调度方式。系统中有一个公共的线程或进程的就绪队列，所有的处理机在空闲时，都可自己从该队列中取出一个进程或线程运行。</span></font></p>
      <p><font color="#FFFFFF"><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">（</span><span lang="EN-US">2</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">）成组调度。这时由系统将一组相关的进程或线程，同时分配到—组处理机上运行，进程或线程与处理机一—对应。</span></font></p>
      <p><font color="#FFFFFF"><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">（</span><span lang="EN-US">3</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">）专用处理机分配方式。它是将同属于一个应用程序的一组线程，分配到一组处理机上，在应用程序末结束前，处理机专用于处理这组线程。</span></font></p>
      <p><span lang="EN-US"><font color="#FFFFFF">&nbsp;<o:p>
      </o:p>
      </font></span></p>
      <p><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><font color="#FFFFFF">4．4．3 
      成组调度<o:p>
      </o:p>
      </font></span></p>
      <p><font color="#FFFFFF"><span lang="EN-US">1</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．面向所有的应用程序平均分配处理机时间</span></font></p>
      <p><font color="#FFFFFF"><span lang="EN-US">2</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．面向所有的线程平均分配处理机时间</span></font></p>
      <p><span lang="EN-US"><font color="#FFFFFF">&nbsp;<o:p>
      </o:p>
      </font></span></p>
      <p><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><font color="#FFFFFF">4．4．4 
      专用处理机分配<o:p>
      </o:p>
      </font></span></p>
      <p><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><font color="#FFFFFF">把这种调度方式用于并发程度相当高的多处理机环境，是根据下述一些理由：</font></span></p>
      <p><font color="#FFFFFF"><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">（</span><span lang="EN-US">1</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">）在具有数十个乃至数百个处理机的高度并行的系统中，单个处理机的利用率已远不像在单机系统中那么重要。</span></font></p>
      <p><font color="#FFFFFF"><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">（</span><span lang="EN-US">2</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">）可以避免了进程或线程的切换，从而可大大地加速程序的完成。</span></font></p>
      <p><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><font color="#FFFFFF">根据实践证明：在同时加工的应用程序中，其线程数的总和不应超过系统中处理机的数目。</font></span></p>
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      <p style="TEXT-ALIGN: center" align="center"><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><font color="#FFFFFF"><a name="ch46"></a>4．6<span style="mso-spacerun: yes">&nbsp; 
      </span>死锁的基本概念<o:p>
      </o:p>
      </font></span></p>
      <p><font color="#FFFFFF"><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">所谓死锁（</span><span lang="EN-US">Deadlock</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">），是指多个进程因竞争资源而造成的一种僵局，若无外力作用，这些进程都将永远不能再向前推进。</span></font></p>
      <p><span lang="EN-US"><font color="#FFFFFF">&nbsp;<o:p>
      </o:p>
      </font></span></p>
      <p><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><font color="#FFFFFF">4．6．1<span style="mso-spacerun: yes">&nbsp; 
      </span>产生死锁的原因<o:p>
      </o:p>
      </font></span></p>
      <p><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><font color="#FFFFFF">产生死锁的原因可归结为两点：</font></span></p>
      <p style="MARGIN-LEFT: 36pt; TEXT-INDENT: -36pt; mso-list: l25 level1 lfo26; tab-stops: list 36.0pt"><font color="#FFFFFF"><span lang="EN-US" style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">（1）<span style="font-style: normal; font-variant: normal; font-weight: normal">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
      </span></span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">竞争资源。</span></font></p>
      <p style="MARGIN-LEFT: 36pt; TEXT-INDENT: -36pt; mso-list: l25 level1 lfo26; tab-stops: list 36.0pt"><font color="#FFFFFF"><span lang="EN-US" style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">（2）<span style="font-style: normal; font-variant: normal; font-weight: normal">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
      </span></span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">进程推进顺序非法。</span></font></p>
      <p><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><font color="#FFFFFF">一、竞争资源引起死锁</font></span></p>
      <p><font color="#FFFFFF"><span lang="EN-US">1</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．可剥夺和非剥夺性资源</span></font></p>
      <p><font color="#FFFFFF"><span lang="EN-US">2</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．竞争非剥夺促资源</span></font></p>
      <p><font color="#FFFFFF"><span lang="EN-US">3</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．竞争临时性资源</span></font></p>
      <p><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><font color="#FFFFFF">二、进程推进顺序不当引起死锁</font></span></p>
      <p style="MARGIN-LEFT: 15.75pt; TEXT-INDENT: -15.75pt; mso-list: l9 level1 lfo33; tab-stops: list 15.75pt"><font color="#FFFFFF"><span lang="EN-US">1．</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">进程推进顺序合法</span></font></p>
      <p style="MARGIN-LEFT: 15.75pt; TEXT-INDENT: -15.75pt; mso-list: l9 level1 lfo33; tab-stops: list 15.75pt"><font color="#FFFFFF"><span lang="EN-US">2．</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">进程推进顺序非法</span></font></p>
      <p><span lang="EN-US"><font color="#FFFFFF">&nbsp;<o:p>
      </o:p>
      </font></span></p>
      <p><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><font color="#FFFFFF">4．6．2<span style="mso-spacerun: yes">&nbsp; 
      </span>产生死锁的必要条件<o:p>
      </o:p>
      </font></span></p>
      <p><font color="#FFFFFF"><span lang="EN-US">1</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．互斥条件</span></font></p>
      <p><font color="#FFFFFF"><span lang="EN-US">2</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．请求和保持条件</span></font></p>
      <p><font color="#FFFFFF"><span lang="EN-US">3</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．不剥夺条件</span></font></p>
      <p><font color="#FFFFFF"><span lang="EN-US">4</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．环路等待条件</span></font></p>
      <p><span lang="EN-US"><font color="#FFFFFF">&nbsp;<o:p>
      </o:p>
      </font></span></p>
      <p><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><font color="#FFFFFF">4．6．3<span style="mso-spacerun: yes">&nbsp; 
      </span>处理死锁的基本方法<o:p>
      </o:p>
      </font></span></p>
      <p><font color="#FFFFFF"><span lang="EN-US">1</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．预防死锁</span></font></p>
      <p><font color="#FFFFFF"><span lang="EN-US">2</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．避免死锁</span></font></p>
      <p><font color="#FFFFFF"><span lang="EN-US">3</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．检测死锁</span></font></p>
      <p><font color="#FFFFFF"><span lang="EN-US">4</span><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．解除死钡</span></font></p>
      <p><span style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><font color="#FFFFFF">死锁的检测和解除措施，有可能使系统获得较好的资源利用宰相系统吞吐量，但在实现上难度也最大。</font></span></p>
      <p>　</td>
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      <p style="TEXT-ALIGN: center" align="center"><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><font color="#FFFFFF"><a name="ch47"></a>4．7 
      死锁的预防和避免<o:p>
      </o:p>
      </font></span></p>
      <p><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><font color="#FFFFFF">4．7．1<span style="mso-spacerun: yes">&nbsp; 
      </span>死锁的预防<o:p>
      </o:p>
      </font></span></p>
      <p><font color="#FFFFFF"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; m