prog_internet/prog_internet_03.xhtml

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   7     <title>Programmation Internet</title>
   8
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  12           content="Copyright &#169; 2013 Kim Nguyễn" />
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  42   </head>
  43   <body>
  44
  45     <div class="sws-slide sws-cover sws-option-nofooter">
  46       <h1>Programmation Internet</h1>
  47       <h1>Cours 2</h1>
  48       <a href="mailto:kn@lri.fr">kn@lri.fr</a><br/>
  49       <a href="http://www.lri.fr/~kn/">http://www.lri.fr/~kn</a>
  50     </div>
  51
  52     <div class="sws-slide" >
  53       <h1> Plan </h1>
  54       <ol >
  55         <li> Systèmes d'exploitation &#10004;
  56           <li class="hi"> Réseau et Internet
  57             <ul class="empty">
  58               <li class="hi"> 2.1 Principes des réseaux</li>
  59               <li> 2.2 TCP/IP</li>
  60               <li> 3
  61             </ul>
  62         </li>
  63       </ol>
  64     </div>
  65
  66     <div class="sws-slide">
  67       <h1> Définitions </h1>
  68       <table class="desc">
  69         <tr>
  70           <td style="width:6.5em;">Programme</td> <td>séquences d'instructions effectuant
  71             une tâche sur un ordinateur</td>
  72         </tr>
  73         <tr>
  74           <td>Exécutable</td> <td>fichier binaire contenant des
  75             instructions machines interprétables par le
  76             microprocesseur</td>
  77         </tr>
  78         <tr>
  79           <td><i>Thread</i> </td>
  80           <td>plus petite unité de traitement (≡
  81             séquence d'instructions) pouvant être ordonnancée par
  82             l'OS
  83           </td>
  84         </tr>
  85         <tr>
  86           <td>Processus</td>
  87           <td> instance d'un programme (≡ « un
  88             programme en cours d'exécution »). Un processus est constitué
  89             de un ou plusieurs <i>threads</i>.</td>
  90         </tr>
  91       </table>
  92     </div>
  93
  94     <div class="sws-slide">
  95       <h1> Exemple: programme </h1>
  96       <p>Dans un fichier « <code> counter.c </code> »
  97         (<span style="color:red;">attention c'est du pseudo
  98           C</span>)</p>
  99       <div style="float:left;clear:both;vertical-align:top;width:45%;display:inline-block;border-right: 1pt solid #494948;">
 100 <code > int count = 0;
 101  int exit = 0;
 102  void <span style="color:green;">display()</span> {
 103     while (exit == 0) {
 104       sleep (3);
 105       printf("%i\n", count);
 106     }
 107  }
 108  void <span style="color:red;">listen()</span> {
 109     while (exit == 0) {
 110       wait_connect(80);
 111       count++;
 112   }
 113  }</code>
 114       </div> <div style="vertical-align:top;display:inline-block;width:45%;">
 115 <code> void <span style="color:blue;">main ()</span> {
 116     run_function(display);
 117     run_function(listen);
 118     while (getc () != '\n') { };
 119     exit = 1;
 120     return;
 121  }</code>
 122       </div>
 123     </div>
 124     <div class="sws-slide">
 125       <h1> Exemple: programme </h1>
 126       <p>Compilation <br/>
 127         <code>
 128           gcc -o counter.exe counter.c
 129         </code><br/>
 130         Le <em>fichier</em> « <code>counter.exe</code> » est un
 131         exécutable (fichier binaire contenant du code machine)<br/>
 132         <code>
 133           ./counter.exe <span style="margin-left:2em;font-size:smaller;color:red;"> ← il faut la permission +x sur le fichier</span>
 134         </code>
 135         <br/>
 136         Le contenu de l'exécutable est copié en mémoire et le processeur
 137         commence à exécuter la première instruction du programme.
 138       </p>
 139     </div>
 140     <div class="sws-slide">
 141       <h1> Exemple: <i>threads</i> </h1>
 142       <ol>
 143         <li class="sws-pause" ><span style="color:white;background:blue">main</span> </li>
 144         <li class="sws-pause" ><span style="color:blue;">attente d'un évènement clavier
 145             →</span><span style="color:red;">←changement de <i>thread</i></span>
 146         </li>
 147         <li class="sws-pause" ><span style="color:white;background:red">listen</span> </li>
 148         <li class="sws-pause" ><span style="color:red;">attente de connexion →</span><span style="color:green;">←changement de <i>thread</i></span>
 149         </li>
 150         <li class="sws-pause" ><span style="color:white;background:green">display</span> (<span style="color:green;">affiche
 151             0 à l'écran)</span> </li>
 152         <li class="sws-pause" ><span style="color:green;">attente pendant 3s →</span> (les
 153           3 <i>threads</i> attendent un évènement externe)<br/>
 154           <span class="sws-pause" >nouvelle connexion sur le port 80</span> <span style="color:red;">←
 155             réveil du <i>thread</i> <code style="color:red;">listen</code></span>
 156         </li>
 157         <li class="sws-pause" ><span style="color:white;background:red">listen</span>
 158           (<span style="color:red;">incrémente <code style="color:red">count</code></span>)<br/>
 159           <span style="color:red;">attente de connexion →</span><br/>
 160           <span>… fin des 3s</span><br/>
 161           <span style="color:green;">←
 162             réveil du <i>thread</i> <code style="color:green;">display</code></span>
 163         </li>
 164         <li class="sws-pause" ><span style="color:white;background:green">display</span> (<span style="color:green;">affiche
 165             1 à l'écran)</span> </li>
 166       </ol>
 167       <p class="sws-pause" >Les <i>threads</i> partagent leur mémoire (variables communes)</p>
 168     </div>
 169     <div class="sws-slide">
 170       <h1>Exemple: processus</h1>
 171       <p>(différence: les processus
 172         <em>ne partagent pas leur espace mémoire</em>)</p>
 173       <ol>
 174         <li>Exécution de <code><span style="color:blue;">coun</span><span style="color:red;">ter</span><span style="color:green;">.exe</span></code> pendant 50㎲
 175         </li>
 176         <li > Exécution
 177           de <code><span style="color:orange;">firefox.exe</span></code>
 178           pendant 50㎲ </li>
 179         <li > Exécution du processus qui dessine le bureau pendant 50
 180           ㎲<br/> … </li>
 181
 182       </ol>
 183       <p>C'est le <em>gestionnaire de processus</em> qui décide quel
 184         programme a la main et pour combien de temps (priorité aux
 185         tâches critiques par exemple)<br/>
 186         Le système d'exploitation stocke pour chaque processus un
 187         ensemble d'informations, le PCB (<i>Process Control Block</i>).
 188       </p>
 189     </div>
 190     <div class="sws-slide">
 191       <h1>Proccess Control Block</h1>
 192       <p>Le PCB contient:</p>
 193       <ul>
 194         <li>l'<em>identificateur du processus</em> (pid)</li>
 195         <li>l'<em>l'état</em> du processus (en attente, en exécution,
 196           bloqué, …)</li>
 197         <li>le compteur d'instructions (<i>i.e.</i> où on en est dans
 198           le programme)</li>
 199         <li>le <em>contexte courant</em>(état des registres, …)</li>
 200         <li>position dans <em>la file d'attente de priorité
 201             globale</em></li>
 202         <li>informations mémoire (zones allouées, zones accessibles,
 203           zones partagées)</li>
 204         <li>listes des fichiers ouverts (en lecture, en écriture),
 205           liste des connexions ouvertes, … <br/> … </li>
 206       </ul>
 207     </div>
 208     <div class="sws-slide">
 209       <h1>Opérations sur les processus</h1>
 210       <ul>
 211         <li><em>création</em> et <em>destruction</em> de
 212           processus</li>
 213         <li><em>suspension</em> et <em>reprise</em></li>
 214         <li><em>duplication</em> (<i>fork</i>)</li>
 215         <li>modification de la <em>priorité</em></li>
 216         <li>modification des <em>permissions </em></li>
 217       </ul>
 218     </div>
 219     <div class="sws-slide">
 220       <h1>États d'un processus</h1>
 221       <p>Un processus change d'état au cours de son exécution</p>
 222       <table class="desc">
 223         <tr><td style="width:6em;">Nouveau</td> <td>le processus est en cours de création</td></tr>
 224         <tr><td>Exécution</td> <td>le processus s'exécute</td></tr>
 225         <tr><td>En attente</td> <td>le processus attend un évènement
 226             particulier (saisie au clavier, écriture sur le disque,
 227             …)</td></tr>
 228         <tr><td>Prêt</td> <td>le processus est prêt à reprendre son
 229             exécution et attend que l'OS lui rende la main</td></tr>
 230         <tr><td>terminé</td> <td>le processus a fini son exécution</td></tr>
 231       </table>
 232     </div>
 233     <div class="sws-slide">
 234       <h1>États d'un processus</h1>
 235       <p>L'OS détermine et modifie l'état d'un processus:</p>
 236       <ul>
 237         <li>En fonction d'évènements internes au processus:
 238           <ul><li>lecture d'un fichier (si le contenu n'est pas
 239               disponible, le processus passe de « prêt » à « en attente
 240               »)</li>
 241             <li>le processus attends volontairement pendant x
 242               secondes<br/>…</li>
 243           </ul>
 244         </li>
 245         <li>
 246           En fonction d'évènements externes au processus:
 247           <ul><li>un fichier devient disponible</li>
 248             <li>un <i>timer</i> arrive à 0</li>
 249             <li>le matériel déclenche une <em>interruption</em></li>
 250           </ul>
 251         </li>
 252       </ul>
 253     </div>
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 255       <h1>États d'un processus</h1>
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 487     <div class="sws-slide">
 488       <h1>La commande <code><em>ps</em></code></h1>
 489       <p>Permet d'avoir des informations sur les processus en cours
 490         d'exécution (voir « <code>man ps</code> » pour les
 491         options):<br/>
 492         <code>$ ps -o user,pid,state,cmd x
 493           USER     PID   S CMD
 494           …
 495           kim      27030 Z [chrome] &lt;defunct&gt;
 496           kim      27072 S /opt/google/chrome/chrome --type=renderer
 497           kim      29146 S bash
 498           kim      29834 S evince
 499           kim      29858 S emacs cours.xhtml
 500           kim      29869 R ps -o user,pid,state,cmd x
 501         </code><br/>
 502       </p>
 503
 504     </div>
 505     <div class="sws-slide">
 506       <h1>États des processus (sous Linux)</h1>
 507       <table class="desc">
 508         <tr> <td>R</td> <td> <i>Running</i> (en cours d'exécution)</td> </tr>
 509         <tr> <td>S</td> <td> <i>Interruptible sleep</i> (en attente,
 510             interruptible) </td> </tr>
 511         <tr> <td>D</td> <td> <i>Uninterruptible sleep</i> (en attente,
 512             non-interruptible) </td> </tr>
 513         <tr> <td>T</td> <td> <i>Stopped</i> (interrompu)</td></tr>
 514         <tr> <td>Z</td> <td> <i>Zombie</i> (terminé mais toujours
 515             listé par le système)</td> </tr>
 516       </table>
 517     </div>
 518
 519     <div class="sws-slide">
 520       <h1>Signaux</h1>
 521       <p>L'OS peut envoyer des <em>signaux</em> à un processus. Sur réception
 522         d'un signal, un processus peut interrompre son comportement normal
 523         et exécuter son <em>gestionnaire de signal</em>. Quelques signaux:
 524       </p>
 525       <table class="simple">
 526         <tr><th>Nom</th> <th>Code</th> <th>Description</th> </tr>
 527         <tr><td>HUP</td> <td>1</td> <td>demande au processus de
 528             s'interrompre</td></tr>
 529         <tr><td>INT</td> <td>2</td> <td>demande au processus de se
 530             terminer</td></tr>
 531         <tr><td>ABRT</td> <td>2</td> <td>interrompt le processus et produit
 532             un <i>dump</i></td></tr>
 533         <tr><td>KILL</td> <td>9</td> <td>interrompt le processus immédiatement
 534         </td></tr>
 535         <tr><td>SEGV</td> <td>11</td> <td>signale au processus une erreur mémoire
 536         </td></tr>
 537         <tr><td>STOP</td> <td>24</td> <td>suspend l'exécution du processus
 538         </td></tr>
 539         <tr><td>CONT</td> <td>28</td> <td>reprend l'exécution d'un processus suspendu
 540         </td></tr>
 541       </table>
 542     </div>
 543     <div class="sws-slide">
 544       <h1>Processus et terminal</h1>
 545       <p >Un processus est lié au <em>terminal</em> dans lequel il est
 546         lancé. Si on exécute un programme dans un terminal et que le
 547         processus ne rend pas la main, le terminal est bloqué
 548 <code >
 549
 550  $ gedit
 551
 552 </code>
 553         On peut envoyer au processus le signal <em>STOP</em> en
 554         tapant <code>ctrl-Z</code> dans le terminal:
 555 <code>
 556
 557  $ gedit
 558  ^Z
 559  [1]+  Stopped            gedit
 560
 561 </code>
 562         Le processus est suspendu, la fenêtre est gelée (ne répond plus).
 563       </p>
 564     </div>
 565     <div class="sws-slide">
 566       <h1>Processus et terminal</h1>
 567       <p> <span>On peut reprendre l'exécution du programme de deux
 568           manières:<br/>
 569           <code> $ fg </code><br/>
 570           Reprend l'exécution du processus et le remet en avant plan (terminal
 571           bloqué)</span><br/>
 572         <span class="sws-pause"><code> $ bg </code><br/>
 573           Reprend l'exécution du processus et le remet en arrière plan (terminal
 574 libre)</span><br/>
 575         <span class="sws-pause">On peut lancer un programme
 576           directement en arrière plan en faisant:<br/>
 577 <code> $ gedit &amp; </code><br/></span>
 578         <span class="sws-pause">On peut envoyer un signal à un
 579           processus avec la commande «&nbsp;<code>kill [-signal] pid</code>&nbsp;»<br/>
 580 <code> $ kill -9 2345  </code></span>
 581         </p>
 582         </div>
 583     <div class="sws-slide">
 584       <h1>Processus et entrées/sorties</h1>
 585       <p>Le terminal et le processus sont liés par trois fichiers
 586       spéciaux:</p>
 587       <ol>
 588         <li> L'entrée standard (<code><em>stdin</em></code>), reliée
 589           au clavier</li>
 590         <li> La sortie standard (<code><em>stdout</em></code>), reliée
 591           à l'affichage</li>
 592         <li> La sortie d'erreur (<code><em>stderr</em></code>), reliée
 593           à l'affichage</li>
 594       </ol>
 595       <p>Dans le <i>shell</i>, on peut utiliser les
 596       opérateurs <code><em>&lt;</em></code>, <code><em>&gt;</em></code>
 597       et <code><em>2&gt;</em></code> pour récupérer le contenu
 598       de <code><em>stdin</em></code>, <code><em>stdout</em></code>
 599       et <code><em>stderr</em></code>:<br/>
 600 <code>
 601 $ sort &lt; toto.txt
 602 $ ls -l  &gt; liste_fichiers.txt
 603 $ ls -l * 2&gt; erreurs.txt
 604 </code>
 605 </p>
 606 </div>
 607     <div class="sws-slide">
 608       <h1>Processus et entrées/sorties</h1>
 609       <p>Dans le <i>shell</i>, l'opérateur <em>|</em> permet
 610       d'enchaîner la sortie d'un programme avec l'entrée d'un
 611       autre:<br/>
 612 <code> $ <span style="color:green;">ls -l *.txt</span> | <span style="color:blue">sort -n -r -k 5</span> | <span style="color:orange">head -n 1</span></code>
 613       </p>
 614       <ol>
 615         <li style="color:green;">affiche la liste détaillée des
 616         fichiers textes</li>
 617         <li style="color:blue;">trie (et affiche) l'entrée standard par ordre
 618         numérique décroissant selon le 5ème champ</li>
 619         <li style="color:orange;">affiche la première ligne de
 620         l'entrée standard</li>
 621       </ol>
 622       <div style="height:5em;position:relative;margin:0 0;padding:0 0;">
 623 <code class="sws-onframe-1" style="position:absolute;color:green;"> -rw-rw-r    1 kim kim 471 Sep 14 16:25 bd.txt
 624  -rw-rw-r    1 kim kim 234 Sep 15 17:46 foo.txt
 625  -rw-rw-r    1 kim kim 1048576 Sep 24 09:20 large.txt</code>
 626 <code class="sws-onframe-2" style="position:absolute;color:blue;"> -rw-rw-r    1 kim kim 1048576 Sep 24 09:20 large.txt
 627  -rw-rw-r    1 kim kim 471 Sep 14 16:25 bd.txt
 628  -rw-rw-r    1 kim kim 234 Sep 15 17:46 foo.txt
 629 </code>
 630 <code class="sws-onframe-3" style="position:absolute;color:orange;"> -rw-rw-r    1 kim kim 1048576 Sep 24 09:20 large.txt
 631 </code>
 632       </div>
 633
 634     </div>
 635 <div class="sws-slide">
 636   <h1>Processus de type <i>daemon</i></h1>
 637 <p>
 638   Un <i>daemon</i> (prononcé démon) est un processus
 639   qui <em>non-interactif</em> qui tourne en tâche de fond (pas
 640   d'entrée/sortie sur le terminal, pas d'interface graphique, …). On
 641   communique avec ce processus via des <em>signaux</em> ou en lisant
 642   ou écrivant dans des fichiers ou connexions réseau. Le plus souvent,
 643   leur but est de fournir un <em>service</em>
 644 </p>
 645 <p>Exemple de scénario: « <i> Les utilisateurs doivent interagir avec
 646     le matériel. L'accès au matériel demande des droits
 647     administrateur.</i> »
 648 </p>
 649 <ul class="empty">
 650   <li>Solution 1 : tout le monde est administrateur (DOS, Win XP,
 651   …)</li>
 652   <li>Solution 2 : on crée un programme particulier qui a les
 653   privilèges suffisants pour la tâche en question. Les utilisateurs
 654   communiquent avec ce programme</li>
 655 </ul>
 656 </div>
 657 <div class="sws-slide">
 658   <h1>Quelques <i>daemons</i> sous Linux</h1>
 659 <table class="simple">
 660 <tr><th>Nom</th> <th>Description</th> </tr>
 661 <tr><td>sshd</td> <td><i>shell</i> distant sécurisé</td> </tr>
 662 <tr><td>crond</td> <td>exécution périodique de programmes</td> </tr>
 663 <tr><td>cupsd</td> <td>serveur d'impressions</td> </tr>
 664 <tr><td>pulseaudio</td> <td>serveur de son (mixe les sons des
 665     différentes applications)</td> </tr>
 666 <tr><td>udevd</td> <td>détection de matériel <i>hotplug</i></td></tr>
 667 <tr><td>nfsd</td> <td>serveur de fichier réseau</td></tr>
 668 <tr><td>smtpd</td> <td>livraison des e-mail</td></tr>
 669 <tr class="sws-pause"><td><em>httpd</em></td> <td>serveur de pages Web</td></tr>
 670 </table>
 671 </div>
 672 <div class="sws-slide">
 673 <h1>Architecture client-serveur</h1>
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1093 <p>
1094   <br/><br/>
1095   Des processus <span style="color:blue;">clients</span> communiquent
1096   avec le <span style="color:orange;">serveur</span> à travers le
1097   réseau. Les clients sont indépendant et ne communiquent pas entre
1098   eux. <em>Attention</em> plusieurs clients peuvent se trouver su la
1099   même machine physique!
1100 </p>
1101 </div>
1102 <div class="sws-slide">
1103   <h1>Architecture client-serveur</h1>
1104 <ul>
1105   <li>Le serveur attend des connexions entrantes</li>
1106   <li>Les clients peuvent se connecter à tout moment</li>
1107   <li>L'application client est généralement légère, envoie une
1108   requête au serveur et attend un résultat</li>
1109   <li>Le serveur est une application plus lourde qui:
1110     <ul><li>effectue des calculs trop coûteux pour le client</li>
1111       <li>gère l'accès à une ressource distante partagée<br/>…</li>
1112     </ul>
1113   </li>
1114 </ul>
1115 <p>Exemples: serveur de bases de données, serveur mail, serveur Web,
1116   terminal de carte bancaire, …</p>
1117 </div>
1118   </body>
1119 </html>