387 lines
16 KiB
HTML
387 lines
16 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="security" content="public" />
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<meta name="Robots" content="index,follow" />
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<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Examples: Using semaphores and shared memory" />
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<meta name="abstract" content="These two examples illustrate programs that support the client/server model." />
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<meta name="description" content="These two examples illustrate programs that support the client/server model." />
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<meta name="DC.Relation" scheme="URI" content="apiexmp.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="apiexusmem" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Examples: Using semaphores and shared memory</title>
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</head>
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<body id="apiexusmem"><a name="apiexusmem"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Examples: Using semaphores and shared memory</h1>
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<div><p>These two examples illustrate programs that support the client/server
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model.</p>
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<div class="section"><div class="note"><span class="notetitle">Note:</span> Read the <a href="codedisclaimer.htm">Code license and disclaimer information</a> for important
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legal information.</div>
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</div>
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<div class="section" id="apiexusmem__HDRIPCSRV"><a name="apiexusmem__HDRIPCSRV"><!-- --></a><h4 class="sectiontitle">Server program</h4><p>This program acts
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as a server to the client program (see <a href="#apiexusmem__HDRIPCCLI">Client program</a>).
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The buffer is a shared memory segment. The process synchronization is done
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using semaphores.</p>
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<p>Use the Create C Module (CRTCMOD) and the Create Program
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(CRTPGM) commands to create this program.</p>
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<p>Call this program with no
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parameters before calling the client program.</p>
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<pre>/*********************************************************************/
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/*********************************************************************/
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/* */
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/* FUNCTION: This program acts as a server to the client program. */
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/* */
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/* LANGUAGE: ILE C */
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/* */
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/* APIs USED: semctl(), semget(), semop(), */
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/* shmat(), shmctl(), shmdt(), shmget() */
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/* ftok() */
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/* */
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/*********************************************************************/
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/*********************************************************************/
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#include <stdio.h>
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#include <string.h>
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#include <sys/ipc.h>
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#include <sys/sem.h>
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#include <sys/shm.h>
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#define SEMKEYPATH "/dev/null" /* Path used on ftok for semget key */
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#define SEMKEYID 1 /* Id used on ftok for semget key */
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#define SHMKEYPATH "/dev/null" /* Path used on ftok for shmget key */
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#define SHMKEYID 1 /* Id used on ftok for shmget key */
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#define NUMSEMS 2 /* Num of sems in created sem set */
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#define SIZEOFSHMSEG 50 /* Size of the shared mem segment */
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#define NUMMSG 2 /* Server only doing two "receives"
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on shm segment */
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int main(int argc, char *argv[])
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{
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int rc, semid, shmid, i;
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key_t semkey, shmkey;
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void *shm_address;
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struct sembuf operations[2];
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struct shmid_ds shmid_struct;
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short sarray[NUMSEMS];
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/* Generate an IPC key for the semaphore set and the shared */
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/* memory segment. Typically, an application specific path and */
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/* id would be used to generate the IPC key. */
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semkey = ftok(SEMKEYPATH,SEMKEYID);
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if ( semkey == (key_t)-1 )
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{
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printf("main: ftok() for sem failed\n");
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return -1;
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}
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shmkey = ftok(SHMKEYPATH,SHMKEYID);
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if ( shmkey == (key_t)-1 )
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{
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printf("main: ftok() for shm failed\n");
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return -1;
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}
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/* Create a semaphore set using the IPC key. The number of */
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/* semaphores in the set is two. If a semaphore set already */
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/* exists for the key, return an error. The specified permissions*/
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/* give everyone read/write access to the semaphore set. */
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semid = semget( semkey, NUMSEMS, 0666 | IPC_CREAT | IPC_EXCL );
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if ( semid == -1 )
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{
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printf("main: semget() failed\n");
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return -1;
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}
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/* Initialize the first semaphore in the set to 0 and the */
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/* second semaphore in the set to 0. */
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/* */
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/* The first semaphore in the sem set means: */
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/* '1' -- The shared memory segment is being used. */
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/* '0' -- The shared memory segment is freed. */
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/* The second semaphore in the sem set means: */
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/* '1' -- The shared memory segment has been changed by */
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/* the client. */
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/* '0' -- The shared memory segment has not been */
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/* changed by the client. */
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sarray[0] = 0;
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sarray[1] = 0;
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/* The '1' on this command is a no-op, because the SETALL command*/
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/* is used. */
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rc = semctl( semid, 1, SETALL, sarray);
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if(rc == -1)
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{
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printf("main: semctl() initialization failed\n");
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return -1;
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}
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/* Create a shared memory segment using the IPC key. The */
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/* size of the segment is a constant. The specified permissions */
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/* give everyone read/write access to the shared memory segment. */
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/* If a shared memory segment already exists for this key, */
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/* return an error. */
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shmid = shmget(shmkey, SIZEOFSHMSEG, 0666 | IPC_CREAT | IPC_EXCL);
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if (shmid == -1)
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{
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printf("main: shmget() failed\n");
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return -1;
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}
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/* Attach the shared memory segment to the server process. */
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shm_address = shmat(shmid, NULL, 0);
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if ( shm_address==NULL )
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{
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printf("main: shmat() failed\n");
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return -1;
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}
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printf("Ready for client jobs\n");
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/* Loop only a specified number of times for this example. */
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for (i=0; i < NUMMSG; i++)
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{
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/* Set the structure passed into the semop() to first wait */
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/* for the second semval to equal 1, then decrement it to */
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/* allow the next signal that the client writes to it. */
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/* Next, set the first semaphore to equal 1, which means */
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/* that the shared memory segment is busy. */
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operations[0].sem_num = 1;
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/* Operate on the second sem */
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operations[0].sem_op = -1;
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/* Decrement the semval by one */
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operations[0].sem_flg = 0;
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/* Allow a wait to occur */
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operations[1].sem_num = 0;
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/* Operate on the first sem */
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operations[1].sem_op = 1;
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/* Increment the semval by 1 */
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operations[1].sem_flg = IPC_NOWAIT;
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/* Do not allow to wait */
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rc = semop( semid, operations, 2 );
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if (rc == -1)
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{
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printf("main: semop() failed\n");
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return -1;
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}
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/* Print the shared memory contents. */
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printf("Server Received : \"%s\"\n", (char *) shm_address);
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/* Signal the first semaphore to free the shared memory. */
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operations[0].sem_num = 0;
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operations[0].sem_op = -1;
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operations[0].sem_flg = IPC_NOWAIT;
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rc = semop( semid, operations, 1 );
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if (rc == -1)
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{
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printf("main: semop() failed\n");
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return -1;
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}
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} /* End of FOR LOOP */
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/* Clean up the environment by removing the semid structure, */
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/* detaching the shared memory segment, and then performing */
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/* the delete on the shared memory segment ID. */
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rc = semctl( semid, 1, IPC_RMID );
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if (rc==-1)
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{
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printf("main: semctl() remove id failed\n");
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return -1;
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}
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rc = shmdt(shm_address);
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if (rc==-1)
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{
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printf("main: shmdt() failed\n");
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return -1;
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}
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rc = shmctl(shmid, IPC_RMID, &shmid_struct);
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if (rc==-1)
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{
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printf("main: shmctl() failed\n");
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return -1;
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}
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return 0;
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}</pre>
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</div>
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<div class="section" id="apiexusmem__HDRIPCCLI"><a name="apiexusmem__HDRIPCCLI"><!-- --></a><h4 class="sectiontitle">Client program</h4><p>This program acts
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as a client to the server program (see <a href="#apiexusmem__HDRIPCSRV">Server program</a>).
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The program is run after the message <tt class="sysout">Ready for client jobs</tt> appears
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from the server program.</p>
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<p>Use the CRTCMOD and CRTPGM commands to create
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this program.</p>
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<p>Call this program with no parameters after calling the
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server program.</p>
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<pre>/*********************************************************************/
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/*********************************************************************/
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/* */
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/* FUNCTION: This program acts as a client to the server program. */
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/* */
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/* LANGUAGE: ILE C */
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/* */
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/* APIs USED: semget(), semop(), */
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/* shmget(), shmat(), shmdt() */
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/* ftok() */
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/* */
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/*********************************************************************/
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/*********************************************************************/
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#include <stdio.h>
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#include <string.h>
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#include <sys/ipc.h>
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#include <sys/sem.h>
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#include <sys/shm.h>
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#define SEMKEYPATH "/dev/null" /* Path used on ftok for semget key */
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#define SEMKEYID 1 /* Id used on ftok for semget key */
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#define SHMKEYPATH "/dev/null" /* Path used on ftok for shmget key */
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#define SHMKEYID 1 /* Id used on ftok for shmget key */
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#define NUMSEMS 2
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#define SIZEOFSHMSEG 50
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int main(int argc, char *argv[])
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{
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struct sembuf operations[2];
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void *shm_address;
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int semid, shmid, rc;
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key_t semkey, shmkey;
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/* Generate an IPC key for the semaphore set and the shared */
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/* memory segment. Typically, an application specific path and */
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/* id would be used to generate the IPC key. */
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semkey = ftok(SEMKEYPATH,SEMKEYID);
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if ( semkey == (key_t)-1 )
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{
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printf("main: ftok() for sem failed\n");
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return -1;
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}
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shmkey = ftok(SHMKEYPATH,SHMKEYID);
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if ( shmkey == (key_t)-1 )
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{
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printf("main: ftok() for shm failed\n");
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return -1;
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}
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/* Get the already created semaphore ID associated with key. */
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/* If the semaphore set does not exist, then it will not be */
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/* created, and an error will occur. */
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semid = semget( semkey, NUMSEMS, 0666);
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if ( semid == -1 )
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{
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printf("main: semget() failed\n");
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return -1;
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}
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/* Get the already created shared memory ID associated with key. */
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/* If the shared memory ID does not exist, then it will not be */
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/* created, and an error will occur. */
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shmid = shmget(shmkey, SIZEOFSHMSEG, 0666);
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if (shmid == -1)
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{
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printf("main: shmget() failed\n");
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return -1;
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}
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/* Attach the shared memory segment to the client process. */
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shm_address = shmat(shmid, NULL, 0);
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if ( shm_address==NULL )
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{
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printf("main: shmat() failed\n");
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return -1;
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}
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/* First, check to see if the first semaphore is a zero. If it */
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/* is not, it is busy right now. The semop() command will wait */
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/* for the semaphore to reach zero before running the semop(). */
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/* When it is zero, increment the first semaphore to show that */
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/* the shared memory segment is busy. */
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operations[0].sem_num = 0;
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/* Operate on the first sem */
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operations[0].sem_op = 0;
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/* Wait for the value to be=0 */
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operations[0].sem_flg = 0;
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/* Allow a wait to occur */
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operations[1].sem_num = 0;
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/* Operate on the first sem */
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operations[1].sem_op = 1;
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/* Increment the semval by one */
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operations[1].sem_flg = 0;
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/* Allow a wait to occur */
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rc = semop( semid, operations, 2 );
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if (rc == -1)
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{
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printf("main: semop() failed\n");
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return -1;
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}
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strcpy((char *) shm_address, "Hello from Client");
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/* Release the shared memory segment by decrementing the in-use */
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/* semaphore (the first one). Increment the second semaphore to */
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|
/* show that the client is finished with it. */
|
||
|
|
operations[0].sem_num = 0;
|
||
|
|
/* Operate on the first sem */
|
||
|
|
operations[0].sem_op = -1;
|
||
|
|
/* Decrement the semval by one */
|
||
|
|
operations[0].sem_flg = 0;
|
||
|
|
/* Allow a wait to occur */
|
||
|
|
|
||
|
|
operations[1].sem_num = 1;
|
||
|
|
/* Operate on the second sem */
|
||
|
|
operations[1].sem_op = 1;
|
||
|
|
/* Increment the semval by one */
|
||
|
|
operations[1].sem_flg = 0;
|
||
|
|
/* Allow a wait to occur */
|
||
|
|
|
||
|
|
rc = semop( semid, operations, 2 );
|
||
|
|
if (rc == -1)
|
||
|
|
{
|
||
|
|
printf("main: semop() failed\n");
|
||
|
|
return -1;
|
||
|
|
}
|
||
|
|
|
||
|
|
/* Detach the shared memory segment from the current process. */
|
||
|
|
rc = shmdt(shm_address);
|
||
|
|
if (rc==-1)
|
||
|
|
{
|
||
|
|
printf("main: shmdt() failed\n");
|
||
|
|
return -1;
|
||
|
|
}
|
||
|
|
|
||
|
|
return 0;
|
||
|
|
}</pre>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div>
|
||
|
|
<div class="familylinks">
|
||
|
|
<div class="parentlink"><strong>Parent topic:</strong> <a href="apiexmp.htm" title="Contains example programs that use APIs and exit programs.">Examples: APIs</a></div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</body>
|
||
|
|
</html>
|