1 <?xml version="1.0" encoding="utf-8"?>

     2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

     3 <!-- This component and the accompanying materials are made available under the terms of the License 

     4 "Eclipse Public License v1.0" which accompanies this distribution, 

     5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

     6 <!-- Initial Contributors:

     7     Nokia Corporation - initial contribution.

     8 Contributors: 

     9 -->

    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-383C128C-15EB-4C64-9A1F-F1EA826323D0" xml:lang="en"><title>Parent

    13 and Child IPC Using Named Pipes or FIFOs</title><prolog><metadata><keywords/></metadata></prolog><conbody>

    14 <p>An alternative approach to using the <xref href="GUID-A9DB6E7C-B8D6-377A-BBE6-39E0A7A09E5D.dita"><apiname>popen()</apiname></xref> function

    15 is to use named pipes, or FIFOs. The advantage of using them over the <xref href="GUID-A9DB6E7C-B8D6-377A-BBE6-39E0A7A09E5D.dita"><apiname>popen()</apiname></xref> mechanism

    16 is that they allow the code in both the parent and child processes to continue

    17 to use file descriptors for communication rather than streams (and avoid modification

    18 to the<codeph> stdin()</codeph>/<codeph>stdout()</codeph> streams of the child

    19 process). </p>

    20 <p>In addition, since each created FIFO is referenced as a file in the file

    21 system, FIFOs allow for more complicated IPC schemes than those offered by

    22 the <xref href="GUID-A9DB6E7C-B8D6-377A-BBE6-39E0A7A09E5D.dita"><apiname>popen()</apiname></xref> function, for example, inter-child process

    23 communication. For more information about the use of FIFOs, see <xref href="http://www.opengroup.org" scope="external">http:\\www.opengroup.org</xref>. </p>

    24 <p><b>Parent process P.I.P.S. example using FIFOs</b></p>

    25 <p>The following code shows how FIFOs can be used in P.I.P.S. by the parent

    26 process.</p>

    27 <codeblock xml:space="preserve">int main(int argc, char *argv[])

    28 {

    29    char fifoFileName[] = "/root/PortDoc/Example2_c/Symbian/fifofile";

    30 

    31    int fifoResult = mkfifo(fifoFileName,S_IXGRP);

    32   

    33    if(fifoResult == -1)

    34    {

    35       //FIFO creation failure.

    36       printf("\n*** failure mkfifo ***\n");

    37 

    38       return EXIT_FAILURE;

    39    }

    40    else

    41    {

    42       //FIFO creation successful.

    43       

    44       //Spawn the child process.

    45       pid_t Childpid;

    46       char execFileName[] = "/root/PortDoc/Example2_c/Symbian/ChildProg";

    47       int RetVal= posix_spawn(&Childpid,execFileName,NULL,NULL,NULL,NULL);

    48       

    49       if(RetVal != 0)

    50       {

    51          printf("\n*** failure posix_spawn ***\n");

    52 

    53          return EXIT_FAILURE;

    54       }

    55       else

    56       {

    57          //Open the FIFO. Parent reads from the FIFO

    58          int ReadFifoFd = open(fifoFileName,O_RDONLY);

    59  

    60          if(ReadFifoFd == -1)

    61          {

    62             //Failed to open the Fifo

    63             printf("\n*** failure Fifo Open ***\n");

    64 

    65             return EXIT_FAILURE;

    66          }

    67          else

    68          {

    69             //create a receive buffer and clear

    70             char RxBuffer[100];

    71             memset(RxBuffer,0,sizeof(RxBuffer));

    72       

    73             //Wait for data from the child process. Child sends a string.

    74             int nbytes = read(ReadFifoFd,RxBuffer,sizeof(RxBuffer));

    75 

    76             printf("\nMessage Received by Parent=%s",RxBuffer);

    77       

    78             //close the FIFO

    79             (void)close(ReadFifoFd);

    80          }

    81 

    82          //wait for the child process to finish      

    83          (void)waitpid(Childpid,NULL,0);

    84    

    85          //unlink the FIFO

    86          unlink(fifoFileName);

    87       }

    88    }

    89    return EXIT_SUCCESS;

    90 }

    91 </codeblock>

    92 <p><b>Child process P.I.P.S. example using FIFOs</b></p>

    93 <p>The following code shows how FIFOs can be used in P.I.P.S. by the child

    94 process. </p>

    95 <codeblock xml:space="preserve">int main(int argc, char *argv[])

    96 {

    97    char fifoFileName[] = "/root/PortDoc/Example2_c/Symbian/fifofile";

    98 

    99    //Open the FIFO. child writes to parent

   100    int WriteFifoFd = open(fifoFileName,O_WRONLY);

   101      

   102    if(WriteFifoFd == -1)

   103    {

   104       //Failed to open the Fifo

   105       printf("\n*** child failure Fifo Open ***\n");

   106       return EXIT_FAILURE;

   107    }

   108    else

   109    {

   110       //create a message to send.

   111       char TxMsg[] = "Hello Parent\n";

   112        

   113       //Wait for data from the child process. Child sends a string.

   114       write(WriteFifoFd,TxMsg,sizeof(TxMsg));

   115      

   116       //close the FIFO

   117      (void)close(WriteFifoFd);

   118    }

   119    return EXIT_SUCCESS;

   120 }

   121 </codeblock>

   122 </conbody></concept>