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<concept id="GUID-4AEBF49C-E62A-5D0D-8181-600BF29DFFC7" xml:lang="en"><title>IPC:
IPC Mechanisms</title><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>This example demonstrates how a parent process communicates with its child
process using various IPC mechanisms. Two executables, a parent and a child
(spawned by the parent) are created to demonstrate these mechanisms. The child
process is created by the parent using the <xref href="GUID-E7C4DE71-BC5B-34AE-ACB3-C34A0DB1FC16.dita"><apiname>posix_spawn()</apiname></xref> function.
The parent process communicates with the child process using the following
IPC mechanisms: </p>
<ul>
<li id="GUID-D1CABBD1-AC3A-5216-B2A6-D860C876DEDE"><p>Named pipes (FIFO -
First in First Out) </p> </li>
<li id="GUID-8FE87BCB-200D-5498-8F1A-851B861F8673"><p>Single pipe (<xref href="GUID-A9DB6E7C-B8D6-377A-BBE6-39E0A7A09E5D.dita"><apiname>popen()</apiname></xref> system
call) </p> </li>
</ul>
<section id="GUID-E584CAE4-BC05-48D5-837C-40B73DD4524F"><title>Download</title><p>Click on the following link to download
the example: <xref href="guid-6013a680-57f9-415b-8851-c4fa63356636/zips/guid-c5b6ac05-a3fb-45df-ab11-bd8ccc13537f.zip" scope="external">IPC.zip</xref></p><p>Click: <xref href="guid-6013a680-57f9-415b-8851-c4fa63356636/guid-c5b6ac05-a3fb-45df-ab11-bd8ccc13537f.html" scope="peer">browse</xref> to view the example code. </p> </section>
<section id="GUID-5513D686-D38A-49A9-B3B2-2259992A69A8"><title>Description</title> <p><b> Spawning the child process</b> </p> <p>The <xref href="GUID-E7C4DE71-BC5B-34AE-ACB3-C34A0DB1FC16.dita"><apiname>posix_spawn()</apiname></xref> function
creates the child process. A pointer to the process ID (<codeph>pid</codeph>)
of the child process and the path of the child process are passed as arguments
to this function. The parent waits for the child to terminate by calling the <xref href="GUID-8F5C89A4-7813-32C7-973E-F7F0F3690BC6.dita"><apiname>waitpid()</apiname></xref> function. </p> <p><b> Creating
a named pipe</b> </p> <p>This example creates a named pipe using the <xref href="GUID-F4749DAA-1B29-3D1D-A3AA-0D52B851E501.dita"><apiname>mkfifo()</apiname></xref> function.
The child writes data into the FIFO and then exits. The parent reads data
from FIFO and writes it to the console. The first argument of the <xref href="GUID-F4749DAA-1B29-3D1D-A3AA-0D52B851E501.dita"><apiname>mkfifo()</apiname></xref> function
indicates the path of the FIFO file. </p> <p><b> Opening a single pipe</b> </p> <p>The
parent creates a child process and a pipe to the child process using the <xref href="GUID-A9DB6E7C-B8D6-377A-BBE6-39E0A7A09E5D.dita"><apiname>popen()</apiname></xref> function.
A file handle to the pipe is returned to the parent and the parent uses this
handle to read the data written to the pipe by the child. The path of the
child process is passed as the first argument to the <xref href="GUID-A9DB6E7C-B8D6-377A-BBE6-39E0A7A09E5D.dita"><apiname>popen()</apiname></xref> function. </p> </section>
<section id="GUID-367A6465-F1C3-46B3-820B-7086E0BE1BEB"><title>Build</title> <p>The following statements are present in all
the <filepath>.mmp</filepath> files of the example: </p> <codeblock id="GUID-09782F92-8B25-5CF5-8027-599685F5726D" xml:space="preserve">SYSTEMINCLUDE epoc32\include\stdapis
LIBRARY libc.lib
STATICLIBRARY libcrt0.lib</codeblock> <p> <b>Note:</b> You require these statements
because of the following reasons: </p> <ul>
<li id="GUID-C735ED4D-4FDD-5535-ACA2-C645C3F10762"><p>The <filepath>epoc32\include\stdapis</filepath> directory
contains header files such as, <filepath>stdio.h</filepath>, <filepath>unistd.h</filepath> and
so on that are required to build an Open Environment application. </p> </li>
<li id="GUID-6351CD50-ED02-5DC9-BAAF-971CB92EEAD3"><p>The <filepath>libc.lib</filepath> file
contains the definitions of all functions that are defined in the header files
associated with this example. </p> </li>
<li id="GUID-C7A1D9C5-07E6-5FD1-B770-24180F04623A"><p>The <filepath>libcrt0.lib</filepath> file
provides the <codeph>E32Main()</codeph> function, which is the entry point
for the <codeph>main()</codeph> function of the example. </p> </li>
</ul> <p> <xref href="GUID-3100800B-B2F7-50EF-BD4C-3C345ECCB2A5.dita">The Symbian
build process</xref> describes how to build this example. The <codeph>IPC</codeph> builds
the following binaries in the standard location (<filepath>\epoc32\release\winscw\<build_variant></filepath> for
Carbide.c++). </p> <ul>
<li id="GUID-1F256024-8210-5C50-8B18-0498C0D5C15F"><p> <b>ipcparent.exe:</b> Executable
of the parent process. </p> </li>
<li id="GUID-1C755509-96FA-510A-944B-3FEA065C9936"><p> <b>ipcchild.exe:</b> Executable
of the child process created using the <xref href="GUID-A9DB6E7C-B8D6-377A-BBE6-39E0A7A09E5D.dita"><apiname>popen()</apiname></xref> function. </p> </li>
<li id="GUID-C056BC80-D664-5F25-A730-35220CA0A6B5"><p> <b>fifochild.exe:</b> Executable
of the child process created using the <xref href="GUID-E7C4DE71-BC5B-34AE-ACB3-C34A0DB1FC16.dita"><apiname>posix_spawn()</apiname></xref> function. </p> </li>
</ul> </section>
<section id="GUID-9F7DC4C5-16C8-4223-80E0-19DDF9E8303E"><title>Runtime setting</title> <p>Two eshells must be opened before
executing this example. The executable, <filepath>ipcparent.exe</filepath> is
run in one eshell and the other eshell is used to run the child process <filepath>fifochild.exe</filepath>.
You can switch between the two eshells by pressing <b>CTRL</b> +<b>ALT</b> +<b>SHIFT</b> +<b>T</b>. </p> </section>
</conbody></concept>