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+++ b/Symbian3/SDK/Source/GUID-545DA961-217E-49CA-A90E-7A41E2C03A99.dita	Thu Jan 21 18:18:20 2010 +0000
@@ -0,0 +1,161 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
+<!-- This component and the accompanying materials are made available under the terms of the License 
+"Eclipse Public License v1.0" which accompanies this distribution, 
+and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
+<!-- Initial Contributors:
+    Nokia Corporation - initial contribution.
+Contributors: 
+-->
+<!DOCTYPE concept
+  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
+<concept id="GUID-545DA961-217E-49CA-A90E-7A41E2C03A99" xml:lang="en"><title>Forking
+without <codeph>exec()</codeph></title><shortdesc>A Unix-like system may create the child process using <codeph>fork()</codeph>,
+which then does not make a subsequent <codeph>exec()</codeph> call. The result
+of this is that the parent and child processes run the same executable. The
+child may communicate with the parent using pipes. One example of a system
+which does this is the email software program Exim (www.exim.org). In addition
+to forking without <codeph>exec()</codeph>, it can also <codeph>re-exec()</codeph> itself
+to regain dropped root privileges.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
+<p>The issues that such systems encounter when porting to P.I.P.S. fall into
+two categories: <ul>
+<li><p><b>Little or no state data passed to child</b></p></li>
+<li><p><b>A lot of data passed to child</b></p></li>
+</ul></p>
+<section><title>Little or no state data passed to child</title><p>The first
+issue is where there is a little/no data passed to the child process on the <codeph>fork()</codeph> operation.
+Many examples of this exist in pre/post forking of listening sockets in TCP
+server applications, for example, in the MPM pre-fork module of the Apache
+server. More details are available at <xref href="http://httpd.apache.org/docs/2.2/mod/prefork.html" scope="external">http://httpd.apache.org/docs/2.2/mod/prefork.html</xref>. </p><p>This
+can be resolved by using the <xref href="GUID-E7C4DE71-BC5B-34AE-ACB3-C34A0DB1FC16.dita"><apiname>posix_spawn()</apiname></xref> operation, and
+passing any data using the <codeph>argv</codeph> parameters or environment
+variables. For more information about the <codeph>posix_spawn()</codeph> operation,
+see <xref href="http://www.opengroup.org/" scope="external">http://www.opengroup.org/</xref>.
+Note that some <codeph>argv</codeph> parameters must be used to distinguish
+the behaviour of the parent process from the subsequent behaviour of the child
+when the <codeph>main()</codeph> function is called; the behaviour of the
+child cannot be identical to the parent.  </p><p>The subsequent sections provide
+the following information: <ul>
+<li><p><b>Parent process forking example</b></p></li>
+<li><p><b>P.I.P.S. equivalent</b></p></li>
+</ul></p></section>
+<section><title>Parent process forking example</title><codeblock xml:space="preserve">#include &lt;stdio.h&gt;
+#include &lt;stdlib.h&gt;
+#include &lt;sys/types.h&gt;
+#include &lt;sys/wait.h&gt;
+#include &lt;unistd.h&gt;
+
+#define NUM_OF_PROCS 5
+
+int main(int argc, char *argv[])
+{
+  pid_t Processpid[NUM_OF_PROCS];
+     
+  int I;
+  
+  for(I=1;i&lt;NUM_OF_PROCS;i++)
+  {
+     Processpid[i] = fork();
+    
+     if(Processpid[i] == 0)
+     {
+        printf("\r\n Child Process Inst[%d] running ***\r\n",I);
+
+        //Terminate child process.5
+        exit(0);
+     }
+     else
+     {
+        //Wait for the child process to terminate before forking the next one.
+        waitpid(Processpid[i],NULL,0);
+     
+        printf("\r\n*** Child int[%d] process finished ***\r\n",I);
+     }
+  }
+   
+  return EXIT_SUCCESS;
+}
+</codeblock><p/></section>
+<section><title>P.I.P.S. equivalent</title><codeblock xml:space="preserve">#include &lt;stdio.h&gt;
+#include &lt;stdlib.h&gt;
+#include &lt;strings.h&gt;
+#include &lt;spawn.h&gt;
+#include &lt;sys/types.h&gt;
+#include &lt;sys/wait.h&gt;
+
+#define NUM_OF_PROCS 5
+
+int main(int argc, char *argv[])
+{
+   if(argc != 2)
+   {
+      printf("\r\n One parameter is needed.  \r\n");
+      
+      return EXIT_FAILURE;
+   }
+   else
+   {
+      int argvAsInt = atoi(argv[1]);
+      
+      if(argvAsInt &gt; NUM_OF_PROCS)
+      {
+         printf("\r\n parameter[%d] one is out of range  \r\n",argvAsInt);
+       
+         return EXIT_FAILURE;
+      }
+      else
+      {      
+         if(argvAsInt == 0)
+         {
+            //parent process.
+            pid_t Processpid[NUM_OF_PROCS];
+   
+            //executable points to the compiled version of this source.
+            char execFileName[] = "/root/PortDoc/Example3_c/Symbian/ParentProg";
+            int RetVal;
+            int I;
+            char iAsString[2];
+            char* spawnedArgs[3];
+            spawnedArgs[0] = argv[0];
+            spawnedArgs[2] = NULL;
+    
+            for(I=1; i&lt;NUM_OF_PROCS;i++)
+            {
+               //store I as a string.
+               bzero(iAsString,sizeof(iAsString));
+               iAsString[0] = 0x30+I;
+       
+               spawnedArgs[1] = iAsString;
+               
+               RetVal= posix_spawn(&amp;Processpid[i],execFileName,NULL,NULL,spawnedArgs,NULL);
+   
+               //wait for chid process to terminate before spawning the next.
+              (void)waitpid(Processpid[i],NULL,0);
+               printf("\r\n*** Child process finished ***\r\n");
+            }
+         }
+         else
+         {
+            //child process
+            printf("\r\n Child Process Inst[%d] running ***\r\n",argvAsInt);
+
+            //Terminate child process.
+            exit(0);
+         }
+      }
+   }
+   return EXIT_SUCCESS;
+}
+</codeblock></section>
+<section><title>A lot of data passed to child</title><p>The second issue is
+where there is too much data to be passed across to the child process using
+the <xref href="GUID-E7C4DE71-BC5B-34AE-ACB3-C34A0DB1FC16.dita"><apiname>posix_spawn()</apiname></xref> call. A common work-around used in systems
+where <codeph>fork()</codeph> is not available is to use POSIX threads, or
+Pthreads. These Pthreads will execute in the same process and share their
+memory space, that is, they can share the same data objects. One critical
+difference between using Pthreads and <codeph>fork()</codeph> is that <codeph>fork()</codeph> creates
+copies of the parent's data objects in the child. The copied data objects
+can then be modified independently by both processes. However, when using
+Pthreads such data objects are shared and extra care, such as the use of mutexes
+and semaphores, is required when accessing them if their values can change. </p></section>
+</conbody></concept>
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