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<concept id="GUID-E7C41361-C0B9-5341-A864-B59770FB7C9B" xml:lang="en"><title>Supporting

Writable Static Data in DLLs </title><prolog><metadata><keywords/></metadata></prolog><conbody>

<section><title>Introduction</title> <p>Many UNIX programs rely

on Writable Static Data (WSD) for data storage. Native Symbian platform applications

have been developed without any support for WSD on an Emulator for dynamic

link libraries. P.I.P.S. supports WSD and a complete implementation is available

for target phones. The implementation of WSD on an Emulator, however, poses

certain restrictions for dynamic link libraries. </p><p>A Symbian project's

MMP file can specify the <codeph>EPOCALLOWDLLDATA</codeph> directive to enforce

a rule that WSD should not be shared between processes. The P.I.P.S. <codeph>STDEXE</codeph>y

target type sets this directive automatically. The rule imposes the restriction

that only one process can load a DLL with WSD. P.I.P.S. provides a mechanism

to avoid these restrictions. </p> </section>

<section><title>A UNIX DLL with WSD</title><codeblock xml:space="preserve">int refCount = 0;

int IncRefCount()

{

  //Increment the reference count

  return ++refCount;

}

int DecRefCount()

{

  //Decrement the reference count

  return --refCount;

}

</codeblock><p/></section>

<section><title>A Symbian DLL with WSD</title><p>The UNIX code above will

provide indeterminate results on a Symbian emulator. If the DLL had <codeph>EPOCALLOWDLLDATA</codeph> in

its MMP file, then only one process would be able to use the reference counting

functions. Without <codeph>EPOCALLOWDLLDATA</codeph>, the reference count

would be global and not process specific. </p><p>The following code demonstrates

the use of the <xref href="GUID-807C676B-5C46-328C-879C-A4FCB638A5B6.dita"><apiname>Pls()</apiname></xref> function (Process Local Storage),

which is the P.I.P.S. WSD solution to the problem. </p><codeblock xml:space="preserve">#include &lt;pls.h&gt;

#ifdef __WINSCW__

//The next code will run only on the emulator

//Put the global count into a structure

struct DLLData

{

   int refCount;

};

//Define a way to access the structure

//On the first call to this function, memory will be allocated with the specified

//UID as an identifier and the Initialization function will be called

//Subsequent calls to this function return the allocated memory

struct DLLData* GetGlobals()

{

   return Pls<DLLData>(KDLLUid3, InitializeGlobals);

}

//Initialization function

TInt InitializeGlobals(DLLData* aData)

{

   aData->refCount = 0;

   return KErrNone;

}

//Access the refCount variable

int& get_refCount()

{

   return GetClobals()->refCount;

}

//Macro to replace the variable with our new method

#define refCount get_refCount()

#else

//Target device code

int refCount;

#endif

int IncRefCount()

{

  return ++refCount;

}

int DecRefCount()

{

  return --refCount;

}

</codeblock></section>