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Revision as of 13:18, 20 May 2008 by Forum Nokia KB (Talk | contribs)

Archived:RMutex - Symbian mutex class

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Template:KBCS

ID CS000969 Creation date May 20, 2008
Platform S60 3rd Edition, MR Tested on devices Nokia N95
Category Symbian C++ Subcategory Code Examples


Keywords (APIs, classes, methods, functions): RMutex, RSemaphore, RThread

Overview

Using RMutex you can make sure that, for example, threads do not change the same value at the same time. RMutex.Wait() acquires a lock that opens with RMutex.Signal().

The following code is an update to the CS000867 - RThread example.

MMP file

The following capabilities and libraries are required:

CAPABILITY        NONE
LIBRARY euser.lib

Header file

Shared data iSharedValue between threads.

class CShared : CBase
{
public:
static CShared* NewL();
virtual ~CShared();
 
private:
CShared();
 
public:
RMutex iMutex;
// Shared data
TInt iSharedValue;
};


Source file

Create a thread and give the CShared data pointer in it.

// Create shared data
iSharedData = CShared::NewL();
 
// Create threads
iMyThread = CMyThread::NewL(*this);
iMyThread->SetShared(iSharedData);
 
iMyThread2 = CMyThread::NewL(*this);
iMyThread2->SetShared(iSharedData);

The thread fuction saysRMutex::Wait() and then sleeps.

TInt CMyThread::ThreadFunction(TAny* aParams)
{
// Add cleanup stack support.
CTrapCleanup* cleanupStack = CTrapCleanup::New();
 
// Get pointer to thread host
CMyThread* host = (CMyThread*)aParams;
 
TRAPD(err,
// Add support for active objects
CActiveScheduler* activeScheduler = new (ELeave) CActiveScheduler;
CleanupStack::PushL(activeScheduler);
CActiveScheduler::Install(activeScheduler);
 
// Create and start CPeriodic class that is executed in this thread
CPeriodic* periodic = CPeriodic::NewL(CActive::EPriorityLow);
CleanupStack::PushL(periodic);
periodic->Start(host->Interval(),host->Interval(),
TCallBack(host->PeriodicTick, host));
 
// NOTE: When adding CActiveScheduler support for threads we have to
// add at least one active object in it or it fails on
// CActiveScheduler::Start().
// CPeriodic is derived from CActive active object so that is good for
// this example.
 
// --> Thread execution starts
CActiveScheduler::Start();
// --> Thread execution ends (waiting for CActiveScheduler::Stop())
 
CleanupStack::PopAndDestroy(periodic);
CleanupStack::PopAndDestroy(activeScheduler);
);
 
 
host->ThreadExecuted(err);
delete cleanupStack;
return KErrNone;
}

After sleeping the thread calls PeriodicTick() where it changes the shared data value and releases RMutex::Signal().

TInt CMyThread::PeriodicTick(TAny* aObject)
{
CMyThread* mythread = (CMyThread*)aObject;
if (mythread)
{
// ---> Acquire the lock
mythread->Shared()->iMutex.Wait();
 
// Change shared data value
mythread->Shared()->iSharedValue++;
 
// ---> Release the lock
mythread->Shared()->iMutex.Signal();
 
// Thread is executed once so time to stop it
CActiveScheduler::Stop();
 
// After this execution continues from CActiveScheduler::Start()
}
// Does not continue again
// Note: Does not work with this CPeriodic class
return EFalse;
}

CShared data implementation

CShared* CShared::NewL()
{
CShared* self = new (ELeave) CShared();
return self;
}
CShared::CShared()
{
iMutex.CreateLocal();
}
CShared::~CShared()
{
iMutex.Close();
}


Postconditions

Threads change shared data value in turns. The other thread waits if RMutex::Wait() is called and continues after RMutes::Signal().

See also

CS000867 - RThread Using RThread

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