Synchronisation -techniques

There are a number of techniques to synchronise or coordinate the activities -of your threads with one another:

Thread Rendezvous

The RThread::Rendezvous() function -allows a thread to signal that it has reached a point in its execution. This -works in a similar way to the Logon() function, except -that Logon() signals the termination of a thread, and Rendezvous() signals -that a particular point within the thread has been reached.

The classic -use for this function is in a server, where the main thread must wait until -the initialisation of the server thread has completed before continuing.

Using Rendezvous

The following example shows code a function -creating a thread and then waiting for it to reach a certain point before -continuing. The code shown here is taken from …\examples\base\threadsandprocesses\Rendezvous\, -which you can build and run.

// create threads to wait for - RThread thread; - - // indicate completion status - TRequestStatus myThreadRendezvousStatus; - - // pass 500 as the parameter to MyThread - TInt r=thread.Create(KMsgMyThreadName, MyThread, KDefaultStackSize, KHeapSize,KHeapSize,(TAny*) 2000000, EOwnerThread); - if (r!=KErrNone) - { - console->Printf(KMsgCreateThreadFailed); - return; - } - // create rendezvous - thread.Rendezvous(myThreadRendezvousStatus); - - //EXCECUTE THREAD! - console->Printf(KMsgStartThread); - thread.Resume(); - - User::WaitForRequest(myThreadRendezvousStatus); - if(myThreadRendezvousStatus==KErrNone) - { - console->Printf(KMsgThreadRendezvousReached); - } - else - { - console->Printf(KMsgSomethingIsWrong); - } - - thread.Close(); - console->Printf(KMsgEndOfTest);

The following function -is the MyThread() function created in the previous example. -The MyThread() function calls the rendezvous function to -signal that the rendezvous point has been reached, MyThread() can -then continue.

TInt MyThread(TAny* aParameter) - { - // simulate some processing - User::After((TInt)aParameter); - - // signal Rendezvous - RThread::Rendezvous(KErrNone); - - // simulate some processing - User::After((TInt)aParameter); - - return(KErrNone); - }

Note: MyThread() can fail before -signalling the rendezvous, for example, if MyThread() panics -with a KERN-EXEC 3, then the rendezvous completes with -the reason code KErrDied or another system wide error code -other than KErrNone.

If <code>MyThread()</code> -enters a never ending loop before the rendezvous is reached, then this situation -cannot be detected and results in the calling thread waiting indefinitely -for the rendezvous. This can be avoided by careful programming.