Archived:Memory allocation in multithreaded Symbian C++ applications

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Compatibility

Platform(s): S60 1st Edition
S60 2nd Edition, FP1, FP2, FP2
S60 3rd Edition
S60 3rd Edition FP1

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Article

Created: User:Technical writer 2 (04 Jul 2007)

Last edited: hamishwillee (14 Jun 2012)

Overview

Calls like User::Alloc() and User::Available() are not thread safe if used in multiple threads with a shared heap.

Description

User::Alloc() and User::Available() calls are not thread safe by themselves. In a multithreaded application it is possible for the parent thread to specify the heap used by a child thread. There are two options: dedicated heap and shared heap. If two or more threads operate on a shared heap, then synchronization (e.g. with mutexes) is required.

Solution

1) Shared heap:
  IMPORT_C TInt Create( const TDesC &aName,
                        TThreadFunction aFunction,
                        TInt aStackSize,
                        RAllocator *aHeap,
                        TAny *aPtr,
                        TOwnerType aType = EOwnerProcess );                   
If the aHeap parameter is set as NULL in the above call, then the thread will be sharing a heap memory with the parent thread.
In this case, memory allocation should be synchronized in their respective threads:
  RMutex sharedMutex;
  ...

  sharedMutex.Wait();
  array[i] = User::Alloc( bytesToAlloc );
  sharedMutex.Signal();
  sharedMutex.Wait();
  TInt heapSize = User::Available( largestBlock );
  sharedMutex.Signal();
2) Dedicated heap:
When the following overloaded version of RThread::Create() is used, the new thread will use its own independent heap.
  IMPORT_C TInt Create( const TDesC &aName,
                        TThreadFunction aFunction,
                        TInt aStackSize,
                        TInt aHeapMinSize,
                        TInt aHeapMaxSize,
                        TAny *aPtr,
                        TOwnerType aType = EOwnerProcess );
With separate heaps, the memory allocation calls do not have to be synchronized.