CODEWITHSUNDEEP
c++multithreadingthread-safetymutexnew-operator
user152949
user152949

Reputation:

Thread safe pass-through operator

I'm overriding new() and new[]() operators for our heap memory manager. new() has a mutex and is thread-safe, but I have not added a mutex to new[](), which works as a pass-through operator, since I suspect it will be on the stack when called. Is it correct that new[]() will be on the stack and will not need a mutex of its own?

/*!
\brief Override the Standard C++ new [] operator
\param size [in] Number of bytes to allocate
\exception std::bad_alloc
\returns Pointer to the start of the allcoated memory block of \c size bytes
\todo Check if this is thread-safe or if it needs a mutex lock, return address probably is on the stack so it should be ok
*/
void *operator new[] (size_t size)
{
    return operator new(size);
}

/*!
\brief Overrides the Standard C++ new operator
\param size [in] Number of bytes to allocate
\exception std::bad_alloc
\returns Pointer to the start of the allcoated memory block of \c size bytes
*/
void *operator new(size_t size) 
{
    MM_ENTER_CRITICAL_SECTION(CMemoryManager::mutex)
    // Memory manager code removed since it's outside of the question context
    MM_LEAVE_CRITICAL_SECTION(CMemoryManager::mutex)
}

Upvotes: 4

Views: 186

Answers (1)

Tony The Lion
Tony The Lion

Reputation: 63250

Is it correct that new will be on the stack and will not need a mutex of its own?

Operator new[]() works just like new() but instead of allocating a single object, it allocates an array of objects. I don't know what that has to do with the stack, the objects allocated are allocated on the heap and a pointer to that memory is returned to you.

The only thing that's on the stack is the pointer itself, but that is the case with both versions of new.

Seeing that new[]() calls new() then I don't see a reason why you'd need a mutex in new[]() because new() is already protected by a mutex. Any thread that calls new[]() will have to wait if another is already inside new().

Upvotes: 2

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