m_DataBuffer may be modified concurrently while StatsFunc() is called, thus
it's unsafe to call size() on it. As write access to m_DataBuffer is already
synchronized by only modifying it from the single work queue thread, instead of
adding a mutex, this commit adds a new std::atomic_size_t which is additionally
updated when modifying m_DataBuffer and can safely be accessed in StatsFunc().
There is no explicit synchronization of access to m_DataBuffer which is fine if
it is only accessed from the single-threaded work queue. However, Stop() also
called Flush() in another thread, leading to concurrent write access to
m_DataBuffer which can result in a crash due to use after free/double free.
Changes in this commit:
* Flush() is renamed to FlushWQ() to show that it should only be called from
the work queue. Additionally, it now asserts that it is running on the work
queue.
* Visibility of some data members is changed from protected to private. No
other classes have to access these at the moment. By this change, accidental
concurrent access from derived classes in the future is prevented.
* Stop() now flushes by posting FlushWQ() to the work queue and joining it.
Julian Brost
Alexander Aleksandrovič Klimov