Memory Synchronisation Issue in FiFo

[elfenpiff]

Required information

Operating system:
Every Operating System on a weak or C++ memory model

Compiler version:
All compiler

Observed result or behaviour:
The data which is pushed into the fifo is not synchronised with a different thread which pop's it out of the fifo.

Expected result or behaviour:
The data has to be synchronised.

Conditions where it occurred / Performed steps:
Unknown