there is some dependencies on both sides: ie don't write to the same location the other side is reading/writing
My technique is for the two parties to synchronize via ping-pong bytes that either are zero or something else. Such a flag can be simultaneously read and written with no ill effects.

an example: a byte indicating by non-zero that thye data block reserved for B to write to is ready to read.
If A read while B is writing non-zero, A will either read zero (the old value) or nonzero (the new value). If reading zero it will try later, if reading non-zero it does not matter if it was during a B write or not. Another byte is used for "A has read the block" in a similar manner.

Erik