RTX - Data integrity

Hello,

I have a pretty generic question about embedded RTOS systems and data integrity.

I'm using RTX and I have several instances of structures that need to be read/written from several task.

As an example, take:

struct demo
{
int var_a;
int var_b;
int var_a_max;
int var_a_min;
}

If I have several global demo instances, what is the 'danger' in allowing several tasks to R/W the global instances?

I understand that the values could change mid execution but say you implemented a simple "lock and copy" procedure before each tasks loop execution.

Would mailboxes really be required in this case?

Further, what if all tasks only ever read/write one of the fields (var_a) do you even need a lock and copy or would simple copy do?

Finally, say I did want to implement a generic mailbox pattern so that any task could request a copy from a managing task and send updates to a managing task. Does any one have an example of such a pattern?

Thanks. I appreciate any discussion and opinion on this topic, I'm looking for the most efficient (time and complexity) way to proceed while still being 'safe' in my logic.

M