Implementing Memory Barriers in Go Concurrency

Concurrency in Go relies heavily on shared memory. However, the Go runtime and underlying hardware may reorder memory operations for performance reasons. This can lead to subtle bugs in concurrent programs if not handled correctly. This challenge focuses on understanding and implementing memory barriers to ensure correct synchronization and visibility of memory operations across goroutines.

Problem Description

You need to implement a mechanism in Go that ensures a specific sequence of memory operations is executed in the intended order, even in the presence of compiler and hardware optimizations that might reorder them. Specifically, you will simulate a producer-consumer scenario where a producer writes data and signals its availability, and a consumer reads the data and acknowledges its consumption. The critical part is to ensure that the write operation by the producer is fully visible to the consumer before the consumer proceeds with its operations.

What needs to be achieved: Implement a Go program that uses memory barriers to enforce the correct ordering of memory operations in a concurrent producer-consumer pattern.

Key requirements:

Producer: A goroutine that sets a value and then signals its readiness.
Consumer: A goroutine that waits for the readiness signal and then reads the value.
Memory Barrier: You must use Go's memory barrier primitives to ensure that the producer's write to the value is visible to the consumer before the consumer proceeds.
Correctness: The program should reliably produce the correct output, demonstrating that the memory barrier is effective.

Expected behavior: The consumer should always read the value written by the producer. Without proper memory barriers, it's possible for the consumer to read a stale or uninitialized value, or for the signal to be processed before the data is actually written.

Edge cases to consider:

Race Conditions: Without proper synchronization, race conditions will occur. The challenge is to prevent these with memory barriers.
Compiler/Hardware Reordering: The solution must work correctly regardless of how the compiler or hardware might optimize memory access.

Examples

Example 1:

Input: No explicit input, the program will run and demonstrate behavior.
Output:
Producer has written: 42
Consumer has read: 42

Explanation: The producer goroutine writes the value 42 to a shared variable and then signals readiness. The consumer goroutine waits for the signal. Upon receiving the signal, it reads the shared variable. The output shows that the consumer successfully read the value 42, indicating that the producer's write operation was visible before the consumer proceeded.

Example 2: (Illustrating potential incorrect behavior without barriers) Imagine a scenario where the following could happen without proper barriers:

Producer sets ready = true.
Producer writes value = 42.
But, due to reordering, the write value = 42 might be perceived by the consumer after it sees ready = true.
Consumer sees ready = true.
Consumer reads value, which might still be its initial zero value (e.g., 0).

This would lead to incorrect output like:

Producer has written: 42
Consumer has read: 0

Your solution should prevent this.

Constraints

The program should run for a short duration to demonstrate the concept, not for extensive benchmarking.
You should use standard Go concurrency primitives (goroutines, channels) in conjunction with memory barrier primitives.
The shared data will be a single integer.
The readiness signal can be a boolean flag.

Notes

Go's sync/atomic package provides primitives that inherently include memory ordering guarantees. You are encouraged to explore and use these.
Consider the difference between atomic.Load and atomic.Store operations and how they relate to memory visibility.
Think about the sequence: data write -> signal write. How do you ensure the former is visible before the latter is acted upon by the consumer?
The primary goal is to understand how memory barriers prevent reordering and ensure correct concurrent behavior.