Simulating Weak Memory Ordering in Go

Understanding memory models is crucial for writing correct concurrent programs, especially when dealing with multiple goroutines accessing shared data. Go's memory model is generally considered relaxed, but it still provides some ordering guarantees. This challenge asks you to simulate a weaker memory model (specifically, a "release-acquire" model) using Go's synchronization primitives, demonstrating how to achieve specific ordering behavior without relying on Go's default guarantees. This is useful for understanding the underlying principles of memory models and for situations where you need to explicitly control memory visibility.

Problem Description

You are tasked with implementing a simplified release-acquire memory model in Go. The core idea is to use a sync.Mutex to act as a "release" point for writing data and an "acquire" point for reading it. Data written before acquiring the mutex should be visible to any goroutine that subsequently acquires the mutex. Data written after releasing the mutex should not be visible to goroutines that haven't acquired it yet.

Specifically, you need to create a data structure containing a shared integer and implement two functions: Release() and Acquire(). Release() should write a value to the shared integer and then release the mutex. Acquire() should acquire the mutex, read the shared integer, and then release the mutex. The goal is to ensure that a reader goroutine (using Acquire()) will only see the value written by a writer goroutine (using Release()) after the writer has released the mutex.

You will be provided with a basic structure to start with. Your task is to complete the Release() and Acquire() functions to enforce the release-acquire semantics.

Examples

Example 1:

Input:
Writer Goroutine: Calls Release(42)
Reader Goroutine: Calls Acquire()

Output:
Reader Goroutine returns 42.

Explanation: The writer sets the shared integer to 42 and releases the mutex. The reader acquires the mutex, reads the integer (which is now 42), and releases the mutex.

Example 2:

Input:
Writer Goroutine 1: Calls Release(10)
Writer Goroutine 2: Calls Release(20)
Reader Goroutine: Calls Acquire()

Output:
Reader Goroutine returns 20.

Explanation: Writer 1 sets the integer to 10 and releases. Writer 2 sets the integer to 20 and releases. The reader acquires the mutex, reads the latest value (20), and releases. The order of releases doesn't matter, but the reader will always see the last value written before the mutex was acquired.

Example 3: (Edge Case - Concurrent Writes)

Input:
Writer Goroutine 1: Calls Release(5)
Writer Goroutine 2: Calls Release(15) (concurrently with Writer 1)
Reader Goroutine: Calls Acquire()

Output:
Reader Goroutine returns 15.

Explanation: Both writers attempt to write concurrently. The reader acquires the mutex, reads the value written by Writer 2 (15), and releases. The exact order of execution is not guaranteed, but the reader will see the last value written before acquiring the mutex.

Constraints

• The shared integer must be accessible and modifiable by both the writer and reader goroutines.
• The Release() function must write a value to the shared integer before releasing the mutex.
• The Acquire() function must read the value from the shared integer after acquiring the mutex.
• The solution must use a sync.Mutex to implement the release-acquire semantics.
• The solution should be thread-safe.
• The integer values used in the examples can be any integer.

Notes

• Think carefully about the order of operations within Release() and Acquire(). The mutex is key to enforcing the ordering.
• This is a simplified model. Real-world memory models are significantly more complex.
• Consider the potential for race conditions if the mutex is not used correctly.
• The goal is to demonstrate the concept of release-acquire, not to create a production-ready memory model implementation.

import "sync"

type SharedData struct {
	value int
	mutex sync.Mutex
}

func NewSharedData() *SharedData {
	return &SharedData{
		value: 0,
		mutex: sync.Mutex{},
	}
}

func (sd *SharedData) Release(val int) {
	// Your code here to release a value
}

func (sd *SharedData) Acquire() int {
	// Your code here to acquire and return a value
}