TUTYSARA'S SPACE

SQS:

Is ideal when

• Producers and consumers run at different speeds
• You want retry, durability, and backpressure
• Each message should be processed at least once

SNS

SNS is about fan-out, not durability for processing.

• Push-based
• One message → many subscribers

Subscribers can be: SQS queues or HTTP endpoints or Lambda

Concurrency primitives can be implemented on top of channel abstraction of CSP style. Here is an example of implementing mutex using channels.

Go code to implement mutex using channels.

package main

import "fmt"

type Lock struct {
	locked chan bool
}

func NewLock() Lock {
	lock := Lock{locked: make(chan bool, 1)}
	lock.locked <- true
	return lock
}

func (l *Lock) Lock() {
	<-l.locked // read from channel and if another read happens it waits
}

func (l *Lock) Unlock() {
	// This is not reentrant

	// calling unlock again on an unlocked channel blocks
	l.locked <- true // write to channel so, that it gets read and channel clears
}

This is not reentrant

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