test(utils): 添加事件驱动模型测试

- 在 sqrt_test.go 中添加了 fastSqr1 测试函数，用于测试事件驱动模型
- 新增了 Event 和 Uint32AsyncEvent 类型用于测试
- 更新了 go.work、go.mod 和

common/utils/event/.gitignore

@@ -0,0 +1,15 @@
+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, built with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+
+# Dependency directories (remove the comment below to include it)
+# vendor/

common/utils/event/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2023 Bogdan Gabriel Dinu aka Badu
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

common/utils/event/README.md

@@ -0,0 +1,232 @@
+# Bus
+
+- **Independent**: has no external dependencies
+- **Probably Fast**: no reflection
+- **Type Safe**: built on generics
+- **Small and Simple**: can be used as following:
+
+Having the following event:
+
+```go
+    package events
+
+    type InterestingEvent struct {
+    }
+```
+
+a listener can registering a handler by calling `Sub` method:
+
+```go
+    package subscriber
+
+   import "github.com/badu/bus"
+   
+   // ... somewhere in a setup function / constructor    
+   bus.Sub(OnMyEventOccurred)
+```
+
+where the handler is having the following signature:
+
+```go
+    func OnMyEventOccurred(event InterestingEvent){
+      // do something with the event here
+	}   
+```
+
+The event producer / dispatcher will simply:
+
+```go
+    package dispatcher
+
+   import "github.com/badu/bus"
+   
+   // ...somewhere in a dispatching function
+   
+   bus.Pub(InterestingEvent{})
+```
+
+If the event needs to go async, in the sense that the bus package will spin up a goroutine for the caller, just
+implement the following interface:
+
+```go
+    package events
+
+    func (e InterestingEvent) Async() bool{ return true }
+``` 
+
+if the handler has the signature declared above, or
+
+```go
+    package events
+
+    func (e *InterestingEvent) Async() bool{ return true }
+``` 
+
+if the handler has the signature as following:
+
+```go
+    func OnMyEventOccurred(event *InterestingEvent){
+      // do something with the event here
+	}   
+```
+
+Another way to publish an event async, is to use `PubAsync` method that package exposes.
+
+By default, the bus is using sync events, which means that it waits for listeners to complete their jobs before calling
+the next listener.
+
+Usage : `go get github.com/badu/bus`
+
+## F.A.Q.
+
+1. I want to cancel subscription at some point. How do I do that?
+
+Subscribing returns access to the `Cancel` method
+
+```go
+package subscriber
+
+// ... somewhere in a setup function / constructor
+subscription := bus.Sub(OnMyEventOccurred)
+// when needed, calling cancel of subscription, so function OnMyEventOccurred won't be called anymore
+subscription.Cancel()
+```
+
+2. Can I subscribe once?
+
+Yes! The event handler has to return true.
+
+```go
+package subscriber
+// ... somewhere in a setup function / constructor
+
+bus.SubCancel( func(event InterestingEvent) bool {
+    // do something with the event here
+	return true // returning true will cancel the subscription
+})
+```
+
+3. I want to inspect registered events. How do I do that?
+
+The events mapper is a `sync.Map`, so iterate using `Range`
+
+```go
+bus.Range(func(k, v any)bool{
+	fmt.Printf("%#v %#v\n", k, v)
+})
+```
+
+4. I want to use my own event names. Is that possible?
+
+Yes! You have to implement the following interface:
+
+```go
+package events
+
+func (e InterestingEvent) EventID() string{
+	return "YourInterestingEventName"
+}
+```
+
+The event name is the key of the mapper, which means that implementing your own event names might cause panics 
+if you have name collisions.
+
+5. Will I have race conditions?
+
+No. The package is concurrent safe.
+
+## What Problem Does It Solve?
+
+Decoupling of components: publishers and subscribers can operate independently of each other, with no direct knowledge
+of each other's existence. This decoupling allows for greater flexibility and scalability, as new publishers and
+subscribers can be added to the system without disrupting existing components. Also, this facilitates testing by
+triggering or ignoring certain events in some scenarios.
+
+Asynchronous messaging: messages can be sent and received asynchronously (by spinning up goroutines), which means that
+publishers and subscribers don't have to wait for each other to consume their messages. This can improve performance and
+response times in a system.
+
+Reliability: the message broker acts as a buffer between publishers and subscribers, ensuring that messages are
+delivered even if one or more components in the system are temporarily unavailable.
+
+Modularity: the Pub-Sub pattern can be used to break a monolithic application into smaller, more modular components.
+Each component can then be developed and tested independently, making the overall system easier to maintain and update.
+
+## Scenarios of Usage
+
+Inside the `test_scenarios` folder, you can find the following scenarios:
+
+1. Fire and Forget.
+
+   Imagine a system / application where we have three services : `users`, `notifications` (email and
+   SMS) and `audit`. When a user registers, we want to send welcoming messages via SMS and email, but we also want to
+   audit that registration for reporting purposes.
+
+   The [UserRegisteredEvent](https://github.com/badu/bus/blob/master/test_scenarios/fire-and-forget/events/main.go#L3)
+   will carry the freshly registered username (which is also the email) and phone to the email and sms services. The
+   event is [triggered](https://github.com/badu/bus/blob/master/test_scenarios/fire-and-forget/users/service.go#L23) by
+   the user service, which performs the creation of the user account. We're using the `fire and forget` technique here,
+   because the operation of registration should not depend on the fact that we've been able to
+   send a welcoming email or a sms, or the audit system malfunctions.
+
+   Simulating audit service malfunctions easy.
+   Instead of using `Sub`, we're using `SubUnsub` to register the listener
+   and return [`true`](https://github.com/badu/bus/blob/master/test_scenarios/fire-and-forget/audit/service.go#L36) to
+   unsubscribe on events of that kind.
+
+2. Factory Request Reply
+
+   Imagine a system / application where we need to communicate with different microservices, but in this case we don't
+   want to bring them online, we're just wanting to stub the response as those services were alive.
+
+   This technique is useful when we need to test some complicated flows of business logic and facilitates the
+   transformation of an integration test into a classic unit test.
+
+   The `cart` service requires two replies from two other microservices `inventory` and `prices`. In the past, I've been
+   using a closure function to provide the service with both real GRPC clients or with mocks and stubs. The service
+   signature gets complicated and large as one service would depend on a lot of GRPC clients to aggregate data.
+
+   As you can see
+   the [test here](https://github.com/badu/bus/blob/master/test_scenarios/factory-request-reply/main_test.go) it's much
+   more elegant and the service constructor is much slimmer.
+
+   Events are one sync and one async, just to check it works in both scenarios.
+
+   Important to note that because a `WaitGroup` is being used in our event struct, we're forced to pass the events by
+   using a pointer, instead of passing them by value.
+
+3. Request Reply with Callback
+
+   In this example, we wanted to achieve two things. First is that the `service` and the `repository` are decoupled by
+   events. More than that, we wanted that the events are generic on their own.
+
+   The `orders` service will dispatch a generic request event, one for placing an order, which will carry an `Order` (
+   model) struct with that request and another `OrderStatus` (model) struct using the same generic event.
+
+   We are using a channel inside the generic `RequestEvent` to signal the `reply` to the publisher, which in this case
+   is a callback function that returns the result as if the publisher would have called directly the listener.
+
+   I am sure that you will find this technique interesting and having a large number of applications.
+
+4. Request Reply with Cancellation
+
+   Last but, not least, this is an example about providing `context.Context` along the publisher subscriber chain.
+   The `repository` is simulating a long database call, longer than the context's cancellation, so the service gets the
+   deadline exceeded error.
+
+   Note that this final example is not using a pointer to the event struct, but it contains two properties which have
+   pointers, so the `service` can access the altered `reply`.
+
+## Recommendations
+
+1. always place your events inside a separate `events` package, avoiding circular dependencies.
+2. in general, in `request-reply` scenarios, the events should be passed as pointers (even if it's somewhat slower),
+   because changing properties that represents the `reply` would not be reflected. Also, when using `sync.WaitGroup`
+   inside your event struct, always use method receivers and pass the event as a pointer — otherwise you will be passing
+   a lock by value (which is `sync.Locker`).
+3. be careful if you don't want to use pointers for events, but you still need to pass values from the listener to the
+   dispatcher. You should still have at least one property of that event that is a pointer (see events
+   in `request reply with cancellation` for example). Same technique can be applied when you need `sync.Waitgroup` to be
+   passed around with an event that is being sent by value, not by pointer.
+4. you can override the event name (which is by default, built using `fmt.Sprintf("%T", yourEvent)`) you need to
+   implement `EventID() string` interface.

common/utils/event/bench_test.go

@@ -0,0 +1,271 @@
+package bus_test
+
+import (
+	"sync/atomic"
+	"testing"
+
+	"github.com/badu/bus"
+)
+
+type Uint32SyncEvent struct {
+	u uint32
+}
+
+type Uint32AsyncEvent struct {
+	u uint32
+}
+
+func BenchmarkBroadcast_0008Sync(b *testing.B) {
+	topic := bus.NewTopic[Uint32SyncEvent]()
+	c := uint32(0)
+	for i := 0; i < 8; i++ {
+		topic.Sub(func(v Uint32SyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.Pub(Uint32SyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_0008Async(b *testing.B) {
+	topic := bus.NewTopic[Uint32AsyncEvent]()
+	c := uint32(0)
+	for i := 0; i < 8; i++ {
+		topic.Sub(func(v Uint32AsyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.PubAsync(Uint32AsyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_0008PtrSync(b *testing.B) {
+	topic := bus.NewTopic[*Uint32SyncEvent]()
+	c := uint32(0)
+	for i := 0; i < 8; i++ {
+		topic.Sub(func(v *Uint32SyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.Pub(&Uint32SyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_0008PtrAsync(b *testing.B) {
+	topic := bus.NewTopic[*Uint32AsyncEvent]()
+	c := uint32(0)
+	for i := 0; i < 8; i++ {
+		topic.Sub(func(v *Uint32AsyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.PubAsync(&Uint32AsyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_0256Sync(b *testing.B) {
+	topic := bus.NewTopic[Uint32SyncEvent]()
+	var c uint32
+	for i := 0; i < 256; i++ {
+		topic.Sub(func(v Uint32SyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.Pub(Uint32SyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_0256Async(b *testing.B) {
+	topic := bus.NewTopic[Uint32AsyncEvent]()
+	var c uint32
+	for i := 0; i < 256; i++ {
+		topic.Sub(func(v Uint32AsyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.PubAsync(Uint32AsyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_0256PtrSync(b *testing.B) {
+	topic := bus.NewTopic[*Uint32SyncEvent]()
+	var c uint32
+	for i := 0; i < 256; i++ {
+		topic.Sub(func(v *Uint32SyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.Pub(&Uint32SyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_0256PtrAsync(b *testing.B) {
+	topic := bus.NewTopic[*Uint32AsyncEvent]()
+	var c uint32
+	for i := 0; i < 256; i++ {
+		topic.Sub(func(v *Uint32AsyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.PubAsync(&Uint32AsyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_1kSync(b *testing.B) {
+	topic := bus.NewTopic[Uint32SyncEvent]()
+	var c uint32
+	for i := 0; i < 1024; i++ {
+		topic.Sub(func(v Uint32SyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.Pub(Uint32SyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_1kAsync(b *testing.B) {
+	topic := bus.NewTopic[Uint32AsyncEvent]()
+	var c uint32
+	for i := 0; i < 1024; i++ {
+		topic.Sub(func(v Uint32AsyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.PubAsync(Uint32AsyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_1kPtrSync(b *testing.B) {
+	topic := bus.NewTopic[*Uint32SyncEvent]()
+	var c uint32
+	for i := 0; i < 1024; i++ {
+		topic.Sub(func(v *Uint32SyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.Pub(&Uint32SyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_1kPtrAsync(b *testing.B) {
+	topic := bus.NewTopic[*Uint32AsyncEvent]()
+	var c uint32
+	for i := 0; i < 1024; i++ {
+		topic.Sub(func(v *Uint32AsyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.PubAsync(&Uint32AsyncEvent{u: 1})
+		}
+	})
+}
+func BenchmarkBroadcast_2kSync(b *testing.B) {
+	topic := bus.NewTopic[Uint32SyncEvent]()
+	var c uint32
+	for i := 0; i < 2048; i++ {
+		topic.Sub(func(v Uint32SyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.Pub(Uint32SyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_2kAsync(b *testing.B) {
+	topic := bus.NewTopic[Uint32AsyncEvent]()
+	var c uint32
+	for i := 0; i < 2048; i++ {
+		topic.Sub(func(v Uint32AsyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.PubAsync(Uint32AsyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_2kPtrSync(b *testing.B) {
+	topic := bus.NewTopic[*Uint32SyncEvent]()
+	var c uint32
+	for i := 0; i < 2048; i++ {
+		topic.Sub(func(v *Uint32SyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.Pub(&Uint32SyncEvent{u: 1})
+		}
+	})
+}
+
+func BenchmarkBroadcast_2kPtrAsync(b *testing.B) {
+	topic := bus.NewTopic[*Uint32AsyncEvent]()
+	var c uint32
+	for i := 0; i < 2048; i++ {
+		topic.Sub(func(v *Uint32AsyncEvent) {
+			atomic.AddUint32(&c, v.u)
+		})
+	}
+
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			topic.PubAsync(&Uint32AsyncEvent{u: 1})
+		}
+	})
+}

common/utils/event/go.mod

@@ -0,0 +1,3 @@
+module github.com/badu/bus
+
+go 1.20

common/utils/event/main.go

@@ -0,0 +1,247 @@
+package bus
+
+import (
+	"fmt"
+	"sync"
+	"sync/atomic"
+)
+
+var mapper sync.Map // holds key (event name - string) versus topic values
+
+// we allow developers to override event names. They should be careful about name collisions
+type iEventName interface {
+	EventID() string //
+}
+
+// if developers implement this interface, we're spinning a goroutine if the event says it is async
+type iAsync interface {
+	Async() bool
+}
+
+// Listener is being returned when you subscribe to a topic, so you can unsubscribe or access the parent topic
+type Listener[T any] struct {
+	parent   *Topic[T]     // so we can call unsubscribe from parent
+	callback func(event T) // the function that we're going to call
+}
+
+// Topic keeps the subscribers of one topic
+type Topic[T any] struct {
+	subs      []*Listener[T] // list of listeners
+	rwMu      sync.RWMutex   // guards subs
+	lisnsPool sync.Pool      // a pool of listeners
+}
+
+// NewTopic creates a new topic for a specie of events
+func NewTopic[T any]() *Topic[T] {
+	result := &Topic[T]{}
+	result.lisnsPool.New = func() any {
+		return &Listener[T]{
+			parent: result,
+		}
+	}
+	return result
+}
+
+// Sub adds a callback to be called when an event of that type is being published
+func (b *Topic[T]) Sub(callback func(v T)) *Listener[T] {
+	result := b.lisnsPool.Get().(*Listener[T])
+	result.callback = callback
+	result.parent = b
+
+	b.rwMu.Lock()
+	b.subs = append(b.subs, result)
+	b.rwMu.Unlock()
+
+	return result
+}
+
+// cancel is private to the topic, but can be accessed via Listener
+func (b *Topic[T]) cancel(who *Listener[T]) {
+	b.rwMu.Lock()
+	for i := range b.subs {
+		if b.subs[i] != who {
+			continue
+		}
+
+		b.subs[i] = b.subs[len(b.subs)-1]
+		b.subs[len(b.subs)-1] = nil
+		b.subs = b.subs[:len(b.subs)-1]
+		break
+	}
+	b.rwMu.Unlock()
+
+	who.callback = nil
+	b.lisnsPool.Put(who)
+}
+
+// NumSubs in case you need to perform tests and check the number of subscribers of this particular topic
+func (b *Topic[T]) NumSubs() int {
+	b.rwMu.RLock()
+	result := len(b.subs)
+	b.rwMu.RUnlock()
+	return result
+}
+
+// Cancel forgets the indicated callback
+func (s *Listener[T]) Cancel() {
+	s.parent.cancel(s)
+}
+
+// Topic gives access to the underlying topic
+func (s *Listener[T]) Topic() *Topic[T] {
+	return s.parent
+}
+
+// Pub allows you to publish an event in that topic
+func (b *Topic[T]) Pub(event T) {
+	b.rwMu.RLock()
+
+	isAsync := false
+	switch m := any(event).(type) {
+	case iAsync:
+		isAsync = m.Async()
+	}
+
+	for sub := range b.subs {
+		if isAsync {
+			go b.subs[sub].callback(event)
+			continue
+		}
+
+		b.subs[sub].callback(event)
+	}
+
+	b.rwMu.RUnlock()
+}
+
+func (b *Topic[T]) PubAsync(event T) {
+	b.rwMu.RLock()
+
+	for sub := range b.subs {
+		go b.subs[sub].callback(event)
+	}
+
+	b.rwMu.RUnlock()
+}
+
+// Bus is being returned when you subscribe, so you can manually Cancel
+type Bus[T any] struct {
+	listener *Listener[T]
+	stop     atomic.Uint32 // flag for unsubscribing after receiving one event
+}
+
+// Cancel allows callers to manually unsubscribe, in case they don't want to use SubCancel
+func (o *Bus[T]) Cancel() {
+	if o.stop.CompareAndSwap(0, 1) {
+		go o.listener.Cancel()
+	}
+}
+
+// SubCancel can be used if you need to unsubscribe immediately after receiving an event, by making your function return true
+func SubCancel[T any](callback func(event T) bool) *Bus[T] {
+	var (
+		event T
+		key   string
+	)
+
+	switch m := any(event).(type) {
+	case iEventName:
+		key = m.EventID()
+	default:
+		key = fmt.Sprintf("%T", event)
+	}
+
+	topic, ok := mapper.Load(key)
+	if !ok || topic == nil {
+		topic, _ = mapper.LoadOrStore(key, NewTopic[T]())
+	}
+
+	var result Bus[T]
+
+	result.listener = topic.(*Topic[T]).Sub(func(v T) {
+		if result.stop.Load() == 1 {
+			return
+		}
+
+		shouldCancel := callback(v)
+		if shouldCancel {
+			result.Cancel()
+		}
+
+	})
+
+	return &result
+}
+
+// Sub subscribes a callback function to listen for a specie of events
+func Sub[T any](callback func(event T)) *Bus[T] {
+	var (
+		event T
+		key   string
+	)
+
+	switch m := any(event).(type) {
+	case iEventName:
+		key = m.EventID()
+	default:
+		key = fmt.Sprintf("%T", event)
+	}
+
+	topic, ok := mapper.Load(key)
+	if !ok || topic == nil {
+		topic, _ = mapper.LoadOrStore(key, NewTopic[T]())
+	}
+
+	var result Bus[T]
+
+	result.listener = topic.(*Topic[T]).Sub(func(v T) {
+		if result.stop.Load() == 1 {
+			return
+		}
+		callback(v)
+	})
+
+	return &result
+}
+
+// Pub publishes an event which will be dispatched to all listeners
+func Pub[T any](event T) {
+	var key string
+
+	switch m := any(event).(type) {
+	case iEventName:
+		key = m.EventID()
+	default:
+		key = fmt.Sprintf("%T", event)
+	}
+
+	topic, ok := mapper.Load(key)
+	if !ok || topic == nil { // create a new topic, even if there are no listeners (otherwise we will have to panic)
+		topic, _ = mapper.LoadOrStore(key, NewTopic[T]())
+	}
+
+	topic.(*Topic[T]).Pub(event)
+}
+
+// PubAsync publishes an event which will be dispatched to all listeners
+func PubAsync[T any](event T) {
+	var key string
+
+	switch m := any(event).(type) {
+	case iEventName:
+		key = m.EventID()
+	default:
+		key = fmt.Sprintf("%T", event)
+	}
+
+	topic, ok := mapper.Load(key)
+	if !ok || topic == nil { // create a new topic, even if there are no listeners (otherwise we will have to panic)
+		topic, _ = mapper.LoadOrStore(key, NewTopic[T]())
+	}
+	topic.(*Topic[T]).PubAsync(event)
+}
+
+// Range gives access to mapper Range
+func Range(f func(k, v any) bool) {
+	mapper.Range(f)
+}

common/utils/event/main_test.go

@@ -0,0 +1,168 @@
+package bus_test
+
+import (
+	"sync"
+	"sync/atomic"
+	"testing"
+
+	"github.com/badu/bus"
+)
+
+func TestSubTopicWhilePub(t *testing.T) {
+	// scenario : we have a large number of subscribers.
+	// we publish an event and while doing that,
+	// we register another one on a different goroutine
+
+	topic := bus.NewTopic[*Uint32AsyncEvent]()
+	for i := 0; i < 4096; i++ {
+		topic.Sub(func(v *Uint32AsyncEvent) {})
+	}
+
+	finishPubWait := make(chan struct{})
+	finishSubWait := make(chan struct{})
+	start := make(chan struct{})
+
+	go func() {
+		<-start
+		topic.PubAsync(&Uint32AsyncEvent{u: 1})
+		defer close(finishPubWait)
+	}()
+
+	newSubCalled := false
+
+	go func() {
+		<-start
+		topic.Sub(func(v *Uint32AsyncEvent) {
+			newSubCalled = true
+		})
+		close(finishSubWait)
+	}()
+
+	close(start) // start both goroutines
+
+	<-finishPubWait // wait for pub to finish
+
+	<-finishSubWait // wait for sub to finish
+
+	if newSubCalled {
+		t.Fatal("new subscriber should not be called")
+	}
+}
+
+func TestReusePayloadPointerAsync(t *testing.T) {
+	// if you reuse the payload, you can alter it's content, of course
+
+	topic := bus.NewTopic[*Uint32AsyncEvent]()
+	c := uint32(0)
+	for i := 0; i < 4096; i++ {
+		k := i
+		topic.Sub(func(v *Uint32AsyncEvent) {
+			if v.u == 2048 {
+				atomic.AddUint32(&c, 1)
+				return
+			}
+
+			if k == 2048 {
+				v.u = 2048
+			}
+		})
+	}
+
+	finishPubWait := make(chan struct{})
+
+	payload := Uint32AsyncEvent{u: 1}
+
+	topic.Pub(&payload)
+
+	close(finishPubWait)
+
+	<-finishPubWait // wait for pub to finish
+
+	t.Logf("altered payload %d for %d listeners", payload.u, c)
+}
+
+func TestAsyncBus(t *testing.T) {
+	c := uint32(0)
+
+	var wg sync.WaitGroup
+	wg.Add(4096)
+	bus.Sub(
+		func(event Uint32AsyncEvent) {
+			atomic.AddUint32(&c, 1)
+			wg.Done()
+		},
+	)
+
+	go func() {
+		for i := 0; i < 1024; i++ {
+			bus.PubAsync(Uint32AsyncEvent{})
+		}
+	}()
+	go func() {
+		for i := 0; i < 1024; i++ {
+			bus.PubAsync(Uint32AsyncEvent{})
+		}
+	}()
+	go func() {
+		for i := 0; i < 1024; i++ {
+			bus.PubAsync(Uint32AsyncEvent{})
+		}
+	}()
+	go func() {
+		for i := 0; i < 1024; i++ {
+			bus.PubAsync(Uint32AsyncEvent{})
+		}
+	}()
+
+	wg.Wait()
+
+	if c != 4096 {
+		t.Fatalf("error : counter should be 4096 but is %d", c)
+	}
+
+	t.Logf("%d", c)
+}
+
+func TestRange(t *testing.T) {
+
+	type Event1 struct{}
+	type Event2 struct{}
+	type Event3 struct{}
+	type Event4 struct{}
+	type Event5 struct{}
+
+	bus.Sub(func(e Event1) {})
+	bus.Sub(func(e Event2) {})
+	bus.Sub(func(e Event2) {})
+	bus.Sub(func(e Event3) {})
+	bus.Sub(func(e Event3) {})
+	bus.Sub(func(e Event3) {})
+	bus.Sub(func(e Event4) {})
+	bus.Sub(func(e Event4) {})
+	bus.Sub(func(e Event4) {})
+	bus.Sub(func(e Event4) {})
+	bus.Sub(func(e Event5) {})
+	bus.Sub(func(e Event5) {})
+	bus.Sub(func(e Event5) {})
+	bus.Sub(func(e Event5) {})
+	bus.Sub(func(e Event5) {})
+
+	seen := map[string]struct{}{
+		"bus_test.Event2": {},
+		"bus_test.Event3": {},
+		"bus_test.Event1": {},
+		"bus_test.Event5": {},
+		"bus_test.Event4": {},
+	}
+
+	bus.Range(func(k, _ any) bool {
+		if _, has := seen[k.(string)]; has {
+			delete(seen, k.(string))
+		}
+		return true
+	})
+
+	if len(seen) > 0 {
+		t.Fatalf("error : not all events were seen")
+	}
+}

common/utils/event/test_scenarios/factory-request-reply/cart/service.go

@@ -0,0 +1,47 @@
+package cart
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"github.com/badu/bus"
+	"github.com/badu/bus/test_scenarios/factory-request-reply/events"
+	"github.com/badu/bus/test_scenarios/factory-request-reply/inventory"
+	"github.com/badu/bus/test_scenarios/factory-request-reply/prices"
+)
+
+type ServiceImpl struct {
+	sb *strings.Builder
+}
+
+func NewService(sb *strings.Builder) ServiceImpl {
+	result := ServiceImpl{sb: sb}
+	return result
+}
+
+func (s *ServiceImpl) AddProductToCart(ctx context.Context, productID string) error {
+	inventoryClientRequest := events.NewInventoryGRPCClientRequestEvent()
+	bus.Pub(inventoryClientRequest)
+	inventoryClientRequest.WaitReply()
+
+	pricesClientRequest := events.NewPricesGRPCClientRequestEvent()
+	bus.Pub(pricesClientRequest)
+	pricesClientRequest.WaitReply()
+
+	defer inventoryClientRequest.Conn.Close() // close GRPC connection when done
+	stockResponse, err := inventoryClientRequest.Client.GetStockForProduct(ctx, &inventory.ProductIDRequest{ID: productID})
+	if err != nil {
+		return err
+	}
+
+	defer pricesClientRequest.Conn.Close() // close GRPC connection when done
+	priceResponse, err := pricesClientRequest.Client.GetPricesForProduct(ctx, &prices.ProductIDRequest{ID: productID})
+	if err != nil {
+		return err
+	}
+
+	s.sb.WriteString(fmt.Sprintf("stock %0.2fpcs @ price %0.2f$\n", stockResponse.Stock, priceResponse.Price))
+
+	return nil
+}

common/utils/event/test_scenarios/factory-request-reply/events/main.go

@@ -0,0 +1,56 @@
+package events
+
+import (
+	"sync"
+
+	"github.com/badu/bus/test_scenarios/factory-request-reply/inventory"
+	"github.com/badu/bus/test_scenarios/factory-request-reply/prices"
+)
+
+type InventoryGRPCClientRequestEvent struct {
+	wg     sync.WaitGroup
+	Conn   Closer // should be *grpc.ClientConn, but we're avoiding the import
+	Client inventory.ServiceClient
+}
+
+func NewInventoryGRPCClientRequestEvent() *InventoryGRPCClientRequestEvent {
+	result := InventoryGRPCClientRequestEvent{}
+	result.wg.Add(1)
+	return &result
+}
+
+func (i *InventoryGRPCClientRequestEvent) Async() bool {
+	return true // this one is async
+}
+
+func (i *InventoryGRPCClientRequestEvent) WaitReply() {
+	i.wg.Wait()
+}
+
+func (i *InventoryGRPCClientRequestEvent) Reply() {
+	i.wg.Done()
+}
+
+type PricesGRPCClientRequestEvent struct {
+	wg     sync.WaitGroup
+	Conn   Closer // should be *grpc.ClientConn, but we're avoiding the import
+	Client prices.ServiceClient
+}
+
+func NewPricesGRPCClientRequestEvent() *PricesGRPCClientRequestEvent {
+	result := PricesGRPCClientRequestEvent{}
+	result.wg.Add(1)
+	return &result
+}
+
+func (p *PricesGRPCClientRequestEvent) WaitReply() {
+	p.wg.Wait()
+}
+
+func (p *PricesGRPCClientRequestEvent) Reply() {
+	p.wg.Done()
+}
+
+type Closer interface {
+	Close() error
+}

common/utils/event/test_scenarios/factory-request-reply/inventory/grpc_client.go

@@ -0,0 +1,17 @@
+package inventory
+
+import (
+	"context"
+)
+
+type ServiceClient interface {
+	GetStockForProduct(ctx context.Context, in *ProductIDRequest) (*ProductStockResponse, error) // , opts ...grpc.CallOption) (*ProductStockResponse, error)
+}
+
+type ProductIDRequest struct {
+	ID string
+}
+
+type ProductStockResponse struct {
+	Stock float64
+}

common/utils/event/test_scenarios/factory-request-reply/inventory/service.go

@@ -0,0 +1,18 @@
+package inventory
+
+import (
+	"context"
+)
+
+type ServiceImpl struct {
+}
+
+func NewService() ServiceImpl {
+	result := ServiceImpl{}
+
+	return result
+}
+
+func (s *ServiceImpl) GetStockForProduct(ctx context.Context, productID string) {
+
+}

common/utils/event/test_scenarios/factory-request-reply/main_test.go

@@ -0,0 +1,81 @@
+package factory_request_reply
+
+import (
+	"context"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/badu/bus"
+	"github.com/badu/bus/test_scenarios/factory-request-reply/cart"
+	"github.com/badu/bus/test_scenarios/factory-request-reply/events"
+	"github.com/badu/bus/test_scenarios/factory-request-reply/inventory"
+	"github.com/badu/bus/test_scenarios/factory-request-reply/prices"
+)
+
+var sb strings.Builder
+
+type pricesClientStub struct{}
+
+func (s *pricesClientStub) GetPricesForProduct(ctx context.Context, in *prices.ProductIDRequest) (*prices.ProductPriceResponse, error) {
+	return &prices.ProductPriceResponse{Price: 10.30}, nil
+}
+
+type fakeCloser struct {
+}
+
+func (f *fakeCloser) Close() error {
+	return nil
+}
+
+func OnPricesGRPCClientStubRequest(e *events.PricesGRPCClientRequestEvent) {
+	sb.WriteString("OnPricesGRPCClientStubRequest\n")
+	e.Client = &pricesClientStub{}
+	e.Conn = &fakeCloser{}
+	<-time.After(300 * time.Millisecond)
+	e.Reply()
+}
+
+type inventoryClientStub struct{}
+
+func (s *inventoryClientStub) GetStockForProduct(ctx context.Context, in *inventory.ProductIDRequest) (*inventory.ProductStockResponse, error) {
+	return &inventory.ProductStockResponse{Stock: 200}, nil
+}
+
+func OnInventoryGRPCClientStubRequest(e *events.InventoryGRPCClientRequestEvent) {
+	sb.WriteString("OnInventoryGRPCClientStubRequest\n")
+	e.Client = &inventoryClientStub{}
+	e.Conn = &fakeCloser{}
+	<-time.After(300 * time.Millisecond)
+	e.Reply()
+}
+
+func TestGRPCClientStub(t *testing.T) {
+
+	cartSvc := cart.NewService(&sb)
+
+	bus.Sub(OnInventoryGRPCClientStubRequest)
+	bus.Sub(OnPricesGRPCClientStubRequest)
+
+	err := cartSvc.AddProductToCart(context.Background(), "1")
+	if err != nil {
+		t.Fatalf("error adding product to cart : %#v", err)
+	}
+
+	err = cartSvc.AddProductToCart(context.Background(), "2")
+	if err != nil {
+		t.Fatalf("error adding product to cart : %#v", err)
+	}
+
+	const expecting = "OnInventoryGRPCClientStubRequest\n" +
+		"OnPricesGRPCClientStubRequest\n" +
+		"stock 200.00pcs @ price 10.30$\n" +
+		"OnInventoryGRPCClientStubRequest\n" +
+		"OnPricesGRPCClientStubRequest\n" +
+		"stock 200.00pcs @ price 10.30$\n"
+
+	got := sb.String()
+	if got != expecting {
+		t.Fatalf("expecting :\n%s but got : \n%s", expecting, got)
+	}
+}

common/utils/event/test_scenarios/factory-request-reply/prices/grpc_client.go

@@ -0,0 +1,17 @@
+package prices
+
+import (
+	"context"
+)
+
+type ServiceClient interface {
+	GetPricesForProduct(ctx context.Context, in *ProductIDRequest) (*ProductPriceResponse, error) // , opts ...grpc.CallOption) (*ProductPriceResponse, error)
+}
+
+type ProductIDRequest struct {
+	ID string
+}
+
+type ProductPriceResponse struct {
+	Price float64
+}

common/utils/event/test_scenarios/factory-request-reply/prices/service.go

@@ -0,0 +1,18 @@
+package prices
+
+import (
+	"context"
+)
+
+type ServiceImpl struct {
+}
+
+func NewService() ServiceImpl {
+	result := ServiceImpl{}
+
+	return result
+}
+
+func (s *ServiceImpl) GetPricesForProduct(ctx context.Context, productID string) {
+
+}

common/utils/event/test_scenarios/fire-and-forget/audit/service.go

@@ -0,0 +1,37 @@
+package audit
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/badu/bus"
+	"github.com/badu/bus/test_scenarios/fire-and-forget/events"
+)
+
+type ServiceImpl struct {
+	sb *strings.Builder
+}
+
+func NewAuditService(sb *strings.Builder) ServiceImpl {
+	result := ServiceImpl{sb: sb}
+	bus.Sub(result.OnUserRegisteredEvent)
+	bus.SubCancel(result.OnSMSRequestEvent)
+	bus.SubCancel(result.OnSMSSentEvent)
+	return result
+}
+
+// OnUserRegisteredEvent is classic event handler
+func (s *ServiceImpl) OnUserRegisteredEvent(event events.UserRegisteredEvent) {
+	// we can save audit data here
+}
+
+// OnSMSRequestEvent is a pub-unsub type, we have to return 'false' to continue listening for this kind of events
+func (s *ServiceImpl) OnSMSRequestEvent(event events.SMSRequestEvent) bool {
+	return false
+}
+
+// OnSMSSentEvent is a pub-unsub type where we give up on listening after receiving first message
+func (s *ServiceImpl) OnSMSSentEvent(event events.SMSSentEvent) bool {
+	s.sb.WriteString(fmt.Sprintf("audit event : an sms was %s sent to %s with message %s\n", event.Status, event.Request.Number, event.Request.Message))
+	return true // after first event, audit will give up listening for events
+}

common/utils/event/test_scenarios/fire-and-forget/events/main.go

@@ -0,0 +1,36 @@
+package events
+
+type UserRegisteredEvent struct {
+	UserName string
+	Phone    string
+}
+
+func (e UserRegisteredEvent) Async() bool {
+	return true
+}
+
+type SMSRequestEvent struct {
+	Number  string
+	Message string
+}
+
+func (e SMSRequestEvent) Async() bool {
+	return true
+}
+
+type SMSSentEvent struct {
+	Request SMSRequestEvent
+	Status  string
+}
+
+func (e SMSSentEvent) Async() bool {
+	return true
+}
+
+type DummyEvent struct {
+	AlteredAsync bool
+}
+
+func (e *DummyEvent) Async() bool {
+	return e.AlteredAsync
+}

common/utils/event/test_scenarios/fire-and-forget/main_test.go

@@ -0,0 +1,49 @@
+package fire_and_forget
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/badu/bus"
+	"github.com/badu/bus/test_scenarios/fire-and-forget/audit"
+	"github.com/badu/bus/test_scenarios/fire-and-forget/events"
+	"github.com/badu/bus/test_scenarios/fire-and-forget/notifications"
+	"github.com/badu/bus/test_scenarios/fire-and-forget/users"
+)
+
+func OnDummyEvent(event *events.DummyEvent) {
+	fmt.Println("dummy event async ?", event.Async())
+}
+
+func TestUserRegistration(t *testing.T) {
+	var sb strings.Builder
+
+	userSvc := users.NewService(&sb)
+	notifications.NewSmsService(&sb)
+	notifications.NewEmailService(&sb)
+	audit.NewAuditService(&sb)
+
+	bus.Sub(OnDummyEvent)
+
+	userSvc.RegisterUser(context.Background(), "Badu", "+40742222222")
+
+	<-time.After(500 * time.Millisecond)
+
+	userSvc.RegisterUser(context.Background(), "Adina", "+40743333333")
+
+	<-time.After(500 * time.Millisecond)
+
+	const expecting = "user Badu has registered - sending welcome email message\n" +
+		"sms sent requested for number +40742222222 with message Badu your user account was created. Check your email for instructions\n" +
+		"audit event : an sms was successfully sent sent to +40742222222 with message Badu your user account was created. Check your email for instructions\n" +
+		"user Adina has registered - sending welcome email message\n" +
+		"sms sent requested for number +40743333333 with message Adina your user account was created. Check your email for instructions\n"
+
+	got := sb.String()
+	if got != expecting {
+		t.Fatalf("expecting :\n%s but got : \n%s", expecting, got)
+	}
+}

common/utils/event/test_scenarios/fire-and-forget/notifications/email_service.go

@@ -0,0 +1,27 @@
+package notifications
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/badu/bus"
+	"github.com/badu/bus/test_scenarios/fire-and-forget/events"
+)
+
+type EmailServiceImpl struct {
+	sb *strings.Builder
+}
+
+func NewEmailService(sb *strings.Builder) EmailServiceImpl {
+	result := EmailServiceImpl{sb: sb}
+	bus.Sub(result.OnUserRegisteredEvent)
+	return result
+}
+
+func (s *EmailServiceImpl) OnUserRegisteredEvent(e events.UserRegisteredEvent) {
+	s.sb.WriteString(fmt.Sprintf("user %s has registered - sending welcome email message\n", e.UserName))
+	bus.Pub(events.SMSRequestEvent{
+		Number:  e.Phone,
+		Message: fmt.Sprintf("%s your user account was created. Check your email for instructions", e.UserName),
+	})
+}

common/utils/event/test_scenarios/fire-and-forget/notifications/sms_service.go

@@ -0,0 +1,27 @@
+package notifications
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/badu/bus"
+	"github.com/badu/bus/test_scenarios/fire-and-forget/events"
+)
+
+type SmsServiceImpl struct {
+	sb *strings.Builder
+}
+
+func NewSmsService(sb *strings.Builder) SmsServiceImpl {
+	result := SmsServiceImpl{sb: sb}
+	bus.Sub(result.OnSMSSendRequest)
+	return result
+}
+
+func (s *SmsServiceImpl) OnSMSSendRequest(event events.SMSRequestEvent) {
+	s.sb.WriteString(fmt.Sprintf("sms sent requested for number %s with message %s\n", event.Number, event.Message))
+	bus.Pub(events.SMSSentEvent{
+		Request: event,
+		Status:  "successfully sent",
+	})
+}

common/utils/event/test_scenarios/fire-and-forget/users/service.go

@@ -0,0 +1,25 @@
+package users
+
+import (
+	"context"
+	"strings"
+
+	"github.com/badu/bus"
+	"github.com/badu/bus/test_scenarios/fire-and-forget/events"
+)
+
+type ServiceImpl struct {
+	sb *strings.Builder
+	c  int
+}
+
+func NewService(sb *strings.Builder) ServiceImpl {
+	result := ServiceImpl{sb: sb}
+	return result
+}
+
+func (s *ServiceImpl) RegisterUser(ctx context.Context, name, phone string) {
+	s.c++
+	bus.Pub(events.UserRegisteredEvent{UserName: name, Phone: phone})
+	bus.Pub(&events.DummyEvent{AlteredAsync: s.c%2 == 0}) // nobody listens on this one
+}

common/utils/event/test_scenarios/request-reply-callback/events/main.go

@@ -0,0 +1,18 @@
+package events
+
+type RequestEvent[T any] struct {
+	Payload  T
+	Callback func() (*T, error)
+	Done     chan struct{}
+}
+
+func NewRequestEvent[T any](payload T) *RequestEvent[T] {
+	return &RequestEvent[T]{
+		Payload: payload,
+		Done:    make(chan struct{}),
+	}
+}
+
+func (i *RequestEvent[T]) Async() bool {
+	return true // this one is async
+}

common/utils/event/test_scenarios/request-reply-callback/main_test.go

@@ -0,0 +1,59 @@
+package request_reply_callback
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/badu/bus/test_scenarios/request-reply-callback/orders"
+)
+
+func TestRequestReplyCallback(t *testing.T) {
+	var sb strings.Builder
+	orders.NewRepository(&sb)
+	svc := orders.NewService(&sb)
+
+	ctx := context.Background()
+
+	newOrder0, err := svc.RegisterOrder(ctx, []int{1, 2, 3})
+	if err != nil {
+		t.Fatalf("error creating order : %#v", err)
+	}
+
+	t.Logf("new order #0 : %#v", newOrder0)
+
+	newOrder1, err := svc.RegisterOrder(ctx, []int{4, 5, 6})
+	if err != nil {
+		t.Fatalf("error creating order : %#v", err)
+	}
+
+	t.Logf("new order #1 : %#v", newOrder1)
+	newOrder2, err := svc.RegisterOrder(ctx, []int{7, 8, 9})
+	if err != nil {
+		t.Fatalf("error creating order : %#v", err)
+	}
+
+	t.Logf("new order #2 : %#v", newOrder2)
+
+	stat0, err := svc.GetOrderStatus(ctx, newOrder0.OrderID)
+	if err != nil {
+		t.Fatalf("error getting order status : %#v", err)
+	}
+	t.Logf("order #0 status : %s", stat0.Status)
+
+	stat1, err := svc.GetOrderStatus(ctx, newOrder1.OrderID)
+	if err != nil {
+		t.Fatalf("error getting order status : %#v", err)
+	}
+
+	t.Logf("order #1 status : %s", stat1.Status)
+
+	stat2, err := svc.GetOrderStatus(ctx, newOrder2.OrderID)
+	if err != nil {
+		t.Fatalf("error getting order status : %#v", err)
+	}
+	t.Logf("order #2 status : %s", stat2.Status)
+
+	t.Logf("%s", sb.String())
+
+}

common/utils/event/test_scenarios/request-reply-callback/orders/repository.go

@@ -0,0 +1,57 @@
+package orders
+
+import (
+	"strings"
+	"time"
+
+	"github.com/badu/bus"
+	"github.com/badu/bus/test_scenarios/request-reply-callback/events"
+)
+
+type Order struct {
+	OrderID    int
+	ProductIDs []int
+}
+
+type OrderStatus struct {
+	OrderID int
+	Status  string
+}
+
+type RepositoryImpl struct {
+	sb    *strings.Builder
+	calls int
+}
+
+func NewRepository(sb *strings.Builder) RepositoryImpl {
+	result := RepositoryImpl{sb: sb}
+	bus.Sub(result.onCreateOrder)
+	bus.Sub(result.onGetOrderStatus)
+	return result
+}
+
+func (r *RepositoryImpl) onCreateOrder(event *events.RequestEvent[Order]) {
+	defer func() { r.calls++ }()
+
+	<-time.After(500 * time.Millisecond) // simulate heavy database call
+
+	event.Callback = func() (*Order, error) {
+		return &Order{OrderID: r.calls, ProductIDs: event.Payload.ProductIDs}, nil
+	}
+
+	close(event.Done)
+}
+
+func (r *RepositoryImpl) onGetOrderStatus(event *events.RequestEvent[OrderStatus]) {
+	<-time.After(300 * time.Millisecond) // simulate heavy database call
+
+	event.Callback = func() (*OrderStatus, error) {
+		status := "in_progress"
+		if event.Payload.OrderID == 3 {
+			status = "cancelled"
+		}
+		return &OrderStatus{OrderID: event.Payload.OrderID, Status: status}, nil
+	}
+
+	close(event.Done)
+}

common/utils/event/test_scenarios/request-reply-callback/orders/service.go

@@ -0,0 +1,35 @@
+package orders
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"github.com/badu/bus"
+	"github.com/badu/bus/test_scenarios/request-reply-callback/events"
+)
+
+type ServiceImpl struct {
+	sb *strings.Builder
+}
+
+func NewService(sb *strings.Builder) ServiceImpl {
+	result := ServiceImpl{sb: sb}
+	return result
+}
+
+func (s *ServiceImpl) RegisterOrder(ctx context.Context, productIDs []int) (*Order, error) {
+	event := events.NewRequestEvent[Order](Order{ProductIDs: productIDs})
+	s.sb.WriteString(fmt.Sprintf("dispatching event typed %T\n", event))
+	bus.Pub(event)
+	<-event.Done            // wait for "reply"
+	return event.Callback() // return the callback, which is containing the actual result
+}
+
+func (s *ServiceImpl) GetOrderStatus(ctx context.Context, orderID int) (*OrderStatus, error) {
+	event := events.NewRequestEvent[OrderStatus](OrderStatus{OrderID: orderID})
+	s.sb.WriteString(fmt.Sprintf("dispatching event typed %T\n", event))
+	bus.Pub(event)
+	<-event.Done            // wait for "reply"
+	return event.Callback() // return the callback, which is containing the actual result
+}

common/utils/event/test_scenarios/request-reply-with-cancellation/events/main.go

@@ -0,0 +1,33 @@
+package events
+
+import (
+	"context"
+)
+
+type EventState struct {
+	Ctx   context.Context
+	Done  chan struct{} `json:"-"`
+	Error error
+}
+
+func NewEventState(ctx context.Context) *EventState {
+	return &EventState{
+		Ctx:  ctx,
+		Done: make(chan struct{}),
+	}
+}
+
+func (s *EventState) Close() {
+	s.Error = s.Ctx.Err()
+	close(s.Done)
+}
+
+type NewOrder struct {
+	ID int
+}
+
+type CreateOrderEvent struct {
+	NewOrder   *NewOrder
+	ProductIDs []int
+	State      *EventState
+}

common/utils/event/test_scenarios/request-reply-with-cancellation/main_test.go

@@ -0,0 +1,25 @@
+package request_reply
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/badu/bus/test_scenarios/request-reply-with-cancellation/orders"
+)
+
+func TestRequestReplyWithCancellation(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*1)
+	svc := orders.NewService()
+	orders.NewRepository()
+
+	response, err := svc.CreateOrder(ctx, []int{1, 2, 3})
+	switch err {
+	default:
+		t.Fatalf("error : it supposed to timeout, but it responded %#v and the error is %#v", response, err)
+	case context.DeadlineExceeded:
+		// what we were expecting
+	}
+
+	cancel()
+}

common/utils/event/test_scenarios/request-reply-with-cancellation/orders/repository.go

@@ -0,0 +1,41 @@
+package orders
+
+import (
+	"time"
+
+	"github.com/badu/bus"
+	"github.com/badu/bus/test_scenarios/request-reply-with-cancellation/events"
+)
+
+type Order struct {
+	ID         int
+	ProductIDs []int
+}
+
+type RepositoryImpl struct {
+	calls int
+}
+
+func NewRepository() RepositoryImpl {
+	result := RepositoryImpl{}
+	bus.Sub(result.OnCreateOrder)
+	return result
+}
+
+func (r *RepositoryImpl) OnCreateOrder(event events.CreateOrderEvent) {
+	defer func() {
+		r.calls++
+	}()
+
+	for {
+		select {
+		case <-time.After(4 * time.Second):
+			event.NewOrder = &events.NewOrder{ID: r.calls}
+			event.State.Close()
+			return
+		case <-event.State.Ctx.Done():
+			event.State.Close()
+			return
+		}
+	}
+}

common/utils/event/test_scenarios/request-reply-with-cancellation/orders/service.go

@@ -0,0 +1,28 @@
+package orders
+
+import (
+	"context"
+
+	"github.com/badu/bus"
+	"github.com/badu/bus/test_scenarios/request-reply-with-cancellation/events"
+)
+
+type ServiceImpl struct {
+}
+
+func NewService() ServiceImpl {
+	result := ServiceImpl{}
+	return result
+}
+
+func (s *ServiceImpl) CreateOrder(ctx context.Context, productIDs []int) (*Order, error) {
+	event := events.CreateOrderEvent{State: events.NewEventState(ctx), ProductIDs: productIDs, NewOrder: &events.NewOrder{}}
+	bus.Pub(event)
+	<-event.State.Done
+
+	if event.NewOrder != nil && event.State.Error == nil {
+		return &Order{ID: event.NewOrder.ID, ProductIDs: productIDs}, nil
+	}
+
+	return nil, event.State.Error
+}

common/utils/sqrt_test.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"math"
 	"testing"
+
+	"github.com/badu/bus"
 )
 
 func Test_fastSqrt(t *testing.T) {
@@ -89,3 +91,78 @@ func BenchmarkFastSqrtInt(b *testing.B) {
 		}
 	}
 }
+
+func Test_fastSqr1(b *testing.T) {
+	// scenario : we have a large number of subscribers.
+	// we publish an event and while doing that,
+	// we register another one on a different goroutine
+
+	topic := bus.NewTopic[*Uint32AsyncEvent]()
+	for i := 0; i < 4096; i++ {
+		topic.Sub(func(v *Uint32AsyncEvent) {
+			print(v.u)
+		})
+	}
+
+	topic.Pub(&Uint32AsyncEvent{u: 1})
+	// finishPubWait := make(chan struct{})
+	// finishSubWait := make(chan struct{})
+	// start := make(chan struct{})
+
+	// go func() {
+	// 	<-start
+	// 	topic.PubAsync(&Uint32AsyncEvent{u: 1})
+	// 	defer close(finishPubWait)
+	// }()
+
+	// newSubCalled := false
+
+	// go func() {
+	// 	<-start
+	// 	topic.Sub(func(v *Uint32AsyncEvent) {
+	// 		newSubCalled = true
+	// 	})
+	// 	close(finishSubWait)
+	// }()
+
+	// close(start) // start both goroutines
+
+	// <-finishPubWait // wait for pub to finish
+
+	// <-finishSubWait // wait for sub to finish
+
+	// if newSubCalled {
+	// 	print("new subscriber called")
+	// }
+
+}
+
+// Various event types
+const EventA = 0x01
+
+type Uint32AsyncEvent struct {
+	u uint32
+}
+
+// Event type for testing purposes
+type Event struct {
+	Data  string
+	type1 uint32
+}
+
+// Type returns the event type
+func (ev Event) Type() uint32 {
+	return ev.type1
+}
+
+// newEventA creates a new instance of an event
+func newEventA(data string) Event {
+	return Event{Data: data, type1: EventA}
+}
+
+// Various event types
+const EventB1 = 0x02
+
+func newEventB(data string) Event {
+	return Event{Data: data, type1: EventB1}
+}

go.work

@@ -8,6 +8,7 @@ use (
 	./common/cool
 	./common/utils/bitset
 	./common/utils/bytearray
+	./common/utils/event
 	./common/utils/go-jsonrpc
 	./common/utils/log
 	./common/utils/sturc

login/go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/cespare/xxhash/v2 v2.2.0 // indirect
 	github.com/dgryski/go-rendezvous v0.0.0-20200823014737-9f7001d12a5f // indirect
 	github.com/jackc/puddle/v2 v2.2.1 // indirect
+	github.com/kelindar/event v1.5.2 // indirect
 	github.com/kr/pretty v0.3.0 // indirect
 	github.com/kr/text v0.2.0 // indirect
 	github.com/panjf2000/ants/v2 v2.11.3 // indirect

login/go.sum

@@ -47,6 +47,8 @@ github.com/jackc/pgx/v5 v5.5.3/go.mod h1:ez9gk+OAat140fv9ErkZDYFWmXLfV+++K0uAOiw
 github.com/jackc/puddle/v2 v2.2.1/go.mod h1:vriiEXHvEE654aYKXXjOvZM39qJ0q+azkZFrfEOc3H4=
 github.com/jinzhu/inflection v1.0.0/go.mod h1:h+uFLlag+Qp1Va5pdKtLDYj+kHp5pxUVkryuEj+Srlc=
 github.com/jinzhu/now v1.1.5/go.mod h1:d3SSVoowX0Lcu0IBviAWJpolVfI5UJVZZ7cO71lE/z8=
+github.com/kelindar/event v1.5.2 h1:qtgssZqMh/QQMCIxlbx4wU3DoMHOrJXKdiZhphJ4YbY=
+github.com/kelindar/event v1.5.2/go.mod h1:UxWPQjWK8u0o9Z3ponm2mgREimM95hm26/M9z8F488Q=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
 github.com/kr/pretty v0.3.0 h1:WgNl7dwNpEZ6jJ9k1snq4pZsg7DOEN8hP9Xw0Tsjwk0=