03 Advanced Go (Concurrency)

Go famous hi Concurrency ke liye hai. Matlab ek saath bahut sare kaam karna.

1. Goroutines (Lightweight Threads) 🏃‍♂️

Agar aap function call ke aage go laga dein, to wo background me chalega (Main program rukega nahi).

package main
import (
    "fmt"
    "time"
)

func sayHello(n int) {
    for i := 0; i < n; i++ {
        fmt.Println("Hello", i)
        time.Sleep(100 * time.Millisecond)
    }
}

func main() {
    go sayHello(5) // Background me chalega
    fmt.Println("Main function chal raha hai...")

    time.Sleep(1 * time.Second) // Wait karna padega warna main khatam ho jayega!
}

Note: Goroutines bahut lightweight hoti hain (sirf 2KB memory).

---

2. Channels (Talking between Goroutines) 📞

Goroutines ek doosre se baat karne ke liye Channels use karti hain.

func main() {
    msgChannel := make(chan string) // Channel banaya

    go func() {
        msgChannel <- "Hi from Goroutine! 👋" // Message bheja
    }()

    msg := <-msgChannel // Message receive kiya
    fmt.Println(msg)
}

Unbuffered vs Buffered

• Unbuffered: Sender block ho jata hai jab tak koi Receiver na ho.
• Buffered: make(chan string, 2). 2 messages tak store kar sakta hai bina block huye.

---

3. WaitGroups (Intezaar karna) ⏳

time.Sleep use karna unprofessional hai. Hum sync.WaitGroup use karte hain.

import "sync"

var wg sync.WaitGroup

func worker(id int) {
    defer wg.Done() // Kaam khatam hone par batao
    fmt.Printf("Worker %d starting\n", id)
}

func main() {
    for i := 1; i <= 3; i++ {
        wg.Add(1) // 1 Worker add kiya
        go worker(i)
    }
    wg.Wait() // Sabke khatam hone ka wait karo
}

---

## 4. Race Conditions & Mutex 🔒

Jab do Goroutines same variable ko ek saath access karein, to data corrupt ho sakta hai (**Race Condition**).
Isse bachne ke liye hum **Mutex (Mutual Exclusion)** use karte hain.

```go
import "sync"

var count = 0
var mu sync.Mutex

func increment() {
    mu.Lock()   // Darwaza band (Koi aur nahi aa sakta)
    count++     // Critical Section
    mu.Unlock() // Darwaza khula
}

5. Select (Multi-Channel Handler) 🚦

Agar multiple channels se data aana ho, to select use karte hain.

select {
case msg1 := <-chan1:
    fmt.Println("Channel 1 se aya:", msg1)
case msg2 := <-chan2:
    fmt.Println("Channel 2 se aya:", msg2)
default:
    fmt.Println("Abhi koi data nahi hai.")
}