Saraf

Status

📜📞🔧🔧❌

Back-End Developer

Interview Process

flowchart LR
    sr(Send Resume) --> hr(HR Call) --> si(Screening Interview) --> ti(Technical Interview) --rejected--x hri(HR Interview) -.-> o(Offer)

Apply Way

Jobvision

Interview Date

• Sent Resume
  1404.07.18

• HR Call
  1404.07.28

• Screening Interview
  1404.07.30

• Technical Interview
  1404.08.05

• Rejection Email
  1404.08.12

Interview Duration

• Screening Interview
  30 minutes

• Technical Interview
  1 hours

Interview Platform

Google Meet

Screening Interview

• Tell me about yourself.

• Explain what a race condition is in an order-matching / exchange system (for example, in a matching engine). Give concrete examples of how race conditions can occur and describe strategies you would use to prevent or resolve them.

• How would you design a system that avoids data loss when using a message broker (for example, RabbitMQ)?

Technical Interview (Live Coding)

• We want to implement a simple token-bucket algorithm in middleware to rate-limit users?

  My Answer

  Run

  package main
  
  import (
      "fmt"
      "time"
  )
  
  type User struct {
      accountID      int64
      capacity       int64
      counter        int64
      refillRate     int64
      lastRefillTime time.Time
  }
  
  func handler(user User, userData map[int64]User) {
      if _, ok := userData[user.accountID]; ok {
          fmt.Println("OK")
          ud := userData[user.accountID]
          if ud.counter >= ud.capacity {
              fmt.Println(ud.counter)
              panic("rate limit reached")
          }
          ud.counter++
          fmt.Println(ud.counter)
          elapsTime := time.Now().Unix() - ud.lastRefillTime.Unix()
          ud.counter += elapsTime * ud.refillRate
      } else {
          u := User{accountID: 123, capacity: 10, counter: 0, refillRate: 1}
          userData[u.accountID] = u
      }
      fmt.Println(user.counter, " ", user.capacity, " ", user.refillRate, " ", user.lastRefillTime)
  }
  
  func main() {
      userData := make(map[int64]User, 0)
      newUser := User{accountID: 123, capacity: 10, counter: 0, refillRate: 1, lastRefillTime: time.Now()}
      for i := range 10 {
          fmt.Println("i:", i)
          handler(newUser, userData)
      }
  }
  

  این‌جا اشتباهم این بود که مقدار map رو عوض کردم دوباره نذاشتم توش.

  Answer

  Run

  package main
  
  import (
      "fmt"
      "sync"
      "time"
  )
  
  type User struct {
      accountID      int64
      capacity       int64
      tokens         int64
      refillRate     int64
      lastRefillTime time.Time
      mutex          sync.Mutex
  }
  
  type TokenBucketManager struct {
      users map[int64]*User
      mutex sync.RWMutex
  }
  
  func NewTokenBucketManager() *TokenBucketManager {
      return &TokenBucketManager{
          users: make(map[int64]*User),
      }
  }
  
  func (tm *TokenBucketManager) GetOrCreateUser(accountID int64, capacity, refillRate int64) *User {
      tm.mutex.Lock()
      defer tm.mutex.Unlock()
  
      if user, exists := tm.users[accountID]; exists {
          return user
      }
  
      user := &User{
          accountID:      accountID,
          capacity:       capacity,
          tokens:         capacity, // Start with full bucket
          refillRate:     refillRate,
          lastRefillTime: time.Now(),
      }
      tm.users[accountID] = user
      return user
  }
  
  func (u *User) refill() {
      now := time.Now()
      elapsed := now.Sub(u.lastRefillTime)
  
      // Calculate tokens to add based on elapsed time
      tokensToAdd := int64(elapsed.Seconds()) * u.refillRate
      if tokensToAdd > 0 {
          u.tokens = min(u.tokens+tokensToAdd, u.capacity)
          u.lastRefillTime = now
      }
  }
  
  func (u *User) AllowRequest() {
      u.mutex.Lock()
      defer u.mutex.Unlock()
  
      // Refill tokens based on time elapsed
      u.refill()
  
      // Check if we have at least one token
      if u.tokens > 0 {
          u.tokens--
          fmt.Printf("Request allowed. Tokens remaining: %d\n", u.tokens)
          return
      }
  
      // If no tokens available, panic
      panic("rate limit reached")
  }
  
  func min(a, b int64) int64 {
      if a < b {
          return a
      }
      return b
  }
  
  // Middleware handler function
  func (tm *TokenBucketManager) RateLimitMiddleware(accountID int64) {
      user := tm.GetOrCreateUser(accountID, 10, 1) // capacity=10, refillRate=1 token/sec
      user.AllowRequest()
  }
  
  func main() {
      tokenManager := NewTokenBucketManager()
  
      // Simulate requests with panic recovery
      for i := 0; i < 15; i++ {
          func() {
              defer func() {
                  if r := recover(); r != nil {
                      fmt.Printf("Request %d: %v\n", i+1, r)
                  }
              }()
  
              fmt.Printf("Request %d: ", i+1)
              tokenManager.RateLimitMiddleware(123)
          }()
  
          // Add some delay to see the refill in action
          if i == 9 { // After 10th request, wait to see refill
              fmt.Println("Waiting 2 seconds for token refill...")
              time.Sleep(2 * time.Second)
          } else {
              time.Sleep(100 * time.Millisecond)
          }
      }
  }
  

Score

6/10

در کل خوب بود. استک php داشتن می‌خواستن سوییچ کنن رو go و تیم فلت بود، تعداد بکندها هم ۶ نفر و این یعنی فشار کاری! یه مقدار شاید اگه مسلط‌تر لایوکد رو می‌زدم اوکی می‌شد اما خب خیلی هم شرکتی نبود که براش ناراحت بشم.