go-concurrent-programming

Practice materials for "Concurrent Programming with Go" course

Concurrency and Parallelism

• Concurrency - have multiple tasks
• Parallelism - execute multiple tasks simultaneously

Goroutines

A goroutine is a lightweight thread managed by the Go runtime.

Threads	Goroutines
Have own execution stack	Have own execution stack
Fixed stack space (~1MB)	Variable stack space (starts @2KB)
Managed by OS	Managed by Go runtime

The Sync Package

The sync package (https://golang.org/pkg/sync) provides basic synchronization primitives to solve the following 2 challenges:

• Coordinating tasks - WaitGroups
  • A WaitGroup waits for a collection of goroutines to finish.
• Shared memory - Mutexes
  • A mutex is a mutual exclusion lock to protect shared memory.

Channels

A channel is a typed conduit through which you can send and receive values. Channel allows goroutines to synchronize without explicit locks or condition variables in a loosely-coupled fashion.

• Creating a Channel

  ch := make(chan int)

• Creating a Buffered Channel

  ch := make(chan int, 5)

• Closing a Channel

  close(ch)

Channel Types

Created channels are always bidirectional. The type can be restricted when the channel is passed into a function:

• Bidirectional

  func myFunction(ch chan int) {
      // ch here is bidirectional
      ch <- 23
      fmt.Println(<-ch)
  }

• Send-only

  func myFunction(ch chan<- int) {
      // ch here is send-only
      ch <- 23
  }

• Receive-only

  func myFunction(ch <-chan int) {
      // ch here is receive-only
      fmt.Println(<-ch)
  }

Working with Channels in Control Flows

• If statements

  if msg, ok := <-ch; ok {
      // Enters here if channel is not closed, i.e. ok == true
  }

• For loops

  for msg := range ch {
      // Iterates until the channel is closed
  }

• Select statements

  ch1 := make(chan int)
  ch2 := make(chan string)
  select {
  case i := <-ch1:
      // Enters here if ch1 has a message to be received
  case ch2 <- "hello":
      // Enters here if ch2 is ready for us to send a message
  default:
      // use default case for non-blocking select
  }