v1 Subscribe with concurrency control (DEPRECATED)

  import 
  
 ( 
  
 "context" 
  
 "fmt" 
  
 "io" 
  
 "sync/atomic" 
  
 "time" 
  
 "cloud.google.com/go/pubsub" 
 ) 
 func 
  
 pullMsgsConcurrencyControl 
 ( 
 w 
  
 io 
 . 
 Writer 
 , 
  
 projectID 
 , 
  
 subID 
  
 string 
 ) 
  
 error 
  
 { 
  
 // projectID := "my-project-id" 
  
 // subID := "my-sub" 
  
 ctx 
  
 := 
  
 context 
 . 
 Background 
 () 
  
 client 
 , 
  
 err 
  
 := 
  
 pubsub 
 . 
  NewClient 
 
 ( 
 ctx 
 , 
  
 projectID 
 ) 
  
 if 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 return 
  
 fmt 
 . 
 Errorf 
 ( 
 "pubsub.NewClient: %w" 
 , 
  
 err 
 ) 
  
 } 
  
 defer 
  
 client 
 . 
 Close 
 () 
  
 sub 
  
 := 
  
 client 
 . 
 Subscription 
 ( 
 subID 
 ) 
  
 // Must set ReceiveSettings.Synchronous to false (or leave as default) to enable 
  
 // concurrency pulling of messages. Otherwise, NumGoroutines will be set to 1. 
  
 sub 
 . 
 ReceiveSettings 
 . 
 Synchronous 
  
 = 
  
 false 
  
 // NumGoroutines determines the number of goroutines sub.Receive will spawn to pull 
  
 // messages. 
  
 sub 
 . 
 ReceiveSettings 
 . 
 NumGoroutines 
  
 = 
  
 16 
  
 // MaxOutstandingMessages limits the number of concurrent handlers of messages. 
  
 // In this case, up to 8 unacked messages can be handled concurrently. 
  
 // Note, even in synchronous mode, messages pulled in a batch can still be handled 
  
 // concurrently. 
  
 sub 
 . 
 ReceiveSettings 
 . 
 MaxOutstandingMessages 
  
 = 
  
 8 
  
 // Receive messages for 10 seconds, which simplifies testing. 
  
 // Comment this out in production, since `Receive` should 
  
 // be used as a long running operation. 
  
 ctx 
 , 
  
 cancel 
  
 := 
  
 context 
 . 
 WithTimeout 
 ( 
 ctx 
 , 
  
 10 
 * 
 time 
 . 
 Second 
 ) 
  
 defer 
  
 cancel 
 () 
  
 var 
  
 received 
  
 int32 
  
 // Receive blocks until the context is cancelled or an error occurs. 
  
 err 
  
 = 
  
 sub 
 . 
 Receive 
 ( 
 ctx 
 , 
  
 func 
 ( 
 _ 
  
 context 
 . 
 Context 
 , 
  
 msg 
  
 * 
 pubsub 
 . 
 Message 
 ) 
  
 { 
  
 atomic 
 . 
 AddInt32 
 ( 
& received 
 , 
  
 1 
 ) 
  
 msg 
 . 
 Ack 
 () 
  
 }) 
  
 if 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 return 
  
 fmt 
 . 
 Errorf 
 ( 
 "sub.Receive returned error: %w" 
 , 
  
 err 
 ) 
  
 } 
  
 fmt 
 . 
 Fprintf 
 ( 
 w 
 , 
  
 "Received %d messages\n" 
 , 
  
 received 
 ) 
  
 return 
  
 nil 
 } 
 

  # subscription_id = "your-subscription-id" 
 pubsub 
  
 = 
  
 Google 
 :: 
 Cloud 
 :: 
  Pubsub 
 
 . 
 new 
 subscription 
  
 = 
  
 pubsub 
 . 
 subscription 
  
 subscription_id 
 # Use 2 threads for streaming, 4 threads for executing callbacks and 2 threads 
 # for sending acknowledgements and/or delays 
 subscriber 
  
 = 
  
 subscription 
 . 
 listen 
  
 streams 
 : 
  
 2 
 , 
  
 threads 
 : 
  
 { 
  
 callback 
 : 
  
 4 
 , 
  
 push 
 : 
  
 2 
 } 
  
 do 
  
 | 
 received_message 
 | 
  
 puts 
  
 "Received message: 
 #{ 
 received_message 
 . 
 data 
 } 
 " 
  
 received_message 
 . 
 acknowledge! 
 end 
 subscriber 
 . 
 start 
 # Let the main thread sleep for 60 seconds so the thread for listening 
 # messages does not quit 
 sleep 
  
 60 
 subscriber 
 . 
 stop 
 . 
 wait!