Runnable vs. Callable

Callable's call() method can :

• Return value : A Future object which can hold the result of computation
• Throw Exception

CyclicBarrier vs. CountDownLatch

SIMILARITY

• Both waits for number of threads on one or more events

DIFFERENCE

• We cannot re-use CountDownLatch once count reaches to zero 
• You can reuse same CyclicBarrier even after barrier is broken

How to pass request header with wget and curl ?

Use --header with wget  

wget --header="Host:my-host.com" 'http://10.106.208.110:80/myservice'

Use -H with curl

curl -H 'Host: my-host.com' http://10.106.208.110:80/myservice

How can you ensure the execution sequence of threads ?

Use join()

• Start from T3
• Call join() so that it calls T2
• Inside T2, call join() again so that it calls T1

By this way, the execution sequence would be T1 -> T2 -> T3