This takes roughly 2,7 seconds to complete, fairly a latency to gather some information. On this instance, each RestTemplate name blocks the thread it’s operating on till the decision returns some information after which arms over the thread to the subsequent RestTemplate name. It really works like this as a result of RestTemplate, by nature, is a synchronous, blocking operation. If you wish to know the way blocking and non-blocking operations work, there’s a detailed rationalization right here.
After studying this, Tracey decides that she will make use of a few of the idle threads on her system to make a number of blocking calls on the similar time. It’s good to filter out a false impression right here: that is referred to as parallelism, not concurrency.
GOTCHA: Parallelism and concurrency usually are not the identical factor
Even when this isn’t a coroutine particular matter, there’s a frequent false impression relating to parallelism and concurrency. These phrases are sometimes used interchangeably, however they signify distinct ideas.
Let’s take a quick journey into the realms of sequential blocking, concurrency, and parallelism by imagining a bustling workplace situation, the place a diligent clerk is actively aiding purchasers.
Sequential/Blocking (No Concurrency or Parallelism):
In our imaginary workplace, this conduct could be seen because the clerk serving to one shopper at a time. Whereas the primary shopper fills within the kind, the clerk waits and would not serve another shopper.
A single-threaded program works in a sequential/blocking method, the place duties are executed one after one other with none concurrent or parallel execution.
Parallelism:
This includes the clerk calling in a colleague to assist. Now, each purchasers are being served concurrently by completely different clerks. Every clerk works independently on their assigned job, resulting in true parallel execution.
In a multi-process or multi-threaded program, duties are genuinely executed concurrently on a number of processors or cores. For instance, two RestTemplate calls will be made on the similar time, however they’ll use and block completely different threads, not sharing their assets.