This takes roughly 2,7 seconds to complete, fairly a latency to gather some knowledge. On this instance, each RestTemplate name blocks the thread it’s operating on till the decision returns some knowledge after which arms over the thread to the following RestTemplate name. It really works like this as a result of RestTemplate, by nature, is a synchronous, blocking operation. If you wish to understand how blocking and non-blocking operations work, there’s a detailed rationalization right here.
After studying this, Tracey decides that she will be able to 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 are usually not the identical factor
Even when this isn’t a coroutine particular subject, 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 short journey into the realms of sequential blocking, concurrency, and parallelism by imagining a bustling workplace situation, the place a diligent clerk is actively helping shoppers.
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 type, the clerk waits and would not serve some other 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 entails the clerk calling in a colleague to assist. Now, each shoppers are being served concurrently by totally different clerks. Every clerk works independently on their assigned process, 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 may use and block totally different threads, not sharing their assets.
