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 working 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 known as parallelism, not concurrency.
GOTCHA: Parallelism and concurrency are usually not the identical factor
Even when this isn’t a coroutine particular matter, there’s a widespread 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 aiding shoppers.
Sequential/Blocking (No Concurrency or Parallelism):
In our imaginary workplace, this habits can be seen because the clerk serving to one shopper at a time. Whereas the primary shopper fills within the kind, the clerk waits and does not serve every 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 includes 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 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 may be made on the similar time, however they’ll use and block totally different threads, not sharing their sources.
