Coroutine Gotchas – Dispatchers | Weblog |

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 palms 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 know the way blocking and non-blocking operations work, there’s a detailed clarification right here.

After studying this, Tracey decides that she will be able to make use of a number of the idle threads on her system to make a number of blocking calls on the identical time. It’s good to filter out a false impression right here: that is referred to as parallelism, not concurrency.

GOTCHA: Parallelism and concurrency should not the identical factor

Even when this isn’t a coroutine particular matter, there’s a frequent false impression concerning parallelism and concurrency. These phrases are sometimes used interchangeably, however they symbolize distinct ideas.

Let’s take a quick journey into the realms of sequential blocking, concurrency, and parallelism by imagining a bustling workplace state of affairs, the place a diligent clerk is actively aiding 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 kind, the clerk waits and would 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.


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 activity, 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 could be made on the identical time, however they’ll use and block totally different threads, not sharing their assets.

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