What does a single-threaded client application do when an API is consumed synchronously?

Question

Exhibit

Options

• AIt receives a slower response from the API service.
• BIt continues processing without waiting for a response.
• CIt receives a quicker response from the API service.
• DIt blocks processing until a response is received from the service.

• A
  5% (1)
• B
  5% (1)
• D
  90% (19)

Explanation

When a single-threaded client calls an API synchronously, execution halts at that call site - the thread cannot do anything else until the response arrives, making D correct. This is the defining characteristic of synchronous (blocking) I/O: the calling thread is held hostage until the operation completes.

Why the distractors are wrong:

• A & C conflate speed of the response with how the client waits - synchronous vs. asynchronous has nothing to do with how fast the server replies; it only determines whether the caller blocks.
• B describes asynchronous behavior, where the client registers a callback or awaits a future and continues executing other work in the meantime.

Memory tip: Think of a synchronous call like a phone call where you stay on the line saying nothing until the other person answers - you're blocked. An asynchronous call is like leaving a voicemail and going about your day until they call back.

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