Timeout with withTimeout in Kotlin - Step-by-Step Execution

Concept Flow - Timeout with withTimeout

Start Coroutine

↓

Call withTimeout

↓

Start block inside withTimeout

↓

Check elapsed time

↓

Throw TimeoutCancellationException

↓

Complete block

↓

Return result or Exception

The coroutine starts with withTimeout, runs the block, checks elapsed time, and throws an exception if time exceeds the limit.

Execution Sample

Kotlin

import kotlinx.coroutines.*

fun main() = runBlocking {
  withTimeout(1000) {
    repeat(5) {
      delay(300)
      println("Tick $it")
    }
  }
}

This code runs a block with a 1-second timeout, printing ticks every 300ms until timeout occurs.

Execution Table

Step	Elapsed Time (ms)	Action	Output	Timeout Check
1	0	Start withTimeout block		Not exceeded
2	300	delay(300), print Tick 0	Tick 0	Not exceeded
3	600	delay(300), print Tick 1	Tick 1	Not exceeded
4	900	delay(300), print Tick 2	Tick 2	Not exceeded
5	1200	delay(300), attempt print Tick 3		Exceeded - throw TimeoutCancellationException

💡

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	Final
Elapsed Time (ms)	0	300	600	900	1200	Timeout Exception thrown
Tick Count (it)	-	0	1	2	3	-

Key Moments - 2 Insights

Why does the program stop after printing Tick 2 and not continue to Tick 4?

Because at step 5, elapsed time exceeds the 1000ms timeout, so withTimeout throws TimeoutCancellationException and stops execution (see execution_table row 5).

Does withTimeout cancel the coroutine immediately when time is exceeded?

Yes, as soon as elapsed time exceeds the timeout, withTimeout throws an exception to cancel the coroutine (execution_table step 5).

Visual Quiz - 3 Questions

Look at the execution table, what is the elapsed time when Tick 1 is printed?

A 300 ms

B 900 ms

C 600 ms

D 1200 ms

💡 Hint

Check the 'Elapsed Time (ms)' column at the row where Output is 'Tick 1'.

At which step does the timeout get exceeded causing the exception?

A Step 5

B Step 4

C Step 3

D Timeout never exceeded

💡 Hint

Look at the 'Timeout Check' column to find when it says 'Exceeded'.

If the timeout was increased to 1600 ms, how many ticks would print before timeout?

A 4 ticks

B 5 ticks

C 3 ticks

D No ticks

💡 Hint

Each tick takes about 300 ms delay; check variable_tracker elapsed times to estimate.

Concept Snapshot

withTimeout(timeMillis) runs a coroutine block with a time limit.
If the block exceeds timeMillis, it throws TimeoutCancellationException.
Use it to stop long-running tasks safely.
Inside, normal code runs until timeout or completion.
Exception cancels coroutine immediately.

Full Transcript

This example shows how Kotlin's withTimeout function works. The coroutine runs a block that repeats a delay and print action. Each delay is 300 milliseconds. The withTimeout is set to 1000 milliseconds. The execution table shows each step with elapsed time and output. At step 5, elapsed time exceeds 1000 ms, so withTimeout throws a TimeoutCancellationException and stops the coroutine. The variable tracker shows elapsed time increasing and tick count. Key moments clarify why execution stops early and how cancellation happens. The quiz tests understanding of timing and behavior. The snapshot summarizes the concept simply.