Stopping coroutines in Unity - Step-by-Step Execution

Concept Flow - Stopping coroutines

Start Coroutine

↓

Coroutine Running

↓

Check Stop Condition?

Yes→Stop Coroutine

No↓

Continue Coroutine

↓

Coroutine Ends Normally

This flow shows how a coroutine starts, runs, checks if it should stop, and either continues or stops.

Execution Sample

Unity

IEnumerator MyCoroutine() {
  while(true) {
    yield return null;
  }
}

Coroutine myCor = StartCoroutine(MyCoroutine());
StopCoroutine(myCor);

Starts a coroutine that runs indefinitely and then stops it.

Execution Table

Step	Action	Coroutine State	Result
1	StartCoroutine(MyCoroutine()) called	Running	Coroutine begins execution
2	Coroutine yields null (waits one frame)	Running	Coroutine pauses, will resume next frame
3	Coroutine resumes next frame	Running	Coroutine continues loop
4	StopCoroutine(myCor) called	Stopping	Coroutine is marked to stop
5	Coroutine stops before next yield	Stopped	Coroutine execution ends
6	Attempt to resume coroutine	Stopped	No action, coroutine already stopped

💡 Coroutine stops when StopCoroutine is called, preventing further execution.

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
Coroutine State	Not started	Running	Stopping	Stopped

Key Moments - 2 Insights

Why does the coroutine stop immediately after StopCoroutine is called?

Because StopCoroutine marks the coroutine to stop, so it does not continue to the next yield or loop iteration as shown in steps 4 and 5 of the execution_table.

Can you stop a coroutine by calling StopCoroutine with the method name directly?

No, you must keep a reference to the started coroutine or use the IEnumerator instance; calling StopCoroutine with the method name alone may not stop the running coroutine properly.

Visual Quiz - 3 Questions

Look at the execution_table, what is the coroutine state after step 2?

A Running

B Stopped

C Not started

D Stopping

💡 Hint

Check the 'Coroutine State' column at step 2 in the execution_table.

At which step does the coroutine stop execution?

A Step 3

B Step 4

C Step 5

D Step 6

💡 Hint

Look for when the 'Coroutine State' changes to 'Stopped' in the execution_table.

If StopCoroutine was never called, what would happen at step 6?

A Coroutine would stop automatically

B Coroutine would continue running

C Coroutine would throw an error

D Coroutine would pause indefinitely

💡 Hint

Refer to the 'Coroutine State' progression in variable_tracker and execution_table.

Concept Snapshot

Stopping coroutines in Unity:
- Use StartCoroutine to begin.
- Coroutine runs until it yields or ends.
- Call StopCoroutine with the coroutine reference to stop it.
- Stopped coroutine does not resume.
- Keep reference to coroutine for reliable stopping.

Full Transcript

This visual trace shows how a coroutine in Unity starts running, yields control, and can be stopped by calling StopCoroutine. Initially, the coroutine is running and yields null to wait one frame. When StopCoroutine is called, the coroutine state changes to stopping and then stopped, preventing further execution. Variables track the coroutine state from not started to running, stopping, and finally stopped. Key moments clarify that StopCoroutine immediately halts the coroutine and that you need a reference to stop it properly. The quiz tests understanding of coroutine states at different steps and the effect of stopping or not stopping the coroutine.