Parallelism in a Child Flow

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Posted on by mbarea

Hi everyone,

I'm looking for some advice regarding a concurrency issue in Power Automate.

I currently have five flows that all have the same structure, but each is triggered by a different "When a new email arrives in a shared mailbox (V2)" trigger. All of these flows perform similar logic and write to the same Excel file.

The problem is: if two of these flows are triggered at the same time, they may attempt to access Excel simultaneously, which causes issues due to Excel’s limitations with concurrent access.

To solve this, I wanted to centralize the logic into a single child flow. Each of the five flows would call this child flow so I could manage the logic in one place. I also hoped to control the execution order by setting concurrency control (parallelism = 1) on the child flow to prevent it from running multiple times at once.

However, Power Automate doesn’t allow me to enable concurrency control on a child flow that ends with a "Respond to a PowerApp or flow" action — which is required when using "Run a Child Flow".

Does anyone know a workaround or best practice to make sure the child flow only runs one instance at a time, even if multiple parent flows call it simultaneously?

Thanks in advance for your help!

Best regards,
M.

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Building flows

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Pstork1 69,110 Most Valuable Professional on at

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What trigger are you using? I just set Concurrency on a manual trigger to 1 in a Child flow that ends with a Respond to Power Apps or Flow Action. Why do you say you can't do it?

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mbarea 17 on at

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Hi!

´When I try to publish it inside my Solution, I have this message (It's a Manual trigger)

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Tomac 4,048 Moderator on at

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A possible solution is to change the structure a bit.

The current When A New Email Arrives flows would instead write to a SharePoint List or Dataverse table or other source that allows concurrent editing. Then have a Flow that runs at a set frequency based on how frequently you need updates, that opens the Excel file and adds/modifies the necessary entries. This would negate the need for Child flows and resolve the Excel concurrency issue.

Maybe not the solution you're looking for but it's an easy fix that resolves all of the issues you're experiencing.

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Riyaz_riz11 4,048 Super User 2026 Season 1 on at

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Hi,

Parent Flows:

Each is triggered independently by email arriving.

Each calls your Child Flow with “Run a Child Flow.”

If emails come in at the same time, multiple Child Flow instances spin up at once, each trying to write to Excel.

Because the Child Flow has a Respond to Flow, you can’t limit concurrency in its settings.

Use a Single “Master” Flow with Multiple Triggers

This is usually the cleanest solution.

How:

Create one flow with all 5 triggers:

In the flow designer, click Add trigger again and pick another When a new email arrives for each mailbox.

You can then branch your logic by examining the trigger outputs:

triggerOutputs()?['headers']['x-ms-user-email']

or whichever property identifies which mailbox the email came from.

In Settings for each trigger:

Enable Concurrency Control

Set Degree of Parallelism = 1

This guarantees:

No matter how many emails arrive, the flow only processes one run at a time.

The Excel file is never accessed by more than one execution.

Why this works:

Concurrency Control on the trigger limits the flow executions globally.

You centralize your logic in one place.

If I have answered your question, please mark it as the preferred solution ✅ . If you like my response, please give it a Thumbs Up 👍.
Regards,
Riyaz

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