Writing to Firestore directly in the middle of a transaction updateFunction causes a deadlock/hang

[mmmulani]

I ran into this code mistake I made recently, and I think it would be nice if the API could help catch this issue.

Steps to reproduce:

Try writing to a document directly while in a transaction.

await db.runTransaction(async t => {
  const docRef = db.collection('cities').doc('Toronto');
  await docRef.set(...);
});

While of course, this is a code issue caused by the programmer, it is particularly frustrating to debug as it seems to cause a deadlock/unfulfilled promise. Possibly the API could help catch this issue by marking the stack and throwing an error (maybe only in dev?).

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[cherylEnkidu]

Hi @mmmulani ,

Could you please be more specific of which problem you are running into and what would you expected SDK behaviour be like? Because set() can be used in transaction.

[mmmulani]

oh sorry, I cleaned up my example but from what I tested, this will cause your Node server to just hang:

await db.runTransaction(async t => {
  const docRef = db.collection('cities').doc('Toronto');
  await docRef.set(...);
});

while the correct code to write is:

await db.runTransaction(async t => {
  const docRef = db.collection('cities').doc('Toronto');
  t.set(docRef, ...);
});

my ideal SDK behaviour would be that the Cloud Firestore API uses something like AsyncLocalStorage to mark when a promise/thread is inside a transaction, and warns you if you use an api like docRef.set() or docRef.get() manually while you are still in the scope of the transaction.

[cherylEnkidu]

Hi @mmmulani ,

I run the code snippet below but the code returns successfully. Can you provide a minimal repo app?

await db.runTransaction(async t => {
  const docRef = db.collection('cities').doc('Toronto');
  await docRef.set(...);
});

[cherylEnkidu]

I will close this ticket for now since the code snippet cannot be reproduced. Please feel free to open it if you have any questions :)