Does Deno.writeTextFile acquire a lock?

[alexgleason]

My original code looked like this:

await Deno.writeTextFile(path, data);

But then it occurred to me that it's really important that multiple Deno processes don't try to write the file at the same time. Thus, I need to acquire a lock. So I rewrote the code:

using file = await Deno.open(path, { write: true, create: true });
await file.lock(true);

const buffer = new TextEncoder().encode(data);

const writer = file.writable.getWriter();
await writer.write(buffer);
await writer.close();

But then I wondered, is it possible that Deno.writeTextFile already does this for me? It's a convenience function, and it would seem intuitive to acquire a lock while writing. But I couldn't find the answer.

[0f-0b]

It does not, which you can confirm by calling writeTextFile while the file is exclusively locked.

By the way, you forgot to truncate the file after locking it. In case lock contention turns out to be a problem, another way to rewrite a file atomically is to write all data into a temporary file and then replace the original file using a rename.

const tempFile = await Deno.makeTempFile({ dir: dirname(path) });
try {
  await Deno.writeTextFile(tempFile, data);
  await Deno.rename(tempFile, path);
} catch (e) {
  await Deno.remove(tempFile);
  throw e;
}

[bartlomieju]

This is the correct answer. I'll be happy to merge PRs that improve the docstrings on relevant types to make it more clear.