WebAPI: FilePrio race condition

[AbeniMatteo]

Bug report

Checklist

• [x] I have read the issue reporting section in the contributing guidelines, so I know how to submit a good bug report with the required information
• [x] I have verified that the issue is not fixed and is reproducible in the latest version
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Description

qBittorrent info

• qBittorrent version: 4.3.6

What is the problem

Calling filePrio WebAPI endpoint multiple times before the previous operation is completed overrides the previous changes.

Causes:

• libtorrent prioritize_files is async
• filePrio respond 200 OK without waiting the priorities to be updated
• filePrio retrieves the possibly not-yet-updated priorities of each file, updates the specified files and sends the entire batch to libtorrent

Detailed steps to reproduce the problem

1. Have a torrent with files A end B, priority=0, in short (A0, B0).
2. Call .../filePrio?hash=abc&id=0&priority=1 and wait for response. Internally reads (A0, B0) and writes (A1, B0).
3. Call .../filePrio?hash=abc&id=1&priority=1 and wait for response. Internally reads (A0, B0) !!wrong!! and writes (A0, B1).
4. Check file A and B priorities, should be (A1, B1) instead it's (A0, B1)

[Chocobo1]

@glassez Do you think this is a libtorrent bug? if it is not then qbt needs additional workaround for it.

[AbeniMatteo]

I don't think so, libtorrent already has a method to merge multiple operations (see https://github.com/arvidn/libtorrent/pull/4151/files). But it only works if you request the update of specific files, qBittorrent is requesting the update of all the files and the last batch wins.

[luzpaz]

@AbeniMatteo is this still an issue ?