Bump file pool size

[ghost]

Reason no 1: Performance:
https://www.libtorrent.org/tuning.html#file-pool

libtorrent keeps an LRU file cache. Each file that is opened, is stuck in the cache. The main purpose of this is because of anti-virus software that hooks on file-open and file close to scan the file. Anti-virus software that does that will significantly increase the cost of opening and closing files. However, for a high performance seed, the file open/close might be so frequent that it becomes a significant cost. It might therefore be a good idea to allow a large file descriptor cache. Adjust this though settings_pack::file_pool_size

Reason no 2: Potential I/O errors:
The error:
#14962 (comment)

Most likely cause:
#14962 (comment)

So basically when the file was closed, some other application(most likely antivirus) opened it for exclusive access, thus resulting in I/O errors when qBt tried to re-open it. If the file pool was large enough there'd be no need to close and reopen files so frequently as to cause collition with other apps.

P.S - I'm not sure what might be a good number for this settings. But I've seen many people use this number(5000) when they tune libtorrent. If keeping too many file descriptors open doesn't incur a much higher cost in comparison to gained performance then it might be worth it to bump this.

[glassez]

Hope it doesn't exceed any system limits...

[ghost]

Some systems may have lower file descriptor limits. But in windows I haven’t heard of any limitations. If this exceeds system limits then qBt would be limited to that number instead by the kernal without any undesired effects.

[ghost]

We can make this change limited to Windows only if we’re concerned about hitting file descriptor limits and failing to keep files/connections open.

[xavier2k6]

We can make this change limited to Windows only if we’re concerned about hitting file descriptor limits and failing to keep files/connections open.

Just to chime in here - my file_pool_size is set at 8,000 & has been for a very long time (windows 10)

Have seen issues before where just raising file_pool_size to say 50 helped (I think it really depends on a users hardware/config)

Example

file_pool_size = 4,000
#12914 (comment)

I believe it will also help when closing qbittorrent - the process seems to exit/disappear quicker in task manager

The accessing/updating of the resume files for users who say don't have anti-virus may be have been impacted by this default setting all along............just a thought!

EDIT:
ref #12825 (comment) onwards

[arvidn]

I believe windows has a much higher default limit for number of file handles, than Linux and MacOS. It might make sense to have different defaults for different systems.

Opening files with exclusive access isn't really a problem on non-windows either.

[xavier2k6]

I believe windows has a much higher default limit for number of file handles, than Linux and MacOS. It might make sense to have different defaults for different systems.

Opening files with exclusive access isn't really a problem on non-windows either.

for reference:

#12825 (comment)

[FranciscoPombal]

@glassez

Hope it doesn't exceed any system limits...

At least on Linux, qBittorrent has been setting this to "unlimited" for a while now anyway: #10853.

[FranciscoPombal]

As others have mentioned, I too have seen instances where bumping this definitely helped. Combined with the fact that on Windows there is practically no limit, and the fact that other systems don't really have issues due to opening with exclusive access, I think this is a welcome change.

[Chocobo1]

@An0n666
Thank you!