Fix a memory leak in `DownloadTaskManager` and `DataTaskManager` #7408

ahoppen · 2024-03-19T15:00:32Z

DownloadTaskManager had a strong reference to URLSession, which retained its delegate, which was the DownloadTaskManager. This formed a retain cycle.

Make the reference from URLSession to the delegate weak and only keep DownloadTaskManager alive as long as DownloadTasks need it. This causes the DownloadTaskManager to be deallocated once nobody holds a reference to it anymore and all the tasks it manages are finished.

Finally, we need to call invalidate on the URLSession to tell it that we’re done and that it should release its delegate (which is now the WeakDownloadTaskManagerwrapper).

This retain cycle was causing a leak in sourcekit-lsp. I verified that the leak no longer exists with this patch.

rdar://125012584

ahoppen · 2024-03-19T15:00:38Z

@swift-ci Please test

Sources/Basics/HTTPClient/URLSessionHTTPClient.swift

ahoppen · 2024-03-20T10:25:13Z

@swift-ci Please test

MaxDesiatov · 2024-03-20T11:13:09Z

@swift-ci test windows

Sources/Basics/HTTPClient/URLSessionHTTPClient.swift

`DownloadTaskManager` had a strong reference to `URLSession`, which retained its delegate, which was the `DownloadTaskManager`. This formed a retain cycle. Make the reference from `URLSession` to the delegate weak and only keep `DownloadTaskManager` alive as long as `DownloadTask`s need it. This causes the `DownloadTaskManager` to be deallocated once nobody holds a reference to it anymore and all the tasks it manages are finished. Finally, we need to call `invalidate` on the `URLSession` to tell it that we’re done and that it should release its delegate (which is now the `WeakDownloadTaskManager`wrapper). rdar://125012584

ahoppen · 2024-03-20T12:57:50Z

@swift-ci Please test

ahoppen · 2024-03-20T13:25:42Z

@swift-ci Please test Windows

MaxDesiatov

Thanks!

@MaxDesiatov

#7416) * **Explanation**: `DownloadTaskManager` had a strong reference to `URLSession`, which retained its delegate, which was the `DownloadTaskManager`. This formed a retain cycle. Make the reference from `URLSession` to the delegate weak and only keep `DownloadTaskManager` alive as long as `DownloadTask`s need it. This causes the `DownloadTaskManager` to be deallocated once nobody holds a reference to it anymore and all the tasks it manages are finished. Finally, we need to call `invalidate` on the `URLSession` to tell it that we’re done and that it should release its delegate (which is now the `WeakDownloadTaskManager` wrapper). This retain cycle was causing a leak in sourcekit-lsp. I verified that the leak no longer exists with this patch. * **Scope**: The change should be transparent to all users of `DataTaskManager` and `DownloadTaskManager` and only prevent the memory leak * **Risk**: I don’t see a risk with this change since the `{Data|Download}TaskManager` is kept alive as long as there is anything left that might call it. * **Testing**: I verified that the leak no longer exists with this patch. * **Issue**: rdar://125012584 * **Reviewer**: @MaxDesiatov on #7408

…ftlang#7408) `DownloadTaskManager` had a strong reference to `URLSession`, which retained its delegate, which was the `DownloadTaskManager`. This formed a retain cycle. Make the reference from `URLSession` to the delegate weak and only keep `DownloadTaskManager` alive as long as `DownloadTask`s need it. This causes the `DownloadTaskManager` to be deallocated once nobody holds a reference to it anymore and all the tasks it manages are finished. Finally, we need to call `invalidate` on the `URLSession` to tell it that we’re done and that it should release its delegate (which is now the `WeakDownloadTaskManager`wrapper). This retain cycle was causing a leak in sourcekit-lsp. I verified that the leak no longer exists with this patch. rdar://125012584

ahoppen requested review from bnbarham, MaxDesiatov and tomerd as code owners March 19, 2024 15:00

MaxDesiatov self-assigned this Mar 19, 2024

MaxDesiatov added the bug label Mar 19, 2024

MaxDesiatov reviewed Mar 19, 2024

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