Fix a memory leak in DownloadTaskManager and DataTaskManager
#7408
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MaxDesiatov
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Mar 19, 2024
MaxDesiatov
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MaxDesiatov
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MaxDesiatov
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`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
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#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
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DownloadTaskManagerhad a strong reference toURLSession, which retained its delegate, which was theDownloadTaskManager. This formed a retain cycle.Make the reference from
URLSessionto the delegate weak and only keepDownloadTaskManageralive as long asDownloadTasks need it. This causes theDownloadTaskManagerto be deallocated once nobody holds a reference to it anymore and all the tasks it manages are finished.Finally, we need to call
invalidateon theURLSessionto tell it that we’re done and that it should release its delegate (which is now theWeakDownloadTaskManagerwrapper).This retain cycle was causing a leak in sourcekit-lsp. I verified that the leak no longer exists with this patch.
rdar://125012584