tests: add hg10 requirement to test-check-module-imports.t This requirement exists to make sure for hg has locate command, which is used in this test file for getting a list of files to check. Since in theory current versions of tests could be run on older hg, it doesn't hurt to mark even this version requirement (as old as it is). See also: a29f071751df.

worker: implement _blockingreader.readinto() (issue6444) The core logic for readinto() was already implemented in read(), so this is mostly extracting that code into its own method. Another fix for issue6444 was committed to the stable branch: 2fe4efaa59af. That is a minimal fix that implements readinto() only on Python versions that require readinto() (3.8.0 and 3.8.1), which is the right approach for the stable branch. However, I think that this changeset has its value. It improves performance in cases when pickle can use readinto(), it reduces code duplication compared to the other patch, and by defining readinto() on all Python versions, it makes behavior more consistent across all Python versions. This changesets reverts the other change.

worker: stop relying on garbage collection to release memoryview On CPython, before resizing the bytearray, all memoryviews referencing it must be released. Before this change, we ensured that all references to them were deleted. On CPython, this was enough to set the reference count to zero, which results in garbage collecting and releasing them. On PyPy, releasing the memoryviews is not necessary because they are implemented differently. If it would be necessary however, ensuring that all references are deleted would not be suffient because PyPy doesn’t use reference counting. By using with statements that take care of releasing the memoryviews, we ensure that the bytearray is resizable without relying on implementation details. So while this doesn’t fix any observable bug, it increases compatiblity with other and future Python implementations.