Konrad `ktoso` Malawski f336404ae9 [Concurrency] TaskGroup children remove their records as they complete ...

If we didn't do this (and we didn't), the tasks get released as we
perform the next() impl, and move the value from the ready task to the
waiting task. Then, the ready task gets destroyed.

But as the task group exists, it performs a cancelAll() and that
iterates over all records. Those records were not removed previously
(!!!) which meant we were pointing at now deallocated tasks.

Previously this worked because we didn't deallocate the tasks, so they
leaked, but we didn't crash. With the memory leak fixed, this began to
crash since we'd attempt to cancel already destroyed tasks.

Solution:
- Remove task records whenever they complete a waiting task.
- This can ONLY be done by the "group owning task" itself, becuause
  the contract of ONLY this task being allowed to modify records. o
  It MUST NOT be done by the completing tasks as they complete, as it
  would race with the owning task modifying this linked list of child
  tasks in the group record.

2021-09-04 20:09:55 +09:00

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