add ets take_first/1 and take_last/1 functions #5896
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erts/emulator/beam/erl_db.c
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| cret = tb->common.meth->db_first(BIF_P, tb, &first); | ||
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| if (cret != DB_ERROR_NONE) { | ||
| db_unlock(tb, LCK_WRITE_REC); | ||
| BIF_ERROR(BIF_P, BADARG); | ||
| } | ||
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| cret = tb->common.meth->db_take(BIF_P, tb, first, &ret); |
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No decision has been made yet to accept this API addition, but I just noticed that
you don't treat '$end_of_table' (first==am_EOT). It just happens to work as long as there is no such key.
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I realize now that if first returns am_EOT then no keys at all exist. But it could actually be a race where someone else inserts key '$end_of_table' and it would make the code more clear to treat am_EOT.
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@nyczol To make a decision we would want a real life use case and what problem the new API addition solves.
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Please note that '$end_of_table' atom can't be used as a key (https://www.erlang.org/doc/man/ets.html).
Functions take_first/1 and take_last/1 can be used to build very efficient FIFO queues using ets.
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Checking agains am_EOT has been added
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I don't think we want to rush this into OTP 25. Especially as I discovered this implementation is not correct for table option |
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I've just fix concurrency issue. |
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It was fast and now it's correct. I think we should aim for both. Keep LCK_WRITE_REC and implement new meth->take_first() functions for hash, tree and catree where we seize the lock once and release it when done. |
Add ets:take_last/1 and ets:take_first/1 func similar to ets:take/2, but return firts/last objects from ets.