[tarantool-patches] [PATCH v3 07/14] wal: remove fiber from a journal_entry structure
Vladimir Davydov
vdavydov.dev at gmail.com
Thu Jun 13 17:17:02 MSK 2019
On Sun, Jun 09, 2019 at 11:44:36PM +0300, Georgy Kirichenko wrote:
> Use a fiber_cond to signal a condition and wake up a waiting fiber.
> This relaxes friction between fiber and transaction life cycles.
I don't see how it relaxes anything ;-)
Please be more specific when writing comments.
>
> Prerequisites: #1254
> ---
> src/box/box.cc | 4 +++-
> src/box/journal.c | 7 ++++---
> src/box/journal.h | 9 +++++++--
> src/box/wal.c | 29 +++++++++--------------------
> 4 files changed, 23 insertions(+), 26 deletions(-)
>
> diff --git a/src/box/wal.c b/src/box/wal.c
> index 0ea15a432..5951817d0 100644
> --- a/src/box/wal.c
> +++ b/src/box/wal.c
> @@ -1172,15 +1166,10 @@ wal_write(struct journal *journal, struct journal_entry *entry)
> batch->approx_len += entry->approx_len;
> writer->wal_pipe.n_input += entry->n_rows * XROW_IOVMAX;
> cpipe_flush_input(&writer->wal_pipe);
> - /**
> - * It's not safe to spuriously wakeup this fiber
> - * since in that case it will ignore a possible
> - * error from WAL writer and not roll back the
> - * transaction.
> - */
> - bool cancellable = fiber_set_cancellable(false);
> - fiber_yield(); /* Request was inserted. */
> - fiber_set_cancellable(cancellable);
> +
> + while (!entry->done)
> + fiber_cond_wait(&entry->done_cond);
> +
Using a fiber_cond to wake up a single fiber is an overkill. You could
as well do
while (!entry->done)
fiber_yield_timeout(TIMEOUT_INFINITY);
Anyway, I have my reservations re how you handle WAL writer wakeups.
Please see my comments to the final patch.
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