Hello!
I'm writing multi-threaded C client with hiredis and their libev adapter. I'm
using multi-threading, because I have several servers to which I send the same
command and await their reply.
First of all, there is no ev default loop. Each ev loop is initialized in main
thread and is then passed on to pthread_create (along with other stuff like
watchers, etc).
Once the thread starts, it create hiredis async handler and attaches libev with
its libev handler and sets up all the callbacks.
After all is initialized and connected, I send commands from main thread to all
servers via redisAsyncCommand.
Questions:
1. Hiredis libev adapter uses two ev_io watchers, one for reading and one for
writing. It's simply calling start and stop on those watchers based on what it
tries to do.
This does not work for me, unless I register another ev_async watcher, that
fires everytime hiredis tries to start/stop the io_watcher. Is that expected? I
would say that once
libev goes into poll/select/etc wait, it will not move out of wait if you
stop the watcher, or start the stopped watcher, right?
2. I tried another approach I saw on the internet. Single ev_io watcher, but
everytime hiredis tries to stop/start read/write, I to ev_io_stop(...) and then
I set EV_READ and/or EV_WRITE flags via ev_io_set and then ev_io_start again.
Also in that case, I need ev_async watcher to wakeup the libev. Would you that
that single IO watcher approach would be better?
Both 1. and 2. I tried protecting changes in watchers with mutex, but no
success.
3. My test program hangs after few minutes, maybe even few seconds (it's
working for atleast 1000 iterations, even 100000 sometimes) after I fire it
(sending SET/GET to one or many servers). It hangs in epoll_wait or select
(tried different EVBACKEND_*). It doesn't receive the ev_async event it seems.
I also have a feeling that there might be some memory corruptions, but I cannot
find any using efence or valgrind.
I've enabled EV_VERIFY 3 and sometimes I get "libev: pending watcher not on
pending queue" when on EVBACKEND_SELECT.
Any hints before I go and completely rewrite it?
Thank you and kind regards,
Dejan
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