[PATCH] box: serialize calls to box.cfg

[Georgy Kirichenko]

Looks good to me

On Tuesday, August 7, 2018 2:09:01 PM MSK Vladimir Davydov wrote:
> On Tue, Aug 07, 2018 at 12:43:26PM +0300, Vladimir Davydov wrote:
> > It is dangerous to call box.cfg() concurrently from different fibers.
> > For example, replication configuration uses static variables and yields
> > so calling it concurrently can result in a crash. To make sure it never
> > happens, let's protect box.cfg() with a lock.
> > 
> > Closes #3606
> > ---
> > https://github.com/tarantool/tarantool/issues/3606
> > https://github.com/tarantool/tarantool/tree/dv/gh-3606-concurrent-replicat
> > ion-cfg-fix> 
> >  src/box/lua/load_cfg.lua       | 21 ++++++++++++++++++---
> >  test/replication/misc.result   | 24 ++++++++++++++++++++++++
> >  test/replication/misc.test.lua | 10 ++++++++++
> >  3 files changed, 52 insertions(+), 3 deletions(-)
> > 
> > diff --git a/src/box/lua/load_cfg.lua b/src/box/lua/load_cfg.lua
> > index 0b668cdc..4de79220 100644
> > --- a/src/box/lua/load_cfg.lua
> > +++ b/src/box/lua/load_cfg.lua
> > @@ -5,6 +5,21 @@ local json = require('json')
> > 
> >  local private = require('box.internal')
> >  local urilib = require('uri')
> >  local math = require('math')
> > 
> > +local fiber = require('fiber')
> > +
> > +-- Function decorator that is used to prevent box.cfg() from
> > +-- being called concurrently by different fibers.
> > +local lock = fiber.channel(1)
> > +local function locked(f)
> > +    return function(...)
> > +        lock:put(true)
> > +        local status = pcall(f, ...)
> > +        lock:get()
> > +        if not status then
> > +            box.error()
> > +        end
> > +    end
> > +end
> 
> Georgy noted that we'd better use error() to re-throw the error returned
> by box.cfg(). Updated on the branch, the incremental diff is below:
> 
> diff --git a/src/box/lua/load_cfg.lua b/src/box/lua/load_cfg.lua
> index 4de79220..c68a3583 100644
> --- a/src/box/lua/load_cfg.lua
> +++ b/src/box/lua/load_cfg.lua
> @@ -13,10 +13,10 @@ local lock = fiber.channel(1)
>  local function locked(f)
>      return function(...)
>          lock:put(true)
> -        local status = pcall(f, ...)
> +        local status, err = pcall(f, ...)
>          lock:get()
>          if not status then
> -            box.error()
> +            error(err)
>          end
>      end
>  end

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