Re: [nmap-svn] r25684 - nmap-exp/calderon/nselib

[Patrick Donnelly <batrick () batbytes com>]

Hi Paulino,

On Tue, Aug 9, 2011 at 3:33 AM,  <commit-mailer () insecure org> wrote:
> Author: paulino
> Date: Tue Aug  9 00:33:52 2011
> New Revision: 25684
>
> Log:
> improvements
>
> Modified:
>   nmap-exp/calderon/nselib/httpspider.lua
>
> Modified: nmap-exp/calderon/nselib/httpspider.lua
> [...]
> +local function add_visited_uri(uri, page_obj)
> +  VISITED_MUTEX "lock"
> +  if nmap.registry[HTTPSPIDER_DATAKEY]["visited"][uri] == nil then
> +    nmap.registry[HTTPSPIDER_DATAKEY]["visited"][uri] = page_obj
>   end
> -  VL_MUTEX "done"
> +  VISITED_MUTEX "done"
>  end

There's no need for this mutex here. Scripts (Lua threads --
coroutines) do not yield asynchronously; that is, they do not yield at
arbitrary locations in the code. Mutexes in NSE are used to serialize
access to some resource *when the script may yield between the lock
and unlock*. Scripts only yield *explicitly* through calls to socket
functions (e.g. socket:connect(...) or nmap.sleep(...)) or through the
concurrency control mechanisms (mutexes and condition variables).

Take a look at [1]. If something is unclear please let us (nmap-dev)
know so we can improve it.

[1] http://nmap.org/book/nse-parallelism.html#nse-parallelism-mutex

-- 
- Patrick Donnelly
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