[HarfBuzz] To HB_NO_MT or not to HB_NO_MT

[Behdad Esfahbod]

On 15-03-28 05:13 PM, Konstantin Ritt wrote:
> 
> 2015-03-29 0:33 GMT+04:00 Behdad Esfahbod <behdad.esfahbod at gmail.com
> <mailto:behdad.esfahbod at gmail.com>>:
> 
>     On 15-03-28 03:28 PM, Konstantin Ritt wrote:
>     > Issue: in a multi-threaded application, there is no possibility to check if HB
>     > library we're linking to is thread-safe -> we blindly assume it is.
> 
>     Right.  I think a shared-library version of HB must always be threadsafe, and
>     if it's not, that's a packaging bug.
> 
>     The biggest user of no-MT is Firefox, which AFAIU always uses HB from one
>     thread and doesn't want to incur the MT cost.
> 
> 
> The cost is rather minimal. I hope they're using the system-wide HB library
> where possible, at least...

Right.


>     > Proposed solution: in case the configure script failed to detect the supported
>     > atomic primitives, proceed with a warning and expect the build to fail if the
>     > user didn't provide his own implementation (ie. in config.h or via some
>     > external include). This way, we could even get rid of HB_NO_MT path -- where
>     > explicitly required, the user would be able to provide his no-MT
>     > implementation (ie. for HB built in a single-threaded application).
>     >
>     > WDYT?
> 
>     I would like to say I'm fine with that; however, the single-threaded
>     implementation is not exactly trivial, so I don't like to leave it to
>     individuals to figure it out.
> 
>     How about this:
> 
>     For both warnings in hb-warnings.cc, that is, the MT warning and the
>     no-Unicode-funcs warnings, make both into hard errors.  For the former, remove
>     mentioning HB_NO_MT, and instead suggest defining correct platform flags.  For
>     the latter, suggest including hb-ucdn into their build.
> 
>     WDYT?
> 
> 
> Sounds good to me.
> I think a configure option like --threading=no, with BIG FAT warning in its
> description, would make sense (here is where configure script will define
> HB_NO_MT).
> 
> \note The no-Unicode-funcs warning is in hb-unicode.cc 

I'll turn the warnings into errors now, and we'll see how many complaints we
will get...