[HarfBuzz] To HB_NO_MT or not to HB_NO_MT

Konstantin Ritt ritt.ks at gmail.com
Sat Mar 28 17:16:33 PDT 2015

Just FYI:


2015-03-29 4:13 GMT+04:00 Konstantin Ritt <ritt.ks at gmail.com>:

> 2015-03-29 0:33 GMT+04:00 Behdad Esfahbod <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...
> > 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
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