Leak mutex to avoid a crashing issue

[chuganzy]

Try to solve #13588
ref: facebook/componentkit#906

Test Plan:

Regression / smoke tests should be enough.

Changelog:

[iOS] [Fixed] - Fix a crashing issue on RCTFont / mutex

[DimitryDushkin]

Ping. Eliminating crash is really important.

[DimitryDushkin]

We've released out app with this patch and this crash gone away.

[chuganzy]

[DimitryDushkin]

Where is my manners. Thank you @chuganzy!

[shergin]

@chuganzy
Wait, wait, what does make you think that the linked crash happens when application is closing? Should we leak all static mutexes?

[shergin]

Here's a quote from Oliver:

Historically, TextKit has had lots of hidden thread-safety issues despite being stated as thread safe. CK locks around all access to TextKit, but there are still issues that have cropped up in the recent past. We built the same text locking system in both CK and ASDK, and they both work this way.

As I can see, that's not how RN works here (and everywhere else) with fonts and co. So, maybe this is the problem.

[chuganzy]

Here's also a quote from @ocrickard. You can see the commit log here.
facebook/componentkit@37bcfdb

OK, looks like std::mutex is not trivially destructible in Clang, so we should probably just leak that mutex. Anyway, I believe this crash is happening on exit() as @gkassabli said above, so it probably has no impact on user experience.

[shergin]

Yes, exactly. My point is that the fix in CK fixes different type of the crash, not the one that promised in this PR's description.
I believe this change will not fix #13588 .

[shergin]

Just chatted with Oliver and... I was a bit wrong. :)
So, this fix seems to fix the one of the crashes mentioned in the assigned issue (but probably not that one which in the description).

As Oliver pointed out, all TextKit-related crashes wich has something like '0x185dfc238 std::__1::mutex::try_lock() + 34' will be fixed with this fix.

[facebook-github-bot]

@shergin is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[chuganzy]

@shergin Thank you, but seems like the issue in its description also indicates that it's crashing when it tries to lock from its line so I am hoping that this solves the issue🤞

[react-native-bot]

@chuganzy merged commit 6082431 into facebook:master.