Bug #87402 Redundant check in ut_rnd_gen_ulint()

• Submitted: 11 Aug 2017 15:59
• Modified: 14 Aug 2017 9:58
• Reporter: Alexey Kopytov
• Status: Verified
• Category: MySQL Server: InnoDB storage engine
• Severity: S5 (Performance)
• Version: 8.0.2
• OS: Any
• CPU Architecture: Any

[11 Aug 2017 15:59] Alexey Kopytov

Description:
In 8.0.2 my_thread_local* variables have been replaced with C++11
thread-local storage. One piece of code which is now redundant due to
that change is the following part of ut_rnd_gen_ulint():

	ulint	rnd = ut_rnd_ulint_counter;
	if (rnd == 0) {
		rnd = 65654363;
	}

The check above was only required because the combination of
my_thread_local_key, my_set_thread_local() and my_get_thread_local()
essentially emulated thread-local storage and did not allow automatic
initialization of thread-local variables.

That check on a critical code path can be avoided if
ut_rnd_ulint_counter is initialized to 65654363 rather than zero in
ut0rnd.cc

How to repeat:
Code analysis of ut_rnd_gen_ulint() and ut_rnd_ulint_counter
initialization.

Suggested fix:
See above.

[14 Aug 2017 9:58] MySQL Verification Team

Hello Alexey,

Thank you for your feedback!
Verifying based on my internal discussion with developer.

Thanks,
Umesh