MySQL Bugs: #60197: random used in a multithreaded context

Bug #60197	random used in a multithreaded context
Submitted:	22 Feb 2011 7:48	Modified:	14 Apr 2011 10:37
Reporter:	Guoliang Jin	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Command-line Clients	Severity:	S5 (Performance)
Version:	5.1.55	OS:	Windows
Assigned to:		CPU Architecture:	Any

Description:
In file mysql-5.1.55/client/mysqlslap.c:1864, random() is used in the multithreaded context run_task, according to the man page of the random function:
"This function should not be used in cases where multiple threads use random() and the behavior should be reproducible.  Use random_r(3) for that purpose.", so random_r should be used here.

How to repeat:
by reviewing the file mysql-5.1.55/client/mysqlslap.c

I verify the fact that random() is used, and what the manpage says:
http://www.kernel.org/doc/man-pages/online/pages/man3/random.3.html\

However, mysqlslap doesn't use a constant seed to generate repeatable random numbers in multiple threads.  It just needs random numbers without being repeatable later.

/* Seed the random number generator if we will be using it. */
  if (auto_generate_sql)
    srandom((uint)time(NULL));

So if the only problem is not having repeatable sequences, is this really a bug at all?

According to http://evanjones.ca/random-thread-safe.html, the reason that random() should not be used in multi-thread context on Linux is that rand() and random() acquire a mutex to ensure thread-safe on Linux, and this could over-synchronize the problem and may lead to performance issue, thus random_r() should be used instead.

Bug 38941 is a previous case related to random().