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glibc renders random() thread-safe by wrapping a futex lock around it; testing reveals that this limits the performance of pgbench on machines with many CPU cores. Rather than switching to random_r(), which is only available on GNU systems and crashes unless you use undocumented alchemy to initialize the random state properly, switch to our built-in implementation of erand48(), which is both thread-safe and concurrent. Since the list of reasons not to use the operating system's erand48() is getting rather long, rename ours to pg_erand48() (and similarly for our implementations of lrand48() and srand48()) and just always use those. We were already doing this on Cygwin anyway, and the glibc implementation is not quite thread-safe, so pgbench wouldn't be able to use that either. Per discussion with Tom Lane.