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BUG/MINOR: tools: seed the statistical PRNG slightly better

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Thomas Baroux reported a very interesting issue. "balance random" would
systematically assign the same server first upon restart. That comes from
its use of statistical_prng() which is only seeded with the thread number,
and since at low loads threads are assigned to incoming connections in
round robin order, practically speaking, the same thread always gets the
same request and will produce the same random number.

We already have a much better RNG that's also way more expensive, but we
can use it at boot time to seed the PRNG instead of using the thread ID
only.

This needs to be backported to 2.4.
This commit is contained in:
Willy Tarreau 2024-03-01 16:17:47 +01:00
parent 31ec9f18bb
commit 7151076522
1 changed files with 1 additions and 1 deletions
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src/tools.c
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@ -6333,7 +6333,7 @@ void *dlopen(const char *filename, int flags)
static int init_tools_per_thread() static int init_tools_per_thread()
{ {
/* Let's make each thread start from a different position */ /* Let's make each thread start from a different position */
statistical_prng_state += tid * MAX_THREADS; statistical_prng_state += ha_random32();
if (!statistical_prng_state) if (!statistical_prng_state)
statistical_prng_state++; statistical_prng_state++;
return 1; return 1;