From 906f7daed16a3b1c4058b77fed44b3c4265e645f Mon Sep 17 00:00:00 2001 From: Willy Tarreau Date: Thu, 26 Aug 2021 15:46:51 +0200 Subject: MINOR: compiler: implement an ONLY_ONCE() macro There are regularly places, especially in config analysis, where we need to report certain things (warnings or errors) only once, but where implementing a counter is sufficiently deterrent so that it's not done. Let's add a simple ONLY_ONCE() macro that implements a static variable (char) which is atomically turned on, and returns true if it's set for the first time. This uses fairly compact code, a single byte of BSS and is thread-safe. There are probably a number of places in the config parser where this could be used. It may also be used to implement a WARN_ON() similar to BUG_ON() but which would only warn once. --- include/haproxy/compiler.h | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/include/haproxy/compiler.h b/include/haproxy/compiler.h index 72d158b37..ca3b844c1 100644 --- a/include/haproxy/compiler.h +++ b/include/haproxy/compiler.h @@ -128,6 +128,14 @@ */ #define DISGUISE(v) ({ typeof(v) __v = (v); ALREADY_CHECKED(__v); __v; }) +/* Implements a static event counter where it's used. This is typically made to + * report some warnings only once, either during boot or at runtime. It only + * returns true on the very first call, and zero later. It's thread-safe and + * uses a single byte of memory per call place. It relies on the atomic xchg + * defined in atomic.h which is also part of the common API. + */ +#define ONLY_ONCE() ({ static char __cnt; !_HA_ATOMIC_XCHG(&__cnt, 1); }) + /* * Gcc >= 3 provides the ability for the program to give hints to the * compiler about what branch of an if is most likely to be taken. This -- cgit v1.2.1