From 574ecbb0fcbddd1937d104d199247052042d9a16 Mon Sep 17 00:00:00 2001
From: Yann Collet <cyan@fb.com>
Date: Sun, 19 Jun 2022 11:38:06 -0700
Subject: [PATCH] display a warning message when using C90 clock_t for MT speed
 measurements.

---
 programs/benchzstd.c | 9 ++++++++-
 programs/timefn.h    | 1 +
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/programs/benchzstd.c b/programs/benchzstd.c
index fa2659efb..6ceca020c 100644
--- a/programs/benchzstd.c
+++ b/programs/benchzstd.c
@@ -13,7 +13,7 @@
 *  Tuning parameters
 ****************************************/
 #ifndef BMK_TIMETEST_DEFAULT_S   /* default minimum time per test */
-#define BMK_TIMETEST_DEFAULT_S 3
+# define BMK_TIMETEST_DEFAULT_S 3
 #endif
 
 
@@ -387,6 +387,13 @@ BMK_benchMemAdvancedNoAlloc(
         RDG_genBuffer(compressedBuffer, maxCompressedSize, 0.10, 0.50, 1);
     }
 
+#if defined(UTIL_TIME_USES_C90_CLOCK)
+    if (adv->nbWorkers > 1) {
+        OUTPUTLEVEL(2, "Warning : time measurements restricted to C90 clock_t. \n")
+        OUTPUTLEVEL(2, "Warning : using C90 clock_t leads to incorrect measurements in multithreading mode. \n")
+    }
+#endif
+
     /* Bench */
     {   U64 const crcOrig = (adv->mode == BMK_decodeOnly) ? 0 : XXH64(srcBuffer, srcSize, 0);
 #       define NB_MARKS 4
diff --git a/programs/timefn.h b/programs/timefn.h
index 3fcd78a28..8ba8ed787 100644
--- a/programs/timefn.h
+++ b/programs/timefn.h
@@ -65,6 +65,7 @@ extern "C" {
 
 #else   /* relies on standard C90 (note : clock_t measurements can be wrong when using multi-threading) */
 
+    #define UTIL_TIME_USES_C90_CLOCK
     typedef clock_t UTIL_time_t;
     #define UTIL_TIME_INITIALIZER 0
 
-- 
2.47.2