From 23751fe2525811e74f8f963668b4b0b5fc80eb54 Mon Sep 17 00:00:00 2001
From: Ondrej Sury <ondrej@isc.org>
Date: Mon, 12 Jul 2021 14:21:21 +0200
Subject: [PATCH] Cache the isc_os_ncpu() result

It was discovered that on some platforms (f.e. Alpine Linux with MUSL)
the result of isc_os_ncpus() call differ when called before and after we
drop privileges.  This commit changes the isc_os_ncpus() call to cache
the result from the first call and thus always return the same value
during the runtime of the named.  The first call to isc_os_ncpus() is
made as soon as possible on the library initalization.
---
 lib/isc/lib.c |  2 ++
 lib/isc/os.c  | 22 ++++++++++++++++------
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/lib/isc/lib.c b/lib/isc/lib.c
index 2d6950ad63..18e3284be0 100644
--- a/lib/isc/lib.c
+++ b/lib/isc/lib.c
@@ -14,6 +14,7 @@
 #include <isc/bind9.h>
 #include <isc/lib.h>
 #include <isc/mem.h>
+#include <isc/os.h>
 #include <isc/tls.h>
 #include <isc/util.h>
 
@@ -45,6 +46,7 @@ isc__initialize(void) {
 	isc__mem_initialize();
 	isc__tls_initialize();
 	isc__trampoline_initialize();
+	(void)isc_os_ncpus();
 }
 
 void
diff --git a/lib/isc/os.c b/lib/isc/os.c
index 5ba4481d36..6a75b60976 100644
--- a/lib/isc/os.c
+++ b/lib/isc/os.c
@@ -9,7 +9,12 @@
  * information regarding copyright ownership.
  */
 
+#include <isc/once.h>
 #include <isc/os.h>
+#include <isc/util.h>
+
+static isc_once_t ncpus_once = ISC_ONCE_INIT;
+static unsigned int ncpus = 0;
 
 #ifdef HAVE_SYSCONF
 
@@ -46,10 +51,8 @@ sysctl_ncpus(void) {
 }
 #endif /* if defined(HAVE_SYS_SYSCTL_H) && defined(HAVE_SYSCTLBYNAME) */
 
-unsigned int
-isc_os_ncpus(void) {
-	long ncpus = 0;
-
+static void
+ncpus_initialize(void) {
 #if defined(HAVE_SYSCONF)
 	ncpus = sysconf_ncpus();
 #endif /* if defined(HAVE_SYSCONF) */
@@ -61,6 +64,13 @@ isc_os_ncpus(void) {
 	if (ncpus <= 0) {
 		ncpus = 1;
 	}
-
-	return ((unsigned int)ncpus);
+}
+
+unsigned int
+isc_os_ncpus(void) {
+	isc_result_t result = isc_once_do(&ncpus_once, ncpus_initialize);
+	RUNTIME_CHECK(result == ISC_R_SUCCESS);
+	INSIST(ncpus > 0);
+
+	return (ncpus);
 }