Use C11's stdatomic.h instead of isc_atomic where available

2025-08-31 06:25:31 +00:00 · 2017-09-19 15:42:54 +05:30
parent fb088a00cf
commit 404c9b1c53
10 changed files with 315 additions and 49 deletions
--- a/3
+++ b/3
@@ -1,3 +1,6 @@
+4728.	[func]		Use C11's stdatomic.h instead of isc_atomic
+			where available. [RT #40668]
+
 4727.	[bug]		Retransferring an inline-signed slave using NSEC3
 			around the time its NSEC3 salt was changed could result
 			in an infinite signing loop. [RT #45080]
--- a/config.h.in
+++ b/config.h.in
@@ -449,6 +449,9 @@ int sigwait(const unsigned int *set, int *sig);
 /* Define to 1 if you have the `setresuid' function. */
 #undef HAVE_SETRESUID

+/* Define to 1 if you have the <stdatomic.h> header file. */
+#undef HAVE_STDATOMIC_H
+
 /* Define to 1 if you have the <stdint.h> header file. */
 #undef HAVE_STDINT_H

--- a/19
+++ b/19
@@ -718,6 +718,7 @@ ISC_PLATFORM_HAVEATOMICSTORE
 ISC_PLATFORM_HAVECMPXCHG
 ISC_PLATFORM_HAVEXADDQ
 ISC_PLATFORM_HAVEXADD
+ISC_PLATFORM_HAVESTDATOMIC
 ISC_PLATFORM_HAVEIFNAMETOINDEX
 ISC_PLATFORM_HAVESTRINGSH
 ISC_PLATFORM_BRACEPTHREADONCEINIT
@@ -20126,6 +20127,21 @@ done
 #
 # Machine architecture dependent features
 #
+for ac_header in stdatomic.h
+do :
+  ac_fn_c_check_header_mongrel "$LINENO" "stdatomic.h" "ac_cv_header_stdatomic_h" "$ac_includes_default"
+if test "x$ac_cv_header_stdatomic_h" = xyes; then :
+  cat >>confdefs.h <<_ACEOF
+#define HAVE_STDATOMIC_H 1
+_ACEOF
+ ISC_PLATFORM_HAVESTDATOMIC="#define ISC_PLATFORM_HAVESTDATOMIC 1"
+else
+  ISC_PLATFORM_HAVESTDATOMIC="#undef ISC_PLATFORM_HAVESTDATOMIC"
+fi
+
+done
+
+
 # Check whether --enable-atomic was given.
 if test "${enable_atomic+set}" = set; then :
  enableval=$enable_atomic; enable_atomic="$enableval"
@@ -20201,11 +20217,14 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 		esac
 		;;
 	no)
+		ISC_PLATFORM_HAVESTDATOMIC="#undef ISC_PLATFORM_HAVESTDATOMIC"
 		use_atomic=no
 		arch=noatomic
 		;;
 esac

+
+
 ISC_PLATFORM_USEOSFASM="#undef ISC_PLATFORM_USEOSFASM"
 ISC_PLATFORM_USEGCCASM="#undef ISC_PLATFORM_USEGCCASM"
 ISC_PLATFORM_USESTDASM="#undef ISC_PLATFORM_USESTDASM"
--- a/configure.in
+++ b/configure.in
@@ -4006,6 +4006,10 @@ AC_CHECK_FUNCS(nanosleep usleep)
 #
 # Machine architecture dependent features
 #
+AC_CHECK_HEADERS(stdatomic.h,
+		 [ISC_PLATFORM_HAVESTDATOMIC="#define ISC_PLATFORM_HAVESTDATOMIC 1"],
+		 [ISC_PLATFORM_HAVESTDATOMIC="#undef ISC_PLATFORM_HAVESTDATOMIC"])
+
 AC_ARG_ENABLE(atomic,
 	[  --enable-atomic	  enable machine specific atomic operations
 			  [[default=autodetect]]],
@@ -4048,11 +4052,14 @@ case "$enable_atomic" in
 		esac
 		;;
 	no)
+		ISC_PLATFORM_HAVESTDATOMIC="#undef ISC_PLATFORM_HAVESTDATOMIC"
 		use_atomic=no
 		arch=noatomic
 		;;
 esac

+AC_SUBST(ISC_PLATFORM_HAVESTDATOMIC)
+
 ISC_PLATFORM_USEOSFASM="#undef ISC_PLATFORM_USEOSFASM"
 ISC_PLATFORM_USEGCCASM="#undef ISC_PLATFORM_USEGCCASM"
 ISC_PLATFORM_USESTDASM="#undef ISC_PLATFORM_USESTDASM"
--- a/lib/isc/include/isc/platform.h.in
+++ b/lib/isc/include/isc/platform.h.in
@@ -306,6 +306,12 @@
 */
@ISC_PLATFORM_HAVECMPXCHG@

+/*
+ * If <stdatomic.h> is available on this architecture,
+ * ISC_PLATFORM_HAVESTDATOMIC will be defined.
+ */
+@ISC_PLATFORM_HAVESTDATOMIC@
+
 /*
 * Define if gcc ASM extension is available
 */
--- a/lib/isc/include/isc/refcount.h
+++ b/lib/isc/include/isc/refcount.h
@@ -18,6 +18,10 @@
 #include <isc/types.h>
 #include <isc/util.h>

+#if defined(ISC_PLATFORM_HAVESTDATOMIC)
+#include <stdatomic.h>
+#endif
+
 /*! \file isc/refcount.h
 * \brief Implements a locked reference counter.
 *
@@ -86,17 +90,59 @@ ISC_LANG_BEGINDECLS
 * Sample implementations
 */
 #ifdef ISC_PLATFORM_USETHREADS
-#ifdef ISC_PLATFORM_HAVEXADD
-
+#if (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE)) || defined(ISC_PLATFORM_HAVEXADD)
 #define ISC_REFCOUNT_HAVEATOMIC 1
+#if (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE))
+#define ISC_REFCOUNT_HAVESTDATOMIC 1
+#endif

 typedef struct isc_refcount {
+#if defined(ISC_REFCOUNT_HAVESTDATOMIC)
+	atomic_int_fast32_t refs;
+#else
 	isc_int32_t refs;
+#endif
 } isc_refcount_t;

 #define isc_refcount_destroy(rp) REQUIRE((rp)->refs == 0)
 #define isc_refcount_current(rp) ((unsigned int)((rp)->refs))

+#if defined(ISC_REFCOUNT_HAVESTDATOMIC)
+
+#define isc_refcount_increment0(rp, tp)				\
+	do {							\
+		unsigned int *_tmp = (unsigned int *)(tp);	\
+		isc_int32_t prev;				\
+		prev = atomic_fetch_add_explicit		\
+			(&(rp)->refs, 1, memory_order_relaxed); \
+		if (_tmp != NULL)				\
+			*_tmp = prev + 1;			\
+	} while (0)
+
+#define isc_refcount_increment(rp, tp)				\
+	do {							\
+		unsigned int *_tmp = (unsigned int *)(tp);	\
+		isc_int32_t prev;				\
+		prev = atomic_fetch_add_explicit		\
+			(&(rp)->refs, 1, memory_order_relaxed); \
+		REQUIRE(prev > 0);				\
+		if (_tmp != NULL)				\
+			*_tmp = prev + 1;			\
+	} while (0)
+
+#define isc_refcount_decrement(rp, tp)				\
+	do {							\
+		unsigned int *_tmp = (unsigned int *)(tp);	\
+		isc_int32_t prev;				\
+		prev = atomic_fetch_sub_explicit		\
+			(&(rp)->refs, 1, memory_order_relaxed); \
+		REQUIRE(prev > 0);				\
+		if (_tmp != NULL)				\
+			*_tmp = prev - 1;			\
+	} while (0)
+
+#else /* ISC_REFCOUNT_HAVESTDATOMIC */
+
 #define isc_refcount_increment0(rp, tp)				\
 	do {							\
 		unsigned int *_tmp = (unsigned int *)(tp);	\
@@ -126,6 +172,8 @@ typedef struct isc_refcount {
 			*_tmp = prev - 1;			\
 	} while (0)

+#endif /* ISC_REFCOUNT_HAVESTDATOMIC */
+
 #else  /* ISC_PLATFORM_HAVEXADD */

 typedef struct isc_refcount {
@@ -176,7 +224,7 @@ typedef struct isc_refcount {
 		UNLOCK(&(rp)->lock);				\
 	} while (0)

-#endif /* ISC_PLATFORM_HAVEXADD */
+#endif /* (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE)) || defined(ISC_PLATFORM_HAVEXADD) */
 #else  /* ISC_PLATFORM_USETHREADS */

 typedef struct isc_refcount {
--- a/lib/isc/include/isc/rwlock.h
+++ b/lib/isc/include/isc/rwlock.h
@@ -18,6 +18,10 @@
 #include <isc/platform.h>
 #include <isc/types.h>

+#if defined(ISC_PLATFORM_HAVESTDATOMIC)
+#include <stdatomic.h>
+#endif
+
 ISC_LANG_BEGINDECLS

 typedef enum {
@@ -27,8 +31,11 @@ typedef enum {
 } isc_rwlocktype_t;

 #ifdef ISC_PLATFORM_USETHREADS
-#if defined(ISC_PLATFORM_HAVEXADD) && defined(ISC_PLATFORM_HAVECMPXCHG)
+#if (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE)) || (defined(ISC_PLATFORM_HAVEXADD) && defined(ISC_PLATFORM_HAVECMPXCHG))
 #define ISC_RWLOCK_USEATOMIC 1
+#if (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE))
+#define ISC_RWLOCK_USESTDATOMIC 1
+#endif
 #endif

 struct isc_rwlock {
@@ -37,7 +44,7 @@ struct isc_rwlock {
 	isc_mutex_t		lock;
 	isc_int32_t		spins;

-#if defined(ISC_PLATFORM_HAVEXADD) && defined(ISC_PLATFORM_HAVECMPXCHG)
+#if defined(ISC_RWLOCK_USEATOMIC)
 	/*
 	 * When some atomic instructions with hardware assistance are
 	 * available, rwlock will use those so that concurrent readers do not
@@ -52,9 +59,15 @@ struct isc_rwlock {
 	 */

 	/* Read or modified atomically. */
+#if defined(ISC_RWLOCK_USESTDATOMIC)
+	atomic_int_fast32_t	write_requests;
+	atomic_int_fast32_t	write_completions;
+	atomic_int_fast32_t	cnt_and_flag;
+#else
 	isc_int32_t		write_requests;
 	isc_int32_t		write_completions;
 	isc_int32_t		cnt_and_flag;
+#endif

 	/* Locked by lock. */
 	isc_condition_t		readable;
@@ -67,7 +80,7 @@ struct isc_rwlock {
 	/* Unlocked. */
 	unsigned int		write_quota;

-#else  /* ISC_PLATFORM_HAVEXADD && ISC_PLATFORM_HAVECMPXCHG */
+#else  /* ISC_RWLOCK_USEATOMIC */

 	/*%< Locked by lock. */
 	isc_condition_t		readable;
@@ -89,7 +102,7 @@ struct isc_rwlock {
 	unsigned int		read_quota;
 	unsigned int		write_quota;
 	isc_rwlocktype_t	original;
-#endif  /* ISC_PLATFORM_HAVEXADD && ISC_PLATFORM_HAVECMPXCHG */
+#endif  /* ISC_RWLOCK_USEATOMIC */
 };
 #else /* ISC_PLATFORM_USETHREADS */
 struct isc_rwlock {
--- a/lib/isc/refcount.c
+++ b/lib/isc/refcount.c
@@ -21,7 +21,7 @@ isc_refcount_init(isc_refcount_t *ref, unsigned int n) {
 	REQUIRE(ref != NULL);

 	ref->refs = n;
-#if defined(ISC_PLATFORM_USETHREADS) && !defined(ISC_PLATFORM_HAVEXADD)
+#if defined(ISC_PLATFORM_USETHREADS) && !defined(ISC_REFCOUNT_HAVEATOMIC)
 	return (isc_mutex_init(&ref->lock));
 #else
 	return (ISC_R_SUCCESS);
--- a/lib/isc/rwlock.c
+++ b/lib/isc/rwlock.c
@@ -39,7 +39,7 @@
 #define RWLOCK_MAX_ADAPTIVE_COUNT 100
 #endif

-#if defined(ISC_PLATFORM_HAVEXADD) && defined(ISC_PLATFORM_HAVECMPXCHG)
+#if defined(ISC_RWLOCK_USEATOMIC)
 static isc_result_t
 isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type);
 #endif
@@ -50,7 +50,7 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type);

 static void
 print_lock(const char *operation, isc_rwlock_t *rwl, isc_rwlocktype_t type) {
-#if defined(ISC_PLATFORM_HAVEXADD) && defined(ISC_PLATFORM_HAVECMPXCHG)
+#if defined(ISC_RWLOCK_USEATOMIC)
 	fprintf(stderr,
 		isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK,
 			       ISC_MSG_PRINTLOCK2,
@@ -105,7 +105,7 @@ isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
 	rwl->magic = 0;

 	rwl->spins = 0;
-#if defined(ISC_PLATFORM_HAVEXADD) && defined(ISC_PLATFORM_HAVECMPXCHG)
+#if defined(ISC_RWLOCK_USEATOMIC)
 	rwl->write_requests = 0;
 	rwl->write_completions = 0;
 	rwl->cnt_and_flag = 0;
@@ -174,7 +174,7 @@ void
 isc_rwlock_destroy(isc_rwlock_t *rwl) {
 	REQUIRE(VALID_RWLOCK(rwl));

-#if defined(ISC_PLATFORM_HAVEXADD) && defined(ISC_PLATFORM_HAVECMPXCHG)
+#if defined(ISC_RWLOCK_USEATOMIC)
 	REQUIRE(rwl->write_requests == rwl->write_completions &&
 		rwl->cnt_and_flag == 0 && rwl->readers_waiting == 0);
 #else
@@ -191,7 +191,7 @@ isc_rwlock_destroy(isc_rwlock_t *rwl) {
 	DESTROYLOCK(&rwl->lock);
 }

-#if defined(ISC_PLATFORM_HAVEXADD) && defined(ISC_PLATFORM_HAVECMPXCHG)
+#if defined(ISC_RWLOCK_USEATOMIC)

 /*
 * When some architecture-dependent atomic operations are available,
@@ -281,7 +281,13 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 			UNLOCK(&rwl->lock);
 		}

+#if defined(ISC_RWLOCK_USESTDATOMIC)
+		cntflag = atomic_fetch_add_explicit(&rwl->cnt_and_flag,
+						    READER_INCR,
+						    memory_order_relaxed);
+#else
 		cntflag = isc_atomic_xadd(&rwl->cnt_and_flag, READER_INCR);
+#endif
 		POST(cntflag);
 		while (1) {
 			if ((rwl->cnt_and_flag & WRITER_ACTIVE) == 0)
@@ -331,7 +337,12 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 		isc_int32_t prev_writer;

 		/* enter the waiting queue, and wait for our turn */
+#if defined(ISC_RWLOCK_USESTDATOMIC)
+		prev_writer = atomic_fetch_add_explicit(&rwl->write_requests, 1,
+							memory_order_relaxed);
+#else
 		prev_writer = isc_atomic_xadd(&rwl->write_requests, 1);
+#endif
 		while (rwl->write_completions != prev_writer) {
 			LOCK(&rwl->lock);
 			if (rwl->write_completions != prev_writer) {
@@ -344,9 +355,18 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 		}

 		while (1) {
-			cntflag = isc_atomic_cmpxchg(&rwl->cnt_and_flag, 0,
-						     WRITER_ACTIVE);
-			if (cntflag == 0)
+#if defined(ISC_RWLOCK_USESTDATOMIC)
+			atomic_int_fast32_t cntflag2 = 0;
+			atomic_compare_exchange_strong_explicit
+				(&rwl->cnt_and_flag, &cntflag2, WRITER_ACTIVE,
+				 memory_order_relaxed, memory_order_relaxed);
+#else
+			isc_int32_t cntflag2;
+			cntflag2 = isc_atomic_cmpxchg(&rwl->cnt_and_flag, 0,
+						      WRITER_ACTIVE);
+#endif
+
+			if (cntflag2 == 0)
 				break;

 			/* Another active reader or writer is working. */
@@ -409,14 +429,26 @@ isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 			return (ISC_R_LOCKBUSY);

 		/* Otherwise, be ready for reading. */
+#if defined(ISC_RWLOCK_USESTDATOMIC)
+		cntflag = atomic_fetch_add_explicit(&rwl->cnt_and_flag,
+						    READER_INCR,
+						    memory_order_relaxed);
+#else
 		cntflag = isc_atomic_xadd(&rwl->cnt_and_flag, READER_INCR);
+#endif
 		if ((cntflag & WRITER_ACTIVE) != 0) {
 			/*
 			 * A writer is working.  We lose, and cancel the read
 			 * request.
 			 */
+#if defined(ISC_RWLOCK_USESTDATOMIC)
+			cntflag = atomic_fetch_sub_explicit
+				(&rwl->cnt_and_flag, READER_INCR,
+				 memory_order_relaxed);
+#else
 			cntflag = isc_atomic_xadd(&rwl->cnt_and_flag,
 						  -READER_INCR);
+#endif
 			/*
 			 * If no other readers are waiting and we've suspended
 			 * new writers in this short period, wake them up.
@@ -432,16 +464,29 @@ isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 		}
 	} else {
 		/* Try locking without entering the waiting queue. */
+#if defined(ISC_RWLOCK_USESTDATOMIC)
+		atomic_int_fast32_t zero = 0;
+		if (!atomic_compare_exchange_strong_explicit
+		    (&rwl->cnt_and_flag, &zero, WRITER_ACTIVE,
+		     memory_order_relaxed, memory_order_relaxed))
+			return (ISC_R_LOCKBUSY);
+#else
 		cntflag = isc_atomic_cmpxchg(&rwl->cnt_and_flag, 0,
 					     WRITER_ACTIVE);
 		if (cntflag != 0)
 			return (ISC_R_LOCKBUSY);
+#endif

 		/*
 		 * XXXJT: jump into the queue, possibly breaking the writer
 		 * order.
 		 */
+#if defined(ISC_RWLOCK_USESTDATOMIC)
+		atomic_fetch_sub_explicit(&rwl->write_completions, 1,
+					  memory_order_relaxed);
+#else
 		(void)isc_atomic_xadd(&rwl->write_completions, -1);
+#endif

 		rwl->write_granted++;
 	}
@@ -456,31 +501,60 @@ isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {

 isc_result_t
 isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
-	isc_int32_t prevcnt;
-
 	REQUIRE(VALID_RWLOCK(rwl));

-	/* Try to acquire write access. */
-	prevcnt = isc_atomic_cmpxchg(&rwl->cnt_and_flag,
-				     READER_INCR, WRITER_ACTIVE);
-	/*
-	 * There must have been no writer, and there must have been at least
-	 * one reader.
-	 */
-	INSIST((prevcnt & WRITER_ACTIVE) == 0 &&
-	       (prevcnt & ~WRITER_ACTIVE) != 0);
+#if defined(ISC_RWLOCK_USESTDATOMIC)
+	{
+		atomic_int_fast32_t reader_incr = READER_INCR;

-	if (prevcnt == READER_INCR) {
+		/* Try to acquire write access. */
+		atomic_compare_exchange_strong_explicit
+			(&rwl->cnt_and_flag, &reader_incr, WRITER_ACTIVE,
+			 memory_order_relaxed, memory_order_relaxed);
 		/*
-		 * We are the only reader and have been upgraded.
-		 * Now jump into the head of the writer waiting queue.
+		 * There must have been no writer, and there must have
+		 * been at least one reader.
 		 */
-		(void)isc_atomic_xadd(&rwl->write_completions, -1);
-	} else
-		return (ISC_R_LOCKBUSY);
+		INSIST((reader_incr & WRITER_ACTIVE) == 0 &&
+		       (reader_incr & ~WRITER_ACTIVE) != 0);
+
+		if (reader_incr == READER_INCR) {
+			/*
+			 * We are the only reader and have been upgraded.
+			 * Now jump into the head of the writer waiting queue.
+			 */
+			atomic_fetch_sub_explicit(&rwl->write_completions, 1,
+						  memory_order_relaxed);
+		} else
+			return (ISC_R_LOCKBUSY);
+
+	}
+#else
+	{
+		isc_int32_t prevcnt;
+
+		/* Try to acquire write access. */
+		prevcnt = isc_atomic_cmpxchg(&rwl->cnt_and_flag,
+					     READER_INCR, WRITER_ACTIVE);
+		/*
+		 * There must have been no writer, and there must have
+		 * been at least one reader.
+		 */
+		INSIST((prevcnt & WRITER_ACTIVE) == 0 &&
+		       (prevcnt & ~WRITER_ACTIVE) != 0);
+
+		if (prevcnt == READER_INCR) {
+			/*
+			 * We are the only reader and have been upgraded.
+			 * Now jump into the head of the writer waiting queue.
+			 */
+			(void)isc_atomic_xadd(&rwl->write_completions, -1);
+		} else
+			return (ISC_R_LOCKBUSY);
+	}
+#endif

 	return (ISC_R_SUCCESS);
-
 }

 void
@@ -489,14 +563,33 @@ isc_rwlock_downgrade(isc_rwlock_t *rwl) {

 	REQUIRE(VALID_RWLOCK(rwl));

-	/* Become an active reader. */
-	prev_readers = isc_atomic_xadd(&rwl->cnt_and_flag, READER_INCR);
-	/* We must have been a writer. */
-	INSIST((prev_readers & WRITER_ACTIVE) != 0);
+#if defined(ISC_RWLOCK_USESTDATOMIC)
+	{
+		/* Become an active reader. */
+		prev_readers = atomic_fetch_add_explicit(&rwl->cnt_and_flag,
+							 READER_INCR,
+							 memory_order_relaxed);
+		/* We must have been a writer. */
+		INSIST((prev_readers & WRITER_ACTIVE) != 0);

-	/* Complete write */
-	(void)isc_atomic_xadd(&rwl->cnt_and_flag, -WRITER_ACTIVE);
-	(void)isc_atomic_xadd(&rwl->write_completions, 1);
+		/* Complete write */
+		atomic_fetch_sub_explicit(&rwl->cnt_and_flag, WRITER_ACTIVE,
+					  memory_order_relaxed);
+		atomic_fetch_add_explicit(&rwl->write_completions, 1,
+					  memory_order_relaxed);
+	}
+#else
+	{
+		/* Become an active reader. */
+		prev_readers = isc_atomic_xadd(&rwl->cnt_and_flag, READER_INCR);
+		/* We must have been a writer. */
+		INSIST((prev_readers & WRITER_ACTIVE) != 0);
+
+		/* Complete write */
+		(void)isc_atomic_xadd(&rwl->cnt_and_flag, -WRITER_ACTIVE);
+		(void)isc_atomic_xadd(&rwl->write_completions, 1);
+	}
+#endif

 	/* Resume other readers */
 	LOCK(&rwl->lock);
@@ -517,8 +610,13 @@ isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 #endif

 	if (type == isc_rwlocktype_read) {
+#if defined(ISC_RWLOCK_USESTDATOMIC)
+		prev_cnt = atomic_fetch_sub_explicit(&rwl->cnt_and_flag,
+						     READER_INCR,
+						     memory_order_relaxed);
+#else
 		prev_cnt = isc_atomic_xadd(&rwl->cnt_and_flag, -READER_INCR);
-
+#endif
 		/*
 		 * If we're the last reader and any writers are waiting, wake
 		 * them up.  We need to wake up all of them to ensure the
@@ -537,8 +635,15 @@ isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 		 * Reset the flag, and (implicitly) tell other writers
 		 * we are done.
 		 */
+#if defined(ISC_RWLOCK_USESTDATOMIC)
+		atomic_fetch_sub_explicit(&rwl->cnt_and_flag, WRITER_ACTIVE,
+					  memory_order_relaxed);
+		atomic_fetch_add_explicit(&rwl->write_completions, 1,
+					  memory_order_relaxed);
+#else
 		(void)isc_atomic_xadd(&rwl->cnt_and_flag, -WRITER_ACTIVE);
 		(void)isc_atomic_xadd(&rwl->write_completions, 1);
+#endif

 		if (rwl->write_granted >= rwl->write_quota ||
 		    rwl->write_requests == rwl->write_completions ||
@@ -576,7 +681,7 @@ isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 	return (ISC_R_SUCCESS);
 }

-#else /* ISC_PLATFORM_HAVEXADD && ISC_PLATFORM_HAVECMPXCHG */
+#else /* ISC_RWLOCK_USEATOMIC */

 static isc_result_t
 doit(isc_rwlock_t *rwl, isc_rwlocktype_t type, isc_boolean_t nonblock) {
@@ -782,7 +887,7 @@ isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 	return (ISC_R_SUCCESS);
 }

-#endif /* ISC_PLATFORM_HAVEXADD && ISC_PLATFORM_HAVECMPXCHG */
+#endif /* ISC_RWLOCK_USEATOMIC */
 #else /* ISC_PLATFORM_USETHREADS */

 isc_result_t
--- a/lib/isc/stats.c
+++ b/lib/isc/stats.c
@@ -24,6 +24,10 @@
 #include <isc/stats.h>
 #include <isc/util.h>

+#if defined(ISC_PLATFORM_HAVESTDATOMIC)
+#include <stdatomic.h>
+#endif
+
 #define ISC_STATS_MAGIC			ISC_MAGIC('S', 't', 'a', 't')
 #define ISC_STATS_VALID(x)		ISC_MAGIC_VALID(x, ISC_STATS_MAGIC)

@@ -32,8 +36,12 @@
 * increment and store operations, just to make
 * the later macros simpler
 */
-#if defined(ISC_PLATFORM_HAVEXADDQ) && defined(ISC_PLATFORM_HAVEATOMICSTOREQ)
+#if (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_LONG_LOCK_FREE)) || \
+	(defined(ISC_PLATFORM_HAVEXADDQ) && defined(ISC_PLATFORM_HAVEATOMICSTOREQ))
 #define ISC_STATS_HAVEATOMICQ 1
+#if (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_LONG_LOCK_FREE))
+#define ISC_STATS_HAVESTDATOMICQ 1
+#endif
 #else
 #define ISC_STATS_HAVEATOMICQ 0
 #endif
@@ -61,20 +69,32 @@
 * Otherwise, just rely on standard 64-bit data types
 * and operations
 */
-#if !ISC_STATS_HAVEATOMICQ && defined(ISC_PLATFORM_HAVEXADD)
+#if !ISC_STATS_HAVEATOMICQ && ((defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE)) || defined(ISC_PLATFORM_HAVEXADD))
 #define ISC_STATS_USEMULTIFIELDS 1
+#if (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE))
+#define ISC_STATS_HAVESTDATOMIC 1
+#endif
 #else
 #define ISC_STATS_USEMULTIFIELDS 0
 #endif

 #if ISC_STATS_USEMULTIFIELDS
 typedef struct {
+#if defined(ISC_STATS_HAVESTDATOMIC)
+	atomic_int_fast32_t hi;
+	atomic_int_fast32_t lo;
+#else
 	isc_uint32_t hi;
 	isc_uint32_t lo;
+#endif
 } isc_stat_t;
 #else
+#if defined(ISC_STATS_HAVESTDATOMICQ)
+typedef atomic_int_fast64_t isc_stat_t;
+#else
 typedef isc_uint64_t isc_stat_t;
 #endif
+#endif

 struct isc_stats {
 	/*% Unlocked */
@@ -232,7 +252,12 @@ incrementcounter(isc_stats_t *stats, int counter) {
 #endif

 #if ISC_STATS_USEMULTIFIELDS
+#if defined(ISC_STATS_HAVESTDATOMIC)
+	prev = atomic_fetch_add_explicit(&stats->counters[counter].lo, 1,
+					 memory_order_relaxed);
+#else
 	prev = isc_atomic_xadd((isc_int32_t *)&stats->counters[counter].lo, 1);
+#endif
 	/*
 	 * If the lower 32-bit field overflows, increment the higher field.
 	 * Note that it's *theoretically* possible that the lower field
@@ -241,11 +266,22 @@ incrementcounter(isc_stats_t *stats, int counter) {
 	 * isc_stats_copy() is called where the whole process is protected
 	 * by the write (exclusive) lock.
 	 */
-	if (prev == (isc_int32_t)0xffffffff)
+	if (prev == (isc_int32_t)0xffffffff) {
+#if defined(ISC_STATS_HAVESTDATOMIC)
+		atomic_fetch_add_explicit(&stats->counters[counter].hi, 1,
+					  memory_order_relaxed);
+#else
 		isc_atomic_xadd((isc_int32_t *)&stats->counters[counter].hi, 1);
+#endif
+	}
 #elif ISC_STATS_HAVEATOMICQ
 	UNUSED(prev);
+#if defined(ISC_STATS_HAVESTDATOMICQ)
+	atomic_fetch_add_explicit(&stats->counters[counter], 1,
+				  memory_order_relaxed);
+#else
 	isc_atomic_xaddq((isc_int64_t *)&stats->counters[counter], 1);
+#endif
 #else
 	UNUSED(prev);
 	stats->counters[counter]++;
@@ -265,13 +301,29 @@ decrementcounter(isc_stats_t *stats, int counter) {
 #endif

 #if ISC_STATS_USEMULTIFIELDS
+#if defined(ISC_STATS_HAVESTDATOMIC)
+	prev = atomic_fetch_sub_explicit(&stats->counters[counter].lo, 1,
+					 memory_order_relaxed);
+#else
 	prev = isc_atomic_xadd((isc_int32_t *)&stats->counters[counter].lo, -1);
-	if (prev == 0)
+#endif
+	if (prev == 0) {
+#if defined(ISC_STATS_HAVESTDATOMIC)
+		atomic_fetch_sub_explicit(&stats->counters[counter].hi, 1,
+					  memory_order_relaxed);
+#else
 		isc_atomic_xadd((isc_int32_t *)&stats->counters[counter].hi,
 				-1);
+#endif
+	}
 #elif ISC_STATS_HAVEATOMICQ
 	UNUSED(prev);
+#if defined(ISC_STATS_HAVESTDATOMICQ)
+	atomic_fetch_sub_explicit(&stats->counters[counter], 1,
+				  memory_order_relaxed);
+#else
 	isc_atomic_xaddq((isc_int64_t *)&stats->counters[counter], -1);
+#endif
 #else
 	UNUSED(prev);
 	stats->counters[counter]--;
@@ -300,9 +352,15 @@ copy_counters(isc_stats_t *stats) {
 			(isc_uint64_t)(stats->counters[i].hi) << 32 |
 			stats->counters[i].lo;
 #elif ISC_STATS_HAVEATOMICQ
+#if defined(ISC_STATS_HAVESTDATOMICQ)
+		stats->copiedcounters[i] =
+			atomic_load_explicit(&stats->counters[i],
+					     memory_order_relaxed);
+#else
 		/* use xaddq(..., 0) as an atomic load */
 		stats->copiedcounters[i] =
 			(isc_uint64_t)isc_atomic_xaddq((isc_int64_t *)&stats->counters[i], 0);
+#endif
 #else
 		stats->copiedcounters[i] = stats->counters[i];
 #endif
@@ -373,7 +431,12 @@ isc_stats_set(isc_stats_t *stats, isc_uint64_t val,
 	stats->counters[counter].hi = (isc_uint32_t)((val >> 32) & 0xffffffff);
 	stats->counters[counter].lo = (isc_uint32_t)(val & 0xffffffff);
 #elif ISC_STATS_HAVEATOMICQ
+#if defined(ISC_STATS_HAVESTDATOMICQ)
+	atomic_store_explicit(&stats->counters[counter], val,
+			      memory_order_relaxed);
+#else
 	isc_atomic_storeq((isc_int64_t *)&stats->counters[counter], val);
+#endif
 #else
 	stats->counters[counter] = val;
 #endif
@@ -382,4 +445,3 @@ isc_stats_set(isc_stats_t *stats, isc_uint64_t val,
 	isc_rwlock_unlock(&stats->counterlock, isc_rwlocktype_write);
 #endif
 }
-