Experiment 4: no prefer writer at all

This reverts commit 5f16c13809.

lib/dns/rbtdb.c

@@ -8400,7 +8400,7 @@ dns_rbtdb_create(isc_mem_t *mctx, const dns_name_t *origin, dns_dbtype_t type,
 		goto cleanup_rbtdb;
 	}
 
-	result = isc_rwlock_init(&rbtdb->tree_lock, 0, 0);
+	result = isc_rwlock_init(&rbtdb->tree_lock, 0, 154123);
 	if (result != ISC_R_SUCCESS) {
 		goto cleanup_lock;
 	}

lib/isc/rwlock.c

@@ -36,7 +36,13 @@ isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
 		unsigned int write_quota) {
 	UNUSED(read_quota);
 	UNUSED(write_quota);
-	REQUIRE(pthread_rwlock_init(&rwl->rwlock, NULL) == 0);
+	if (write_quota == 154124) {
+		pthread_rwlockattr_t attr;
+		pthread_rwlockattr_setkind_np(&attr, PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP);
+		REQUIRE(pthread_rwlock_init(&rwl->rwlock, &attr) == 0);
+	} else {
+		REQUIRE(pthread_rwlock_init(&rwl->rwlock, NULL) == 0);
+	}
 	atomic_init(&rwl->downgrade, false);
 	return (ISC_R_SUCCESS);
 }