Add log level check simply before logging. (#10080)

Motivation:

In general, we will close the debug log in a product environment. However, logging without external level check may still affect performance as varargs will need to allocate an array.

Modification:

Add log level check simply before logging.

Result:

Improve performance slightly in a product environment.

common/src/main/java/io/netty/util/NetUtil.java

@@ -291,7 +291,10 @@ public final class NetUtil {
                         }
                     }
                 } catch (Exception e) {
-                    logger.debug("Failed to get SOMAXCONN from sysctl and file {}. Default: {}", file, somaxconn, e);
+                    if (logger.isDebugEnabled()) {
+                        logger.debug("Failed to get SOMAXCONN from sysctl and file {}. Default: {}",
+                                file, somaxconn, e);
+                    }
                 } finally {
                     if (in != null) {
                         try {

common/src/main/java/io/netty/util/internal/NativeLibraryLoader.java

@@ -137,10 +137,12 @@ public final class NativeLibraryLoader {
             return;
         } catch (Throwable ex) {
             suppressed.add(ex);
+            if (logger.isDebugEnabled()) {
                 logger.debug(
                         "{} cannot be loaded from java.library.path, "
                                 + "now trying export to -Dio.netty.native.workdir: {}", name, WORKDIR, ex);
             }
+        }
 
         String libname = System.mapLibraryName(name);
         String path = NATIVE_RESOURCE_HOME + libname;

handler/src/main/java/io/netty/handler/ssl/SslHandler.java

@@ -1163,11 +1163,13 @@ public class SslHandler extends ByteToMessageDecoder implements ChannelOutboundH
                         return true;
                     }
                 } catch (Throwable cause) {
+                    if (logger.isDebugEnabled()) {
                         logger.debug("Unexpected exception while loading class {} classname {}",
                                 getClass(), classname, cause);
                     }
                 }
             }
+        }
 
         return false;
     }

resolver-dns/src/main/java/io/netty/resolver/dns/UnixResolverDnsServerAddressStreamProvider.java

@@ -71,7 +71,9 @@ public final class UnixResolverDnsServerAddressStreamProvider implements DnsServ
             return nameServerCache.mayOverrideNameServers() ? nameServerCache
                                                             : DefaultDnsServerAddressStreamProvider.INSTANCE;
         } catch (Exception e) {
+            if (logger.isDebugEnabled()) {
                 logger.debug("failed to parse {} and/or {}", ETC_RESOLV_CONF_FILE, ETC_RESOLVER_DIR, e);
+            }
             return DefaultDnsServerAddressStreamProvider.INSTANCE;
         }
     }
@@ -254,10 +256,12 @@ public final class UnixResolverDnsServerAddressStreamProvider implements DnsServ
         DnsServerAddresses existingAddresses = domainToNameServerStreamMap.put(domainName, addresses);
         if (existingAddresses != null) {
             domainToNameServerStreamMap.put(domainName, existingAddresses);
+            if (logger.isDebugEnabled()) {
                 logger.debug("Domain name {} already maps to addresses {} so new addresses {} will be discarded",
                         domainName, existingAddresses, addresses);
             }
         }
+    }
 
     /**
      * Parse a file of the format <a href="https://linux.die.net/man/5/resolver">/etc/resolv.conf</a> and return the

transport/src/main/java/io/netty/channel/ChannelHandlerMask.java

@@ -173,8 +173,10 @@ final class ChannelHandlerMask {
                 try {
                     m = handlerType.getMethod(methodName, paramTypes);
                 } catch (NoSuchMethodException e) {
+                    if (logger.isDebugEnabled()) {
                         logger.debug(
                             "Class {} missing method {}, assume we can not skip execution", handlerType, methodName, e);
+                    }
                     return false;
                 }
                 return m != null && m.isAnnotationPresent(Skip.class);