[improvement] Save resources on the BK threads by not accessing the m…

…etrics context (#1961)

(cherry picked from commit 200f21a)

### Motivation

Save resources on the BK threads by not accessing the metrics context.

### Modifications

Record metric in the `sendResponseScheduler`.

Co-authored-by: Enrico Olivelli <[email protected]>

kafka-impl/src/main/java/io/streamnative/pulsar/handlers/kop/KafkaCommandDecoder.java

@@ -32,11 +32,13 @@
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.BiConsumer;
+import java.util.function.Consumer;
 import lombok.Getter;
 import lombok.Setter;
 import lombok.extern.slf4j.Slf4j;
 import org.apache.bookkeeper.common.util.MathUtils;
 import org.apache.bookkeeper.common.util.OrderedScheduler;
+import org.apache.bookkeeper.stats.OpStatsLogger;
 import org.apache.kafka.common.errors.ApiException;
 import org.apache.kafka.common.errors.AuthenticationException;
 import org.apache.kafka.common.errors.UnsupportedVersionException;
@@ -196,22 +198,21 @@ public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception
         ByteBuf buffer = (ByteBuf) msg;
         requestStats.getNetworkTotalBytesIn().addCount(buffer.readableBytes());
 
+        OpStatsLogger requestParseLatencyStats = requestStats.getRequestParseLatencyStats();
         // Update parse request latency metrics
         final BiConsumer<Long, Throwable> registerRequestParseLatency = (timeBeforeParse, throwable) -> {
-            requestStats.getRequestParseLatencyStats().registerSuccessfulEvent(
+            requestParseLatencyStats.registerSuccessfulEvent(
                     MathUtils.elapsedNanos(timeBeforeParse), TimeUnit.NANOSECONDS);
         };
 
-        // Update handle request latency metrics
-        final BiConsumer<ApiKeys, Long> registerRequestLatency = (apiKey, startProcessTime) -> {
-            requestStats.getRequestStatsLogger(apiKey, KopServerStats.REQUEST_LATENCY)
-                    .registerSuccessfulEvent(MathUtils.elapsedNanos(startProcessTime), TimeUnit.NANOSECONDS);
-        };
-
         // If kop is enabled for authentication and the client
         // has not completed the handshake authentication,
         // execute channelPrepare to complete authentication
         if (isActive.get() && !channelReady()) {
+            final BiConsumer<ApiKeys, Long> registerRequestLatency = (apiKey, startProcessTime) -> {
+                requestStats.getRequestStatsLogger(apiKey, KopServerStats.REQUEST_LATENCY)
+                        .registerSuccessfulEvent(MathUtils.elapsedNanos(startProcessTime), TimeUnit.NANOSECONDS);
+            };
             try {
                 channelPrepare(ctx, buffer, registerRequestParseLatency, registerRequestLatency);
                 return;
@@ -235,6 +236,13 @@ public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception
         // potentially blocking until there is room in the queue for the request.
         registerRequestParseLatency.accept(timeBeforeParse, null);
 
+        OpStatsLogger requestStatsLogger = requestStats.getRequestStatsLogger(kafkaHeaderAndRequest.header.apiKey(),
+                KopServerStats.REQUEST_LATENCY);
+        // Update handle request latency metrics
+        final Consumer<Long> registerRequestLatency = (startProcessTime) -> {
+            requestStatsLogger
+                    .registerSuccessfulEvent(MathUtils.elapsedNanos(startProcessTime), TimeUnit.NANOSECONDS);
+        };
         try {
             if (log.isDebugEnabled()) {
                 log.debug("[{}] Received kafka cmd {}, the request content is: {}",
@@ -255,12 +263,15 @@ public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception
                     return;
                 }
 
-                registerRequestLatency.accept(kafkaHeaderAndRequest.getHeader().apiKey(),
-                        startProcessRequestTimestamp);
-
-                sendResponseScheduler.executeOrdered(channel.remoteAddress().hashCode(), () -> {
+                if (sendResponseScheduler != null) {
+                    sendResponseScheduler.executeOrdered(channel.remoteAddress().hashCode(), () -> {
+                        registerRequestLatency.accept(startProcessRequestTimestamp);
+                        writeAndFlushResponseToClient(channel);
+                    });
+                } else {
+                    registerRequestLatency.accept(startProcessRequestTimestamp);
                     writeAndFlushResponseToClient(channel);
-                });
+                }
             });
             // potentially blocking until there is room in the queue for the request.
             requestQueue.put(ResponseAndRequest.of(responseFuture, kafkaHeaderAndRequest));