Code and javadoc refinement

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/ClusterErrorMessages.java

@@ -25,7 +25,7 @@ public final class ClusterErrorMessages {
     public static final String UNEXPECTED_STATUS = "unexpected status";
     public static final String TOO_MANY_REQUESTS = "too many requests (client side)";
     public static final String REQUEST_TIME_OUT = "request time out";
-    public static final String CLIENT_NOT_READY = "client not ready (not running or initializing)";
+    public static final String CLIENT_NOT_READY = "client not ready";
     public static final String NO_RULES_IN_SERVER = "no rules in token server";
 
     private ClusterErrorMessages() {}

sentinel-cluster/sentinel-cluster-server-default/src/main/java/com/alibaba/csp/sentinel/cluster/flow/rule/ClusterFlowRuleManager.java

@@ -104,6 +104,7 @@ public final class ClusterFlowRuleManager {
     }
 
     public static void setPropertySupplier(Function<String, SentinelProperty<List<FlowRule>>> propertySupplier) {
+        AssertUtil.notNull(propertySupplier, "flow rule property supplier cannot be null");
         ClusterFlowRuleManager.propertySupplier = propertySupplier;
     }
 

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/flow/controller/RateLimiterController.java

@@ -44,17 +44,12 @@ public class RateLimiterController implements TrafficShapingController {
 
     @Override
     public boolean canPass(Node node, int acquireCount, boolean prioritized) {
-        /*
-            1. Pass when acquire count is less or equal than 0
-            2. Reject when count is less or equal than 0.
-               Otherwise,the costTime will be max of long and waitTime will overflow in some cases.
-               This will lead to pass of following request.It's dangerous!!!
-         */
-
+        // Pass when acquire count is less or equal than 0.
         if (acquireCount <= 0) {
             return true;
         }
-
+        // Reject when count is less or equal than 0.
+        // Otherwise,the costTime will be max of long and waitTime will overflow in some cases.
         if (count <= 0) {
             return false;
         }

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/flow/controller/WarmUpController.java

@@ -27,32 +27,37 @@ import com.alibaba.csp.sentinel.slots.block.flow.TrafficShapingController;
  * rate-based, which means that we need to translate rate to QPS.
  * </p>
  *
+ * <p>
  * Requests arriving at the pulse may drag down long idle systems even though it
  * has a much larger handling capability in stable period. It usually happens in
- * scenarios that require extra time for initialization, e.g. DB
- * establishes a connection; connects to a remote service, and so on.
- *
- * That’s why we need “warm up”.
- *
- * Sentinel's "warm-up" implementation is based on the guava-based algorithm.
- * However, Guava’s implementation focus on adjusting the request interval, in
- * other words, a Leaky bucket. Sentinel pays more attention to controlling the
- * count of incoming requests per second without calculating its interval, it is
- * more like a “Token bucket.”
+ * scenarios that require extra time for initialization, e.g. DB establishes a connection,
+ * connects to a remote service, and so on. That’s why we need “warm up”.
+ * </p>
  *
+ * <p>
+ * Sentinel's "warm-up" implementation is based on the Guava's algorithm.
+ * However, Guava’s implementation focuses on adjusting the request interval,
+ * which is similar to leaky bucket. Sentinel pays more attention to
+ * controlling the count of incoming requests per second without calculating its interval,
+ * which resembles token bucket algorithm.
+ * </p>
  *
+ * <p>
  * The remaining tokens in the bucket is used to measure the system utility.
  * Suppose a system can handle b requests per second. Every second b tokens will
  * be added into the bucket until the bucket is full. And when system processes
  * a request, it takes a token from the bucket. The more tokens left in the
  * bucket, the lower the utilization of the system; when the token in the token
  * bucket is above a certain threshold, we call it in a "saturation" state.
+ * </p>
  *
+ * <p>
  * Base on Guava’s theory, there is a linear equation we can write this in the
  * form y = m * x + b where y (a.k.a y(x)), or qps(q)), is our expected QPS
  * given a saturated period (e.g. 3 minutes in), m is the rate of change from
  * our cold (minimum) rate to our stable (maximum) rate, x (or q) is the
  * occupied token.
+ * </p>
  *
  * @author jialiang.linjl
  */

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/logger/LogSlot.java

@@ -38,7 +38,7 @@ public class LogSlot extends AbstractLinkedProcessorSlot<DefaultNode> {
                 context.getOrigin(), count);
             throw e;
         } catch (Throwable e) {
-            RecordLog.info("Entry exception", e);
+            RecordLog.warn("Unexpected entry exception", e);
         }
 
     }
@@ -48,7 +48,7 @@ public class LogSlot extends AbstractLinkedProcessorSlot<DefaultNode> {
         try {
             fireExit(context, resourceWrapper, count, args);
         } catch (Throwable e) {
-            RecordLog.info("Entry exit exception", e);
+            RecordLog.warn("Unexpected entry exit exception", e);
         }
     }
 }

sentinel-core/src/main/java/com/alibaba/csp/sentinel/util/PidUtil.java

@@ -22,7 +22,13 @@ import java.lang.management.ManagementFactory;
  */
 public final class PidUtil {
 
+    /**
+     * Resolve and get current process ID.
+     *
+     * @return current process ID
+     */
     public static int getPid() {
+        // Note: this will trigger local host resolve, which might be slow.
         String name = ManagementFactory.getRuntimeMXBean().getName();
         return Integer.parseInt(name.split("@")[0]);
     }