[ agent ] [ executor ]- optimize the command executor cache log

agent/src/main/java/io/wdd/agent/executor/thread/LogToArrayListCache.java

@@ -2,6 +2,7 @@ package io.wdd.agent.executor.thread;
 
 
 import lombok.extern.slf4j.Slf4j;
+import org.apache.commons.collections.CollectionUtils;
 import org.springframework.stereotype.Component;
 
 import java.io.BufferedReader;
@@ -13,6 +14,7 @@ import java.util.List;
 
 /**
  * utils to cache store the command execution logs
+ *
  */
 @Component
 @Slf4j
@@ -70,8 +72,39 @@ public class LogToArrayListCache {
     private int hashStreamKeyToCachedArrayListIndex(String streamKey) {
 
         int size = CachedCommandLog.size();
+        int result = Math.abs(streamKey.hashCode() % size);
+        boolean hasRehashed = false;
 
-        return Math.abs(streamKey.hashCode() % size);
+        if (CollectionUtils.isNotEmpty(CachedCommandLog.get(result))) {
+            for (int index = result+1; index < CachedCommandLog.size(); index++) {
+                // from the index to the end
+                if (CollectionUtils.isEmpty(CachedCommandLog.get(index))){
+                    hasRehashed = true;
+                    result = index;
+                    break;
+                }
+            }
+            if (!hasRehashed) {
+                for (int index = 0; index < result; index++) {
+                    // from begin to the index
+                    if (CollectionUtils.isEmpty(CachedCommandLog.get(index))){
+                        hasRehashed = true;
+                        result = index;
+                        break;
+                    }
+                }
+            }
+
+            if (!hasRehashed) {
+                // reach here means no empty cache array list
+                CachedCommandLog.add(
+                        new ArrayList<>(256)
+                );
+                result = size;
+            }
+        }
+
+        return result;
     }
 
 }