feat(gax-grpc): optimize ChannelPool resize and add thread safety comment

Author: lqiu96

sdk-platform-java/gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/ChannelPool.java

@@ -84,15 +84,13 @@ class ChannelPool extends ManagedChannel {
   private final AtomicInteger indexTicker = new AtomicInteger();
   private final String authority;
 
-  // The number of consecutive resize cycles to wait before logging a warning about repeated
-  // resizing.
-  // This is an arbitrary value chosen to detect repeated requests for changes (multiple continuous
-  // increase or decrease attempts) without being too sensitive.
+  // The number of consecutive resize cycles to wait before logging a warning about repeated resizing.
+  // This is an arbitrary value chosen to detect repeated requests for changes (multiple continuous increase or decrease attempts) without being too sensitive.
   private static final int CONSECUTIVE_RESIZE_THRESHOLD = 5;
 
-  // Tracks the number of consecutive resize cycles where a resize actually occurred (either expand
-  // or shrink).
+  // Tracks the number of consecutive resize cycles where a resize actually occurred (either expand or shrink).
   // Used to detect repeated resizing activity and log a warning.
+  // Note: This field is only accessed within the synchronized resize() method, so it does not need to be atomic.
   private int consecutiveResizes = 0;
 
   static ChannelPool create(
@@ -331,7 +329,7 @@ void resize() {
     // We only count as "resized" if the thresholds are crossed and we actually attempt to scale.
     // Checking (dampenedTarget != currentSize) would cause false positives when the pool is within
     // bounds but not at the target, because the target aims for the middle of the bounds.
-    boolean resized = (localEntries.size() < minChannels || localEntries.size() > maxChannels);
+    boolean resized = (currentSize < minChannels || currentSize > maxChannels);
     if (resized) {
       consecutiveResizes++;
     } else {
@@ -341,9 +339,12 @@ void resize() {
     // Log warning only once when the threshold is reached to avoid spamming logs.
     // Using == instead of >= ensures we don't log on every subsequent resize cycle.
     if (consecutiveResizes == CONSECUTIVE_RESIZE_THRESHOLD) {
-      LOG.warning(
-          "Channel pool is repeatedly resizing. Consider adjusting `initialChannelCount` or `maxResizeDelta` to a more reasonable value. "
-              + "See https://docs.cloud.google.com/java/docs/troubleshooting to enable logging and set `com.google.api.gax.grpc.ChannelPool.level=FINEST` to log the channel pool resize behavior.");
+      StringBuilder sb = new StringBuilder();
+      sb.append("Channel pool is repeatedly resizing. ");
+      sb.append("Consider adjusting `initialChannelCount` or `maxResizeDelta` to a more reasonable value. ");
+      sb.append("See https://docs.cloud.google.com/java/docs/troubleshooting to enable logging ");
+      sb.append("and set `com.google.api.gax.grpc.ChannelPool.level=FINEST` to log the channel pool resize behavior.");
+      LOG.warning(sb.toString());
     }
 
     // Only resize the pool when thresholds are crossed