Cache max size metric (#87)

* report cache max size, change interface

* update

Author: Kishan Sairam Adapa

platform-metrics/src/main/java/org/hypertrace/core/serviceframework/metrics/PlatformMetricsRegistry.java

@@ -4,6 +4,8 @@
 import com.codahale.metrics.Metric;
 import com.codahale.metrics.MetricRegistry;
 import com.google.common.cache.Cache;
+import com.google.common.cache.CacheBuilder;
+import com.google.common.cache.CacheLoader;
 import com.typesafe.config.Config;
 import io.github.mweirauch.micrometer.jvm.extras.ProcessMemoryMetrics;
 import io.github.mweirauch.micrometer.jvm.extras.ProcessThreadMetrics;
@@ -39,6 +41,7 @@
 import io.prometheus.client.CollectorRegistry;
 import io.prometheus.client.dropwizard.DropwizardExports;
 import io.prometheus.client.exporter.PushGateway;
+import java.lang.reflect.Field;
 import java.time.Duration;
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -73,6 +76,7 @@ public class PlatformMetricsRegistry {
   private static final String LOGGING_REPORTER_NAME = "logging";
   private static final String TESTING_REPORTER_NAME = "testing";
   private static final String CONSOLE_REPORTER_NAME = "console";
+  private static final String CACHE_MAX_SIZE_GAUGE = "cache.max.size";
 
   /**
    * List of tags that need to be reported for all the metrics reported by this service. The tags
@@ -451,6 +455,45 @@ public static <K, V> void registerCache(
     GuavaCacheMetrics.monitor(meterRegistry, guavaCache, cacheName, toIterable(tags));
   }
 
+  /**
+   * Registers metrics for GuavaCaches using micrometer's GuavaCacheMetrics under the given
+   * cacheName for the cache built using builder and also reports maximum size configured
+   */
+  public static <K, V> Cache<K, V> registerAndGetCache(
+      String cacheName,
+      CacheBuilder<Object, Object> guavaCacheBuilder,
+      CacheLoader<? super K, V> loader,
+      Map<String, String> tags) {
+    reportCacheMaxSize(cacheName, guavaCacheBuilder);
+    Cache<K, V> guavaCache = guavaCacheBuilder.build(loader);
+    GuavaCacheMetrics.monitor(meterRegistry, guavaCache, cacheName, toIterable(tags));
+    return guavaCache;
+  }
+
+  /**
+   * Registers metrics for GuavaCaches using micrometer's GuavaCacheMetrics under the given
+   * cacheName for the cache built using builder and also reports maximum size configured
+   */
+  public static <K, V> Cache<K, V> registerAndGetCache(
+      String cacheName, CacheBuilder<Object, Object> guavaCacheBuilder, Map<String, String> tags) {
+    reportCacheMaxSize(cacheName, guavaCacheBuilder);
+    Cache<K, V> guavaCache = guavaCacheBuilder.build();
+    GuavaCacheMetrics.monitor(meterRegistry, guavaCache, cacheName, toIterable(tags));
+    return guavaCache;
+  }
+
+  private static <K, V> void reportCacheMaxSize(
+      String cacheName, CacheBuilder<K, V> guavaCacheBuilder) {
+    try {
+      Field maximumSizeField = guavaCacheBuilder.getClass().getDeclaredField("maximumSize");
+      maximumSizeField.setAccessible(true);
+      long maximumSize = maximumSizeField.getLong(guavaCacheBuilder);
+      registerGauge(CACHE_MAX_SIZE_GAUGE, Map.of("cache", cacheName), maximumSize);
+    } catch (NoSuchFieldException | IllegalAccessException e) {
+      // ignore
+    }
+  }
+
   /**
    * Registers metrics for the given executor service with the service's metric registry and reports
    * them periodically to the configured reporters. Apart from the given tags, the reporting