Ensure that only one thread will compute the missing object in the cache. The others will wait.

3 files changed, 31 insertions, 13 deletions

diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/ServerCache.java b/configserver/src/main/java/com/yahoo/vespa/config/server/ServerCache.java
index ad544005ace..85bf5df3c71 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/ServerCache.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/ServerCache.java
@@ -9,6 +9,7 @@ import com.yahoo.vespa.config.protocol.ConfigResponse;
 
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Function;
 
 /**
  * Cache that holds configs and config definitions (builtin and user config definitions).
@@ -23,11 +24,14 @@ public class ServerCache {
     // NOTE: The reason we do a double mapping here is to de-dupe configs that have the same md5.
     private final Map<ConfigCacheKey, String> md5Sums = new ConcurrentHashMap<>();
     private final Map<String, ConfigResponse> md5ToConfig = new ConcurrentHashMap<>();
-
+    private final Object [] stripedLocks = new Object[113];
 
     public ServerCache(ConfigDefinitionRepo builtinConfigDefinitions, ConfigDefinitionRepo userConfigDefinitions) {
         this.builtinConfigDefinitions = builtinConfigDefinitions;
         this.userConfigDefinitions = userConfigDefinitions;
+        for (int i = 0; i < stripedLocks.length; i++) {
+            stripedLocks[i] = new Object();
+        }
     }
 
     // For testing only
@@ -35,17 +39,34 @@ public class ServerCache {
         this(new StaticConfigDefinitionRepo(), new UserConfigDefinitionRepo());
     }
 
-    public void put(ConfigCacheKey key, ConfigResponse config, String configMd5) {
+    private void put(ConfigCacheKey key, ConfigResponse config) {
+        String configMd5 = config.getConfigMd5();
         md5Sums.put(key, configMd5);
         md5ToConfig.put(configMd5, config);
     }
 
-    public ConfigResponse get(ConfigCacheKey key) {
+    ConfigResponse get(ConfigCacheKey key) {
         String md5 = md5Sums.get(key);
         if (md5 == null) return null;
         return md5ToConfig.get(md5);
     }
 
+    public ConfigResponse computeIfAbsent(ConfigCacheKey key, Function<ConfigCacheKey, ConfigResponse> mappingFunction) {
+        ConfigResponse config = get(key);
+        if (config != null) {
+            return config;
+        }
+        synchronized (stripedLocks[Math.abs(key.hashCode()%stripedLocks.length)]) {
+            String md5 = md5Sums.get(key);
+            if (md5 == null) {
+                config = mappingFunction.apply(key);
+                put(key, config);
+                return config;
+            }
+            return md5ToConfig.get(md5);
+        }
+    }
+
     @Override
     public String toString() {
         StringBuilder sb = new StringBuilder();
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/application/Application.java b/configserver/src/main/java/com/yahoo/vespa/config/server/application/Application.java
index 2133850e674..0afb3049f6e 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/application/Application.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/application/Application.java
@@ -111,15 +111,12 @@ public class Application implements ModelResult {
 
         ConfigResponse config;
         if (useCache(req)) {
-            config = cache.get(cacheKey);
-            if (config != null) {
-                log.log(Level.FINE, () -> TenantRepository.logPre(getId()) + ("Found config " + cacheKey + " in cache"));
-            } else {
-                config = createConfigResponse(configKey, req, responseFactory);
-                cache.put(cacheKey, config, config.getConfigMd5());
+            config = cache.computeIfAbsent(cacheKey, (ConfigCacheKey key) -> {
+                var response = createConfigResponse(configKey, req, responseFactory);
                 metricUpdater.setCacheConfigElems(cache.configElems());
                 metricUpdater.setCacheChecksumElems(cache.checkSumElems());
-            }
+                return response;
+            });
         } else {
             config = createConfigResponse(configKey, req, responseFactory);
         }
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/ServerCacheTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/ServerCacheTest.java
index 35449238f78..9fca80b7a11 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/ServerCacheTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/ServerCacheTest.java
@@ -48,9 +48,9 @@ public class ServerCacheTest {
 
         cache = new ServerCache(new TestConfigDefinitionRepo(), userConfigDefinitionRepo);
 
-        cache.put(fooBarCacheKey, SlimeConfigResponse.fromConfigPayload(ConfigPayload.empty(), 2, false, configMd5), configMd5);
-        cache.put(bazQuuxCacheKey, SlimeConfigResponse.fromConfigPayload(ConfigPayload.empty(), 2, false, configMd5), configMd5);
-        cache.put(fooBarCacheKeyDifferentMd5, SlimeConfigResponse.fromConfigPayload(ConfigPayload.empty(), 2, false, configMd5_2), configMd5_2);
+        cache.computeIfAbsent(fooBarCacheKey, (ConfigCacheKey key) -> SlimeConfigResponse.fromConfigPayload(ConfigPayload.empty(), 2, false, configMd5));
+        cache.computeIfAbsent(bazQuuxCacheKey, (ConfigCacheKey key) -> SlimeConfigResponse.fromConfigPayload(ConfigPayload.empty(), 2, false, configMd5));
+        cache.computeIfAbsent(fooBarCacheKeyDifferentMd5, (ConfigCacheKey key) -> SlimeConfigResponse.fromConfigPayload(ConfigPayload.empty(), 2, false, configMd5_2));
     }
 
     @Test