Fix JVM <clinit> deadlock using targeted bridge methods

Alternative approach to #48667 that avoids Class.forName() entirely.
Each getXxxAccessor() fallback now calls a targeted bridge method
(e.g., BridgeInternal.initializeCosmosAsyncClientAccessor()) that
directly invokes the specific class's initialize() method. This
eliminates classloader risks and is compile-time checked.

Adds per-class initialize methods to BridgeInternal (17),
ModelBridgeInternal (20), and UtilBridgeInternal (1).

Also includes:
- Missing static { initialize(); } blocks for 3 classes
- CosmosItemSerializer <clinit> ordering fix
- Renamed misnamed accessor in CosmosDiagnosticsThresholdsHelper
- Forked-JVM deadlock regression test (invocationCount=5, 12 threads)
- Behavioral enforcement test for static { initialize(); } blocks

Fixes: #48622
Fixes: #48585

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jeet1995

sdk/cosmos/azure-cosmos-tests/src/test/java/com/azure/cosmos/implementation/ImplementationBridgeHelpersTest.java

@@ -7,7 +7,8 @@
 #### Breaking Changes
 
 #### Bugs Fixed
-Fixing an NPE caused due to boxed Boolean conversion. - See [PR 48656](https://github.com/Azure/azure-sdk-for-java/pull/48656/)
+* Fixing an NPE caused due to boxed Boolean conversion. - See [PR 48656](https://github.com/Azure/azure-sdk-for-java/pull/48656/)
+* Fixed JVM `<clinit>` deadlock when multiple threads concurrently trigger Cosmos SDK class loading for the first time. - See [PR 48667](https://github.com/Azure/azure-sdk-for-java/pull/48667)
 
 #### Other Changes
 

sdk/cosmos/azure-cosmos/CHANGELOG.md

@@ -625,4 +625,39 @@ public static void  initializeAllAccessors() {
         ReadConsistencyStrategy.initialize();
         Http2ConnectionConfig.initialize();
     }
+
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeCosmosClientAccessor() { CosmosClient.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeCosmosAsyncClientEncryptionKeyAccessor() { CosmosAsyncClientEncryptionKey.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeCosmosAsyncContainerAccessor() { CosmosAsyncContainer.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeCosmosAsyncDatabaseAccessor() { CosmosAsyncDatabase.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeCosmosClientBuilderAccessor() { CosmosClientBuilder.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeCosmosDiagnosticsAccessor() { CosmosDiagnostics.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeCosmosDiagnosticsContextAccessor() { CosmosDiagnosticsContext.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeCosmosRequestContextAccessor() { CosmosRequestContext.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeCosmosExceptionAccessor() { CosmosException.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeDirectConnectionConfigAccessor() { DirectConnectionConfig.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeCosmosAsyncClientAccessor() { CosmosAsyncClient.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeCosmosDiagnosticsThresholdsAccessor() { CosmosDiagnosticsThresholds.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeCosmosContainerProactiveInitConfigAccessor() { CosmosContainerProactiveInitConfig.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeSessionRetryOptionsAccessor() { SessionRetryOptions.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeCosmosItemSerializerAccessor() { CosmosItemSerializer.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeReadConsistencyStrategyAccessor() { ReadConsistencyStrategy.initialize(); }
+    @Warning(value = INTERNAL_USE_ONLY_WARNING)
+    public static void initializeHttp2ConnectionConfigAccessor() { Http2ConnectionConfig.initialize(); }
 }

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/BridgeInternal.java

@@ -1201,4 +1201,6 @@ public Integer getTargetMaxMicroBatchSize(CosmosDiagnosticsContext ctx) {
                     }
                 });
     }
+
+    static { initialize(); }
 }

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/CosmosDiagnosticsContext.java

@@ -30,6 +30,9 @@
  */
 public abstract class CosmosItemSerializer {
 
+    // Register the accessor before any static fields that may trigger other classes'
+    // <clinit> which need this accessor (e.g., DefaultCosmosItemSerializer).
+    static { initialize(); }
 
     /**
      * Gets the default Cosmos item serializer. This serializer is used by default when no custom serializer is
@@ -163,6 +166,4 @@ public ObjectMapper getItemObjectMapper(CosmosItemSerializer serializer) {
                 }
             });
     }
-
-    static { initialize(); }
 }

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/CosmosItemSerializer.java

@@ -217,4 +217,6 @@ public CosmosRequestContext create(OverridableRequestOptions requestOptions) {
                 }
                 );
     }
+
+    static { initialize(); }
 }

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/CosmosRequestContext.java

@@ -30,7 +30,7 @@
  */
 public abstract class CosmosQueryRequestOptionsBase<T extends CosmosQueryRequestOptionsBase<?>> implements OverridableRequestOptions {
     private final static ImplementationBridgeHelpers.CosmosDiagnosticsThresholdsHelper.CosmosDiagnosticsThresholdsAccessor thresholdsAccessor =
-        ImplementationBridgeHelpers.CosmosDiagnosticsThresholdsHelper.getCosmosAsyncClientAccessor();
+        ImplementationBridgeHelpers.CosmosDiagnosticsThresholdsHelper.getCosmosDiagnosticsThresholdsAccessor();
 
     private ConsistencyLevel consistencyLevel;
     private ReadConsistencyStrategy readConsistencyStrategy;

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/CosmosQueryRequestOptionsBase.java

@@ -14,7 +14,7 @@
 
 public final class CosmosQueryRequestOptionsImpl extends CosmosQueryRequestOptionsBase<CosmosQueryRequestOptionsImpl> {
     private final static ImplementationBridgeHelpers.CosmosDiagnosticsThresholdsHelper.CosmosDiagnosticsThresholdsAccessor thresholdsAccessor =
-        ImplementationBridgeHelpers.CosmosDiagnosticsThresholdsHelper.getCosmosAsyncClientAccessor();
+        ImplementationBridgeHelpers.CosmosDiagnosticsThresholdsHelper.getCosmosDiagnosticsThresholdsAccessor();
     private String partitionKeyRangeId;
     private Boolean scanInQueryEnabled;
     private Boolean emitVerboseTracesInQuery;