Isolate Persistence objects in different threads. (#1166)

Author: dimas-b

polaris-core/src/main/java/org/apache/polaris/core/PolarisCallContext.java

@@ -61,7 +61,7 @@ public PolarisCallContext(
 
   public static PolarisCallContext copyOf(PolarisCallContext original) {
     return new PolarisCallContext(
-        original.getMetaStore(),
+        original.getMetaStore().detach(),
         original.getDiagServices(),
         original.getConfigurationStore(),
         original.getClock());

polaris-core/src/main/java/org/apache/polaris/core/persistence/BasePersistence.java

@@ -392,4 +392,15 @@ boolean hasChildren(
       @Nullable PolarisEntityType optionalEntityType,
       long catalogId,
       long parentId);
+
+  /**
+   * Performs operations necessary to isolate the state of {@code this} {@link BasePersistence}
+   * instance from the state of the returned instance as far as multithreaded usage is concerned. If
+   * the implementation has state that is not supposed to be accessed or modified by multiple
+   * threads, it may return a copy from this method. If the implementation is thread-safe, it may
+   * return {@code this}.
+   */
+  default BasePersistence detach() {
+    return this;
+  }
 }