From 6ee69cdac4289a3ef81c2ab989f40522149b89ce Mon Sep 17 00:00:00 2001
From: Robert Varga <robert.varga@pantheon.tech>
Date: Tue, 11 Jun 2019 18:53:18 +0200
Subject: [PATCH] Deduplicate concurrent SchemaContext loads

In case we are running concurrent SchemaContext computation, if
the result is not cached we will have multiple results. These
need to be reconciled with the cache, so that those results will
be squashed into a single instance.

JIRA: YANGTOOLS-1004
Change-Id: I82df2b32a534d0acc803548579fb8ad138853c68
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
---
 .../repo/SharedSchemaContextFactory.java      | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/yang/yang-parser-impl/src/main/java/org/opendaylight/yangtools/yang/parser/repo/SharedSchemaContextFactory.java b/yang/yang-parser-impl/src/main/java/org/opendaylight/yangtools/yang/parser/repo/SharedSchemaContextFactory.java
index 5f2214444d..10a81fa01e 100644
--- a/yang/yang-parser-impl/src/main/java/org/opendaylight/yangtools/yang/parser/repo/SharedSchemaContextFactory.java
+++ b/yang/yang-parser-impl/src/main/java/org/opendaylight/yangtools/yang/parser/repo/SharedSchemaContextFactory.java
@@ -24,6 +24,7 @@ import com.google.common.util.concurrent.FutureCallback;
 import com.google.common.util.concurrent.Futures;
 import com.google.common.util.concurrent.ListenableFuture;
 import com.google.common.util.concurrent.MoreExecutors;
+import com.google.common.util.concurrent.SettableFuture;
 import java.util.Collection;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
@@ -31,6 +32,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
+import java.util.concurrent.ExecutionException;
 import org.antlr.v4.runtime.ParserRuleContext;
 import org.eclipse.jdt.annotation.NonNull;
 import org.opendaylight.yangtools.antlrv4.code.gen.YangStatementParser.StatementContext;
@@ -101,20 +103,31 @@ final class SharedSchemaContextFactory implements EffectiveModelContextFactory {
         final ListenableFuture<EffectiveModelContext> cf = Futures.transformAsync(sf, assembleSources,
             MoreExecutors.directExecutor());
 
-        // Populate cache when successful
+        final SettableFuture<EffectiveModelContext> rf = SettableFuture.create();
         Futures.addCallback(cf, new FutureCallback<EffectiveModelContext>() {
             @Override
             public void onSuccess(final EffectiveModelContext result) {
-                cache.put(uniqueSourceIdentifiers, result);
+                // Deduplicate concurrent loads
+                final EffectiveModelContext existing;
+                try {
+                    existing = cache.get(uniqueSourceIdentifiers, () -> result);
+                } catch (ExecutionException e) {
+                    LOG.warn("Failed to recheck result with cache, will use computed value", e);
+                    rf.set(result);
+                    return;
+                }
+
+                rf.set(existing);
             }
 
             @Override
             public void onFailure(final Throwable cause) {
                 LOG.debug("Failed to assemble sources", cause);
+                rf.setException(cause);
             }
         }, MoreExecutors.directExecutor());
 
-        return cf;
+        return rf;
     }
 
     private ListenableFuture<ASTSchemaSource> requestSource(final @NonNull SourceIdentifier identifier) {
-- 
2.36.6