From 8d2d52fcfd3c42a82b7f86c6f3c5009461f1de9f Mon Sep 17 00:00:00 2001
From: Christian Mollekopf <chrigi_1@fastmail.fm>
Date: Sun, 1 Apr 2018 09:41:28 +0200
Subject: Avoid missing revision updates while a query is running.

Instead we have to remember that something has changed and rerun an
incremental query.
---
 common/queryrunner.cpp | 53 ++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 45 insertions(+), 8 deletions(-)

(limited to 'common/queryrunner.cpp')

diff --git a/common/queryrunner.cpp b/common/queryrunner.cpp
index 2c50fca..c0c1d00 100644
--- a/common/queryrunner.cpp
+++ b/common/queryrunner.cpp
@@ -21,6 +21,8 @@
 #include <limits>
 #include <QTime>
 #include <QPointer>
+#include <thread>
+#include <chrono>
 
 #include "commands.h"
 #include "asyncutils.h"
@@ -97,6 +99,13 @@ QueryRunner<DomainType>::~QueryRunner()
     SinkTraceCtx(mLogCtx) << "Stopped query";
 }
 
+
+template <class DomainType>
+void QueryRunner<DomainType>::delayNextQuery()
+{
+    mDelayNextQuery = true;
+}
+
 //This function triggers the initial fetch, and then subsequent calls will simply fetch more data of mBatchSize.
 template <class DomainType>
 void QueryRunner<DomainType>::fetch(const Sink::Query &query, const QByteArray &bufferType)
@@ -115,11 +124,20 @@ void QueryRunner<DomainType>::fetch(const Sink::Query &query, const QByteArray &
     auto resourceContext = mResourceContext;
     auto logCtx = mLogCtx;
     auto state = mQueryState;
+    bool addDelay = mDelayNextQuery;
+    mDelayNextQuery = false;
     const bool runAsync = !query.synchronousQuery();
     //The lambda will be executed in a separate thread, so copy all arguments
     async::run<ReplayResult>([=]() {
         QueryWorker<DomainType> worker(query, resourceContext, bufferType, resultTransformation, logCtx);
-        return worker.executeInitialQuery(query, *resultProvider, batchSize, state);
+        const auto result =  worker.executeInitialQuery(query, *resultProvider, batchSize, state);
+
+        //For testing only
+        if (addDelay) {
+            std::this_thread::sleep_for(std::chrono::seconds(1));
+        }
+
+        return result;
     }, runAsync)
         .then([=](const ReplayResult &result) {
             if (!guardPtr) {
@@ -137,7 +155,12 @@ void QueryRunner<DomainType>::fetch(const Sink::Query &query, const QByteArray &
             resultProvider->initialResultSetComplete(result.replayedAll);
             if (mRequestFetchMore) {
                 mRequestFetchMore = false;
+                //This code exists for incemental fetches, so we don't skip loading another set.
                 fetch(query, bufferType);
+                return;
+            }
+            if (mRevisionChangedMeanwhile) {
+                incrementalFetch(query, bufferType).exec();
             }
         })
         .exec();
@@ -146,15 +169,17 @@ void QueryRunner<DomainType>::fetch(const Sink::Query &query, const QByteArray &
 template <class DomainType>
 KAsync::Job<void> QueryRunner<DomainType>::incrementalFetch(const Sink::Query &query, const QByteArray &bufferType)
 {
-    if (!mInitialQueryComplete) {
-        SinkWarningCtx(mLogCtx) << "Can't start the incremental query before the initial query is complete";
+    if (!mInitialQueryComplete && !mQueryInProgress) {
+        //We rely on this codepath in the case of newly added resources to trigger the initial fetch.
         fetch(query, bufferType);
         return KAsync::null();
     }
     if (mQueryInProgress) {
-        //Can happen if the revision come in quicker than we process them.
+        //If a query is already in progress we just remember to fetch again once the current query is done.
+        mRevisionChangedMeanwhile = true;
         return KAsync::null();
     }
+    mRevisionChangedMeanwhile = false;
     auto resultProvider = mResultProvider;
     auto resourceContext = mResourceContext;
     auto logCtx = mLogCtx;
@@ -162,22 +187,34 @@ KAsync::Job<void> QueryRunner<DomainType>::incrementalFetch(const Sink::Query &q
     auto resultTransformation = mResultTransformation;
     Q_ASSERT(!mQueryInProgress);
     auto guardPtr = QPointer<QObject>(&guard);
+    bool addDelay = mDelayNextQuery;
+    mDelayNextQuery = false;
     return KAsync::start([&] {
             mQueryInProgress = true;
         })
         .then(async::run<ReplayResult>([=]() {
                 QueryWorker<DomainType> worker(query, resourceContext, bufferType, resultTransformation, logCtx);
-                return worker.executeIncrementalQuery(query, *resultProvider, state);
+                const auto result = worker.executeIncrementalQuery(query, *resultProvider, state);
+                ////For testing only
+                if (addDelay) {
+                    SinkWarning() << "Sleeping in incremental query";
+                    std::this_thread::sleep_for(std::chrono::seconds(1));
+                }
+
+                return result;
             }))
-        .then([query, this, resultProvider, guardPtr](const ReplayResult &newRevisionAndReplayedEntities) {
+        .then([query, this, resultProvider, guardPtr, bufferType](const ReplayResult &newRevisionAndReplayedEntities) {
             if (!guardPtr) {
                 //Not an error, the query can vanish at any time.
-                return;
+                return KAsync::null();
             }
             mQueryInProgress = false;
-            // Only send the revision replayed information if we're connected to the resource, there's no need to start the resource otherwise.
             mResourceAccess->sendRevisionReplayedCommand(newRevisionAndReplayedEntities.newRevision);
             resultProvider->setRevision(newRevisionAndReplayedEntities.newRevision);
+            if (mRevisionChangedMeanwhile) {
+                return incrementalFetch(query, bufferType);
+            }
+            return KAsync::null();
         });
 }
 
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