Use a queryrunner to execute queries.

The queryrunner is responsible for running queries and keeping them
up to date. This is required for self-updating queries.

To get this to work properly the ResultProvider/emitter had to be fixed.
The emitter now only lives as long as the client holds a reference to
it, allowing the provider to detect when it is no longer necessary to
keep the query alive (because noone is listening).

In the process various lifetime issues have been fixed, that we're
caused by lambdas capturing smartpointers, that then extended the
lifetime of the associated objects unpredictably.

1 files changed, 50 insertions, 1 deletions

diff --git a/common/facade.h b/common/facade.h
index 98bcb38..f9b5a83 100644
--- a/common/facade.h
+++ b/common/facade.h
@@ -30,6 +30,55 @@
 #include "domainadaptor.h"
 #include "entitybuffer.h"
 
+/**
+ * A QueryRunner runs a query and updates the corresponding result set.
+ * 
+ * The lifetime of the QueryRunner is defined by the resut set (otherwise it's doing useless work),
+ * and by how long a result set must be updated. If the query is one off the runner dies after the execution,
+ * otherwise it lives on the react to changes and updates the corresponding result set.
+ * 
+ * QueryRunner has to keep ResourceAccess alive in order to keep getting updates.
+ */
+class QueryRunner : public QObject
+{
+    Q_OBJECT
+public:
+    typedef std::function<Async::Job<qint64>(qint64 oldRevision, qint64 newRevision)> QueryFunction;
+
+    QueryRunner(const Akonadi2::Query &query) : mLatestRevision(0) {};
+    /**
+     * Starts query
+     */
+    Async::Job<void> run(qint64 newRevision = 0)
+    {
+        //TODO: JOBAPI: that last empty .then should not be necessary
+        return queryFunction(mLatestRevision, newRevision).then<void, qint64>([this](qint64 revision) {
+            mLatestRevision = revision;
+        }).then<void>([](){});
+    }
+
+    /**
+     *
+     */
+    void setQuery(const QueryFunction &query)
+    {
+        queryFunction = query;
+    }
+
+public slots:
+    /**
+     * Rerun query with new revision
+     */
+    void revisionChanged(qint64 newRevision)
+    {
+        run(newRevision).exec();
+    }
+
+private:
+    QueryFunction queryFunction;
+    qint64 mLatestRevision;
+};
+
 namespace Akonadi2 {
     class ResourceAccess;
 /**
@@ -80,7 +129,7 @@ protected:
         return Async::null<void>();
     }
 
-private:
+protected:
     //TODO use one resource access instance per application => make static
     QSharedPointer<Akonadi2::ResourceAccess> mResourceAccess;
 };