Add Qt.callLater() function.

Calling the new Qt.callLater() multiple times in quick succession with the same
JS function as argument will result in a single call to that function, thus
eliminating redundant unnecessary calls.

Based on previous patches by Mathias Malmqvist <mathias.malmqvist@nokia.com>
and Chris Adams <chris.adams@jollamobile.com>

Change-Id: Ie71b60d4d48fa73d3deae723775cf36662d199ae
Task-number: QTBUG-22400
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>

5 files changed, 33 insertions, 7 deletions

diff --git a/src/qml/qml/v8/qqmlbuiltinfunctions.cpp b/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
index 333b1903f5..ac40b627d9 100644
--- a/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
+++ b/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
@@ -45,6 +45,7 @@
 #include <private/qqmlstringconverters_p.h>
 #include <private/qqmllocale_p.h>
 #include <private/qv8engine_p.h>
+#include <private/qqmldelayedcallqueue_p.h>
 #include <QFileInfo>
 
 #include <private/qqmldebugconnector_p.h>
@@ -149,6 +150,8 @@ Heap::QtObject::QtObject(QQmlEngine *qmlEngine)
     o->defineAccessorProperty(QStringLiteral("inputMethod"), QV4::QtObject::method_get_inputMethod, 0);
 #endif
     o->defineAccessorProperty(QStringLiteral("styleHints"), QV4::QtObject::method_get_styleHints, 0);
+
+    o->defineDefaultProperty(QStringLiteral("callLater"), QV4::QtObject::method_callLater);
 }
 
 
@@ -1934,6 +1937,30 @@ ReturnedValue GlobalExtensions::method_string_arg(CallContext *ctx)
     return ctx->d()->engine->newString(value.arg(arg->toQString()))->asReturnedValue();
 }
 
+/*!
+\qmlmethod Qt::callLater(function)
+\qmlmethod Qt::callLater(function, argument1, argument2, ...)
+Use this function to eliminate redundant calls to a function or signal.
+
+The function passed as the first argument to \l{QML:Qt::callLater()}{Qt.callLater()}
+will be called later, once the QML engine returns to the event loop.
+
+When this function is called multiple times in quick succession with the
+same function as its first argument, that function will be called only once.
+
+For example:
+\snippet doc/src/snippets/qml/qtLater.qml 0
+
+Any additional arguments passed to \l{QML:Qt::callLater()}{Qt.callLater()} will
+be passed on to the function invoked. Note that if redundant calls
+are eliminated, then only the last set of arguments will be passed to the
+function.
+*/
+ReturnedValue QtObject::method_callLater(CallContext *ctx)
+{
+    QV8Engine *v8engine = ctx->engine()->v8Engine;
+    return v8engine->delayedCallQueue()->addUniquelyAndExecuteLater(ctx);
+}
 
 QT_END_NAMESPACE
 
diff --git a/src/qml/qml/v8/qqmlbuiltinfunctions_p.h b/src/qml/qml/v8/qqmlbuiltinfunctions_p.h
index 53468f062b..99c8b69724 100644
--- a/src/qml/qml/v8/qqmlbuiltinfunctions_p.h
+++ b/src/qml/qml/v8/qqmlbuiltinfunctions_p.h
@@ -124,6 +124,8 @@ struct QtObject : Object
     static ReturnedValue method_get_inputMethod(CallContext *ctx);
 #endif
     static ReturnedValue method_get_styleHints(CallContext *ctx);
+
+    static ReturnedValue method_callLater(CallContext *ctx);
 };
 
 struct ConsoleObject : Object
diff --git a/src/qml/qml/v8/qv8engine.cpp b/src/qml/qml/v8/qv8engine.cpp
index 89f128a0e7..73128f6344 100644
--- a/src/qml/qml/v8/qv8engine.cpp
+++ b/src/qml/qml/v8/qv8engine.cpp
@@ -149,6 +149,7 @@ QV8Engine::QV8Engine(QJSEngine* qq)
 
     m_v4Engine = new QV4::ExecutionEngine;
     m_v4Engine->v8Engine = this;
+    m_delayedCallQueue.init(m_v4Engine);
 
     QV4::QObjectWrapper::initializeBindings(m_v4Engine);
 }
diff --git a/src/qml/qml/v8/qv8engine_p.h b/src/qml/qml/v8/qv8engine_p.h
index 9054c731db..c5041c54e0 100644
--- a/src/qml/qml/v8/qv8engine_p.h
+++ b/src/qml/qml/v8/qv8engine_p.h
@@ -70,6 +70,7 @@
 #include <private/qv4object_p.h>
 #include <private/qv4identifier_p.h>
 #include <private/qqmlcontextwrapper_p.h>
+#include <private/qqmldelayedcallqueue_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -78,12 +79,6 @@ namespace QV4 {
     struct ExecutionEngine;
 }
 
-// Uncomment the following line to enable global handle debugging.  When enabled, all the persistent
-// handles allocated using qPersistentNew() (or registered with qPersistentRegsiter()) and disposed
-// with qPersistentDispose() are tracked.  If you try and do something illegal, like double disposing
-// a handle, qFatal() is called.
-// #define QML_GLOBAL_HANDLE_DEBUGGING
-
 #define V4THROW_ERROR(string) \
     return ctx->engine()->throwError(QString::fromUtf8(string));
 
@@ -186,6 +181,7 @@ public:
     QQmlEngine *engine() { return m_engine; }
     QJSEngine *publicEngine() { return q; }
     QV4::ReturnedValue global();
+    QQmlDelayedCallQueue *delayedCallQueue() { return &m_delayedCallQueue; }
 
     void *xmlHttpRequestData() { return m_xmlHttpRequestData; }
 
@@ -221,6 +217,7 @@ public:
 protected:
     QJSEngine* q;
     QQmlEngine *m_engine;
+    QQmlDelayedCallQueue m_delayedCallQueue;
 
     QV4::ExecutionEngine *m_v4Engine;
 
diff --git a/src/qml/qml/v8/v8.pri b/src/qml/qml/v8/v8.pri
index 3d6a012481..4592022939 100644
--- a/src/qml/qml/v8/v8.pri
+++ b/src/qml/qml/v8/v8.pri
@@ -9,4 +9,3 @@ SOURCES += \
     $$PWD/qv4domerrors.cpp \
     $$PWD/qv4sqlerrors.cpp \
     $$PWD/qqmlbuiltinfunctions.cpp
-