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>

8 files changed, 347 insertions, 9 deletions

diff --git a/src/qml/qml/qml.pri b/src/qml/qml/qml.pri
index 4d84cc82ae..91d883c29f 100644
--- a/src/qml/qml/qml.pri
+++ b/src/qml/qml/qml.pri
@@ -50,7 +50,8 @@ SOURCES += \
     $$PWD/qqmltypewrapper.cpp \
     $$PWD/qqmlfileselector.cpp \
     $$PWD/qqmlobjectcreator.cpp \
-    $$PWD/qqmldirparser.cpp
+    $$PWD/qqmldirparser.cpp \
+    $$PWD/qqmldelayedcallqueue.cpp
 
 HEADERS += \
     $$PWD/qqmlglobal_p.h \
@@ -122,7 +123,8 @@ HEADERS += \
     $$PWD/qqmlfileselector_p.h \
     $$PWD/qqmlfileselector.h \
     $$PWD/qqmlobjectcreator_p.h \
-    $$PWD/qqmldirparser_p.h
+    $$PWD/qqmldirparser_p.h \
+    $$PWD/qqmldelayedcallqueue_p.h
 
 include(ftw/ftw.pri)
 include(v8/v8.pri)
diff --git a/src/qml/qml/qqmldelayedcallqueue.cpp b/src/qml/qml/qqmldelayedcallqueue.cpp
new file mode 100644
index 0000000000..250d5f20f3
--- /dev/null
+++ b/src/qml/qml/qqmldelayedcallqueue.cpp
@@ -0,0 +1,206 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQml module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qqmldelayedcallqueue_p.h"
+#include <private/qv8engine_p.h>
+#include <private/qqmlengine_p.h>
+#include <private/qqmljavascriptexpression_p.h>
+#include <private/qv4value_p.h>
+#include <private/qv4qobjectwrapper_p.h>
+
+#include <QQmlError>
+
+QT_BEGIN_NAMESPACE
+
+//
+// struct QQmlDelayedCallQueue::DelayedFunctionCall
+//
+
+void QQmlDelayedCallQueue::DelayedFunctionCall::execute(QV4::ExecutionEngine *engine) const
+{
+    if (!m_guarded ||
+            (!m_objectGuard.isNull() &&
+             !QQmlData::wasDeleted(m_objectGuard) &&
+             QQmlData::get(m_objectGuard) &&
+             !QQmlData::get(m_objectGuard)->isQueuedForDeletion)) {
+
+        QV4::Scope scope(engine);
+
+        const int argCount = m_args.count();
+        QV4::ScopedCallData callData(scope, argCount);
+        callData->thisObject = QV4::Encode::undefined();
+
+        for (int i = 0; i < argCount; i++) {
+            callData->args[i] = m_args[i].value();
+        }
+
+        const QV4::FunctionObject *callback = m_function.as<QV4::FunctionObject>();
+        Q_ASSERT(callback);
+        callback->call(callData);
+
+        if (scope.engine->hasException) {
+            QQmlError error = scope.engine->catchExceptionAsQmlError();
+            error.setDescription(error.description() + QLatin1String(" (exception occurred during delayed function evaluation)"));
+            QQmlEnginePrivate::warning(QQmlEnginePrivate::get(scope.engine->qmlEngine()), error);
+        }
+    }
+}
+
+//
+// class QQmlDelayedCallQueue
+//
+
+QQmlDelayedCallQueue::QQmlDelayedCallQueue()
+    : QObject(0), m_engine(0), m_callbackOutstanding(false)
+{
+}
+
+QQmlDelayedCallQueue::~QQmlDelayedCallQueue()
+{
+}
+
+void QQmlDelayedCallQueue::init(QV4::ExecutionEngine* engine)
+{
+    m_engine = engine;
+
+    const QMetaObject &metaObject = QQmlDelayedCallQueue::staticMetaObject;
+    int methodIndex = metaObject.indexOfSlot("ticked()");
+    m_tickedMethod = metaObject.method(methodIndex);
+}
+
+QV4::ReturnedValue QQmlDelayedCallQueue::addUniquelyAndExecuteLater(QV4::CallContext *ctx)
+{
+    const QV4::CallData *callData = ctx->d()->callData;
+
+    if (callData->argc == 0)
+        V4THROW_ERROR("Qt.callLater: no arguments given");
+
+    const QV4::FunctionObject *func = callData->args[0].as<QV4::FunctionObject>();
+
+    if (!func)
+        V4THROW_ERROR("Qt.callLater: first argument not a function or signal");
+
+    QPair<QObject *, int> functionData = QV4::QObjectMethod::extractQtMethod(func);
+
+    QVector<DelayedFunctionCall>::Iterator iter;
+    if (functionData.second != -1) {
+        // This is a QObject function wrapper
+        iter = m_delayedFunctionCalls.begin();
+        while (iter != m_delayedFunctionCalls.end()) {
+            DelayedFunctionCall& dfc = *iter;
+            QPair<QObject *, int> storedFunctionData = QV4::QObjectMethod::extractQtMethod(dfc.m_function.as<QV4::FunctionObject>());
+            if (storedFunctionData == functionData) {
+                break; // Already stored!
+            }
+            ++iter;
+        }
+    } else {
+        // This is a JavaScript function (dynamic slot on VMEMO)
+        iter = m_delayedFunctionCalls.begin();
+        while (iter != m_delayedFunctionCalls.end()) {
+            DelayedFunctionCall& dfc = *iter;
+            if (callData->argument(0) == dfc.m_function.value()) {
+                break; // Already stored!
+            }
+            ++iter;
+        }
+    }
+
+    const bool functionAlreadyStored = (iter != m_delayedFunctionCalls.end());
+    if (functionAlreadyStored) {
+        DelayedFunctionCall dfc = *iter;
+        m_delayedFunctionCalls.erase(iter);
+        m_delayedFunctionCalls.append(dfc);
+    } else {
+        m_delayedFunctionCalls.append(QV4::PersistentValue(m_engine, callData->argument(0)));
+    }
+
+    DelayedFunctionCall& dfc = m_delayedFunctionCalls.last();
+    if (dfc.m_objectGuard.isNull()) {
+        if (functionData.second != -1) {
+            // if it's a qobject function wrapper, guard against qobject deletion
+            dfc.m_objectGuard = QQmlGuard<QObject>(functionData.first);
+            dfc.m_guarded = true;
+        } else if (func->scope()->type == QV4::Heap::ExecutionContext::Type_QmlContext) {
+            QV4::QmlContext::Data *g = static_cast<QV4::QmlContext::Data *>(func->scope());
+            Q_ASSERT(g->qml->scopeObject);
+            dfc.m_objectGuard = QQmlGuard<QObject>(g->qml->scopeObject);
+            dfc.m_guarded = true;
+        }
+    }
+    storeAnyArguments(dfc, callData, 1, m_engine);
+
+    if (!m_callbackOutstanding) {
+        m_tickedMethod.invoke(this, Qt::QueuedConnection);
+        m_callbackOutstanding = true;
+    }
+    return QV4::Encode::undefined();
+}
+
+void QQmlDelayedCallQueue::storeAnyArguments(DelayedFunctionCall &dfc, const QV4::CallData *callData, int offset, QV4::ExecutionEngine *engine)
+{
+    dfc.m_args.clear();
+    dfc.m_args.reserve(callData->argc - offset);
+    for (int j = offset; j < callData->argc; j++) {
+        dfc.m_args.append(QV4::PersistentValue(engine, callData->args[j]));
+    }
+}
+
+void QQmlDelayedCallQueue::executeAllExpired_Later()
+{
+    // Make a local copy of the list and clear m_delayedFunctionCalls
+    // This ensures correct behavior in the case of recursive calls to Qt.callLater()
+    QVector<DelayedFunctionCall> delayedCalls = m_delayedFunctionCalls;
+    m_delayedFunctionCalls.clear();
+
+    QVector<DelayedFunctionCall>::Iterator iter = delayedCalls.begin();
+    while (iter != delayedCalls.end()) {
+        DelayedFunctionCall& dfc = *iter;
+        dfc.execute(m_engine);
+        ++iter;
+    }
+}
+
+void QQmlDelayedCallQueue::ticked()
+{
+    m_callbackOutstanding = false;
+    executeAllExpired_Later();
+}
+
+QT_END_NAMESPACE
diff --git a/src/qml/qml/qqmldelayedcallqueue_p.h b/src/qml/qml/qqmldelayedcallqueue_p.h
new file mode 100644
index 0000000000..7eb014cfdf
--- /dev/null
+++ b/src/qml/qml/qqmldelayedcallqueue_p.h
@@ -0,0 +1,104 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQml module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QQMLDELAYEDCALLQUEUE_P_H
+#define QQMLDELAYEDCALLQUEUE_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtCore/qglobal.h>
+#include <QtCore/qobject.h>
+#include <QtCore/qmetaobject.h>
+#include <QtCore/qmetatype.h>
+#include <private/qqmlguard_p.h>
+#include <private/qv4context_p.h>
+
+QT_BEGIN_NAMESPACE
+
+class QV8Engine;
+class QQmlDelayedCallQueue : public QObject
+{
+    Q_OBJECT
+public:
+    QQmlDelayedCallQueue();
+    ~QQmlDelayedCallQueue();
+
+    void init(QV4::ExecutionEngine *);
+
+    QV4::ReturnedValue addUniquelyAndExecuteLater(QV4::CallContext *ctx);
+
+public Q_SLOTS:
+    void ticked();
+
+private:
+    struct DelayedFunctionCall
+    {
+        DelayedFunctionCall() {}
+        DelayedFunctionCall(QV4::PersistentValue function)
+            : m_function(function), m_guarded(false) { }
+
+        void execute(QV4::ExecutionEngine *engine) const;
+
+        QV4::PersistentValue m_function;
+        QList<QV4::PersistentValue> m_args;
+        QQmlGuard<QObject> m_objectGuard;
+        bool m_guarded;
+    };
+
+    void storeAnyArguments(DelayedFunctionCall& dfc, const QV4::CallData *callData, int offset, QV4::ExecutionEngine *engine);
+    void executeAllExpired_Later();
+
+    QV4::ExecutionEngine *m_engine;
+    QVector<DelayedFunctionCall> m_delayedFunctionCalls;
+    QMetaMethod m_tickedMethod;
+    bool m_callbackOutstanding;
+};
+
+QT_END_NAMESPACE
+
+#endif // QQMLDELAYEDCALLQUEUE_P_H
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
-