Docs: implications of creating network access managers in other threads

Task-number: QTBUG-16032

1 files changed, 33 insertions, 20 deletions

diff --git a/src/declarative/qml/qdeclarativenetworkaccessmanagerfactory.cpp b/src/declarative/qml/qdeclarativenetworkaccessmanagerfactory.cpp
index d22798d..36e9721 100644
--- a/src/declarative/qml/qdeclarativenetworkaccessmanagerfactory.cpp
+++ b/src/declarative/qml/qdeclarativenetworkaccessmanagerfactory.cpp
@@ -46,27 +46,44 @@ QT_BEGIN_NAMESPACE
 /*!
     \class QDeclarativeNetworkAccessManagerFactory
     \since 4.7
-    \brief The QDeclarativeNetworkAccessManagerFactory class provides a factory for QNetworkAccessManager for use by a Qt Declarative engine.
+    \brief The QDeclarativeNetworkAccessManagerFactory class creates QNetworkAccessManager instances for a QML engine.
 
-    QNetworkAccessManager is used for all network access by QML.
-    By implementing a factory it is possible to create custom
-    QNetworkAccessManager with specialized caching, proxy and
-    cookie support.
+    A QML engine uses QNetworkAccessManager for all network access.
+    By implementing a factory, it is possible to provide the QML engine
+    with custom QNetworkAccessManager instances with specialized caching,
+    proxy and cookies support.
 
-    To implement a factory, subclass QDeclarativeNetworkAccessManagerFactory and implement
-    the create() method.
+    To implement a factory, subclass QDeclarativeNetworkAccessManagerFactory and
+    implement the virtual create() method, then assign it to the relevant QML
+    engine using QDeclarativeEngine::setNetworkAccessManagerFactory().
 
-    To use a factory, assign it to the relevant QDeclarativeEngine using
-    QDeclarativeEngine::setNetworkAccessManagerFactory().
+    Note the QML engine may create QNetworkAccessManager instances
+    from multiple threads. Because of this, the implementation of the create()
+    method must be \l{Reentrancy and Thread-Safety}{reentrant}. In addition,
+    the developer should be careful if the signals of the object to be
+    returned from create() are connected to the slots of an object that may
+    be created in a different thread:
 
-    Note: the create() method may be called by multiple threads, so ensure the
-    implementation of this method is reentrant.
+    \list
+    \o The QML engine internally handles all requests, and cleans up any
+       QNetworkReply objects it creates. Receiving the
+       QNetworkAccessManager::finished() signal in another thread may not
+       provide the receiver with a valid reply object if it has already
+       been deleted.
+    \o Authentication details provided to QNetworkAccessManager::authenticationRequired()
+       must be provided immediately, so this signal cannot be connected as a
+       Qt::QueuedConnection (or as the default Qt::AutoConnection from another
+       thread).
+    \endlist
+
+    For more information about signals and threads, see
+    \l {Threads and QObjects} and \l {Signals and Slots Across Threads}.
 
-    \sa QDeclarativeEngine::setNetworkAccessManagerFactory(), {declarative/cppextensions/networkaccessmanagerfactory}{NetworkAccessManagerFactory example}
+    \sa {declarative/cppextensions/networkaccessmanagerfactory}{NetworkAccessManagerFactory example}
 */
 
 /*!
-  The destructor is empty.
+    Destroys the factory. The default implementation does nothing.
  */
 QDeclarativeNetworkAccessManagerFactory::~QDeclarativeNetworkAccessManagerFactory()
 {
@@ -75,13 +92,9 @@ QDeclarativeNetworkAccessManagerFactory::~QDeclarativeNetworkAccessManagerFactor
 /*!
     \fn QNetworkAccessManager *QDeclarativeNetworkAccessManagerFactory::create(QObject *parent)
 
-    Implement this method to create a QNetworkAccessManager with \a parent.
-    This allows proxies, caching and cookie support to be setup appropriately.
-
-    This method must return a new QNetworkAccessManager each time it is called.
-    The parent of the QNetworkAccessManager must be the \a parent provided.
-    The QNetworkAccessManager(s) created by this
-    function will be destroyed automatically when their parent is destroyed.
+    Creates and returns a network access manager with the specified \a parent.
+    This method must return a new QNetworkAccessManager instance each time
+    it is called.
 
     Note: this method may be called by multiple threads, so ensure the
     implementation of this method is reentrant.