PluginManager: Introduce global future synchronizer

The global synchronizer will be destructed after the
asynchronous shutdown phase and prior to deleting
all the plugins (i.e. synchronously). It's assumed that
between deleting the synchronizer and the point when all
plugin destructors are finished no new futures are added
to the global future synchronizer.

Change-Id: Ibc839b04f2c2bbd35980b8baed51b29c2c4f7c76
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/extensionsystem/pluginmanager.cpp

@@ -32,6 +32,7 @@
 #include <utils/benchmarker.h>
 #include <utils/executeondestruction.h>
 #include <utils/fileutils.h>
+#include <utils/futuresynchronizer.h>
 #include <utils/hostosinfo.h>
 #include <utils/mimeutils.h>
 #include <utils/qtcassert.h>
@@ -422,6 +423,11 @@ QString PluginManager::systemInformation()
     return result;
 }
 
+static FutureSynchronizer *futureSynchronizer()
+{
+    return d->m_futureSynchronizer.get();
+}
+
 /*!
     The list of paths were the plugin manager searches for plugins.
 
@@ -976,6 +982,8 @@ void PluginManagerPrivate::nextDelayedInitialize()
 PluginManagerPrivate::PluginManagerPrivate(PluginManager *pluginManager) :
     q(pluginManager)
 {
+    m_futureSynchronizer.reset(new FutureSynchronizer);
+    m_futureSynchronizer->setCancelOnWait(true);
 }
 
 
@@ -1043,6 +1051,7 @@ void PluginManagerPrivate::stopAll()
 */
 void PluginManagerPrivate::deleteAll()
 {
+    m_futureSynchronizer.reset(); // Synchronize all futures from all plugins
     Utils::reverseForeach(loadQueue(), [this](PluginSpec *spec) {
         loadPlugin(spec, PluginSpec::Deleted);
     });