add DeferCall to replace QMetaObject::invokeMethod (#48101)

Author: jkarneges

src/core/core.pri

@@ -43,6 +43,7 @@ HEADERS += \
 	$$PWD/timerwheel.h \
 	$$PWD/jwt.h \
 	$$PWD/rtimer.h \
+	$$PWD/defercall.h \
 	$$PWD/logutil.h \
 	$$PWD/uuidutil.h \
 	$$PWD/zutil.h \
@@ -66,6 +67,7 @@ SOURCES += \
 	$$PWD/timerwheel.cpp \
 	$$PWD/jwt.cpp \
 	$$PWD/rtimer.cpp \
+	$$PWD/defercall.cpp \
 	$$PWD/logutil.cpp \
 	$$PWD/uuidutil.cpp \
 	$$PWD/zutil.cpp \

src/core/defercall.cpp

@@ -0,0 +1,65 @@
+/*
+* Copyright (C) 2025 Fastly, Inc.
+*
+* This file is part of Pushpin.
+*
+* $FANOUT_BEGIN_LICENSE:APACHE2$
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*     http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*
+* $FANOUT_END_LICENSE$
+*/
+
+#include "defercall.h"
+#include <assert.h>
+
+static thread_local DeferCall *g_instance = nullptr;
+
+DeferCall::DeferCall() = default;
+
+DeferCall::~DeferCall() = default;
+
+void DeferCall::defer(std::function<void ()> handler)
+{
+	Call c;
+	c.handler = handler;
+
+	deferredCalls_.push_back(c);
+
+	QMetaObject::invokeMethod(this, "callNext", Qt::QueuedConnection);
+}
+
+DeferCall *DeferCall::global()
+{
+	if(!g_instance)
+		g_instance = new DeferCall;
+
+	return g_instance;
+}
+
+void DeferCall::cleanup()
+{
+	delete g_instance;
+	g_instance = nullptr;
+}
+
+void DeferCall::callNext()
+{
+	// there can't be more invokeMethod resolutions than queued calls
+	assert(!deferredCalls_.empty());
+
+	Call c = deferredCalls_.front();
+	deferredCalls_.pop_front();
+
+	c.handler();
+}

src/core/defercall.h

@@ -0,0 +1,67 @@
+/*
+* Copyright (C) 2025 Fastly, Inc.
+*
+* This file is part of Pushpin.
+*
+* $FANOUT_BEGIN_LICENSE:APACHE2$
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*     http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*
+* $FANOUT_END_LICENSE$
+*/
+
+#ifndef DEFERCALL_H
+#define DEFERCALL_H
+
+#include <QObject>
+
+// queues calls to be run after returning to the event loop
+class DeferCall : public QObject
+{
+	Q_OBJECT
+
+public:
+	DeferCall();
+	~DeferCall();
+
+	// queue handler to be called after returning to the event loop. if
+	// handler contains references, they must outlive DeferCall. the
+	// recommended usage is for each object needing to perform deferred calls
+	// to keep a DeferCall as a member variable, and only refer to the
+	// object's own data in the handler. that way, any references are
+	// guaranteed to live long enough.
+	void defer(std::function<void ()> handler);
+
+	static DeferCall *global();
+	static void cleanup();
+
+	template <typename T>
+	static void deleteLater(T *p)
+	{
+		global()->defer([=]() { delete p; });
+	}
+
+private slots:
+	void callNext();
+
+private:
+	class Call
+	{
+	public:
+		std::function<void ()> handler;
+	};
+
+	std::list<Call> deferredCalls_;
+};
+
+#endif

src/core/zhttprequest.cpp

@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2012-2021 Fanout, Inc.
- * Copyright (C) 2023 Fastly, Inc.
+ * Copyright (C) 2023-2025 Fastly, Inc.
  *
  * This file is part of Pushpin.
  *
@@ -30,6 +30,7 @@
 #include "bufferlist.h"
 #include "log.h"
 #include "rtimer.h"
+#include "defercall.h"
 #include "zhttpmanager.h"
 #include "uuidutil.h"
 
@@ -105,6 +106,7 @@ class ZhttpRequest::Private : public QObject
 	bool quiet;
 	Connection expTimerConnection;
 	Connection keepAliveTimerConnection;
+	DeferCall deferCall;
 
 	Private(ZhttpRequest *_q) :
 		QObject(_q),
@@ -163,15 +165,15 @@ class ZhttpRequest::Private : public QObject
 		{
 			expTimerConnection.disconnect();
 			expireTimer->setParent(0);
-			expireTimer->deleteLater();
+			DeferCall::deleteLater(expireTimer);
 			expireTimer = 0;
 		}
 
 		if(keepAliveTimer)
 		{
 			keepAliveTimerConnection.disconnect();
 			keepAliveTimer->setParent(0);
-			keepAliveTimer->deleteLater();
+			DeferCall::deleteLater(keepAliveTimer);
 			keepAliveTimer = 0;
 		}
 
@@ -367,7 +369,7 @@ class ZhttpRequest::Private : public QObject
 		if(!pendingUpdate)
 		{
 			pendingUpdate = true;
-			QMetaObject::invokeMethod(this, "doUpdate", Qt::QueuedConnection);
+			deferCall.defer([&]() { doUpdate(); });
 		}
 	}
 
@@ -935,7 +937,6 @@ class ZhttpRequest::Private : public QObject
 			return ErrorGeneric;
 	}
 
-public slots:
 	void doUpdate()
 	{
 		pendingUpdate = false;
@@ -1157,7 +1158,6 @@ public slots:
 		}
 	}
 
-public:
 	void expire_timeout()
 	{
 		state = Stopped;

src/handler/handlerenginetest.cpp

@@ -33,6 +33,7 @@
 #include "zhttpresponsepacket.h"
 #include "packet/httpresponsedata.h"
 #include "rtimer.h"
+#include "defercall.h"
 #include "handlerengine.h"
 
 namespace {
@@ -309,6 +310,7 @@ private slots:
 		delete wrapper;
 
 		RTimer::deinit();
+		DeferCall::cleanup();
 	}
 
 	void acceptNoHold()

src/handler/handlermain.cpp

@@ -24,6 +24,7 @@
 #include <QCoreApplication>
 #include <QTimer>
 #include "rtimer.h"
+#include "defercall.h"
 #include "handlerapp.h"
 
 class HandlerAppMain
@@ -60,6 +61,7 @@ int handler_main(int argc, char **argv)
 
 	// deinit here, after all event loop activity has completed
 	RTimer::deinit();
+	DeferCall::cleanup();
 
 	return ret;
 }

src/proxy/app.cpp

@@ -31,6 +31,7 @@
 #include <QFileInfo>
 #include "processquit.h"
 #include "rtimer.h"
+#include "defercall.h"
 #include "log.h"
 #include "settings.h"
 #include "xffrule.h"
@@ -299,6 +300,7 @@ class EngineThread : public QThread
 
 		// deinit here, after all event loop activity has completed
 		RTimer::deinit();
+		DeferCall::cleanup();
 	}
 
 private:

src/proxy/domainmap.cpp

@@ -35,6 +35,7 @@
 #include <QFileSystemWatcher>
 #include "log.h"
 #include "rtimer.h"
+#include "defercall.h"
 #include "routesfile.h"
 
 #define WORKER_THREAD_TIMERS 1
@@ -756,6 +757,7 @@ class DomainMap::Thread : public QThread
 		delete worker;
 
 		RTimer::deinit();
+		DeferCall::cleanup();
 	}
 
 public:

src/proxy/proxyenginetest.cpp

@@ -38,6 +38,7 @@
 #include "packet/httpresponsedata.h"
 #include "packet/statspacket.h"
 #include "rtimer.h"
+#include "defercall.h"
 #include "zhttpmanager.h"
 #include "statsmanager.h"
 #include "domainmap.h"
@@ -636,6 +637,7 @@ private slots:
 
 		QCoreApplication::instance()->sendPostedEvents();
 		RTimer::deinit();
+		DeferCall::cleanup();
 	}
 
 	void passthrough()