基本上我需要在
Java中完成同样的事情：
SwingUtilities.invokeLater(()->{/* function */});
或者在javascript中这样：
setTimeout(()=>{/* function */},0);
但是用Qt和lambda.所以有些伪代码：
Qt::queuePushMagic([]() { /* function */ });
作为一个额外的复杂性,我需要这个在多线程上下文中工作.我实际上要做的是在正确的线程中自动运行某些方法.那么代码看起来如何：
SomeClass::threadSafeAsyncMethod() {
if(this->thread() != QThread::currentThread()) {
Qt::queuePushMagic([this]()=>{ this->threadSafeAsyncMethod() });
return;
}
}
这该怎么做？
解决方法
您的问题是
How to leverage Qt to make a QObject method thread-safe?让我们根据您的使用情况调整那里提供的解决方案.首先,让我们考虑安全检查：
bool isSafe(QObject * obj) {
Q_ASSERT(obj->thread() || qApp && qApp->thread() == QThread::currentThread());
auto thread = obj->thread() ? obj->thread() : qApp->thread();
return thread == QThread::currentThread();
}
你建议的方法需要一个仿函数,并让编译器处理在仿函数中打包参数(如果有的话)：
template <typename Fun> void postCall(QObject * obj,Fun && fun) {
qDebug() << __FUNCTION__;
struct Event : public QEvent {
using F = typename std::decay<Fun>::type;
F fun;
Event(F && fun) : QEvent(QEvent::None),fun(std::move(fun)) {}
Event(const F & fun) : QEvent(QEvent::None),fun(fun) {}
~Event() { fun(); }
};
QCoreApplication::postEvent(
obj->thread() ? obj : qApp,new Event(std::forward<Fun>(fun)));
}
第二种方法在事件中显式存储所有参数的副本,并且不使用仿函数：
template <typename Class,typename... Args>
struct CallEvent : public QEvent {
// See https://stackoverflow.com/a/7858971/1329652
// See also https://stackoverflow.com/a/15338881/1329652
template <int ...> struct seq {};
template <int N,int... S> struct gens { using type = typename gens<N-1,N-1,S...>::type; };
template <int ...S> struct gens<0,S...> { using type = seq<S...>; };
template <int ...S> void callFunc(seq<S...>) { (obj->*method)(std::get<S>(args)...); }
Class * obj;
void (Class::*method)(Args...);
std::tuple<typename std::decay<Args>::type...> args;
CallEvent(Class * obj,void (Class::*method)(Args...),Args&&... args) :
QEvent(QEvent::None),obj(obj),method(method),args(std::move<Args>(args)...) {}
~CallEvent() { callFunc(typename gens<sizeof...(Args)>::type()); }
};
template <typename Class,typename... Args> void postCall(Class * obj,Args&& ...args) {
qDebug() << __FUNCTION__;
QCoreApplication::postEvent(
obj->thread() ? static_cast<QObject*>(obj) : qApp,new CallEvent<Class,Args...>{obj,method,std::forward<Args>(args)...});
}
它的用法如下：
struct Class : QObject {
int num{};
QString str;
void method1(int val) {
if (!isSafe(this))
return postCall(this,[=]{ method1(val); });
qDebug() << __FUNCTION__;
num = val;
}
void method2(const QString &val) {
if (!isSafe(this))
return postCall(this,&Class::method2,val);
qDebug() << __FUNCTION__;
str = val;
}
};
测试工具：
// https://github.com/KubaO/stackoverflown/tree/master/questions/safe-method-40382820 #include <QtCore> // above code class Thread : public QThread { public: Thread(QObject * parent = nullptr) : QThread(parent) {} ~Thread() { quit(); wait(); } }; void moveToOwnThread(QObject * obj) { Q_ASSERT(obj->thread() == QThread::currentThread()); auto thread = new Thread{obj}; thread->start(); obj->moveToThread(thread); } int main(int argc,char ** argv) { QCoreApplication app{argc,argv}; Class c; moveToOwnThread(&c); const auto num = 44; const auto str = QString::fromLatin1("Foo"); c.method1(num); c.method2(str); postCall(&c,[&]{ c.thread()->quit(); }); c.thread()->wait(); Q_ASSERT(c.num == num && c.str == str); }
输出：
postCall postCall postCall method1 method2
以上编译和使用Qt 4或Qt 5.
