Qt：用 __thread 关键字让每个线程有自己的全局变量

在GUN标准中，提供了__thread关键字，配合static后，可以实现让一个线程拥有自己的全局变量。

我对__thread进行了简单的封装，可以用于存储class。并且防止了内存泄露（如果使用Qt线程类）。

测试中，我一共开启了两个线程，从输出可以得知每个线程都拥有自己的变量，并且在线程退出后被正常释放。

测试代码：

// Qt lib import
#include <QtCore>
#include <QtConcurrent>

class MyClass
{
public:
MyClass()
 {
 qDebug() << "MyClass" << this << QThread::currentThread();
 }

 ~MyClass()
 {
 qDebug() << "~MyClass" << this << QThread::currentThread();
 }
};

template< class T >
class ThreadStore
{
public:
T &getQuote()
 {
 if ( !t )
 {
 t = new T;

 auto thread = qobject_cast< QThread * >( QThread::currentThread() );
 if ( thread && thread->isRunning() )
 {
QObject::connect( QThread::currentThread(), &QThread::finished, [ this ]()
 {
 if ( t )
 {
 delete t;
 t = nullptr;
 }
 } );
 }
 }

 return *t;
 }

private:
T *t;
};

int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);

 auto myTest = []()
 {
 static __thread ThreadStore< MyClass > threadStore;

 auto &myData = threadStore.getQuote();

 qDebug() << "myData:" << &myData;

QThread::sleep( 1 );
 };

QThreadPool::globalInstance()->setMaxThreadCount( 2 );

QtConcurrent::run( myTest );
QtConcurrent::run( myTest );
QtConcurrent::run( myTest );
QtConcurrent::run( myTest );

QThreadPool::globalInstance()->waitForDone();

 return a.exec();
}

输出结果：

MyClass 0x7fe842e09b10 QThread(0x7fe842d0cbe0, name = "Thread (pooled)")
MyClass 0x7fe842c1d6a0 QThread(0x7fe842d0df60, name = "Thread (pooled)")
myData: 0x7fe842e09b10
myData: 0x7fe842c1d6a0
myData: 0x7fe842e09b10
myData: 0x7fe842c1d6a0
~MyClass 0x7fe842e09b10 QThread(0x7fe842d0cbe0, name = "Thread (pooled)")
~MyClass 0x7fe842c1d6a0 QThread(0x7fe842d0df60, name = "Thread (pooled)")