Single Application

如果限制一个程序同时只能启动一个实例，有几个可以使用的库

• QtSingleApplication

  以前可以免费使用，后来只有商业版能里能用，在 Github 上也有一个 LGPL 协议的实现，地址为https://github.com/qtproject/qt-solutions/tree/master/qtsingleapplication

• SingleApplication

  This is a replacement of the QSingleApplication for Qt5，地址为 https://github.com/itay-grudev/SingleApplication

• RunGuard

  使用共享内存、简单、轻量化的实现，缺点是程序间不能通信，双击程序图标的时候不会激活已运行的实例显示到最前面，下面介绍 RunGuard 的使用

main.cpp

      限制程序同时只能启动一个实例只需要在 main() 函数里调用 if (!guard.tryToRun()) { return 0; } 即可。

#include "RunGuard.h"
 
int main(int argc, char *argv[]) {
RunGuard guard("9F0FFF1A-77A0-4EF0-87F4-5494CA8181C7");
 
if (!guard.tryToRun()) {
return 0;
}
 
QApplication a(argc, argv);
a.exec();
}

RunGuard.h

#ifndef RUNGUARD_H
#define RUNGUARD_H
 
#include <QObject>
#include <QSharedMemory>
#include <QSystemSemaphore>
 
class RunGuard {
public:
RunGuard(const QString& key);
~RunGuard();
 
bool isAnotherRunning();
bool tryToRun();
void release();
 
private:
const QString key;
const QString memLockKey;
const QString sharedmemKey;
 
QSharedMemory sharedMem;
QSystemSemaphore memLock;
 
Q_DISABLE_COPY(RunGuard)
};
#endif // RUNGUARD_H

RunGuard.cpp

#include "RunGuard.h"
#include <QCryptographicHash>
 
namespace {
 
QString generateKeyHash(const QString& key, const QString& salt) {
QByteArray data;
 
data.append(key.toUtf8());
data.append(salt.toUtf8());
data = QCryptographicHash::hash(data, QCryptographicHash::Sha1).toHex();
 
return data;
}
 
}
 
 
RunGuard::RunGuard(const QString &key)
: key(key)
, memLockKey(generateKeyHash(key, "_memLockKey"))
, sharedmemKey(generateKeyHash(key, "_sharedmemKey"))
, sharedMem(sharedmemKey)
, memLock(memLockKey, 1) {
memLock.acquire();
{
QSharedMemory fix(sharedmemKey); // Fix for *nix: http://habrahabr.ru/post/173281/
fix.attach();
}
memLock.release();
}
 
RunGuard::~RunGuard() {
release();
}
 
bool RunGuard::isAnotherRunning() {
if (sharedMem.isAttached()) {
return false;
}
 
memLock.acquire();
const bool isRunning = sharedMem.attach();
if (isRunning) {
sharedMem.detach();
}
memLock.release();
 
return isRunning;
}
 
bool RunGuard::tryToRun() {
if (isAnotherRunning()) { // Extra check
return false;
}
 
memLock.acquire();
const bool result = sharedMem.create(sizeof(quint64));
memLock.release();
 
if (!result) {
release();
return false;
}
 
return true;
}
 
void RunGuard::release() {
memLock.acquire();
 
if (sharedMem.isAttached()) {
sharedMem.detach();
}
 
memLock.release();
}